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To assess patient recall of intraoperative pain, anxiety, fear, and sensory (visual and auditory) perceptions during second eye clear corneal cataract surgery using assisted topical anaesthesia (ATA), in comparison with first eye cataract surgery using the same technique.This prospective, consecutive, observational study was conducted in a free-standing dedicated ophthalmic day surgery centre. A voluntary questionnaire was distributed to 129 consecutive patients who underwent clear corneal cataract surgery using ATA. Two patients had to be converted to block anaesthesia, and were excluded. Patients were asked to rate intraoperative pain, anxiety, and fear using a visual analogue scale (VAS), and recollection of intraoperative visual and auditory perceptions. Results were analysed using the Mann-Whitney U and Spearman correlation tests.There were 70/127 (55%) patients undergoing first eye cataract surgery and 57/127 (45%) undergoing second eye surgery. There was no significant difference in mean pain, anxiety, and fear scores between those undergoing the second eye operation compared with those undergoing their first eye operation. Similarly, there was no significant difference in sensory perceptions between the two cohorts. Overall, there was a small but significant positive correlation between recall of visual and auditory perceptions and combined pain, fear, and anxiety scores (r=0.33, P=0.0002).There was no significant difference in levels of intraoperative pain, anxiety, fear, and sensory perceptions experienced by patients between the first eye and second eye surgeries. We recommend that preoperative counselling for a patient's second eye be as comprehensive as for the first eye surgery.

The primary aim of this study was to define the secretory dynamics of oxytocin and vasopressin in pituitary venous effluent from ambulatory horses during acute endotoxaemia, a stimulus that may release both hormones. Our secondary aim was to investigate the role of oxytocin in regulating adrenocorticotropic hormone (ACTH) secretion by comparing oxytocin, vasopressin, corticotropin-releasing hormone (CRH) and ACTH secretory profiles during endotoxaemia and by monitoring the ACTH response to oxytocin administration. Pituitary venous blood was collected nonsurgically continuously and divided into 1-min segments from eight follicular phase mares. Four mares were sampled for 30 min before and 3.5 h after receiving an i.v. infusion of bacterial endotoxin (TOX). Four control mares were sampled for 2.5 h without infusion of TOX. Another three follicular phase mares were given 5 U of oxytocin to replicate the peak response to TOX and pituitary blood collected every 1 min for 10 min before and 15 min after injection. Endotoxin raised the secretion rates of all hormones measured. All hormones were released episodically throughout the experiment, with TOX increasing the amplitude of peaks in each hormone. Peaks in oxytocin and vasopressin were coincident in each treated mare. Similarly, ACTH peaks were coincident with peaks of oxytocin and vasopressin in each treated mare, and with peaks of CRH in three mares. However, oxytocin administration did not affect ACTH secretion. We conclude that during endotoxaemia in horses: (i) oxytocin and vasopressin are secreted synchronously; (ii) oxytocin is unlikely to be acting as an ACTH secretagogue since inducing peak oxytocin concentrations observed during TOX does not raise ACTH; and therefore (iii) the close relationship between oxytocin and ACTH secretion is circumstantial and due to the fact that oxytocin secretion is concurrent with that of vasopressin, a proven ACTH secretagogue in horses.

Alpha-2-adrenoceptor activation may lower adrenocorticotropic hormone (ACTH) by reducing secretagogue input and/or increasing the release of an inhibitory factor (CIF). To investigate this, we gave clonidine, an alpha-2-agonist, to seven horses, and collected pituitary venous blood every minute for 20 min before treatment and 40 min after treatment. Six horses were given saline vehicle. Mean secretion rates of corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP) and ACTH were calculated before and during four 5-min then two 10-min periods after clonidine or saline. Reduction in ACTH secretion without corresponding changes in CRH and/or AVP would imply the presence of CIF. Secretion rates of ACTH (P = 0.008) and AVP (P = 0.0005) fell after clonidine and remained lower than baseline values for 20 min and 10 min, respectively. The CRH secretion rate decreased slightly but not significantly after clonidine. In controls, hormone secretion rates did not alter during the experiment. Multiple linear regression showed that CRH and AVP secretion accounted for 69% (treated) or 45% (controls) of the variation in ACTH secretion (P < 0.0001 for each). CRH alone contributed 80% (treated) or 76% (controls) of the fit to this model, which is consistent with the concept that CRH 'sets the gain' of the response of corticotrophs to fluctuations in AVP. Accordingly, minute-to-minute changes in pituitary concentrations of AVP and ACTH were synchronous when all data were considered (% concordant changes: controls, 68%, P < 0.0001; treated, 76%, P < 0.0001) and the percentage of concordant movement was unaffected by clonidine (before 72%; after 73%; P = 0.80). In treated horses but not controls, the ratio between the secretion rates of ACTH and AVP fell (P = 0.009), while the ACTH : CRH ratio tended to fall after clonidine, implying reduced responsiveness to stimulation. Moreover, one horse showed a drop in ACTH and a rise in CRH and AVP secretion after clonidine. We conclude that in horses alpha-2-adrenoceptor activation lowers ACTH secretion primarily by reducing the secretion of AVP and possibly CRH. While there was some evidence that a CIF may participate in the clonidine-induced suppression of ACTH, the subtlety of the discordance between ACTH and its secretagogues in most horses and the rarity of complete dissociation indicate that it does not play a major role.

The aim was to define precisely the FSH secretion pattern in mares during the two ovulatory cycles before, and for 24 days after, the last ovulation of the season and to compare this with the profiles of other reproductive hormones and follicular growth to identify changes which may lead to the termination of follicular cycles. Jugular blood was collected every 6 h from ten light horse mares for 6 weeks in autumn. Samples were assayed for FSH, LH, prolactin, inhibin, oestrone conjugates and progesterone. Luteolysis occurred earlier and periovulatory oestrone, but not inhibin, concentrations were significantly lower in the last than in the second to last cycles. In ovulatory and anovulatory cycles, daily mean FSH concentrations were low at the expected time of ovulation and high between days 9 and 11 (day 0 = ovulation), which were usually after luteolysis. However, the periovulatory FSH nadir was prolonged in the last compared with the second to last cycles, and the difference between peak and trough values was not significant in anovulatory cycles. Between day 5 and day 8, the FSH interpulse interval was approximately 2 days, and did not vary in successive cycles. The LH profile also showed progressive changes as mares entered acyclicity; the surge terminated sooner in the last than in the second to last cycles, and failed to occur when expected in acyclicity. Sporadic prolactin pulses occurred at luteolysis in a similar proportion of ovulatory and anovulatory cycles. These results indicate that inadequate gonadotrophin stimulation in early dioestrus may be a critical event leading to suboptimal follicular and luteal development, and eventually acyclicity. Moreover, the time relationships amongst changes in pituitary and ovarian hormones and follicular growth become increasingly disrupted during the autumn transition, which may contribute to the cessation of cyclicity.

In mares, dioestrous FSH profiles based on once-a-day sampling are variable; however, the pulsatility of plasma FSH, which has been suggested by limited windows of intensive sampling, may contribute to this variability. Jugular blood from six mares was sampled at 4 h intervals throughout an ovulatory cycle to determine cyclic FSH and LH patterns more accurately and to measure gonadotrophin pulse frequency during dioestrus. Synchronous pulses of FSH and LH occurred regularly in all mares between day 4 and day 12 (ovulation = day 0) with a mean (+/- SEM) frequency of 1.9 +/- 0.1 (FSH) or 1.6 +/- 0.1 (LH) pulses day-1. LH pulse amplitude declined (P < 0.0001) between day 4 and day 10, but FSH pulse amplitude remained large and stable, dipping slightly but not significantly on day 6. Daily mean FSH concentrations exceeded (P < 0.0001) early oestrous values between day 4 and day 5, and between day 7 and day 10. However, significantly different patterns were obtained when once-a-day sampling was simulated by selecting samples collected at 08:00 h or noon. LH was higher during the periovulatory surge than during dioestrus (P < 0.0001) and profiles were similar whether daily means or selected samples were used. It is concluded that: (1) the marked pulsatility of plasma FSH during dioestrus makes once-a-day sampling misleading for determining FSH profiles; (2) the dioestrous pattern of large, slow FSH pulses was consistent among mares, unlike that of the daily mean FSH profiles; and (3) no discrete FSH 'surges' were observed during dioestrus, although FSH pulse amplitude tended to undergo alternate increases and decreases. A period of higher amplitude FSH pulses preceded ovulation by 10.2 +/- 0.7 days, which corresponds to the approximate time the ovulatory follicle emerges. Therefore, it is possible that the signal for follicular recruitment in mares is intermittent excursions of plasma FSH above a threshold value.

Plasma cortisol is largely bound to corticosteroid-binding globulin (CBG), which regulates its bioavailability by restricting exit from capillaries. Levels of CBG may be altered by several factors including stress and this can influence the amount of cortisol reaching cells. This study investigated the effect of social instability on plasma concentrations of CBG, total and free (not protein bound) cortisol in horses. Horses new to our research herd ('newcomers') were confined in a small yard with four dominant resident horses for 3-4 h daily for 3-4 (n = 5) or 9-14 (n = 3) days. Jugular blood was collected in the mornings from newcomers before the period of stress began ('pre-stress'), and then before each day's stress. Residents were bled before stress on the first and thirteenth day. Residents always behaved aggressively towards newcomers. By the end of the stress period, all newcomers were subordinate to residents. In newcomers (n = 8) after 3-4 days of social stress, CBG binding capacity had fallen (P = 0.0025), while free cortisol concentrations had risen (P = 0.0016) from pre-stress values. In contrast, total cortisol did not change. In residents, CBG had decreased slightly but significantly (P = 0.0162) after 12 days of stress. Residents and newcomers did not differ in pre-stress CBG binding capacity, total or free cortisol concentrations. However, by the second week of stress, CBG binding capacity was lower (P = 0.015) and free cortisol higher (P = 0.030) in newcomers (n = 3) than in residents. Total cortisol did not differ between the groups. In conclusion social stress clearly affected the adrenal axis of subordinate newcomer horses, lowering the binding capacity of CBG and raising free cortisol concentrations. However, no effect of stress could be detected when only total cortisol was measured. Therefore, to assess adrenal axis status accurately in horses, it is essential to monitor the binding capacity of CBG and free cortisol concentrations in addition to total cortisol levels.

Exposure to estrogenic compounds may pose a developmental hazard to infants. Soy products, which contain the phytoestrogens, genistein and daidzein, are becoming increasingly popular as infant foods. To begin to evaluate the potential of the phytoestrogens in these products to affect infants, we measured total genistein and daidzein contents of commercially available soy-based infant formulas, infant cereals, dinners, and rusks. We also assayed phytoestrogens in dairy-based formulas and in breast milk from omnivorous or vegetarian mothers. In most cases, the glucoside forms of the phytoestrogens were hydrolyzed before separation by HPLC. Mean (+/-SEM) total genistein and daidzein contents in four soy infant formulas were 87+/-3 and 49+/-2 microg/g, respectively. The phytoestrogen content of cereals varied with brand, with genistein ranging from 3-287 microg/g and daidzein from 2-276 microg/g. By contrast, no phytoestrogens were detected in dairy-based infant formulas or in human breast milk, irrespective of the mother's diet (detection limit = 0.05 microg/ml). When fed according to the manufacturer's instruction, soy formulas provide the infant with a daily dose rate of total isoflavones (i.e., genistein + daidzein) of approximately 3 mg/kg body weight, which is maintained at a fairly constant level between 0-4 months of age. Supplementing the diet of 4-month-old infants with a single daily serving of cereal can increase their isoflavone intake by over 25%, depending on the brand chosen. This rate of isoflavone intake is much greater than that shown in adult humans to alter reproductive hormones. Since the available evidence suggests that infants can digest and absorb dietary phytoestrogens in active forms and since neonates are generally more susceptible than adults to perturbations of the sex steroid milieu, we suggest that it would be highly desirable to study the effects of soy isoflavones on steroid-dependent developmental processes in human babies.

To study the effect of hypoglycaemia on secretion rates of corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP) and ACTH in a non-ruminant species, a non-surgical method was used to collect pituitary venous (PitVen) blood every 0·5 or 1 min from seven horses before and after insulin administration (0·4 U/kg i.v.). To assess the effect of PitVen cannulation on results, peripheral hormones were also measured before and after insulin in five horses without PitVen cannulae. Insulin administration lowered plasma glucose in all horses (Pt-test). Cortisol concentrations, which were similar in horses with and without PitVen cannulae before insulin, rose significantly after insulin administration in both groups. Most horses showed discomfort as glucose fell. When data from horses with and without PitVen cannulae were pooled, the peak fractional change in cortisol (Spearman's rank correlation coefficient (rs)= −0·94, Prs= −0·61, PPPPrs=−0·96, Prs= −0·81, Prs=0·81, P We suggest that in horses AVP is the primary acute signal for ACTH release both before and during hypoglycaemia; however, the increasing magnitude of ACTH increments induced by greater degrees of hypoglycaemia is determined largely by selective CRH release, which then augments corticotroph responses to AVP. Journal of Endocrinology (1997) 153, 401–409

To study the mechanisms responsible for the unusually slow decline of the ovulatory LH surge in mares, secretion patterns of GnRH, LH and FSH were monitored in pituitary venous blood collected every 2 or 5 min for 10.5\p=n-\18.0h from five mares on the third (n = 4) or fifth day after ovulation (first sampling period). To determine the effectiveness of progesterone negative feedback, mares were then given a luteolytic dose of a prostaglandin analogue (PGF2\g=a\) and pituitary venous sampling (every 2 or 5 min for 16 h) recommenced 20\p=n-\22h later (second sampling period). During the declining arm of the LH surge, large peaks (detected by the Cluster algorithm) of concurrent LH and FSH secretion occurred infrequently, with four peaks being detected in a combined sampling period of 75 h. Outside the peaks, LH or FSH secretion continued (as assessed by a pituitary to jugular\p=n-\venous concentration ratio \m=ge\1.25) during 46% \m=+-\13 or 40% \m=+-\10, respectively, of the sampling period. GnRH immunoactivity was detected during each spontaneous gonadotrophin peak, but at other times was generally at assay sensitivity. After PGF2\g=a\, plasma progesterone fell (ng ml \m=-\1, mean \m=+-\ SEM; first sampling period: 8.6 \m=+-\ 0.8; second: 2.0 \m=+-\ 0.3; P = 0.001) and the frequency of LH (P < 0.05) and FSH (P < 0.02) peaks rose, with 28 peaks detected for each hormone in a total of 80 h sampling. Peaks in LH were smaller during the second period, with decreases observed in maximum (P= 0.027) and mean (P= 0.025) secretion rates. Maximum GnRH secretion rate during peaks also declined (P= 0.010); however, the decrement (\m=-\30 \m=+-\6%) was less than that in maximum LH secretion rate (\m=-\82 \m=+-\5%; P = 0.040), suggesting that other factors contribute to the reduced LH peak amplitude. In summary, gonadotrophin peak frequency during the downswing of the surge in mares is slow, as in the midluteal phase, and the slow rate of decline in peripheral gonadotrophin concentrations is due, at least in part, to continued secretion between pulses. Moreover, progesterone negative feedback is highly effective in early dioestrus, in that lessening it without complete removal markedly accelerates gonadotrophin pulse frequency.

Conflicting views exist on the mode of gonadotrophinreleasing hormone (GnRH) secretion during the ovulatory LH surge and the relative importance of changes in pituitary responsiveness to GnRH in generating the LH surge. This disagreement may stem from species differences and/or methodological problems. To provide data on the exact relationship between GnRH and gonadotrophin secretion during the spontaneous LH surge, we collected pituitary venous (PV) blood every 30 s for 3–4 h from eight mares and then assayed GnRH (in six of the mares), FSH and LH. Jugular blood was also collected from twelve mares without PV cannulae either thrice daily during the surge (n =8) or hourly for 24 h when close to ovulation (n=4) and assayed for LH. Hormone peaks in PV blood were detected by the Cluster program and PV hormone patterns were scanned for underlying periodicity using spectral analysis. Jugular LH concentrations rose slowly and steadily without abrupt increase during the prolonged ovulatory surge, suggesting that hormone secretory patterns seen during the periods of rapid sampling were typical of the surge. Jugular LH concentrations were similar in mares with and without PV cannulae. Intensive sampling of PV blood showed that GnRH, FSH and LH were secreted in frequent (two to five per h) brief (5–7 min) peaks. Secretion was not detectable in 24%, 28% and 57% of the total sampling time for GnRH, LH and FSH respectively. GnRH and LH peaks appeared to be irregular in time and amplitude in most mares. However, spectral analysis of the data revealed an underlying periodicity in the secretion of all three hormones, with the dominant period ranging from 20 to 65 min in individual mares. The spectra of GnRH, FSH and LH were highly coherent at this dominant frequency, and 90% of GnRH peaks were concurrent with LH peaks, which is consistent with the dogma that GnRH is the primary secretagogue for both FSH and LH. Although PV FSH and LH concentrations were closely correlated, PV GnRH and gonadotrophin concentrations were only weakly correlated, implying that there was no consistent relationship between the magnitudes of changes in GnRH and gonadotrophin secretion. When compared with our published mid-luteal phase values, the daily GnRH secretion rate during the LH surge was trebled, while the LH responsiveness to endogenous GnRH, as assessed by the between newly secreted LH and PV GnRH concentrations, was four times greater. We conclude that during the mare's ovulatory LH surge (1) GnRH, LH and FSH are secreted together, probably discontinuously, in frequent brief peaks, with the same underlying periodicity, which implies the existence of a pulse generator, (2) changes in pituitary responsiveness play an important role in generating the mare's LH surge, and (3) GnRH is the major signal for both FSH and LH secretion; however, other factors acutely modulate pituitary response to GnRH. Journal of Endocrinology (1994) 140, 283–295

We used our unique nonsurgical technique for collecting pituitary venous (pit) blood to study GnRH, FSH, and LH secretion patterns in midluteal phase mares. This method does not perturb endocrine function and allows continuous monitoring of GnRH and gonadotropin (Gn) secretion, determination of the amount of GnRH perfusing gonadotropes, and direct measurements of the amounts of Gn secreted. In a total of 80 h of 5-min sampling in four mares, eight Gn peaks occurred; however, more frequent sampling was needed to define secretory events precisely. Therefore, pit blood was collected continuously and split into 30-sec segments in six mares. To ensure a peak during sampling, the opioid antagonist naloxone was given after 4-6 h of sampling to try to replicate a physiological signal for GnRH release. Naloxone induced Gn peaks in jugular blood that were indistinguishable in amplitude from spontaneous peaks. Intensive sampling of pit blood showed that jugular peaks reflected major episodes of GnRH and Gn secretion lasting 30-55 min, which were similar in profile whether naloxone induced or spontaneous and consisted of a train of three to six peaks of diminishing amplitude. Peaks of GnRH and, less often, Gn also occurred outside major episodes. Despite markedly variable size, GnRH peak maxima were correlated with the amount of LH and FSH secreted in concurrent peaks. Likewise, cross-correlation analyses (n = 960 samples/mare) showed close correspondence between patterns of GnRH and secreted FSH and LH. The delay (+/- SEM) between GnRH and Gn maxima was 0.62 +/- 0.18 min for LH and 0.18 +/- 0.22 min for FSH. The majority of GnRH and Gn peaks were concurrent; however, 34.7% of GnRH peaks occurred without Gn peaks. These peaks had a lower amplitude than those with Gn peaks (P0.001). For Gn, secretion (i.e. ratio between pit and jugular concentrations,1.5) continued at a low level for 40 +/- 9% (LH) or 64 +/- 14% (FSH) of the time between Cluster-defined peaks during the basal period. We conclude that in the luteal phase 1) the predominant mode of GnRH and Gn secretion is as concurrent, large amplitude, prolonged episodes that appeared to be the summation of a train of peaks; and 2) a GnRH dose-Gn response relationship operates endogenously. This along with the synchronicity of secretion patterns of the three hormones suggest that GnRH is the major secretagogue for both LH and FSH.

Removal of opioid inhibition of GnRH neurones is thought to be a critical event in generating the ovulatory surge in some species. In the present study, a nonsurgical technique was used to collect pituitary venous blood samples from eight mares every 0.5-1.0 min for 1 h before and after administration of the opioid receptor antagonist naloxone (0.2 mg kg(-1), i.v.), to investigate whether opioid inhibition is also important in mares. Jugular blood samples were taken at 10-15 min intervals. Mares were studied 0, 1 or 2 days before ovulation. Naloxone administration increased mean rates of GnRH (P0.01), LH (P0.001) and FSH (P0.001) secretion. The size of the increment did not vary with proximity to ovulation for any hormone. The amplitude of GnRH pulses rose after naloxone administration (P0.05) and the frequency and amplitude of LH pulses increased (frequency, P0.05; amplitude, P0.02), as did FSH pulse frequency (P0.001). Jugular LH and FSH concentrations tended to rise after naloxone administration; however, these changes were not significant. It is concluded that endogenous opioids inhibit GnRH secretion during the period of increasing LH concentration in the ovulatory surge, thereby slowing its rate of increase. It is postulated that treatment with opioid antagonists could be a physiological and non-antigenic way to accelerate and amplify the ovulatory surge in the breeding season. Although a single injection of naloxone is inadequate to do this, it is likely that continuing antagonism, for example with a long-acting, orally-active analogue such as naltrexone, would maintain increased GnRH and LH secretion for sufficient time to raise peripheral LH concentrations and decrease the time until ovulation.

The aim of this study was to investigate the effect of different breeding stimuli on uterine contractility and pituitary oxytocin release in five oestrous mares, in order to design better treatments for mares with defective physical uterine clearance mechanisms. Electrodes and strain gauges were implanted surgically on the uterine myometrium and myometrial activity was monitored with a Grass polygraph. A catheter was placed non-surgically in the intercavernous sinus of each oestrous mare to sample pituitary venous blood and a second catheter was placed in the jugular vein. Continuous sampling was performed for 2 h to determine the baseline value and during sequentially applied stimuli of: (i) stallion call; (ii) visual contact with a stallion; (iii) active teasing; and (iv) artificial insemination. No association was observed between uterine contraction and pituitary oxytocin release episodes during baseline recording. Exposure of the mares to any of the breeding stimuli was associated with rapid onset of myometrial contractions (P0.0001). The application of a stimulus significantly increased pituitary oxytocin release (P0.02) and contraction duration (P0.05), and the response to artificial insemination was greater than the responses to the other treatments (P0.05). The onset of oxytocin secretion was generally simultaneous with the increase in uterine contraction, rather than preceding it, and in some instances the responses were dissociated, making a cause and effect relationship less likely. In conclusion, interactions between stallions and mares are important components of the uterine clearance mechanism around the time of breeding. Knowledge of these physiological responses may be useful in designing therapeutic regimens for mares with endometritis due to defective uterine contractions.

Jugular blood samples were collected at 4 h intervals from six mares during an oestrous cycle to study the hormonal events that occur around the time of luteolysis. Blood samples from day 10 (day 0 = ovulation) until day 3 of oestrus were assayed for prostaglandin metabolite 13,14-dihydro-15-keto PGF2alpha (PGFM), oxytocin, prolactin, progesterone and oestrogen conjugates. PGF2alpha (0.5 or 1.5 mg) was administered to six mid-dioestrous mares and the oxytocin and prolactin responses were measured. One to five large (peakor =2 x nadir) pulses of PGFM, oxytocin and prolactin were detected in mares during the 3 day period starting on day 13 +/- 0.5. The first PGFM pulse was preceded or accompanied by one or more oxytocin pulses and, overall, large PGFM and oxytocin pulses occurred coincidentally (P0.001). During the period of oxytocin and PGFM pulses, progesterone concentrations decreased (P0.001) from mid-dioestrous to oestrous values. The first large prolactin pulse occurred as progesterone concentrations approached the nadir and preceded an increase in oestrogen conjugate concentrations by 1.9 +/- 0.6 days. Both PGF2alpha doses significantly increased prolactin concentrations, whereas only the larger dose increased oxytocin concentrations. It is concluded that in mares: (i) PGFM and oxytocin secretion patterns are consistent with the ruminant model of the initiation of luteolysis, in which pulsatile secretion of oxytocin from the posterior pituitary triggers episodic release of uterine PGF2alpha; and (ii) the timing of large prolactin pulses in relation to progesterone and oestrogen conjugates changes indicates that prolactin is more likely to have a role in follicular maturation than in luteolysis.

To evaluate an office-based Lanindar (light and nociceptive interaction noting distress and response) test to assist in the assessment of patient suitability for assisted topical anaesthesia (ATA) during phacoemulsification.The Lanindar test was carried out at the preoperative assessment of 716 consecutive patients in the office of one of the authors (ICF). A standard desk lamp was shone in each patient's eye after pupillary dilation, while simultaneously elevating the upper eyelid digitally. A negative test indicated patient hypersensitivity to the light and aversion to digital pressure on the upper eyelid. A positive test was indicated by the patient feeling comfort and lack of blepharospasm and withdrawal in response to the light and digital pressure. chi (2) and Fisher's exact tests were used to assess the association between Lanindar results and suitability for ATA. The positive predictive value and specificity of the test as an indicator of patient suitability for ATA were calculated. Visual acuities at 1 and 4 weeks post-operative periods were compared between the ATA and ALA/GA (assisted local anaesthesia/general anaesthesia) group of patients.About 86.7% were Lanindar positive and 98.9% of these patients tolerated ATA. chi (2) and Fisher's exact tests demonstrated a significant association of a positive Lanindar test with successful ATA (chi (2)=660, P0.001, Fisher's: P0.001). The positive predictive value and specificity of the test were 98% (95% CI=98.04-99.7%) and 93.14% (95% CI=88.23-98.04%), respectively. Visual acuity outcomes were similar in the ATA and ALA/GA groups.The Lanindar is a simple, highly specific, office-based test to determine patient suitability for phacoemulsification under ATA.

We used our nonsurgical technique for collecting pituitary venous blood to relate the dynamics of thyrotrophin-releasing hormone (TRH) secretion to the secretion patterns of both prolactin and thyrotrophin in periovulatory mares, either euthyroid (n = 5) or made hypothyroid by treatment with propyl-thiouracil (n = 5). Pituitary venous blood was collected continuously and divided into 1-min aliquots for 4 h. To test the effect of dopamine on the relationship between secretion patterns, sulpiride, a selective D2 receptor antagonist, was given i.m. after 2 h of sampling. Thorough testing of the model and blood collection procedure revealed no sites of TRH loss. Hypothyroidism increased the mean secretion rates of TRH (P = 0.04) and thyrotrophin (P < 0.0001) but not prolactin. Sulpiride increased prolactin secretion rates in hypothyroid (P < 0.0001) and control (P = 0.007) mares, but did not alter TRH or thyrotrophin secretion rates. In both groups of mares, all three hormones were secreted episodically but not rhythmically. In both groups, the secretion pattern of TRH was almost always significantly related to that of thyrotrophin, as assessed by cross correlation and cross approximate entropy (ApEn) analysis. However, the degree of linear correlation was weak, with only 14% (hypothyroid) or 8% (controls) of the variation in thyrotrophin secretion rates attributable to TRH. Prolactin and TRH secretion patterns before sulpiride were coupled on cross ApEn analysis in both groups, and the minute-to-minute secretion rates of the two hormones were correlated in four hypothyroid and three euthyroid mares. Overall, the small, but significant, degree of association between TRH and prolactin was similar to that between TRH and thyrotrophin. In hypothyroid mares, sulpiride increased (P = 0.02) the synchrony between TRH and prolactin patterns. We conclude that in horses: (i) little TRH degradation occurs during passage through the pituitary or in blood after 1 h at 37 degrees C; (ii) TRH is not the major factor controlling minute-to-minute fluctuations in either thyrotrophin or prolactin; and (iii) reducing two strongly inhibitory inputs (i.e. dopamine and thyroid hormones) may magnify the stimulatory effect of TRH on prolactin secretion.

Our objectives were to determine whether repeated administration of prostaglandin F2alpha (PGF2alpha) to simulate the endogenous mode of secretion would be more effective than a single injection in inducing luteolysis and enable use of smaller doses less likely to cause adverse side effects. The main study comprised 43 dioestrous mares, who were given im. either a single 10 mg dose of natural PGF2alpha (n = 22) or 2 doses of 0.5 mg PGF2, 24 h apart (n = 21). The intensity of side effects was assessed in 8 dioestrous mares given 5, 1.5, 0.5 or 0 mg PGF2alpha in consecutive cycles. Two doses of 0.5 mg PGF2alpha 24 h apart caused lysis of the corpus luteum in all mares, whether this was determined from a fall in plasma progesterone concentrations or reproductive tract/behavioural changes; and when 10 mg PGF2, was given, the corpus luteum was lysed in 17 of 22 mares i.e. a lower proportion (P = 0.0485). A single dose of 0.5 mg PGF2a was no more effective than saline in inducing luteolysis.The intensity of side effects of PGF2alpha increased with dose. Although the 0.5 mg dose was no more likely than saline to cause sweating or muscle spasms, it raised plasma cortisol concentrations and prevented the decline in heart rate seen after saline. We conclude that a 2 dose regimen of administration increases the luteolytic efficacy of PGF2alpha and thereby provides a way to minimise adverse side effects.

Alpha-2-adrenoceptor activation may lower adrenocorticotropic hormone (ACTH) by reducing secretagogue input and/or increasing the release of an inhibitory factor (CIF). To investigate this, we gave clonidine, an alpha-2-agonist, to seven horses, and collected pituitary venous blood every minute for 20 min before treatment and 40 min after treatment. Six horses were given saline vehicle. Mean secretion rates of corticotrophin-releasing hormone (CRH), arginine vasopressin (AVP) and ACTH were calculated before and during four 5-min then two 10-min periods after clonidine or saline. Reduction in ACTH secretion without corresponding changes in CRH and/or AVP would imply the presence of CIF. Secretion rates of ACTH (P = 0.008) and AVP (P = 0.0005) fell after clonidine and remained lower than baseline values for 20 min and 10 min, respectively. The CRH secretion rate decreased slightly but not significantly after clonidine. In controls, hormone secretion rates did not alter during the experiment. Multiple linear regression showed that CRH and AVP secretion accounted for 69% (treated) or 45% (controls) of the variation in ACTH secretion (P0.0001 for each). CRH alone contributed 80% (treated) or 76% (controls) of the fit to this model, which is consistent with the concept that CRH 'sets the gain' of the response of corticotrophs to fluctuations in AVP. Accordingly, minute-to-minute changes in pituitary concentrations of AVP and ACTH were synchronous when all data were considered (% concordant changes: controls, 68%, P0.0001; treated, 76%, P0.0001) and the percentage of concordant movement was unaffected by clonidine (before 72%; after 73%; P = 0.80). In treated horses but not controls, the ratio between the secretion rates of ACTH and AVP fell (P = 0.009), while the ACTH : CRH ratio tended to fall after clonidine, implying reduced responsiveness to stimulation. Moreover, one horse showed a drop in ACTH and a rise in CRH and AVP secretion after clonidine. We conclude that in horses alpha-2-adrenoceptor activation lowers ACTH secretion primarily by reducing the secretion of AVP and possibly CRH. While there was some evidence that a CIF may participate in the clonidine-induced suppression of ACTH, the subtlety of the discordance between ACTH and its secretagogues in most horses and the rarity of complete dissociation indicate that it does not play a major role.

The effect of an acute fall in plasma cortisol on the secretion of CRH, arginine vasopressin (AVP), and ACTH was studied using our nonsurgical technique for collecting pituitary venous (PV) blood from horses. PV blood from six mares was collected continuously and divided into 30-sec segments for 0.5 h before and during a 3-h infusion of metyrapone, an 11-beta-hydroxylase inhibitor. During treatment, plasma cortisol fell (P0.01) to a mean nadir of 15% of pretreatment levels, and 11-deoxy-cortisol rose (P0.02). Three mares became mildly agitated during treatment. Mean PV concentrations of CRH (P0.025), AVP (P0.05), and ACTH (P0.005) were higher during the second hour of treatment than before. For AVP (P0.05) and ACTH (P0.01), the amount secreted in peaks detected by CLUSTER analysis increased during treatment, whereas peak frequency did not. Responses, particularly in CRH and AVP, tended to be amplified during agitation. Increases in CRH, AVP, and ACTH secretion commenced when cortisol had fallen to 50-59% of the initial value (P0.005 for each). By contrast, the cortisol concentration at this point varied 3-fold among mares. The ratio between PV concentrations of ACTH and CRH, which was used as an index of pituitary responsiveness to endogenous CRH, also rose (P0.005) as cortisol fell. The increase in this ratio preceded any significant change in CRH secretion and was maintained to the end of the experiment. We suggest that the initial response to falling cortisol in the horse is at the pituitary, via increased responsiveness to CRH. If cortisol continues to fall, AVP and then CRH secretion are stimulated. However, the magnitude of the hypothalamic response to hypocortisolemia may be augmented by concurrent stress. Last, the hypothalamo-pituitary-adrenal axis of the horse appears to monitor changes in plasma cortisol and not concentrations, at least in the short term.

We have used the technique which we have developed for collecting pituitary venous blood from conscious, undisturbed horses to study the effect of acute vigorous exercise on the secretion of CRF, arginine vasopressin (AVP) and ACTH. Pituitary venous (pit) blood was collected every 1-5 min from nine trained racehorses at rest in the stable. The horses then trotted quietly for 10 min, after which they galloped as fast as possible for 4-6 min, before returning to the stable where sampling continued. In Exp 1 (n = 5) no blood samples were taken during exercise, whereas in Exp 2 (n = 4), pit blood was collected every 30 sec during exercise. Immediately after exercise, significant elevations in heart rate (P less than 0.001), body temperature (P less than 0.01) and hematocrit (P less than 0.001) were observed as compared with preexercise values. Jugular cortisol levels were higher after exercise (301.9 +/- 35.2 nmol/liter; mean +/- SEM) than before (187.3 +/- 34.8; P less than 0.01; n = 9). Likewise, jugular AVP levels increased with exercise (before, 0.65 +/- 0.11 pmol/liter; after 3.2 +/- 0.6; P less than 0.01; n = 6), whereas jugular CRF was not altered by exercise (before, 0.38 +/- 0.08 pmol/liter; after, 0.93 +/- 0.31; n = 6; NS). In Exp 1, no significant changes in pit ACTH, AVP, or CRF were observed after exercise. However in Exp 2 when pit blood was sampled during exercise all horses showed an immediate and dramatic rise in ACTH (P less than 0.01) and AVP (P less than 0.005) secretion which peaked during galloping with mean fractional changes above resting levels of 23.6 +/- 9.9 for ACTH and 51.7 +/- 24.0 for AVP. After exercise pit AVP levels were not different from resting, whereas ACTH remained elevated (11.4 +/- 6.9-fold above resting levels). By contrast, pit CRF levels were not altered by exercise. In both experiments together, pit AVP and ACTH concentrations were correlated in eight of the nine horses, whereas pit CRF and ACTH concentrations were positively correlated in only one of seven horses. We conclude that acute exercise causes a transient increase in ACTH secretion which occurs synchronously with an increase in AVP secretion. CRF does not appear to play a major role in mediating the initial ACTH response to exercise.

Mean plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) levels and their pulse frequencies and the size of the largest ovarian follicle increased during spring in 12 mares studied twice monthly from deep anoestrus to the occurrence of the first ovulation of the breeding season. Mean FSH levels were reduced significantly in deep anoestrus and when a pre-ovulatory follicle was present, whereas mean LH levels were highest close to ovulation. Five of these 12 research mares and 20 of 40 maiden or barren Standardbred mares at a commercial studfarm were given daily intramuscular (i.m.) injections of 150 mg progesterone in oil for 12 days when their ovaries were considered to contain developing follicles on rectal palpation. In the research mares, the size of the largest follicle in the ovaries during progesterone treatment did not differ from pre-treatment or control values; nevertheless, the 5 mares ovulated synchronously 11.2 +/- 0.4 (s.d.) days after progesterone withdrawal. Ovulation was less synchronized after progesterone withdrawal in the commercial mares (23 +/- 9.5 [s.d.] days) and in neither group did progesterone treatment advance the mean date of first ovulation compared with the untreated control mares. Mean plasma LH levels were not affected and mean FSH levels were slightly, but not significantly, elevated during progesterone administration in the research mares. In contrast, mean FSH levels fell steadily with time in both the progesterone treated and the control commercial mares. LH and FSH pulse frequencies in treated and control research mares differed only after progesterone withdrawal, when pulse frequency was higher in controls. We conclude that exogenous progesterone has no consistent effect on follicular development and gonadotrophin secretion patterns in transition phase mares, and in the present study it did not advance the mean date of the first ovulation of the breeding season compared with untreated control mares.

For aqueous extracts of pituitary glands of oestrous mares, luteinizing hormone (LH) profiles were found to be similar to each other and to earlier work after chromatofocussing (CF) and isoelectricfocussing (IEF). After CF, both LH and follicle-stimulating hormone (FSH) in pituitary extracts focussed in multiple peaks in the acidic range, with 86% of LH and 80% of FSH found between pH 4 and 6. By contrast, in pituitary venous plasma, only 18% of the LH focussed in this range, whereas a significantly greater proportion (P less than 0.01) eluted above pH 7 than occurred in pituitary extracts (37% vs 2%, respectively). For pituitary venous FSH, there was only a slight shift in the distribution of isoforms compared with the pituitary extract, with a rise in the percentage of strongly acidic molecules in pituitary venous plasma (pH less than 3.65; 34% vs 16%). These results show that at oestrus, horse LH (which differs from that of other species because it has a heavily sialylated C-terminal extension to the beta-subunit, as does eCG), is much more alkaline when secreted as opposed to when it is stored in the pituitary. The authors of this report suggest that this modification is made after entry into a preferentially released pool of LH. Modulation of the forms of LH and FSH that are secreted may play a role in regulating target tissue responses.

In vitro, the prolactin response of perifused anterior pituitary cells of horses to thyrotrophin-releasing hormone (TRH) (0.1, 1.0, 10 and 100 nM), correlated significantly with hours of daylight (P less than 0.01). Baseline concentrations of prolactin also were significantly correlated with daylength (P less than 0.01). When response and baseline data were fitted by nonlinear least squares to a cosine function, the circannual phase was -0.06072 (+/- 0.02170) and -0.05560 (+/- 0.0255), respectively, which are not significantly different from that of daylength. In vivo, prolactin secretion was measured in jugular plasma and pituitary venous effluent. Prolactin secretion by the pituitary (20- to 30-sec samples) showed pulses of 2-7 min duration above a varying baseline. Jugular prolactin concentrations correlated significantly with daylength (P less than 0.01, n = 20). The fractional plasma clearance rate was 2.50 x 10(-2) and 3.31 x 10(-2)/min in 2 horses. Seasonal changes in prolactin secretion in vivo and in vitro may reflect the amount of prolactin available for release.

In an experiment conducted late in the physiological breeding season, 5 stallions were fitted with indwelling pituitary venous cannulae that permitted unobtrusive collection of blood coming from the pituitary and the hypothalamo-hypophyseal portal vessels. The next day, blood samples were collected at 5 min intervals for several hours while the stallions were resting. Pulses of gonadotrophin-releasing hormone (GnRH), follicle-stimulating hormone (FSH) and luteinizing hormone (LH) occurred approximately once per hour. After this, an oestrous mare was brought into contact with each stallion for 8-30 min. This exposure rapidly induced pulses of GnRH, FSH and LH secretion in all stallions, showing that sexual arousal stimulates the hormones of the reproductive axis.

Plasma ACTH, arginine vasopressin (AVP), and catecholamines were measured at 5-min intervals in the pituitary venous effluent of the unanesthetized horse. Pulses of ACTH and AVP were found to be surprisingly brief (usually of less than 10-min duration) and frequent (averaging between 15-25 min). A highly significant relationship in the changes in concentration of these two hormones was demonstrated (P less than 0.0002) both at rest and after a mild hypoglycemic stimulus. Although there was also a significant correlation (P less than 0.005) between simultaneous plasma ACTH and AVP values the pulse amplitude ratio of AVP to ACTH showed a considerable variation. A rise in cortisol appeared to have a greater suppressive effect on the amplitude of ACTH than AVP pulses. The gradient in hormonal concentration between pituitary effluent and jugular plasma was at times over 50-fold for ACTH, and 500-fold for AVP. A gradient was also found for epinephrine, norepinephrine, and dopamine. A highly significant correlation (P less than 0.005) was demonstrated between changes in norepinephrine, ACTH, and AVP concentrations, but no such relationship could be shown for epinephrine and dopamine. It is concluded that there is a close temporal relationship between changes in ACTH, AVP, and norepinephrine concentrations. Pulses of these hormones are greater in amplitude and more frequent than would have been suspected from sampling peripheral plasma. The variability in the pulse amplitude ratio of ACTH and AVP may suggest that other factors are affecting ACTH secretion. The ability to sample frequently for several hormones and to obtain a marked gradient in hormonal secretion between the pituitary venous effluent and jugular plasma suggest that the horse should provide an excellent animal model in which to study the regulation of hypothalamic and pituitary hormone secretion.

We have developed a non-surgical technique for longterm collection of pituitary venous blood which consists of slightly diluted hypophysial portal blood into which pituitary hormones have been secreted. In these experiments jugular and pituitary venous blood samples were collected from five unmedicated, ambulatory mares at 5-min intervals for 2–6 h on 11 occasions during the 6 days surrounding the ovulatory LH peak. Jugular blood only was collected from another five periovulatory mares without pituitary cannulae. The duration of oestrus was similar in mares with and without pituitary cannulae and all mares ovulated, showing that the procedure did not affect the reproductive axis. In all pituitary-cannulated mares the secretion of gonadotrophin-releasing hormone (GnRH), FSH and LH occurred almost continuously with broad, concurrent pulses of the three hormones superimposed upon this tonic background. Only 9% of the GnRH pulses appeared to be ineffective in inducing a rise in gonadotrophin levels. When measured in pituitary blood, gonadotrophin pulse frequency varied from 0·45 pulses/h early in the LH surge to 1·87 pulses/h at the time of ovulation. In contrast, mean pulse frequency measured in jugular blood did not exceed 1 pulse/h throughout the periovulatory period in cannulated or non-cannulated mares. The low amplitude of jugular pulses (< 50% fractional increase) may have caused problems in identifying the pulses. In the two mares in which pituitary venous blood was sampled during more than one period before ovulation, GnRH secretion tended to be lower on the day of ovulation (day 0) than earlier in oestrus (ratio day 0:day −1; mare WV = 0·58, mare LS = 0·66), whereas LH secretion rate was higher on the day of ovulation (ratio day 0:day −1; mare WV = 1·54, mare LS = 6·68). These studies show that the painless and non-invasive collection of pituitary venous blood, which is possible only in horses, can provide a useful tool for studying hypothalamic-pituitary interactions under completely physiological conditions. J. Endocr. (1987) 114, 351–362

Plasma ACTH, arginine vasopressin (AVP), and alpha MSH were measured in pituitary venous effluent at 5-min intervals from five unanesthetized horses during cortisol infusion and after an iv bolus of AVP or ovine (o) CRF. In control experiments (no hormone) there was a significant overall correlation between the timing of concentration changes in ACTH and alpha MSH. Cortisol infusion increased jugular cortisol levels by 70% and was associated with a reduction in mean ACTH, AVP, and alpha MSH secretion rates and ACTH peak secretion rate, but did not alter the observed pulse frequencies of these hormones. Administration of AVP raised plasma concentrations to a level comparable to the spontaneous peaks in pituitary venous blood and resulted in an increase in the secretion of ACTH and alpha MSH in all horses. Furthermore, spontaneous AVP peaks occurred in pituitary venous blood between 90 and 180 min after AVP injection, indicating that the exogenous hormone did not suppress AVP secretion. oCRF administration led to a prolonged elevation in plasma CRF and an increase in secretion of ACTH and alpha MSH, but not AVP, in all horses. The pulsatile secretion of ACTH and alpha MSH was maintained despite plasma CRF levels in excess of 400 pmol/liter, and the timing of concentration changes in AVP and ACTH continued to be highly correlated. It is concluded that pulsatile ACTH secretion continues during cortisol, oCRF, or AVP administration. Like that of ACTH, alpha MSH secretion is stimulated by oCRF and AVP administration and suppressed by cortisol. Although the timing of concentration changes in ACTH and alpha MSH is highly correlated, the correlation of the actual concentrations of these two hormones varies considerably in different animals.

Luteinizing hormone release induced by a range of small (3·3–33 μg) and large (300–500 μg) i.v. doses of gonadotrophin-releasing hormone (GnRH) was measured in acyclic (n = 4), luteal phase (n = 3) and follicular phase (n = 5) mares and compared with endogenously generated LH pulses in the same reproductive states. Extrapolation from log–linear dose–response curves showed that an LH pulse comparable to an endogenous one would be simulated by i.v. injection of 7·0 (n = 4) and 4·1 (n = 6) μg GnRH in luteal and follicular phase mares respectively; a much smaller dose than the 500 μg usually given clinically or experimentally. In acyclic mares (n = 4), LH pulses occurred too infrequently to be characterized. At small doses of GnRH the amount of LH released by the same dose was similar in all three reproductive states, although the steroid hormone milieu differed markedly. This implies that observed differences between states in mean (± s.e.m.) serum LH concentrations (0·7 ± 0·01, 1·2 ± 0·03 and 11·6 ± 0·33 (μg/l) in acyclic, luteal and follicular phase mares respectively) were produced by differences in GnRH pulse frequency and/or amplitude and not by steroid-mediated changes in pituitary response to GnRH. In acyclic, luteal and follicular phase mares, LH pulse frequency was: immeasurably low, 0·09 and 1·14 pulses/h respectively, which supports the important contribution of pulse frequency to determining mean LH concentration. The LH response to large doses of GnRH was significantly greater in the luteal than in the follicular phase, and was greater than the response to 33 μg in the luteal phase but not in the other two states. Thus, to a large but not to a small dose of GnRH, the pituitary appeared most responsive in the luteal phase. Therefore, in studies of the physiology of the hypothalamic-pituitary system, small doses of GnRH, which induce physiologically sized LH responses, may be preferred to large doses, which result in a level of stimulation to which the pituitary is never naturally exposed and to which it may respond in a non-physiological manner. J. Endocr. (1986) 110, 19–26

Arginine vasopressin (AVP) is released in response to changes in blood osmolality and is also a putative secretagogue for ACTH. However, it is unclear whether osmotically generated increases in AVP in the physiological range influence ACTH secretion. We have studied this question using our unique noninvasive technique for collecting pituitary venous blood in six normal conscious horses that received an iv infusion of hypertonic saline (HS; 5%, 0.07 ml/kg.min) for 45-60 min. Pituitary and jugular venous samples were collected every 5 min for 40 min before, during, and for 20 min after HS. During HS, mean blood osmolality rose (P less than 0.01), with a mean peak increase of 14.8 mosmol/kg (range, +6-+37 mosmol/kg). Jugular AVP rose (P less than 0.01) from 0.56 +/- 0.18 pmol/liter (mean +/- SEM) before HS to 2.16 +/- 0.86 pmol/liter during HS. Mean jugular AVP and osmolality were correlated (r = 0.82; P less than 0.05) during HS. Mean jugular ACTH concentrations increased (P less than 0.01) from 49 +/- 9 ng/liter before HS to 148 +/- 54 ng/liter during HS, while mean cortisol levels during and after HS exceeded basal levels (P less than 0.05). Pituitary AVP and ACTH concentrations exceeded jugular concentrations by up to 100-fold, and mean (P less than 0.01 for both) and peak (P less than 0.001 for both) levels increased during HS. AVP and ACTH secretion during HS were pulsatile. The mean and peak changes in pituitary AVP were significantly correlated with those in ACTH. For the six horses together, pituitary ACTH and AVP concentration changes occurred synchronously during the experiment (P less than 0.001), and the paired AVP and ACTH concentrations were highly correlated (r = 0.73; n = 129 pairs; P less than 0.001). We conclude that 1) physiological changes in AVP secretion are closely associated with comparable changes in ACTH secretion, and 2) osmotic signals that presumably activate the magnocellular neurons of the supraoptic and paraventricular nuclei may be physiologically relevant regulators of corticotrope function.

Nine mares received cannulae to collect blood from the pituitary venous outflow in the intercavernous sinus (ICS) and the jugular vein; in 4 mares, only jugular cannulae were used. Those 4 mares and 3 of the mares with cannulae in both positions received 7.5 mg luprostiol i.m. and 1 mare with both cannulae was treated with 3.75 mg uprostiol i.v. Blood samples were kept before and after treatment at 2-, 5- or 10-min intervals and concentrations of LH, FSH and GnRH were determined by RIA. Treatments resulted in an immediate sharp rise of LH and FSH in ICS and jugular blood samples within 2-10 min, with ICS concentrations rising earlier, and with peak levels of LH 8 to 100 times higher, respectively. In ICS samples, GnRH was elevated consistently only after LH and FSH had reached peak levels. At both locations, LH and FSH concentrations remained elevated 60-120 min after treatment, but had returned to baseline by 240 min. In 5 untreated mares with cannulae at both locations, sampling at 5-min intervals for 12 or 24h revealed no pulses of LH or FSH in 3 mares, and only one pulse a day, preceded by several small rises of GnRH during the hour before the pulses, in 2 mares.

A direct method for measuring the capacity of the high-affinity binding protein, CBG, based on charcoal adsorption, was validated for use in the horse. Several unique aspects of cortisol binding in the horse were observed: (1) CBG content at birth was the lowest of any species studied, (2) CBG concentration increased with age whereas in other species it decreases, (3) the plasma of the new born foal has a binding protein, not reported for other species, which binds as much cortisol as does CBG. Its capacity and affinity are intermediate between albumin and CBG. It may be involved prenatally in increasing dam to fetus transfer of cortisol, and post-natally in buffering the effects of the huge stress-related peripartum release of cortisol.

FSH was measured in the pituitary, and in pituitary venous and jugular blood collected at frequent intervals from mares in various reproductive states, using 3 validated and highly specific radioimmunoassay systems based on different antibodies, 'o', 'h' and 'e'. In the pituitary, 4 forms of FSH were found which differed in isoelectric point and relative potency in the 3 assays. In jugular blood, mean FSH concentrations and short-term patterns depended on the assay used and the reproductive state of the mare. In pituitary venous blood, although FSH concentrations were greatly elevated above jugular values, the relationship amongst the 3 assays was similar to that in jugular blood. However, the pulsatility of FSH secretion at oestrus (1-2 pulses per h in 4 of 5 mares) could be observed only in pituitary blood. When the rate of folliculogenesis was slow (acyclicity, oestrus), FSH concentrations measured in assay 'o' were relatively high and showed smaller fluctuations than in assays 'h' and 'e'. By contrast, when folliculogenesis was rapid (transitional phase, dioestrus), FSH tended to be lowest in assay 'o' and pulses had a similar magnitude in all assays. These results suggest that plasma FSH is polymorphic and that changes in the circulating form may have functional importance. Furthermore, since FSH polymorphism affects immunoactivity, the choice of a radioimmunoassay for clinical or research use is difficult without further FSH structure-function studies to determine which form of the hormone should be measured in a given situation.

Myocardial blood flow and distribution in animals with righ ventricular (RV) hypertrophy have not been studied extensively in the experimental laboratory. This study was carried out to investigate whether or not ischemia can be induced in the hypertrophied right ventricle. Ten adult foxhounds underwent banding of the pulmonary artery. One year later coronary flow and distribution were studied by use of radioactive microspheres. Myocardial oxygen supply and demand were estimated by planimetry of aortic and RV pressure tracings. Data were obtained in the control state, during atrial pacing to a heart rate of 200 +/- 4 beats/min (mean +/- SD), during aorta-right atrial shunting to reduce mean aortic pressure to 60 +/- 6mm Hg, and during aortic constriction to produce a mean aortic pressure of 145 +/- 8mm Hg. RV weight/body weight ratio was 2.2 +/- 0.2 gm/kg(normal, 1.3 +/- 0.1 gm/kg) (p less than 0.001). RV free wall thickness was 11.3 +2- 0.7 mm (normal, 6.7 +/- 0.4 mm) (p less than 0.001). At rest, RV oxygen supply/demand ration was 4.7, and the RV subendocardial/subepicardial (Endo/Epi) flow ratio was 0.93. During atrial pacing, RV supply/demand was 54% of control (p less than 0.01), RV Endo/Epi ratio was 1.00 (p less than 0.05), and right coronary artery (RCA) resistance was 59% of control (p less than 0.01). Aorto-right atrial shunting resulted in an RV supply/demand ratio of 31% of control (p less than 0.01), RV Endo/Epi ratio of 0.95, and RCA resistance of 45% of control (p less than 0.01). During aortic constriction, RV supply/demand ratio was 132% of control (p less than 0.05), RV Endo/Epi ratio was 0.92, and RCA resistance was 146% of control (p less than 0.01). Phasic RCA flowmeter tracings demonstrated an increased proportion of diastolic flow in the study animals as compared to normal animals. In conclusion, myocardial blood flow and distribution in the hypertrophied right ventricle remained normal at rest and during hemodynamic stress. Compensatory mechanisms which maintain normal flow and distribution may include changes in RCA resistance and phasic flow patterns. Under the imposed conditions, RV ischemia and failure did not occur.

Pituitary venous blood was collected by a painless non-surgical cannulation method from five ambulatory stallions at 5-min intervals for 5–6 h during the breeding season. In four adult stallions, statistical analysis showed that pulses of gonadotrophin-releasing hormone (GnRH) and LH were coincident (P P In the four adult stallions the amplitude of pituitary venous gonadotrophin pulses varied markedly but no correlation with GnRH pulse amplitude was observed. Peak secretion of FSH, but not LH, during pulses was correlated with the length of the interpulse interval. Consequently, the ratio of FSH to LH during peaks was least (P Two stallions had regular contact with oestrous mares, and in these horses the secretion of GnRH and gonadotrophins occurred almost continuously with rapid, rhythmic pulses superimposed upon a tonic background. Mean (± s.d.) interval between GnRH pulses was 31·4 ± 9·8 min and 27·7 ± 10·1 min. This secretory pattern was not observed in the two stallions which had infrequent contact with oestrous mares, although the small numbers precluded statistical testing of this apparent difference. No GnRH pulses were observed in one of these stallions, while in the other mean (± s.d.) GnRH pulse interval was 45·0 ± 48·7 min, the large variance being partly due to rapid pulses during a period in which the stallion teased mares. The fifth stallion was pubertal, and GnRH and LH secretion occurred in 15 and 0% of samples respectively, while low levels of FSH secretion were observed in 37% of samples and jugular testosterone levels were immeasurably low. We conclude that there is a statistically significant synchrony between pulses of GnRH, LH and FSH in the pituitary venous blood of stallions. Furthermore, decreasing intervals between gonadotrophin pulses result in a significant reduction in secretion of FSH but not LH. J. Endocr. (1988) 117, 197–206

The possibility of seasonal variation in the feedback effect of testosterone or oestradiol was investigated by giving replacement treatment to geldings for 2-3 weeks during breeding and non-breeding seasons. In the non-breeding season, testosterone suppressed LH values (mean +/- s.e.m., ng/ml) in all geldings (before treatment, 7.5 +/- 2.3; final treatment week, 1.8 +/- 0.2; P less than 0.05), whereas early in the breeding season, testosterone caused a prolonged rise in LH (before, 6.8 +/- 2.3; final week, 18.9 +/- 6.4; P less than 0.05). In all testosterone experiments, LH returned to pretreatment levels within 2 weeks after treatment. Oestradiol treatment caused a prolonged increase (P less than 0.05) in LH concentrations (mean +/- s.e.m., ng/ml) in both seasons (breeding: before 5.2 +/- 1.1; final week, 16.2 +/- 4.8; non-breeding before, 10.9, 20.1 +/- 5.2). We conclude that in geldings the feedback effect of testosterone varies with season and, further, that testosterone replacement may be able to restore to geldings the stallion's seasonal pattern of LH secretion. The results suggest that, in male horses, testosterone and possibly oestradiol, are important components in the neuroendocrine pathway controlling seasonal breeding and, moreover, are essential for the generation of a positive signal for LH secretion in the breeding season.

A non-surgical, non-stressful technique was used for collection of pituitary venous blood from five conscious horses every minute for two 10-min periods before and during isolation from the herd, which caused a predictable, yet humane and physiological, emotional stress. Pituitary blood was also sampled every 5 min for two approximately 90-min periods before and after isolation, while jugular blood was sampled every 15 min throughout the experiment. During isolation, all horses became agitated, hyperventilating and sweating. Packed red cell volume increased, as did pituitary venous concentrations of adrenaline (mean ± s.e.m. concentration before isolation, 621·5±112·3 pmol/l; peak during isolation, 2665·4 ± 869·8 pmol/l; P PP P P P P P We conclude that isolation stress increases AVP secretion and may alter the temporal relationship between pituitary venous concentrations of AVP and ACTH. Furthermore, the magnitude of the responses of AVP, ACTH and α-MSH to isolation is significantly affected by the prevailing cortisol level. J. Endocr. (1988) 116, 325–334