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Background: Hydrocortisone therapy is based on a dosing regimen derived from estimates of cortisol secretion, but little is known of how the dose should be distributed throughout the 24 h. We have used deconvolution analysis of 24-h serum cortisol profiles to determine 24-h cortisol secretion and distribution to inform hydrocortisone dosing schedules in young children and older adults., Methods: Twenty four hour serum cortisol profiles from 80 adults (41 men, aged 60-74 years) and 29 children (24 boys, aged 5-9 years) were subject to deconvolution analysis using an 80-min half-life to ascertain total cortisol secretion and distribution throughout the 24-h period., Results: Mean daily cortisol secretion was similar between adults (6.3 mg/m(2) body surface area/day, range 5.1-9.3) and children (8.0 mg/m(2) body surface area/day, range 5.3-12.0). Peak serum cortisol concentration was higher in children compared with adults, whereas nadir serum cortisol concentrations were similar. Timing of the peak serum cortisol concentration was similar (07.05-07.25), whereas that of the nadir concentration occurred later in adults (midnight) compared with children (22.48) (P = 0.003). Children had the highest percentage of cortisol secretion between 06.00 and 12.00 (38.4%), whereas in adults this took place between midnight and 06.00 (45.2%)., Conclusions: These observations suggest that the daily hydrocortisone replacement dose should be equivalent on average to 6.3 mg/m(2) body surface area/day in adults and 8.0 mg/m(2) body surface area/day in children. Differences in distribution of the total daily dose between older adults and young children need to be taken into account when using a three or four times per day dosing regimen., (© 2012 Blackwell Publishing Ltd.)

Objective: To study endocrine and metabolic variables that affect growth in patients with glycogen storage disease type 1 (GSD-1) receiving standard dietary therapy., Design: Observational study., Patients and Measurements: Thirty-eight patients with GSD-1, age range 0.6-32.9 years, were investigated on their usual dietary regimens. Data on height, height velocity in prepubertal children, endocrine and metabolic responses to oral glucose load, 24-h serum cortisol and GH concentration profiles and serum IGF-1 concentrations were collected., Results: The population studied was shorter than average, with a median height standard deviation score (SDS) of -1.60, but significantly taller than a historical population studied at the same institution that had not received dietary therapy at the time of study. A wide range of height SDS was encountered (-5.28 to 1.21) and a subset still exhibit marked growth failure. Median body mass index (BMI) SDS was 0.72 (range -1.34 to 3.96). Those patients with the greatest BMI SDS had the lowest serum GH concentrations but serum IGF-1 concentrations were within the normal range. Patients with the poorest growth exhibit low serum insulin concentration responses to glucose load, GH insensitivity and higher mean 24-h plasma cortisol levels when compared to those patients who were better grown., Conclusion: This study shows that overall the growth of this group of patients with glycogen storage disease type 1 has improved compared to that of a historical control group. There remains a subset of this population with poor growth despite therapy. The measured endocrine responses in this subset are similar to those reported for untreated patients. To improve the growth further in these individuals it will be necessary to understand whether this is failure of prescribed therapy or failure to comply with therapy.

Objectives: Pulsatile GH release in humans is thought to involve the coordinated interaction of growth hormone-releasing hormone (GHRH) and somatostatin (SS). Disordered GH secretion is seen in most patients following high dose (> 30 Gy) cranial irradiation in childhood and could result from dysregulation of these hypothalamic hormones or reflect direct pituitary damage. We have used a peptide 'clamp' to assess the relative roles of continuous GHRH and intermittent SS in GH pulse generation in healthy volunteers and short-and long-term survivors of childhood brain tumours., Design: Randomized controlled study., Patients: 12 adult male long-term survivors of childhood brain tumours (median age 17.0 years (15.2-19. 7); 12.2 years (5.8-14.0) postradiotherapy, > 30Gy whole brain irradiation) with 9 matched control volunteers and 6 short-term survivors of childhood brain tumours (median age 6.4 years (5.9-7. 7); 2.5 years (1.7-3.6) post radiotherapy, > 30Gy whole brain irradiation) with 6 matched controls (studies of spontaneous GH release alone)., Measurements: Serum GH concentrations in 24 h spontaneous GH profiles and during three 'clamp' studies: continuous GHRH(1-29)NH2 (60 ng/kg/minutes, subcutaneous infusion, 24 h); intermittent SS(1-14) withdrawal (20microg/m2/hour, intravenous infusion, 3 h on/1 h off, 2-3 cycles over 8-12 h); intermittent SS and continuous GHRH combined (2-3 cycles over 8-12 h). Data were analysed by spectral analysis, 'peak' and 'trough' determination and serial array averaging., Results: In normal adults, discrete pulsatility was seen in all profiles of spontaneous GH secretion. Continuous GHRH amplified peak GH concentrations (median basal peak 21.1 mU/l vs. GHRH 62.0 mU/l, P = 0.008) whilst pulse timing remained unaffected. Rebound GH release following SS withdrawal alone was variable. Combining continuous GHRH with intermittent SS produced regular GH responses upon SS withdrawal (20.3 mU/l; range 2. 3-105.4). Heterogeneous patterns of spontaneous GH release were seen in the irradiated subjects. Spontaneous peak GH release was reduced in the children following irradiation (Irradiation 14.9 mU/l vs. Control 25.1 mU/l, P = 0.007). Peak GH concentrations were significantly amplified by GHRH in half of them. Adult long-term survivors had lower spontaneous GH concentrations and continuous GHRH amplified GH release in most subjects (Spontaneous 4.2 mU/l vs. GHRH 6.5 mU/l, P = 0.008) but peak concentrations remained far less than those of controls. Combining intermittent SS with continuous GHRH regularized GH release in many patients but the GH responses remained attenuated (4.6 mU/l; 2.5-17.5)., Conclusion: GH pulsatility can be generated in normal volunteers by the combination of continuous GHRH and intermittent SS and provides indirect evidence for a role for GHRH in GH synthesis and replenishment of stored GH pools at times of high SS tone. Patterns of GH release in short-and long-term survivors of childhood brain tumours are heterogeneous suggesting that combined hypothalamic deficiencies of GHRH and SS occur following high dose radiotherapy. The attenuated GH release seen in long-term survivors compared to controls suggests that GH secretory dysfunction does not simply reflect reduced GHRH and SS secretion, and that trophic effects or pituitary damage may be important with time.

Objective: Growth hormone (GH) is secreted in a pulsatile fashion promoting growth and a number of diverse metabolic actions. The precise components of the pulsatile signal involved in growth regulation are unclear., Design: A retrospective analysis of 24 h serum GH concentration profiles to evaluate the relative contribution of peak and trough serum GH concentrations to growth regulation, GH response to insulin induced hypoglycaemia (ITT) and serum insulin like growth factor-1 (IGF-1) concentration., Patients: Fifty short prepubertal children (age 5.2-11.9 years)., Measurement: Analysis of the hormone profile by a concentration distribution method that determines the concentration at or below which the serum GH concentrations in the 24 hour profile spend a percentage of the total time. The method generates an estimate of the observed concentrations (OC) below which 95% and 5% of the values in the time series lie: OC 95 (peaks) and OC5 (troughs)., Results: Twenty six of the children were growing at a normal rate for short children with a height velocity standard deviation score (HVSDS) between +0.4 and -0.8 whereas twenty four were growing more slowly (HVSDS between -0.9 to -3.9). The former group had a mean peak GH response to ITT of 27.3 (11.1) mU/l whereas the latter had a mean value of 8.7 (6.5) mU/l. There was no relationship between (peak and trough GH concentration) and the age of the individual or body mass index. Peak GH levels were positively related to HVSDS and serum IGF-1 values (r = 0.44; P = 0.002 and r = 0.53; P = 0.002, respectively). GH trough levels were inversely related to these measurements (r = -0.29; P = 0.05; and r = -0.46; P = 0.002, respectively). Further analysis showed that individuals with the slowest growth rates and lowest IGF-1 concentrations had the lowest peak and highest trough GH concentrations (ANOVA F = 6.0; P = 0.002). Similarly, the peak GH response to ITT was lowest in those individuals with high troughs and low peaks (ANOVA F = 9.99; P < 0.001)., Conclusions: These results suggest that the peak values of a GH concentration profile influence growth rate and the IGF-1 axis whereas elevated trough values have the greatest influence on growth rate and IGF-1 values when GH peaks are low.

Objective: Hexarelin is a synthetic six-amino-acid compound capable of releasing GH in animals and in man. Its mechanism of action is not understood and little is known about the GH response after repeated administration. The aim of this study was to determine the GH response to the administration of two intravenous boluses of hexarelin, growth hormone releasing hormone (GHRH) or hexarelin with GHRH., Design: Single boluses of hexarelin (1 microgram/kg), GHRH-(1-29)-NH2 (1 microgram/kg) or hexarelin with GHRH-(1-29)-NH2 were administered intravenously. Each study was performed on two further occasions, with a second bolus being administered 60 or 120 minutes after the first. A control study was performed giving saline intravenously. Studies were performed in a random order., Subjects: Six healthy adult males (25.4-34.1 years) were studied., Measurements: Serum GH was measured by radioimmunoassay. GH secretion rates were derived from the measured serum GH concentrations using the technique of deconvolution analysis., Results: The peak GH secretion rate following the first intravenous bolus of hexarelin was greater than that following the first bolus of GHRH-(1-29)-NH2 (P < 0.001), and was greatest following the administration of hexarelin with GHRH-(1-29)-NH2 (P < 0.001). The coadministration of the two secretagogues resulted in peak GH secretion rates significantly greater than the arithmetic sum of those following their isolated administration (P = 0.001), demonstrating synergism. Compared to saline, the administration of a second bolus of hexarelin, GHRH-(1-29)-NH2 or both resulted in significant further GH secretion (P = 0.02, P = 0.002, P = 0.03, respectively). The administration of a second bolus of hexarelin or hexarelin with GHRH-(1-29)-NH2 120 minutes after the first bolus resulted in lower peak GH secretion rates (P = 0.03). The reductions in peak GH secretion rates following the 60-minute boluses were not statistically significant. The peak GH secretion rates following the first GHRH-(1-29)-NH2 boluses were similar to those following the 60 and 120-minute GHRH-(1-29)-NH2 boluses (P = NS). Irrespective of the interval between the boluses of hexarelin with GHRH-(1-29)-NH2, the peak GH secretion rates following the second boluses were not significantly different from the arithmetic sum of those following the administration of the second boluses of hexarelin or GHRH-(1-29)-NH2, indicating loss of synergism on repeated administration., Conclusion: This study shows that hexarelin is a potent GH secretagogue active after two successive doses; the magnitude of the GH response to the second dose was influenced by the dosing interval. Hexarelin and GHRH-(1-29)-NH2 are synergistic, a property which is lost after repeated administration. These findings may help our understanding of GHRPs and may have implications for the potential use of hexarelin and other GHRPs as therapeutic agents.

Objective: Reversibility of GH insufficiency with a change of environment is characteristic of psychosocial dwarfism, and excludes an organic endocrinopathy. However, the change in GH pulsatility has not previously been described. We therefore wished to study spontaneous GH secretion before and after change to a more favourable environment in 11 children with psychosocial deprivation and short stature in order to evaluate if separation from the families can modify their patterns of GH secretion., Patients and Design: We describe 11 prepubertal children (6 M and 5 F; 2.2-13.5 years of age) who had growth failure and psychosocial deprivation. They were diagnosed by a multidisciplinary team as having environmental growth failure after admission to hospital for 3 weeks. Six of them were discovered to have been sexually abused. During the uninterrupted hospital admission parental access was restricted. Three sets of 18-hour GH profiles were performed on each child, except one child who had only two, during the 3-week admission., Measurements: Pulse analysis of GH profiles was by Fourier transformation., Results: On the first day of admission spontaneous GH secretion demonstrated a spectrum of abnormalities in the pattern of basal values, pulse frequency and pulse amplitude. Such GH insufficiency showed reversibility during the 3 weeks in hospital. Indeed, there was a significant increase in GH secretion which was amplitude modulated without any significant modification in pulse frequency., Conclusion: Our data indicate that there is abnormal physiological GH secretion in children with psychosocial deprivation, which is associated with growth failure. Despite a pathological situation, each child retained his own characteristic pattern of GH pulsatility. The pattern of reversibility of abnormal GH pulsatility provides information for the mechanism of the control of GH secretion.

Objective: It has been proposed that low IGF-I levels and reduced IGF-I bioactivity may lead to elevated GH levels in adolescents with insulin dependent diabetes (IDDM). We have therefore studied the effects of human recombinant insulin-like growth factor I (rhIGF-I) administration on GH levels and GH secretion in adolescents with IDDM., Patients: Nine late pubertal adolescents (four male and five female) with IDDM., Design: A double-blind placebo controlled study of rhIGF-I administered subcutaneously in a dose of 40 micrograms/kg body weight at 1800 h., Measurements: IGF-I and GH concentrations were measured at regular intervals throughout the study. Twenty-two hour GH secretory rates were calculated by deconvolution analysis. Overnight GH profiles were analysed by distribution analysis, and Fourier transformations were performed on both overnight GH concentrations and GH secretory rates., Results: Mean IGF-I levels over the 22-hour study period were significantly elevated following rhIGF-I administration (350 +/- 26 vs 205 +/- 21 micrograms/l (mean +/- SEM), P < 0.01). Mean 22-hour GH levels were reduced following rhIGF-I administration (19.4 +/- 4.0 compared with 33.6 +/- 5.8 mU/l; P = 0.01). Distribution analysis demonstrated that the reduction in GH levels was due to changes in the proportion of values at both high and low concentrations. Deconvolution analysis also revealed a significant overall reduction in GH secretory rate following IGF-I administration (1.81 +/- 0.30 vs 2.98 +/- 0.47 mU/min, P = 0.01) which was still apparent during the final 5.5 hours of the study period (1.51 +/- 0.30 vs 2.76 +/- 0.61 mU/min, P = 0.02). The dominant periodicity of GH secretory episodes as determined by Fourier transformation was between 120 and 180 minutes after both IGF-I and placebo., Conclusions: In late pubertal adolescents with IDDM the rise in IGF-I levels following rhIGF-I administration in a subcutaneous dose of 40 micrograms/kg body weight leads to a significant reduction in GH levels and GH secretory rate. The reduction in GH secretion is due to changes in pulse amplitude rather than frequency. A reduction in GH secretion was apparent at the beginning and also towards the end of the 22-hour study period.

Objective: The secretion of luteinizing hormone (LH), follicle stimulating hormone (FSH) and testosterone in the adult male was studied by means of 48-hour profiles. The aim of the study was to examine the effects of the endogenous circadian variation in serum testosterone concentration on LH pulsatility, and to determine the temporal relationships between FSH and LH, and between LH and testosterone by cross-correlation, and the pulse frequency of these hormones by spectral analysis, as revealed by extended sampling periods., Design: Hormone profiles were obtained by 20-minute sampling over 48 hours., Subjects: Six healthy adult males, aged between 21 and 23 years., Measurements: LH and FSH were measured using an immunoradiometric assay and testosterone with a solid-phase radioimmunoassay., Results: The profiles showed pulsatile secretion of all three hormones, and a circadian rhythm with levels highest between 0200 and 0600 h. Cross-correlation analysis: There was a significant relationship between LH and FSH (r = 0.5; P = 0.001) at 0 minutes (i.e. no time lag). A pulse of testosterone followed on average 60 minutes after a pulse of LH (r = 0.26; P = 0.001). Fourier transformation: Spectral analysis showed the dominant period for LH and FSH pulsatility to be 200 minutes. The dominant period for testosterone pulsatility was 400 minutes. The effect of endogenous variations in serum testosterone concentrations: The LH profiles were divided into periods when the serum testosterone concentration was high or low, and Fourier transformation carried out on these shorter periods. These transforms showed that the dominant period during high serum testosterone concentration was 180 minutes, and during low serum testosterone was 120 minutes (P < or = 0.025)., Conclusions: FSH and LH are co-secreted, and a pulse of testosterone follows a pulse of LH by 60 minutes. The physiological changes in serum testosterone concentration that occur during the day result in changes in the pulse frequency of LH. Testosterone concentrations thus have rapidly acting feedback activity at hypothalamic level.

Objective: High overnight plasma growth hormone (GH) levels in insulin-dependent diabetes mellitus (IDDM) are reflected in both an increase in the GH pulse amplitude and elevated baseline GH concentrations. To determine whether these are a result of an increase in GH secretory episodes, we undertook deconvolution analysis of overnight GH profiles using previously determined half-life data., Design: Deconvolution of overnight GH profiles (2000-0800 h) was undertaken from normal and diabetic adolescents (either on their usual insulin regime (n = 15), during overnight euglycaemic clamp using a variable rate insulin infusion (n = 29), or during clamp plus 100 mg pirenzepine to suppress endogenous GH (n = 7))., Patients: Thirty-five normal and 29 diabetic adolescents of both sexes at all stages of puberty., Measurements: GH secretory rates were calculated from deconvolution analysis, and Fourier transformation was increased mean overnight GH secretion when analysed by sex and by puberty stage compared to normal subjects; overnight GH secretion median (range) of diabetic group 1.88 (0.56-3.81) mU/min; control group 0.62 (0.32-1.92) mU/min (P < 0.001). Fourier transform analysis of these secretory episodes showed greater pulse frequency in the diabetics with dominant pulse periodicity of 90 minutes compared with 135 minutes in normal subjects. During overnight euglycaemia, mean +/- SEM overnight GH secretory rates were comparable to subjects' usual regime night (1.82 +/- 0.33 vs 1.91 +/- 0.37 mU/min) and there was no change in the dominant pulse periodicity of 90 minutes. Pirenzepine administration in diabetic subjects significantly reduced overnight GH secretion from 1.57 +/- 0.19 to 0.71 +/- 0.80 mU/min (P < 0.001) showing a median (range) reduction of 63 (9.3-82.8)% when compared to the subjects' clamp night. However, dominant pulse periodicity was not altered by pirenzepine administration, and remained at 90 minutes., Conclusion: In patients with insulin-dependent diabetes mellitus there is an increase in both the amplitude and frequency of pulsatile GH secretion compared to normal subjects, which is not affected by maintenance of overnight normoglycaemia. The anticholinergic drug pirenzepine appears to suppress the amplitude of GH pulse secretion but has no effect on frequency.

Objectives: We compared a sensitive assay for GH (ELISA) with a conventional immunoradiometric (IRMA) assay with particular reference to the oscillatory activity detected by Fourier transformation and the estimation of trough concentrations using occupancy analysis., Design: Eight healthy adult male volunteers underwent 24-hour profiles during which samples were drawn at 20-minute intervals. Samples were analysed by an ELISA and an IRMA system., Measurements: The 24-hour serum GH concentration profiles were subjected to Fourier transformation and to occupancy analysis., Results: No additional GH periodicities could be determined in the ELISA data other than the well documented 180-200-minute periodicity. Median observed concentrations (OC) at 5% occupancy were 0.035 mU/l (range 0.004-0.22) for the ELISA and 0.035 mU/l (range 0.001-0.50) for the IRMA. For all OC parameters, 5, 50 and 95%, there was a good correlation between the ELISA and IRMA systems. The mean difference (bias) between the ELISA and IRMA were -0.05, -0.28 and -1.40 mU/l at OC values of 5, 50 and 95% respectively and the standard deviations of the difference at the same OC values were 0.10, 0.50 and 1.61 mU/l., Conclusion: Although there is a qualitative improvement on visual inspection of individual 24-hour serum GH profiles obtained using the ELISA system, there is little additional information gained in terms of pulse periodicity or occupancy analysis.

Objective: To estimate the half-life of growth hormone in young adult patients with type I (insulin-dependent) diabetes mellitus following bolus injection and prolonged exposure for the purpose of deconvolution analysis of plasma growth hormone profiles to determine growth hormone secretory rates., Design: In the bolus study, an intravenous bolus injection of 100 mU of biosynthetic human growth hormone was given while endogenous growth hormone was suppressed by a continuous infusion of somatostatin under three different glucose clamp conditions: normoglycaemia (5 mmol/l) with normoinsulinaemia (65 pmol/l); hyperglycaemia (12 mmol/l) with normoinsulinaemia; and normoglycaemia with hyperinsulinaemia (360 pmol/l). In the infusion study, the effect of prolonged and repeated growth hormone exposure upon the growth hormone half-life was estimated. Three pulses of 60 minutes growth hormone infusion (6 mU/kg/pulse) two hours apart under euglycaemic somatostatin suppression were applied., Patients: Six young adult patients with type I (insulin-dependent) diabetes mellitus were studied in both the bolus and the infusion study., Results: Mean GH half-lives by mono-exponential analysis were not significantly different remaining unaltered by the short-term metabolic changes of hyperglycaemia and hyperinsulinaemia. Data were therefore pooled yielding an overall mean GH half-life of 13.6 minutes (range 11.9-19.4). Applying a bi-exponential model mean GH half-lives were 3.1 minutes (range 2.5-5.9) for the rapid phase of distribution of the hormone and 13.8 minutes (range 9.6-16.9) for the decay of GH from the circulation. The GH half-life during the infusions studies did not vary with repeated exposure but was significantly longer (mean half-life of 25.7 minutes; range 19.4-37.1) than during the bolus studies (P less than 0.001)., Conclusions: The half-life of exogenous r-hGH is not affected by glucose or insulin concentrations but increases after prolonged GH exposure in young adults with type I (insulin-dependent) diabetes mellitus.

Objective: To determine whether duration of exposure to GH and/or rate of change of serum GH concentration are important factors in determining the growth rate of short children., Design: An analysis of parameters of occupancy percentage and rate of change of serum GH concentration was performed as part of a prospective study investigating the relationship between growth and GH in childhood., Patients: Sixty-four short prepubertal children (48 male, 16 female) aged between 4.7 and 11.9 years were studied. Thirty-one children were growing with a height velocity standard deviation score between 0 and -0.8 and were defined as short normal. Thirty-three children were growing with a height velocity standard deviation score less than -0.8 and were defined as short slowly growing., Measurements: Twenty-four hour serum GH concentration profiles were constructed by withdrawing samples at 20-minute intervals. Analysis of occupancy percentage was performed on each data array by determining cumulative distributions and plotting these as linear probits against log serum GH concentration. Estimates of peak (OC95), intermediate (OC50) and trough (OC5) occupancies were calculated. A first-order derivative of the concentration-time data array was determined for each profile as a measure of rate changes., Results: First-order derivative values were significantly greater in the short normal group than in the short slowly growing children (short normal median 1.41 mU/l/min; short slowly growing median 0.72 mU/l/min; P less than 0.001). OC95 values were significantly higher in the short normal group (median 19.31 mU/l) than the short slowly growing group (median 7.69 mU/l) (P less than 0.001). There was no difference in OC50 values. OC5 values were lower in short normal children (median 0.20 mU/l) than in the short slowly growing children (0.55 mU/l) (P less than 0.003). The most important factor in determining growth rate was the rate of change in serum GH concentration (FOD). Occupancy percentage played no part in the relationship. The regression equation was Height velocity SDS = 1.16 (In FOD) - 1.03; r = 0.75; P less than 0.001, Conclusions: These data suggest that the pattern of presentation of GH in the circulation is an important factor in determining target organ response. Although occupancy percentages at differing serum GH concentrations differ between short slowly growing and short normal children, it is the rate of change of the hormone in the circulation which appears to be the more important 'signal' in terms of modulating growth.

Objective: To study the regulation of the growth hormone (GH) response to growth hormone releasing hormone (GHRH) in the presence or absence of somatostatin pretreatment., Design: Seven healthy adult male volunteers of normal height and weight and aged between 19 and 29 years underwent four separate studies (each containing three cycles in one day) in random order. The studies were separated from each other by at least a week. On day 1, three consecutive cycles (between 0800 and 2000 hours) consisted each of a saline infusion for 3 hours which was stopped prior to a bolus injection of saline and followed by 60 minutes of more intensive blood sampling. On day 2, the bolus injections were of GHRH given after saline infusion. On days 3 and 4 somatostatin infusions were administered instead of saline over the 3-hour periods followed by bolus injections of saline or GHRH respectively. In all studies, samples were collected for the measurement of serum GH concentration at 15-minute intervals from time 0 to 180 minutes and then at 5-minute intervals for a further 60 minutes, this cycle being repeated three times., Measurements: Serum GH concentrations were analysed by serial array averaging., Results: Prompt release of GH was observed in response to GHRH given against a saline background (day 2, cycle 1) (mean at 60 minutes 49.2 +/- 14.7 mU/l) but the responses observed during the second and third cycles were attenuated (mean at 60 minutes 17.2 +/- 4.0 mU/l; P = 0.025). GH release between somatostatin infusions (somatostatin withdrawal; day 3) occurred twice as often as that observed during saline infusions (62% day 3: 29% day 1). The response, although qualitatively similar to that induced by GHRH, was reduced in amplitude and the time of onset variable (5-45 minutes). On day 4, the administration of GHRH as a bolus injection combined with somatostatin withdrawal led to consistent and repeatable GH responses (mean at 60 minutes, cycle 1, 39.7 +/- 10.8 mU/l; cycles 2 and 3, 37.4 +/- 9.4 mU/l) which were similar to those observed with GHRH alone (day 2, cycle 1) (mean 39.7 +/- 10.8 mU/l) (P = NS)., Conclusions: These data suggest that endogenous somatostatin secretion is important in determining the ability of the somatotroph to respond to repeated growth hormone releasing hormone stimulation and that for regular GH pulse generation a close interplay between growth hormone releasing hormone and somatostatin is required.

Objective: The aim was to investigate the relationship between the nocturnal pulsatile secretory patterns of immunoreactive and bioactive luteinizing hormone in normal children at various stages of puberty., Design: Blood samples were taken at 15-minute intervals from 2000 hours to 0800 hours. Pubertal stage was assessed by the method of Tanner (1962)., Patients: Thirty-four healthy siblings (17 males, 17 females) of diabetic children were recruited (median age 13.1, range 9.1-20.9 years). They were of normal height, non-obese, and covered the range of puberty., Measurements: Follicle stimulating and luteinizing hormone levels were measured by radioimmunoassay in all 34 subjects; bioactive LH (B-LH) was assayed in a subgroup of 13 subjects selected to encompass the range of normal puberty. Oestradiol (girls) and testosterone (boys) were also measured at hourly intervals., Results: Immunoreactive luteinizing and follicle stimulating hormone concentrations showed a progressive rise during puberty in both sexes. FSH concentrations were significantly higher in females than in males at all stages of puberty. Overnight mean bioactive luteinizing hormone concentrations were higher than immunoreactive luteinizing hormone levels in all the girls studied (n = 7). Although the number of bioactive luteinizing hormone pulses (31) was greater than immunoreactive pulses (27), the profiles were generally very similar. In the early pubertal girls an increase in the bioactive: immunoreactive ratio was observed during the middle of the night with the onset of pulsatility. Oestrogen was detected in the girls in breast stage 4-5 but not in two of the early pubertal girls, despite pulses of immunoreactive and bioactive luteinizing hormone. The boys had higher mean bioactive than immunoreactive luteinizing hormone levels and overall bioactive and immunoreactive luteinizing hormone and testosterone concentrations increased with puberty stage. Concordance between bioactive and immunoreactive hormone pulses was good although more immunoreactive pulses (16) were seen than bioactive pulses (14). As in the girls, an increase in the bioactive: immunoreactive ratio was observed in the middle of the night with the onset of pulsatility at genital stage 2 but, in contrast to the oestrogen data in the girls, testosterone secretion always followed luteinizing hormone pulsatility overnight., Conclusion: We conclude that mean overnight immunoreactive luteinizing and follicle stimulating hormone concentrations increase during puberty in both sexes. Bioactive luteinizing hormone levels are two to three times higher than immunoreactive luteinizing hormone in both sexes, but there is very little discordance between immunoreactive and bioactive luteinizing hormone pulsatility. The bioactive: immunoreactive ratio increases with the occurrence of pulsatility overnight in early pubertal children. The relationship between these changes in bioactive and immunoreactive luteinizing hormone and sex steroids is clearest in boys where the nocturnal testosterone rise always follows pulsatile LH secretion.

Objective: To develop a method for quantifying the distribution of concentrations present in hormone profiles, which would allow an observer-unbiased estimate of the time concentration attribute and to make an assessment of the baseline., Design: The log-transformed concentrations (regardless of their temporal attribute) are sorted and allocated to class intervals. The number of observations in each interval are then determined and expressed as a percentage of the total number of samples drawn in the study period. The data may be displayed as a frequency distribution or as a cumulative distribution. Cumulative distributions may be plotted as sigmoidal ogives or can be transformed into discrete probabilities (linear probits), which are then linear, and amenable to regression analysis. Probability analysis gives estimates of the mean (the value below which 50% of the observed concentrations lie, which we term 'OC50'). 'Baseline' can be defined in terms of percentage occupancy--the 'Observed Concentration for 5%' (which we term 'OC5') which is the threshold at or below which the hormone concentrations are measured 5% of the time., Patients: We report the use of applying this method to 24-hour growth hormone (GH) profiles from 63 children, 26 adults and one giant., Results: We demonstrate that GH effects (growth or gigantism) in these groups are more related to the baseline OC5 concentration than peak concentration (OC5 +/- 95% confidence limits: adults 0.05 +/- 0.04, peak-height-velocity pubertal 0.39 +/- 0.22, giant 8.9 mU/l)., Conclusions: Pulsatile hormone profiles can be analysed using this method in order to assess baseline and other concentration domains.

Objective: To study the reproducibility of 24-h serum growth hormone (GH) concentration profiles in adults., Design: 24-h serum GH concentrations were constructed by drawing blood samples at 20-min intervals. Four study occasions over a period of 1 year were chosen to assess the reproducibility., Subjects: Six healthy adult male volunteers of normal height and weight and aged between 20 and 22 years., Measures: The resulting GH data arrays were analysed by Fourier transformation. Between and within individual variations were calculated and expressed in terms of coefficients of variation and data plotted to show variations between groups and individuals., Results: The frequency component of GH secretion occurred with a dominant periodicity of between 160 and 240 min. Precise estimates of spectral power (strength of oscillatory activity) and period were obtained for group data, but such estimates cannot be inferred from a single profile. There was no significant difference in 24-h mean serum GH concentration over the year of study: occasion 1 (February) mean 2.0 mU/l (SD 0.5); occasion 2 (March) mean 3.7 mU/l (SD 2.8); occasion 3 (July) mean 2.7 mU/l (SD 1.4); occasion 4 (February) 2.5 mU/l (SD 1.5) (mean within individual coefficient of variation 35%, range 9-58). The concentrations of factors known to influence GH synthesis and secretion, insulin-like growth factor I, thyroxine, testosterone and oestradiol, varied little over the year of study., Conclusions: These data demonstrate that group data are reproducible in terms of oscillatory activity and the amount of GH secreted and that 24-h GH profiles should be used predominantly for analysing group data. The variability between individual profiles limits their value in the investigation of children with growth failure and suspected GH insufficiency.

We have studied the serum growth hormone (GH) response to two consecutive doses of growth hormone releasing hormone (GHRH) (50, 100, 200 micrograms) given 1, 2 or 3 h apart in seven adult males. The serum GH profile was analysed by deconvulution incorporating a variable half-life for GH. All three doses of GHRH stimulated maximal GH secretion: 50 micrograms, 146.0 mU/min (SEM 24.0); 100 micrograms, 128.1 mU/min (SEM 14.3); 200 micrograms, 134.1 mU/min (SEM 20.5) (one-way ANOVA, P = NS). The magnitude of the second secretory burst after the second dose of GHRH was less than that induced by the first injection of GHRH, particularly when doses of 200 micrograms were used. Factors influencing the response to the second dose were the GH secretory status at the point that the stimulus was applied and the time interval between administration of the first and second doses. These studies demonstrate that the pituitary gland is capable of responding to two consecutive doses of GHRH although the second response is always less than the first. The data demonstrate the importance of using methods of assessing GH secretion and not relying simply on measured serum GH concentration values.

We have investigated the relation between nocturnal insulin requirements and nocturnal growth hormone (GH) release in 26 diabetic adolescents at various puberty stages and have examined the effect of nocturnal GH suppression on pre-breakfast insulin requirement. In all the studies, euglycaemia was maintained overnight using a computer-calculated variable-rate insulin infusion, and 15-min blood samples were collected for GH assay. During initial clamp studies, insulin infusion rates were greater from 0500-0800 h (15.22 +/- 0.95 mU/kg/h, mean +/- SEM) than from 0100-0400 h (12.42 +/- 0.84 mU/kg/h, P less than 0.001). The increase in insulin infusion rate correlated with mean overnight GH concentration (r = 0.68, P less than 0.001), and was maximal at puberty stage 3 in both sexes. In seven of the subjects, a second identical clamp was performed following administration of 100 mg oral pirenzepine. During these studies, mean overnight GH levels were reduced by 11-85%, from 17.6 +/- 1.6 to 7.5 +/- 2.2 mU/l; P less than 0.01. Insulin requirements were not significantly different between the periods 0100-0400 and 0500-0800 h during these studies, and the reduction in pre-breakfast (0500-0800 h) insulin requirement when compared with the baseline studies correlated with the fall in GH secretion (rs = 0.82, P less than 0.01). The dawn increase in insulin requirement in adolescents with IDDM is related to the overnight GH secretion during puberty, and pre-breakfast insulin requirement can be reduced by suppressing nocturnal GH release.

A deconvolution analysis model to calculate pituitary growth hormone (GH) secretion rate from measured serum GH concentration has been developed. This uses an iterative method of 'curve-stripping' based on an estimate of the half-life. The model has been applied to serum GH profiles and demonstrates that GH secretion occurs in discrete bursts with quiescent periods between secretory episodes, an 'on-off' phenomenon. The model can clearly dissect complicated concentration profiles such as the serum GH concentration response to growth hormone releasing hormone. The estimate was derived from calculating the half-life of serum GH in 10 subjects following an intravenous bolus injection of 50 mU of biosynthetic human growth hormone (b-hGH) and following infusions of the exogenous hormone (3 mU/kg/h) for 15, 30, 60 and 180 min. Endogenous GH secretion was suppressed by a continuous infusion of somatostatin (1-14). An asymptotic relationship between the duration of GH infusion and the GH half-life was established. A half-life of 15.3 min was achieved after exposure to GH for 60 min and a maximum half-life of 15.7 min after 180 min exposure.

GH release is abnormally regulated in insulin-dependent diabetes (IDDM), and paradoxical stimulation of GH release after TRH has been reported. However, overnight GH pulsatility is increased in IDDM, and it may be difficult to distinguish TRH-stimulated release from spontaneous secretory episodes. To resolve this question, we carried out two overnight GH profiles followed by either TRH or saline control tests in six adolescents with IDDM; ages 11.4-14.7 years, duration IDDM 2.4-6.7 years. A rise in GH was seen in four of six following TRH, but with no consistent pattern. A rise was also seen in four of six following saline. Peak GH levels were similar after TRH and saline (19.3 +/- 4.4 vs 25.8 +/- 5.5 mU/l; mean +/- SEM). Mean blood glucose was no different during TRH and saline tests (9.5 +/- 1.6 vs 7.5 +/- 0.6 mmol/l). The two subjects who had an early GH peak after TRH were those in whom GH levels had already begun to rise, suggesting the coincident occurrence of a spontaneous GH pulse. The timing of the next GH pulse could be predicted equally well after TRH and saline from the overnight secretory profile using autocorrelation. Paradoxical GH stimulation after TRH is not seen in adolescents with IDDM, but apparent responses may be due to timing coincident with the increased spontaneous pulsatility.

The effects of 8 day continuous subcutaneous (s.c.) infusions of growth hormone releasing hormone analogue (NLE27GRF(1-29)NH2 (GHRH.A)) on growth hormone (GH) secretion were studied in 14 normal adult male volunteers. GHRH.A was administered in doses which ranged from 7.5 to 120 ng/kg/min in doubling steps. Baseline GH profiles obtained during a 24 h infusion of normal saline in each subject were compared with profiles performed on days 1 and 8 of the infusion. Doses above 30 ng/kg/min augmented GH pulse amplitude and frequency. Doses of 60 ng/kg/min and 120 ng/kg/min appeared more satisfactory as these represented doses on the upwards slope of the dose response curve. However, at a dose of 120 ng/kg/min the GH secretion did not return to baseline for 12 of the 24 h. There was no evidence of desensitization or of depletion of the releasable GH pool with any dose. The possibility of treatment of short children with depot preparations of GHRH.A appears promising.

The in-vivo half-lives of insulin and C-peptide have been assessed in normal man by a method which examines the decline of endogenously produced insulin and C-peptide after somatostatin suppression of secretion. Venous blood samples were taken each minute from seven normal subjects: i.v. glucose (0.1 g/kg ideal body weight) was given over 1 min to stimulate secretion, followed by a bolus of 250 micrograms of somatostatin-14 and an infusion of a further 250 micrograms somatostatin-14 over the subsequent 30 min. Plasma samples were analysed for C-peptide, glucose and insulin. The initial mono-exponential half-lives over 8 min were 3.9 +/- 0.3 and 10.2 +/- 0.7 min respectively (mean +/- SEM), with subsequent slower declines. Log transformed insulin and C-peptide yielded biphasic declinations which were assessed by a two-pool model. The rate constant of clearance of insulin implied avid uptake, while the kinetics of C-peptide clearance were slower, and irreversible loss might be explained by glomerular filtration alone. The somatostatin suppression method of measuring hormone kinetics could be used for newly described hormones which are not available for in-vivo studies.

Mid childhood growth has been studied in 26 short children (18M;8F) aged between 5.2 and 11.9 years growing with height velocity standard deviation score (SDS) between 0 and -0.8 and 24 short children (17M;7F) growing with height velocity SDS less than 0.8. Twenty-four hour GH profiles were analysed by an iterative method of pulse detection and subjected to time series analysis to determine dominant periodicity within the data arrays. Children aged less than 7 years displayed no dominant periodicity but after this age a periodicity of 200 min emerged. In the whole sample, differences between growth rate could be explained entirely by pulse amplitude. Nevertheless, the normal decline in height velocity over this age period occurred despite a significant shift in periodicity and an increase in GH pulse amplitude. This modulation of childhood growth by GH pulse amplitude persisted into puberty and the pubertal growth spurt of 14 tall girls was shown to be amplitude modulated with the periodicity unchanged. We conclude that mid childhood and pubertal growth is GH pulse amplitude modulated with a periodicity of approximately 200 min.

We have estimated the half-life of serum growth hormone (GH) in six subjects on 14 occasions following an intravenous bolus injection of either 50 or 500 mU of biosynthetic human growth hormone (B-hGH) while endogenous GH secretion was suppressed by a continuous infusion of somatostatin. The disappearance curve of serum GH was mono-exponential and the mean half-life was 8.9 min (SD 1.5). This is less than previously reported and has important implications for the performance of GH profiles, which should be performed with 10-15 min sampling intervals, and the calculation of pituitary GH secretion rates.

We have performed 24 h growth hormone (GH) profiles in 50 short prepubertal children aged between 5.2 and 12.9 years, growing with height velocity standard deviation scores (SDS) between 0.4 and -3.9. There was an asymptotic relationship between height velocity and spontaneous GH secretion described by the equation: height velocity SDS = A-B(e-cx), where A, B and C are constants and x is a measure of spontaneous GH secretion. We considered GH pulse amplitude to be the better description of spontaneous GH secretion as duration of the GH pulse (the time component of area under the curve) contributed little to the relationship between height velocity and area under the pulse. The distribution of GH secretion was continuous and there was no dividing point between GH insufficiency and sufficiency. Similar overlap was observed when the results of GH responses to insulin induced hypoglycaemia were considered; 14% of slowly growing children (height velocity SDS less than -0.8), had a response greater than 15 mU/l. Likewise serum IGF-I concentrations could not clearly separate slowly growing children from normal individuals. We conclude that height velocity, which ultimately determines height achieved, is controlled predominantly by GH pulse amplitude. The findings suggest that short normal children growing along or parallel to the third height centile could be made to grow faster by the administration of exogenous GH.