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To avoid inappropriate conclusions being drawn from the extensive use of in vitro preparations of sperm-oviduct epithelial binding, it is recalled that events in the genital tract of mammals are regulated by the gonads, primarily by their changing secretion of steroid hormones. Key observations from in vivo models are used to emphasise the dynamic interactions between viable sperm cells and the caudal (distal) portion of the oviduct isthmus, the site of the functional sperm reservoir. These include (1) pre-ovulatory arrest and epithelial binding of intact sperm cells and thereby suppression of completion of capacitation, (2) peri-ovulatory activation and release from binding of discrete sub-populations of competent spermatozoa, and (3) post-ovulatory liberation of large numbers of spermatozoa. These observations underline the influence of endocrine regulation of sperm binding and release by peri-ovulatory Graafian follicles, a point brought out by the enhanced sperm release prompted by diverse treatments with solutions of progesterone. In the light of this evidence, the suitability of in vitro preparations for clarifying physiological events should be questioned, especially if myosalpingeal catecholamines diffusing out of the autonomic nervous system contribute to sperm activation and/or release. None of this is to infer that sperm cells themselves are without influence on their epithelial binding reaction(s). Nor is it to suggest that in vitro models of sperm-oviduct binding are without relevance to the development of sperm evaluation technologies. However, pre-ovulatory sperm-epithelial binding and a regulated peri-ovulatory release should be seen as vital tactics in the overall strategy of achieving successful monospermic fertilisation., ((c) 2007 Wiley-Liss, Inc.)

After recalling male gonadal physiology in respect of tissue temperatures within the scrotal sac, and raising questions concerning abdominal testes, attention turned to mature Graafian follicles and ovarian stroma. Temperature gradients between such tissues were summarized for human, rabbit, pig, and cow, and generally fell in the range of 1.3-1.7 degrees C: follicles were always cooler than stroma. Measurements were made principally by means of a thermo-sensing camera at midventral laparotomy, but also using microelectrodes or thermistor probes sited in the follicular antrum of rabbits and pigs, respectively. When thermo-imaged under the fimbriated extremity of the Fallopian tube, mature pig follicles and stroma could still be distinguished. Such follicles cooled slightly more rapidly during the first 10 s of a 60-s recording interval, after which curves for the two tissues remained parallel. Arresting ovarian blood supply for 5 min had a negligible influence on the temperature differentials. Endoscopy in three models recorded mean differentials of 0.6 +/- 0.1 degrees C - 1.1 +/- 0.1 degrees C between follicles and stroma, but such follicles had not attained mature diameter. Temperature gradients were thought to be generated at least in part by endothermic reactions within mature follicles, reflecting hydration of large extracellular matrix molecules such as proteoglycans. A contribution to the cooling process from the products of leukocyte activity in the follicle wall and antrum could also be involved. Temperature gradients would be maintained locally by counter-current heat exchange mechanisms and, in this context, the microvasculature and lymphatic flow of individual follicles were found to be appropriate. Observations on the temperature of preovulatory follicles appear relevant to procedures of in vitro maturation and in vitro fertilization.

This essay argues strongly that for those sperm cells involved in fertilisation, the process of capacitation represents an active and specific coordination within succeeding regions of the female tract and one whose completion is synchronised with the events of ovulation. Observations on the time-course of capacitation when spermatozoa are first exposed to the uterus and then progress to the Fallopian tubes indicate a synergistic influence of these adjoining portions of the female tract on the rate of capacitation. Three concepts on the control of capacitation are introduced to emphasise the importance of integration in vivo, namely that (1) completion of capacitation is a peri-ovulatory event, (2) suppression of completion of capacitation is an essential storage strategy during a long pre-ovulatory interval, and (3) the process of capacitation comes under the influence of local and systemic ovarian control mechanisms, especially the secretion of progesterone from Graafian follicles soon to ovulate. The last would act to coordinate the final maturation and meeting of male and female gametes. Despite the preceding points, the requirement for such integrated in vivo programming of sperm cell maturation can clearly be overridden in systems of culture. The most reasonable interpretation here would be that a microdrop of culture medium containing eggs, follicular cells and components of follicular fluid would to a considerable extent represent a post-ovulatory environment. Within such a preparation, there would be leaching of the sperm surface among the relatively vast and heterogeneous population of cells, and a proportion of spermatozoa could then respond to 'post-ovulatory signals', not least to molecular influences of the zona pellucida and vitelline products for completion of capacitation. Nonetheless, a physiologically meaningful interpretation of capacitation calls for a stepwise analysis of the dynamic interactions between sperm cell and female tract at successive stages between the uterus and ampullary-isthmic junction., (Copyright 2004 Wiley-Liss, Inc.)

As a means of determining whether ovarian follicular fluid reaches the functional sperm reservoir in the caudal isthmus of the Fallopian tube shortly after ovulation, 0.01-0.02 ml aliquots of whole or steroid-free follicular fluid were introduced into the distal extremity of the isthmus within 1 hr before ovulation. Eggs were recovered during a second intervention 4 hr 45 min-6 hr 10 min after treatment and examined by phase-contrast microscopy for the normality of fertilisation. In a separate experiment, 0.01-0.02 ml aliquots of 10 microM calcium ionophore solution were introduced into the same site in comparable animals. Sixty-nine fertilised eggs were recovered from 12 fallopian tubes treated with whole follicular fluid, of which 24 (34.8%) were polyspermic. The 12 contralateral control tubes (PBS-treated) yielded 47 fertilised eggs, of which only one (2.1%) was polyspermic (P < 0.001). Steroid-free aliquots of the same follicular fluid introduced bilaterally into eight fallopian tubes (4 animals) resulted in recovery of 59 fertilised eggs, of which only one (1.7%) was polyspermic. Treatment with ionophore solution yielded a 41.6% incidence of polyspermy (10 of 24 eggs from four tubes) compared with 3.8% polyspermy (1 egg) from the control tubes (P < 0.01). Dispermy was the principal form of polyspermy. The numbers of accessory spermatozoa on/in the zona pellucida were increased by the experimental treatment. Follicular fluid passing down the fallopian tube ampulla at ovulation was therefore considered not to be the physiological stimulus for an initial, tightly-controlled release of spermatozoa from epithelial binding in the caudal isthmus. Indeed, because such sperm activation commences shortly before ovulation, a locally transmitted ovarian programming with relatively high concentrations of follicular hormones remains the favoured model. Although pre-ovulatory progesterone is considered to be the coordinating steroid of increasing influence in these pre-fertilisation events, its effects are proposed to be modulated in the endosalpinx by mobilisation of Ca2+ ions into a discrete population of bound spermatozoa. Results of the steroid-free follicular fluid and calcium ionophore treatments stand in support., (Copyright 1999 Wiley-Liss, Inc.)

This review considers the problem of ovotestis formation in animals of 38,XX chromosome complement. After a clinical description, attention focuses on the condition of the gonads and genital tract. A complete spectrum of gonadal types has been found, ranging from a single ovotestis almost invariably on the right-hand side to both gonads appearing as testicular-like structures, sometimes with a distinct tunica albuginea. The ovotestis or testis-like structure may have descended to an inguinal or scrotal location. Although interstitial cells of Leydig and seminiferous tubules were always abundant in testicular tissue, germ cells were never present. The lumen of the seminiferous tubules was packed with pale-staining, Sertoli-like cells. A bicornuate uterus was characteristic but suppression of the proximal portion of the Müllerian duct always adjoined an ovotestis; a corresponding development of the Wolffian duct featured as a convoluted epididymis. Inhibition of the Fallopian tube was attributed to a local influence of AMH from the Sertoli cells, as was the failure of small Graafian follicles within an ovotestis to respond to injected gonadotrophins. As to the aetiology of an ovotestis, defective colonisation of the genital ridges by primordial germ cells is considered, as is evidence for incorporation of adrenal cells into the embryonic gonad. Molecular probing has failed to reveal the classical sex-determining gene, Sry, and other Y-related DNA sequences such as Zfy and DYZI in almost all the intersex animals examined. Currently favoured as an explanation for ovotestis formation is a mutation in the inhibin gene within granulosa cells of Graafian follicles. Such a mutation would prompt secretion of the closely comparable glycoprotein molecule AMH in these genetic females, with a resultant progressive virilisation of gonadal tissue. The proposed mutation may be carried as an autosomal recessive gene by certain boars. Varying amounts of AMH secretion or differing timescales for the transition from inhibin to AMH could in part explain differing degrees of ovotestis formation. Despite this proposition, interactions between genes that prescribe functional testicular tissue, enhanced rates of gonadal development, and left-right asymmetries between the paired gonads now require systematic study.

This essay considers the means whereby sperm/egg ratios close to unity are generated during the initial stages of fertilisation in placental mammals. Pre-ovulatory graafian follicles and their contents are seen to be key structures orchestrating the events of sperm progression and coordinating the subsequent meeting of male and female gametes. Three levels of control over the numbers of spermatozoa activated and released from the functional reservoir in the caudal region of the fallopian tube isthmus are proposed. A primary control would be obtained by means of a countercurrent transfer of ovarian follicular progesterone from the ovarian vein into the tubal branch of the ovarian artery. The concentration of progesterone so transferred would be proportional to the number of preovulatory follicles, and thus to the number of eggs to be shed, and would act progressively to reduce sperm binding to the endosalpinx of the caudal isthmus. Differential timing of the release from epithelial binding may be a crucial means of achieving the initial low sperm/egg ratios. a secondary regulation of the release of graded numbers of viable spermatozoa towards the ampullary-isthmic junction of the fallopian tubes would be by means of molecular messages derived from the mucified oocyte-cumulus complex shortly before and after the time of ovulation. Third would be reorientation of sperm trajectories by molecular gradients within the cumulus cell mass to direct competent spermatozoa to those oocytes as yet unpenetrated. Together these differing levels of control would impose low sperm/egg ratios during the initial stages of fertilisation, such strict quantitative regulation of male gametes lasting at least until the block to polyspermy is fully established and the vitellus is no longer at risk from further sperm penetration.

Studies on protein molecules in oviduct luminal fluid are viewed historically, and then in terms of more recent studies on a possible involvement of unique glycoproteins in embryonic development. As a caution, however, it is noted that incorporation of such molecules into the vitellus may be nonspecific. The question is raised as to whether oviduct glycoproteins could be acting primarily in a physical sense to stabilize differing chemical environments along the oviduct. Equally or more importantly, glycoproteins might be acting as carrier molecules to present cations and metabolic substrates at appropriate concentrations to the vitelline membrane. This latter possibility is examined in some detail and could be tested by manipulating the composition of the perivitelline fluid. Glycoproteins may also be critically involved in regulating the physiological competence of spermatozoa in the pre- and peri-ovulatory oviduct, in maintaining a coordinated pattern of cilial beat, and in immunosuppressive functions within the oviduct, not least in those associated with the masking of paternal antigens on both spermatozoa and embryos.

Reasoning from the premises that 1) the sperm:egg ratio at the time of activation of the secondary oocyte in mammals is close to unity under conditions of spontaneous mating, 2) a majority of eggs within the cumulus oophorus of a polytocous species is fertilized in a reasonably short interval of time, and 3) spermatozoa would find it difficult to reverse their approach to the zona pellucida, it is proposed that molecular gradients exist to divert spermatozoa penetrating the cumulus mass away from eggs already activated and towards eggs as yet unfertilized. Possible sources of such molecular cues are considered, as is the event that triggers their release.

Because the exceptionally high incidence of polyspermic fertilisation has been emphasised as a major defect in systems of in vitro fertilisation in pigs, the aetiology of the condition has been analysed in a series of experiments in vivo in the search for a common underlying cause and possible means of mitigation. Whereas the defense mechanism against polyspermy in pig oocytes is classically viewed as zona reaction, more recent evidence suggests a secondary block at the vitelline surface. Both blocks may be compromised in situations leading to polyspermy, although deleterious influences seem to be expressed principally in an inadequate zona block, as judged by the presence of perivitelline spermatozoa. Postovulatory aging of mammalian oocytes prior to sperm penetration leads to polyspermy, as can be demonstrated in pig eggs. The primary lesion may concern the cortical reaction, owing to a delayed and incomplete exocytosis of the vesicular contents. Eggs ovulated after gonadotrophin treatment during the luteal phase of the cycle show a high incidence of polyspermic penetration (60.6%), as do those shed at estrus in animals treated with progesterone systemically (40%) or by local microinjections in the oviduct wall (32.3%). Whereas progesterone may be modifying interactions of the gametes and responses of the egg organelles in all four above experimental situations, enhanced numbers of spermatozoa ascending a more patent isthmus appear to be the principal cause of polyspermy.(ABSTRACT TRUNCATED AT 250 WORDS)