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Search for other papers by Timothy G Jenkins in
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Andrology and IVF Laboratories, Department of Physiology, Department of Surgery
Andrology and IVF Laboratories, Department of Physiology, Department of Surgery
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Recent work in the field of male fertility has yielded significant increases in our understanding of the sperm epigenome and its potential role in embryonic development. These new findings have enabled a broad classification of a normal epigenetic state in the male gamete and have provided insight into the possible etiologies of some idiopathic male infertility cases. Histone retention and modification, protamine incorporation into the chromatin, DNA methylation, and spermatozoal RNA transcripts appear to play important roles in the epigenetic state of mature sperm. These epigenetic factors may reveal a historical record of spermatogenesis, portend future functions in embryogenesis, and help to elucidate mechanism of pluripotency. In contrast to the once held dogma regarding the importance of the paternal epigenome, the unique epigenetic landscape in sperm appears to serve more than the gamete itself and is likely influential in the developing embryo. In fact, growing evidence suggests that mature sperm provide appropriate epigenetic marks that drive specific genes toward activation and contribute to the pluripotent state of the embryonic cells. Although not definitive, the current literature provides evidence for the role of the sperm epigenome in the embryo. Future work must be focused on the characterization of epigenetic abnormalities commonly found in individuals with compromised fertility to further establish this role. Additionally, studies should target the effects of environment and aging on the sperm epigenetic program and subsequent fertility loss to determine the etiology of aberrant epigenetic profiles.
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Summary. The effect of the removal of one testis from cross-bred lambs at 1, 4, 8 or 12 weeks of age on plasma FSH, LH and testosterone was studied until 16 weeks of age. Hemicastration at all ages elicited a significant increase in plasma FSH compared to controls without a corresponding change in plasma LH or testosterone. The raised FSH after hemicastration at 1 or 4 weeks of age was suppressed to control levels between weeks 7 and 8; such a suppression was not observed in the 4 weeks following hemicastration at 8 or 12 weeks of age. The weight of the remaining testis had increased compared with the control by 12 weeks of age after hemicastration at 1 week ( + 69%), 4 weeks ( +13%) and 8 weeks (+ 40%); hemicastration at 12 weeks of age also resulted in growth of the remaining testis at 16 weeks ( +82%). The total androgen production of interstitial cells in response to ovine LH stimulation in vitro did not differ significantly between lambs of 1 and 12 weeks of age, or in animals of 4, 8 and 12 weeks of age after hemicastration at 1 week of age.
Subdermal implantation of oestradiol-17β into 1-week hemicastrated lambs at the time of operation or at 6 weeks of age increased plasma oestradiol concentrations by approximately 2–4-fold, prevented the FSH and testicular growth responses to hemicastration and suppressed plasma LH and testosterone to levels lower than those in control lambs. The total androgen response of interstitial cells from the remaining testis of oestradiol-implanted lambs at 12 weeks of age was significantly reduced.
We suggest that the pituitary—testis axis varies in sensitivity during the prepubertal period although the interstitial cellular response of the testis to LH stimulation remains constant.
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Summary. Rhythmic contractions occur in the sheep uterus at oestrus and during pregnancy from about 65 days to term (145 days). To define factors responsible for these contractions we have examined and quantified the degree of synchronization of electrical activity in the uterus and isolated segments of myometrium in 3 types of experiments. In the first, a segment of myometrium was totally separated from the uterus. After a period of 9–16 days the isolated tissue developed a typical pattern of uterine activity which showed no significant degree of synchronization with EMG bursts in the body of the uterus. During labour, the isolated tissue showed changes in activity similar to those observed in the uterus. In the 2nd experiment, the tubal end of one of the uterine horns was severed from the uterus, but a connection was retained with the uterus via the oviduct and ovarian blood vessels. Activity in the partly isolated segment remained in synchrony with the uterus. In a 3rd experiment, impulse propagation through nerves and smooth muscle to the tip of a horn was disrupted by severing 'the tip' from the uterus while its blood supply from the ovarian vessels was retained. The blood vessels were momentarily frozen, and denervation confirmed by monoamine histofluorescence. In 5 out of 6 animals the operated tissue showed activity that was not synchronous with the rest of the uterus. These data indicate that: (1) isolated uterine muscle in vivo has rhythmicity resembling that of intact myometrium and (2) systemic or local circulating factors are not responsible for synchronizing uterine activity before parturition, although circulating factors do play a major role in increasing the uterine activity which occurs at parturition and at oestrus, and (3) hydraulic continuity between different regions of the uterus is not essential for maintaining co-ordinated activity.
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Sixteen-day-old fetal mouse ovaries were slowly frozen in 1.5 mol dimethylsulfoxide ml−1 and subjected to one of two thawing procedures – fast thaw or slow thaw. Fresh and frozen–thawed fetal ovaries were transplanted orthotopically (to the bursal cavity) to either bilaterally or unilaterally ovariectomized adult female recipients. Fresh fetal ovaries were also transplanted heterotopically (under the kidney capsule) to intact, bilaterally or unilaterally ovariectomized adult females. Transplantation of fetal ovaries to bilaterally ovariectomized adult recipients resulted in restoration of cyclic activity within 20.5 ± 4.7 (mean ± sem) days or 23.4 ± 0.8 days in orthotopic and heterotopic groups, respectively. Developing follicles and corpora lutea were observed within 4 weeks after transplantation of fetal ovaries to heterotopic sites and within 6 weeks after transplantation to orthotopic sites. After orthotopic transplantation, 33% of the recipients became pregnant. Orthotopic or heterotopic transplantation to intact of unilaterally ovariectomized recipients resulted in quiescence of the fetal ovary. After cryopreservation, transplantation of fetal ovaries to bilaterally ovariectomized recipients resulted in restoration of cyclic activity within 19.3 ± 2.1 days and 23.4 ± 5.1 days after transplantation in slow thaw and fast thaw groups, respectively. Fertility was restored to 86% of fast thawed and 25% of slow thawed fetal ovary transplants to bilaterally ovariectomized adult recipients. No ovarian tissue was observed on the side of the fetal graft in unilaterally ovariectomized recipients that received frozen–thawed fetal ovaries. These results demonstrate that cryopreserved fetal ovarian tissue can be transplanted to adult recipients with subsequent restoration of fertility and that this process is dependent on the absence of the ovaries of the recipients.
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Summary. Rat testicular interstitial fluid and hydroxycholesterol both stimulated testosterone production by isolated Leydig cells in vitro in a dose-dependent manner, but the dose—response lines were not parallel. The addition of cycloheximide blocked the stimulation by interstitial fluid but not that of hydroxycholesterol. Use of the compounds SU 10603 and cyanoketone (which inhibit 3β-hydroxysteroid dehydrogenase and 17α-hydroxylase respectively) or aminoglutethimide (which acts on the cholesterol side-chain cleavage enzyme) showed that the stimulatory factor(s) in interstitial fluid stimulated steroidogenesis at the cholesterol side-chain cleavage enzyme, before the conversion of pregnenolone. This enzyme is rate-limiting in the synthesis of testosterone by Leydig cells and a site of action of LH; therefore, these results support the view that an interstitial fluid factor may be involved in the paracrine regulation of testicular steroidogenesis.
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Summary. The concentration of progesterone in maternal plasma of the bandicoot increased from 3·9 to 12·6 ng/ml between 11 and 4 days before parturition and remained at this level for at least 7 days. Concentrations of 13,14-dihydro-15-keto-prostaglandin F-2α increased from basal levels of 288 pg/ml (4 days before birth) to maximal levels of 2534 pg/ml immediately after parturition, then decreased progressively. It is suggested that PGF-2α, but not progesterone, influences the initiation of parturition in this species.
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Summary. In sheep the basal concentration of LH in jugular vein plasma was significantly higher during the first 50 days of gestation than in late pregnancy or at parturition. The pituitary response to a single i.v. injection of 200 μg synthetic LH-RH was determined at different stages of gestation and compared with that of anoestrous and cyclic sheep. Pituitary response to LH-RH decreased progressively with advancing gestation: by 56 days after mating the response had declined to 35% and by parturition to 14% of the value in anoestrous sheep. The pituitary response to LH-RH increased after parturition and the pattern of recovery differed in non-lactating and lactating sheep. By 63 days post partum the response to LH-RH in non-lactating and lactating animals had returned to values similar to those in sheep during anoestrus and sheep during the luteal phase of the oestrous cycle.
A decrease in pituitary responsiveness during pregnancy was associated with a decrease in pituitary content of LH. The quantity of LH released in response to a standard injection of LH-RH was linearly related to pituitary LH content.
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Summary.
A double isotope derivative assay and a simple competitive protein-binding assay were used to measure peripheral plasma progesterone levels during the pig oestrous cycle. In view of the similarity between the results, the more convenient protein-binding method was employed to determine progesterone levels during prepuberty, the oestrous cycle, early and late pregnancy, parturition and lactation. Peripheral plasma oestradiol-17β levels were measured during the oestrous cycle, early pregnancy and around the time of parturition.
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Endometrial oxytocin receptor concentrations and oxytocin-induced plasma concentrations of 13,14,dihydro-15-keto prostaglandin F2α were investigated on days 14 and 17 of the oestrous cycle and on days 14, 17, 25, 65, 85 and 145 of gestation in ewes. Total 13,14,dihydro-15-keto prostaglandin F2α release in response to a bolus injection of oxytocin was significantly (P < 0.05) higher at luteolysis (day 17 of the oestrous cycle) than at any other stage of the oestrous cycle or in early gestation. On days 65, 85 and 145 of gestation, total prostaglandin release was significantly (P < 0.05) increased compared with earlier in gestation. Maximum concentrations of 13,14,dihydro-15-keto prostaglandin F2α in response to oxytocin followed a similar pattern. Oxytocin receptor concentrations reflected total oxytocin-induced 13,14,dihydro-15-keto prostaglandin F2α release, with increased oxytocin receptor concentrations occurring on day 17 of the oestrous cycle, compared with those observed on day 14 of the oestrous cycle and on days 14, 17 and 25 of gestation. By day 65 of gestation, oxytocin receptor concentrations were again increased. However, on days 85 and 145 of gestation, oxytocin receptor concentrations had decreased to concentrations similar to those observed in early gestation. These results indicate that oxytocin-induced 13,14,dihydro-15-keto prostaglandin F2α release during early gestation is minimal despite the presence of endometrial oxytocin receptors. In mid-gestation, oxytocin-stimulated 13,14,dihydro-15-keto prostaglandin F2α release is increased with a concomitant increase in uterine oxytocin receptor concentrations. However, by the later stages of gestation, oxytocin receptor concentrations, but not oxytocin-stimulated 13,14,dihydro-15-keto prostaglandin F2α release, were again decreased. Thus, there appears to be a dissociation between the response to oxytocin and endometrial oxytocin concentrations at specific stages of the reproductive cycle in sheep.
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Introduction
The morphological features and associations of the Sertoli and Leydig cells in the adult have clear implications for their functional characteristics and for their development in the maturing testis. For example, adult Sertoli cells form intimate cellular associations with germ cells through both physical contact and gap junctions with significance for metabolic cooperation between the two cell types. Inter-Sertoli cell junctional specializations are influential in the context of the 'blood—testis barrier'. They also establish the polarity of these cells with their basal aspect against a peritubular myoid cell layer and a luminal aspect from which fluid is secreted. Leydig cells are associated with the peritubular myoid cells and with the interstitial blood vessels, being surrounded to varying extents according to species by interstitial spaces and fluid. There is a positive correlation between the amount of testosterone secreted by perfused testes in vitro of various species and the volume of
