Endogenous Gonadotropin Secretion Research Articles

SAT336 A Successful Ovulation Induction And Embryo Generation In A Woman With P450-oxidoreductase Deficiency From Mutation G539R, Which Preferentially Impairs 17,20-lyase Activity

Abstract Disclosure: S. Charoensri: None. M. Thakur: None. R.J. Auchus: None. Introduction: Cytochrome P450 oxidoreductase (POR) deficiency is an autosomal recessive disorder causing decreased activity of several P450 enzymes, including CYP21A2, CYP17A1, and CYP19A1 that are essential for steroidogenesis in the adrenals and gonads. Female POR deficiency patients are typically manifested with genital ambiguity, abnormal menstruation, and infertility. Very few pregnancies have been documented from these patients. Case presentation: During an evaluation for infertility, a 35-year-old woman with late menarche, irregular cycles, and unruptured ovarian follicles was diagnosed with POR deficiency due to compound heterozygous pathogenic variant c.1615G>C (G539R) and a large deletion c.1669+5_1669+32del in the POR gene. Because mutation G539R preferentially impairs the 17,20-lyase activity of CYP17A1, she underwent in-vitro fertilization (IVF) with the protocol that has been used successfully to achieve pregnancy in incomplete 17-hydroxylase deficiency. Oral dexamethasone of 0.5 mg/day was given to suppress the adrenal-derived progesterone. After one menstrual cycle induced with estradiol and progesterone priming, leuprolide acetate was used to down-regulate endogenous gonadotropin secretion, then the oocyte maturation was induced with recombinant follicle-stimulating hormone (rFSH) and highly purified menotrophin. In the first cycle, 6 eggs were retrieved, 2 that were mature and fertilized with intracytoplasmic sperm injection (ICSI); however, none advanced to the blastocyst stage. She underwent the same protocol in a second IVF cycle with higher rFSH dosing. Despite increasing dexamethasone to 1.5 mg/day, progesterone rose to 4.9 ng/mL, while estradiol peaked at 120 pg/mL, consistent with progesterone accumulation in the developing ovarian follicles due to POR deficiency. From 6 eggs retrieved, 5 eggs were mature and all fertilized, and 3 developed past day 3. On day 6, one embryo (grading 5BB) was biopsied for preimplantation genetic testing and frozen. The second phase of the treatment plan is to lower adrenal-derived progesterone with a combination of hydrocortisone and prednisolone, prepare the endometrium with estradiol followed by progesterone, and perform embryo transfer. Conclusions: Very few examples of pregnancy in women with POR deficiency have been reported, and we describe the first example of successful ovulation induction and embryo generation in a woman with POR deficiency caused by the G539R mutation, which preferentially impairs 17,20-lyase activity. The complex array of steroid excess and deficiencies, from both adrenal and ovarian origin, must be systematically managed during assisted reproduction treatment for these women. Presentation: Saturday, June 17, 2023

Comparative study between agonist and antagonist protocols in PCOS patients undergoing ICSI: a cross-sectional study

BackgroundPolycystic ovary syndrome (PCOS) is one of the most common endocrinopathies affecting 5–10% of women of reproductive age. The syndrome is surrounded by controversies regarding both its diagnosis and treatment. The introduction of long-acting GnRH agonists in the late 1980s revolutionized the approach to ovarian stimulation in assisted reproductive technologies by providing the means to downregulate endogenous pituitary gonadotropin secretion and thereby prevent a premature luteinizing hormone surge during exogenous gonadotropin stimulation. The relatively recent introduction of GnRH antagonists in clinical practice has provided another option for ovarian stimulation in IVF. The purpose of this study was to compare the efficacy of the fixed GnRH antagonist vs. GnRH agonist long protocol in patients with polycystic ovary syndrome treated by ICSI.ResultsThere is a statistically significant difference between both groups in view of the received dose of gonadotrophin (1901.7 ± 400.6 vs. 1789 ± 368 with p = .004) and duration of stimulation (11.3 ± 0.8 vs. 10.3 ± 1.1 with p = .017). There is no significant difference between both groups in view of pregnancy outcome (37% vs. 32% with p = .125). There is a significant difference between both groups in view of ovarian hyperstimulation syndrome (OHSS) incidence where the rates were 15%, 6%, and 1.5% vs. 4.5%, 2.5%, and .05% with p = 0.04 for mild, moderate, and severe, respectively, form of OHSS in group 1 and group 2.ConclusionThe antagonist protocol may be the preferred stimulation protocol for PCOS patients treated by ICSI in view of the reduction of OHSS incidence rates without compromising the pregnancy outcome.

Clinical practice guidance for the use of clomiphene citrate in Male Hormone Replacement Therapy (HRT)

Introduction: Inhibition of pituitary gonadotropin secretion in men by testosterone (T) is principally mediated by aromatization to estrogen (E), which inhibits hypothalamic secretion of gonadotropin-releasing hormone (GnRH). Material and Methods: Longitudinal clinical investigation unit-based evaluation of the clinical and biochemical response to E-receptor blockade. Initial monotherapy with 50 mg of clomiphene citrate (CC) daily for a period of 9 months, with diurnal morning peak testosterone and luteinizing hormone (LH) levels evaluated at three-month intervals thereafter. The patient then resumed hormone replacement therapy (HRT) using T cream with adjuvant CC therapy. Main Outcome Measures were Baseline and stimulated T and LH levels; effect on sexual function. Result(S): CC therapy resulted in complete normalization of pulsatile gonadotropin secretion, serum T level, and sexual function. Conclusion(S): Isolated hypogonadotropic hypogonadism (IHH) may result from an acquired defect of enhanced hypothalamic sensitivity to E-mediated negative feedback. Whereas direct T replacement therapy can further suppress endogenous gonadotropin secretion, treating IHH men with gonadotropins can stimulate endogenous T secretion and enhance fertility potential. Reversal of gonadotropin deficiency with CC was found to have a similar biological effect.

Transition in endocrinology: induction of puberty.

Puberty is the period during which we attain adult secondary sexual characteristics and reproductive capability. Its onset depends upon reactivation of pulsative GNRH, secretion from its relative quiescence during childhood, on the background of intact potential for pituitary-gonadal function. This review is intended: to highlight those current practices in diagnosis and management that are evidence based and those that are not; to help clinicians deal with areas of uncertainty with reference to physiologic first principles; by sign-posting relevant data arising from other patient groups with shared issues; to illustrate how recent scientific advances are (or should be) altering clinician perceptions of pubertal delay; and finally, to emphasise that the management of men and women presenting in advanced adult life with absent puberty cannot simply be extrapolated from paediatric practice. There is a broad spectrum of pubertal timing that varies among different populations, separated in time and space. Delayed puberty usually represents an extreme of the normal, a developmental pattern referred to as constitutional delay of growth and puberty (CDGP), but organic defects of the hypothalamo-pituitary-gonadal axis predisposing to hypogonadism may not always be initially distinguishable from it. CDGP and organic, or congenital hypogonadotrophic hypogonadism are both significantly more common in boys than girls. Moreover, around 1/3 of adults with organic hypogonadotrophic hypogonadism had evidence of partial puberty at presentation and, confusingly, some 5-10% of these subsequently may exhibit recovery of endogenous gonadotrophin secretion, including men with Kallmann syndrome. However, the distinction is crucial as expectative ('watch-and-wait') management is inappropriate in the context of hypogonadism. The probability of pubertal delay being caused by organic hypogonadism rises exponentially both with increasing age at presentation and the presence of associated 'red flag' clinical features. These 'red flags' comprise findings indicating lack of prior 'mini-puberty' (such as cryptorchidism or micropenis), or the presence of non-reproductive congenital defects known to be associated with specific hypogonadal syndromes, e.g. anosmia, deafness, mirror movements, renal agenesis, dental/digital anomalies, clefting or coloboma would be compatible with Kallmann (or perhaps CHARGE) syndrome. In children, interventions (whether in the form or treatment or simple reassurance) have been historically directed at maximising height potential and minimising psychosocial morbidity, though issues of future fertility and bone density potential are now increasingly 'in the mix'. Apubertal adults almost invariably harbour organic hypogonadism, requiring sensitive acknowledgement of underlying personal issues and the timely introduction of sex hormone replacement therapy at more physiological doses.

It’s time to pay attention to the endometrium

The physiologic importance of the endometrium in assisted reproductive technology is now receiving much research attention. The historical importance of ultrasound for determination of endometrial pattern, thickness and contractility is reviewed and speculation provided for a possible mechanism of the adverse effect of thin endometrium on implantation.

Contribution of endogenous LH secretion to hCG-stimulated androgen production in women with polycystic ovary syndrome

OBJECTIVE: In polycystic ovary syndrome (PCOS), hyperandrogenemia is a result of enhanced theca cell androgen production driven by abnormally increased LH secretion. To determine the extent to which endogenous gonadotropin secretion may contribute to ovarian androgen overproduction in PCOS women, we measured basal and stimulated serum androgen levels following intravenous (iv) injection of r-hCG before and after administration of a GnRH antagonist.

Modulating peripheral gonadotrophin levels affects follicular expression of mRNAs encoding insulin-like growth factor binding proteins in sheep

Evidence suggests that the insulin-like growth factor binding proteins (IGFBPs) are involved in modulating the role that IGF-I and -II play in regulating follicular growth and development in sheep. However, little information exists as to the role that key peripheral factors play in regulating the expression of IGFBP components within the follicle. The present study investigated the regulatory effects of FSH and LH on gene expression for IGFBP-2 to -6 in ovine follicles, using bovine follicular fluid (bFF) and gonadotrophin-releasing hormone antagonist (GnRHa) model systems to perturb endogenous gonadotrophin secretion. Gene expression studies were carried out using in situ hybridisation with sheep-specific ribonucleotide probes. Treatment of ewes with bFF had few consistent effects on IGFBP-3 and -4 mRNA expression in follicles, whereas bFF treatment resulted in significant decreases in IGFBP-2 and IGFBP-6 mRNA expression in only medium follicles 60 h after onset of bFF, and in follicles 12 h after the onset of bFF, respectively. Treatment of ewes with GnRHa resulted in transient significantly increased IGFBP-2 mRNA in healthy follicles in comparison to early atretic or atretic follicles 12 h post-GnRHa ( P < 0.05), in IGFBP-3 mRNA in early atretic and atretic follicles 36 h post-GnRHa ( P < 0.001), and IGFBP-5 mRNA in follicles 12 h post-GnRHa ( P < 0.001). In contrast, GnRHa treatment resulted in significant decreases in IGFBP-4 ( P < 0.001) and IGFBP-6 ( P < 0.01) mRNA expression in large follicles 36 h post-GnRHa, and atretic follicles by 60 h post-GnRHa, respectively. These data highlight that FSH and LH are involved, at least in part, in mediating the proliferative and differentiative changes in intrafollicular IGFBP levels that are observed during follicular growth and atresia in the sheep.

Oral contraceptive pretreatment in women undergoing controlled ovarian stimulation in ganirelix acetate cycles may, for a subset of patients, be associated with low serum luteinizing hormone levels, reduced ovarian response to gonadotropins, and early pregnancy loss

Oral contraceptive pretreatment facilitated scheduling of pure FSH/GnRH antagonist cycles but in a small subset of patients was associated with low serum LH levels, reduced ovarian response, and early pregnancy loss. Supplementation with LH could be examined as a possible way to improve cycle outcome.

Modulating peripheral gonadotrophin levels affects follicular expression of mRNAs encoding insulin-like growth factors and receptors in sheep

Evidence suggests that the insulin-like growth factor (IGF) system is involved in follicular growth and development in sheep. However, little information exists as to the role that key peripheral factors play in regulating the expression of IGF components within the follicle. The present study investigated the regulatory effects of FSH and LH on gene expression for IGF ligands and receptors in ovine follicles, using bovine follicular fluid (bFF) and gonadotrophin-releasing hormone antagonist (GnRHa) model systems to perturb endogenous gonadotrophin secretion. Gene expression studies were carried out using in-situ hybridisation with sheep-specific ribonucleotide probes. Treatment of ewes with bFF had no effect on IGF-I mRNA levels. However, IGF-II mRNA levels, particularly in small follicles, and follicular type II IGF-R gene expression significantly increased following bFF administration ( P < 0.001). Conversely, there was a significant ( P < 0.001) decrease in type I IGF-R mRNA levels after only 12 h of bFF treatment, especially in healthy follicles, although this was transient and was followed by a significant ( P < 0.01) increase in gene expression levels by 60 h of bFF treatment. Treatment of ewes with GnRHa resulted in a significant increase in mRNA levels encoding IGF-I ( P < 0.001), IGF-II in early atretic and large follicles ( P < 0.05), and type II IGF-R in healthy and early atretic follicles ( P < 0.001). In contrast, GnRHa administration decreased type I IGF-R gene expression levels after 60 h of treatment ( P < 0.001). These data highlight the roles that endogenous FSH and LH play in regulating IGF ligand and receptor gene expression in the sheep follicle.

Aromatase inhibitors in ovarian stimulation

The selective estrogen receptor modulator, clomiphene citrate (CC), has been the principal drug used for induction of ovulation in women with polycystic ovarian syndrome (PCOS). CC is associated with adverse side effects and low pregnancy rates attributed to long-lasting estrogen receptor depletion. Anastrozole and letrozole are potent, non-steroidal, reversible aromatase inhibitors, developed for postmenopausal breast cancer therapy. We hypothesized that aromatase inhibitors could mimic the action of CC in reducing estrogen negative feedback on follicle stimulating hormone (FSH) secretion, without depleting estrogen receptors. In a series of preliminary studies, we reported the success of aromatase inhibition in inducing ovulation in anovulatory women with PCOS. Moreover, we showed that concomitant use of aromatase inhibitors resulted in a significant reduction of the FSH dose needed for controlled ovarian hyperstimulation. We suggest that aromatase inhibitors act through an increase in endogenous gonadotropin secretion as well as through increased intraovarian androgen levels that may increase ovarian FSH receptors. Recently, we demonstrated the safety of aromatase inhibitors in pregnancy outcome studies examining spontaneous pregnancy loss, multiple pregnancy rates and congenital anomalies compared to a control group of infertility patients treated with CC.

Complete reversal of adult-onset isolated hypogonadotropic hypogonadism with clomiphene citrate

Inhibition of pituitary gonadotropin secretion in men by T is principally mediated by aromatization to estrogen (E), which inhibits hypothalamic secretion of GnRH. We hypothesized that adult-onset isolated hypogonadotropic hypogonadism (IHH) might result from an altered central set-point for E-mediated negative feedback. Longitudinal clinical investigation unit-based evaluation of the clinical and biochemical response to E-receptor blockade. A 31-year-old man presenting with an 18-month history of sexual dysfunction resulting from severe adult-onset IHH (LH 1.7 U/L, FSH 2.0 U/L, T 3.5 nmol/L). Initial therapy with 50 mg of clomiphene citrate (CC) three times a day for 7 days, with overnight LH pulse profiling and 9 am T levels evaluated at baseline and on completion. A 2-month washout period, followed by low-dose maintenance therapy (25-50 mg/d) for 4 months. Baseline and stimulated T levels and LH pulsatility; effect on sexual function. Clomiphene therapy resulted in complete normalization of pulsatile gonadotropin secretion, serum T level, and sexual function. Isolated hypogonadotropic hypogonadism may result from an acquired defect of enhanced hypothalamic sensitivity to E-mediated negative feedback. Whereas direct T replacement therapy can further suppress endogenous gonadotropin secretion, treating IHH men with gonadotropins can stimulate endogenous T secretion and enhance fertility potential. On theoretical grounds, reversal of gonadotropin deficiency with CC might be expected to have a similar biological effect.

O-166: FSH levels predict success in hyperresponders: How much “coasting” can a follicle withstand?

Withdrawing gonadotropins to delay hCG administration is commonly used to prevent ovarian hyperstimulation syndrome in patients with elevated estradiol (E2) levels. However, this technique of “coasting” also places patients at risk for cycle cancellation due to unpredictably falling E2 levels when follicular growth is not supported by exogenous FSH. Our objective was to determine whether monitoring FSH during coasting could predict subsequent E2 levels, cycle cancelllation, and IVF outcomes. In patients who underwent a period of coasting, we compared FSH levels in IVF cycles that proceeded on to oocyte retrieval with those that were cancelled secondary to a significant drop (>20%) in E2 following hCG. From January 2004 to January 2006, all patients who coasted 1-4 days during an IVF cycle using a GnRH agonist and ejaculated spermatozoa were included. Baseline patient characteristics, duration of coasting, and FSH values on the IVF start day were recorded. Serum samples prepared by centrifugation at 3,000 rpm for seven minutes and stored at -80°C untill assayed. Serum samples during each day of coasting were collected and FSH measured on an Immulite 2000 Analyzer (DPC). FSH levels on the day of hCG trigger (D1), the day prior to hCG trigger (D-1), and two days prior to hCG trigger (D-2) were assessed. Single factor ANOVA, chi square, and t-test were used for analysis. One hundred and twenty-nine patients were identified within our inclusion criteria. Of these, 16 cycles were cancelled after coasting secondary to a decrease in E2>20% following hCG administration and 113 continued to oocyte retrieval. There was no difference in cancelled and non-cancelled cycles in patient age, BMI, parity, cause of infertility, number of prior IVF cycles, gonadotropins consumed, or duration of coasting. Baseline FSH values reflecting their endogenous gonadotropin secretion while on a GnRH agonist were also compared and found to be no different between the two groups. FSH values on the day of hCG were significantly lower in the cancelled cycles compared to non-cancelled 3.1 ± 1.8 vs. 5.5 ± 2.7 (p<0.01). The FSH of D-1 samples were also found to be lower in the cancelled group 5.36 ± 3.2 vs. 7.4 ± 3.8 (p<0.05). D-2 FSH values in cancelled cycles trended lower than retrieved cycles 7.6 ± 3.1 vs. 9.2 ± 5.6 but were not significant. In a sub-analysis, the group that proceeded to embryo transfer was then divided into those with FSH values <5 mIU/ml (n=57) and those ≥5mIU/ml (n=49) on the day of hCG trigger and their outcomes compared. This discriminatory value was based upon our previous work showing an association between the FSH levels <5 mIU/ml and impaired pregnancy rates. There was no difference in total oocyte yield (15.1 vs. 15.7) or MII (12.2 vs. 13.7) oocytes per patient. However, fertilization was markedly impaired 13.2% vs. 75.1% (P<0.01) in the group with lower FSH values on the day of hCG. Clinical pregnancy rate 53.6% vs. 60.2% (p=0.06) was also compromised in this group of patients. Measuring FSH levels during stimulation is a useful tool to guide clinical decision making in coasting patients. Profoundly low levels are predictive of a subsequent dramatic decrease in E2 which may be an indication to abandon coasting and supplement with low doses of gonadotropins. FSH values <5mIU/ml on the day of hCG also predict poor fertilization rates and may assist in counseling these patients on whether to proceed to oocyte retrieval.

Editorial Commentary

Editorial Commentary

Pubertal Augmentation in Juvenile Rhesus Monkey Testosterone Production Induced by Invariant Gonadotropin Stimulation Is Inhibited by Estrogen

Experimental and epidemiological studies have indicated the adverse impact of changing estrogen [17beta-estradiol (E2)] milieu or of endocrine disrupters on testis development and function. This study examines the direct impact of elevated E2 levels on gonadotropin-induced pubertal testis development and function in the primate. Juvenile monkeys, which have characteristically little endogenous gonadotropin secretion, were treated with pulsatile infusions of recombinant monkey (rm) FSH (rmFSH) and LH (rmLH) in the presence (experiment 1, approximately 100 pg/ml for about 15-20 wk; experiment 2, approximately 400 pg/ml for about 5 wk) or absence (control group) of elevated E2 in the circulation. Changes in circulating concentrations of E2, gonadotropins, testosterone (T), and inhibin B were monitored throughout the study. The number of Leydig cells per testis was determined after immunohistochemical staining for 3-beta hydroxysteroid dehydrogenase in experiment 2. Exogenous gonadotropin treatment produced physiological, episodic, and similar circulating concentrations of FSH and LH in both groups. Exposure to approximately 100 pg/ml of E2 appeared to blunt testicular T production. Exposure to approximately 400 pg/ml of E2 led to a significant (approximately 75%) inhibition of T production together with a marked (approximately 40%) decrease in Leydig cell numbers per testis and a notable inhibition in the growth of the testis. In contrast, E2 exposure had little effect on inhibin B production. The direct testicular impact of elevated E2 is on Leydig cell number, T production, and testicular growth, but not on inhibin B production. This experimental paradigm provides a powerful primate model for the examination of the direct impact of E2 or other endocrine disrupters on pubertal testicular development.

Norethisterone enanthate has neither a direct effect on the testis nor on the epididymis: a study in adult male cynomolgus monkeys (Macaca fascicularis)

Norethisterone enanthate (NETE) is evaluated in trials of hormonal male contraception. It has been speculated that progestins may exert their contraceptive effects not only by suppressing gonadotropins but also by direct effects on male organs. NETE was given to monkeys in which endogenous gonadotropin secretion was suppressed by a gonadotropin releasing hormone (GnRH) antagonist, and replaced by human follicle-stimulating hormone (FSH) and human chorionic gonadotropin (hCG). If NETE has a direct effect on spermatogenesis and/or epididymal function, some changes in testicular histology, sperm motility and/or morphology should occur soon after exposure to NETE. Fifteen adult intact male monkeys were grouped and treated for a 38-day period. Group I received GnRH antagonist, FSH, hCG and NETE while group II received a regime identical to group I without NETE and group III received only NETE and vehicle. Ejaculates, body weight, testicular biopsies and volume, and hormones were evaluated. There was a similar pattern of serum FSH and testosterone in groups I and II. Testicular volume and the proportion of tubuli exhibiting spermatids was significantly decreased in group III. There were no significant differences between group I and group II in any parameters measured. The forward progression of sperm was not affected by NETE treatment. The consistently low percentages of grade c sperm indicated no sign of hyperactivation. No changes in the gross morphology of the acrosome were detected. Short-term NETE treatment has neither a direct effect on the testis nor on the epididymis in this nonhuman primate model and its contraceptive effects appear to be exerted exclusively through gonadotropin suppression.

Norethisterone enanthate has neither direct effect on the testis nor on the epididymis: A study in adult male cynomolgus monkeys (Macaca fascicularis)

Norethisterone enanthate (NETE) is currently evaluated in trials of hormonal male contraception. NETE acts suppressing gonadotropin secretion. In this study we analysed whether NETE has a direct effect on the testis and/or on the epididymis in adult monkeys. NETE was given to cynomolgous monkeys in which endogenous gonadotropin secretion was suppressed by a GnRH antagonist (Cetrorelix), and replaced by injecting recombinant human FSH and human chorionic gonadotropin (hCG). We postulated that, if NETE has a direct effect on spermatogenesis and/or epididymal function, some changes in testicular histology, sperm motility and/or morphology should be found to occur soon after exposure to NETE. Fifteen adult intact male monkeys were allocated to three groups and treated for a 38 day period. Group I received GnRH antagonist, recombinant FSH, hCG and NETE while group II received a regime identical to group I without NETE and group III received only NETE and vehicle. Ejaculates, body weight, testicular volume and hormones were evaluated. Testicular biopsies were taken before and after treatment. There was a similar pattern of serum FSH and testosterone in group I and II throughout the study period, whereas serum FSH and testosterone dropped below the limit of detection in group III. Testicular volume and the proportion of tubuli exhibiting elongated and round spermatids was significantly decreased in group III. No significant differences were found between group I and group II in any parameters measured. The forward progression of sperm was not affected by NETE treatment. The low percentages of grade c sperm indicated no sign of NETE-induced hyperactivation. No changes in the acrosome gros morphology were detected among the different treatment groups. These results suggest that short-term NETE treatment has neither direct effects on the testis nor on the epididymis in this non-human primate model.

Gonadotropin-Independent Proliferation of the Pale Type A Spermatogonia in the Adult Rhesus Monkey (Macaca mulatta)1

The goal of the present study was to examine the relative roles of testosterone (T) and FSH in the proliferation and differentiation of pale type A (Ap) spermatogonia in the rhesus monkey (Macaca mulatta). Twenty adult male monkeys were treated with daily injections of a GnRH-receptor antagonist, acyline, to suppress endogenous gonadotropin secretion during an experiment comprising three phases. Phase 1 established a chronic hypogonadotropic state marked by a profound decrease in testicular size. During phase 2, half the monkeys were implanted with T-filled capsules, and the other half received control implants. Treatment with T produced circulating T levels of approximately 15 ng/ml and normal testicular T content. At the end of phase 2, monkeys were fitted with indwelling i.v. catheters and housed in remote sampling cages for the final phase. During phase 3, five monkeys from the T- and non-T-treated groups were stimulated with recombinant human FSH. The remaining five monkeys from each group received an infusion of vehicle. On the last day of FSH or vehicle infusion, monkeys were bilaterally castrated after receiving an i.v. bolus of bromodeoxyuridine (BrdU). The BrdU labeling of Ap spermatogonia was robust in the hypogonadotropic group and was uninfluenced by treatment with T and FSH, either alone or in combination. In contrast, both T and FSH stimulated spermatogonial differentiation, and this effect was amplified by combined treatment. We conclude that marked Ap spermatogonial proliferation occurs constitutively and in a gonadotropin-independent manner and that differentiation of Ap into B spermatogonia is absolutely gonadotropin dependent and may be driven by either T or FSH.

Chlormadinone acetate (CMA) in oral contraception – A new opportunity

Chlormadinone acetate (CMA) is a derivative of naturally secreted progesterone that shows high affinity and activity at the progesterone receptor. It has an anti-estrogenic effect and, in contrast to natural progesterone, shows moderate anti-androgenic properties. CMA acts by blocking androgen receptors in target organs and by reducing the activity of skin 5α-reductase. It suppresses gonadotropin secretion and thereby reduces ovarian and adrenal androgen production. CMA shows high contraceptive efficacy by inhibiting ovulation due to its ability to suppress or disrupt endogenous gonadotropin secretion and, by this, inhibits follicular growth and maturation. In addition, it suppresses endometrial thickness and increases the viscosity of cervical mucus. Pharmacokinetic studies have shown rapid and almost complete absorption after oral administration, and CMA is being bound to albumin rather than SHBG (Sex-Hormone-Binding-Globulin). Multiple dosing studies have demonstrated that steady state is reached by day 7 after oral administration with peak plasma concentrations in the region of 2 ng/ml. After a single dose of CMA the half-life time is around 34 hours and after multiple dose administration approximately 38 hours. Safety studies have indicated that CMA has no clinically relevant effect on a wide range of metabolic parameters in normal subjects. Further studies in groups at high thromboembolic risk have shown that CMA alone produces a relative risk of 0.8 which is not considered significant. These results indicated the potential for CMA to be combined with ethinylestradiol in an oral contraceptive which provides highly effective contraception and excellent cycle control.

In the adult male rhesus monkey (Macaca mulatta), unilateral orchidectomy in the face of unchanging gonadotropin stimulation results in partial compensation of testosterone secretion by the remaining testis.

This study examined, in adult monkeys, the role that gonadotropin-independent mechanisms play in compensation of testosterone (T) secretion by the testis that remains after unilateral orchidectomy (UO). We employed a model (testicular clamp), in which endogenous gonadotropin secretion was abolished with a GnRH receptor antagonist, and the gonadotropin drive to the testes was concomitantly replaced with an invariant iv pulsatile infusion of recombinant human LH and FSH (1-min pulse every 2.5 h: LH, 0.08-0.12 IU/kg.pulse; FSH, 0.12-0.32 IU/kg.pulse) that provided the Leydig cells with a physiological stimulus. Within 5 h of UO (n = 5), circulating T concentrations had declined to 43% of pre-UO levels. By d 4, however, loss of the first testis was partially compensated, as reflected by the finding that circulating T had reached a plateau of 67% of the pre-UO level, where it remained for the duration of the study (39 d). That the recovery in circulating T was the result of increased T secretion by the remaining testis was suggested by the finding that the pulsatile pattern and decay of T during the intergonadotropin pulse interval before and after UO were indistinguishable. Interestingly, inhibin B production by the remaining testis also showed a delayed, albeit, minor, compensation (13% on d 10-11; P > 0.05) after loss of the first testis. These results suggest that compensation in T production by the remaining testis after UO in adult monkeys may be achieved in part by a gonadotropin-independent mechanism that probably involves direct neural inputs to the primate testis.

Endocrine and paracrine control of follicular development and ovulation rate in farm species

Productivity in farm species is controlled by many factors, including ovulation rate. In cattle, single ovulations occur most frequently and in sheep (and goats) the number of ova released can range from one to many depending upon the breed, whilst the pig is polyovular. The processes of recruitment and selection determine the number of ovulatory follicles in all these species with FSH and subsequently LH playing major roles. GnRH-agonist models in which endogenous gonadotrophin secretion is suppressed and exogenous LH and/or FSH are administered at specific concentrations in defined patterns, are useful in all three species for elucidating the precise roles of specific hormones in stimulating follicular development. Differences in the hypothalamic–pituitary–ovarian feedback response lead to the differences in the number of ovulatory follicles, as does the pool of antral follicles from which the ovulatory ones are selected. Precocious development of follicles is also associated with more ovulations, as is the case with the Booroola due to the single gene acting through bone morphogenetic proteins (BMPs). It is well established that ovulation rate can also be influenced by exogenous hormone administration and by environmental factors such as nutrition. It has become apparent that these nuritional effects are mediated by a direct action at the level of the ovary, involving insulin, insulin-like growth factors (IGF) I and II and their binding proteins among other factors. These factors can also affect the quality of the oocyte and consequently embryo development and survival. Recently, the regulation of follicular angiogenesis has been shown to be important for the development of ovulatory follicles, particularly vascular endothelial growth factor (VEGF) which is produced primarily by the granulosa cells within the ovary and can be stimulated by gonadotrophins. Administration of VEGF has been shown to stimulate pre-antral follicular growth and increase the number of pre-ovulatory follicles. In summary both extra- and intra-ovarian factors are involved in the control of ovulation rate. Manipulation of the angiogenic process may also provide new opportunities for regulating the quality and number of follicles that ovulate.