Mechanism delineating differential effect of an antiestrogen, tamoxifen, on the serum LH and FSH in adult male rats.

Tamoxifen, a synthetic non-steroidal antiestrogen with residual estrogenic activity, administered to adult male rats reduces their fertility. A decrease in the circulating LH and testosterone levels with a transient rise or no change in circulating FSH levels was observed. The present study was carried out to delineate the mechanism causing the differential effect of tamoxifen on circulating gonadotropins by correlating it to changes in the hypothalamic LHRH, pituitary gonadotropins and testicular inhibin/activin. Hypothalamus, pituitary-hypothalamus complex (PHC) and intact pituitary (PI) from control and tamoxifen-treated male rats were superfused in vitro, and pulsatile release of LHRH by hypothalamus and that of LH and FSH by the PHC and PI were studied. Concomitantly, testicular immunoexpression of alpha and betaB subunits of inhibin/activin were studied by immunohistochemistry and enzyme-linked immunosorbent assays (ELISA). At 0.4 mg/kg/day dose of tamoxifen a decrease in mean hypothalamic LHRH and LH pulse frequency from PHC construct was observed. FSH pulse frequency was not affected under the same experimental conditions. At the same dose of tamoxifen, testicular expression of both alpha and betaB subunits of inhibin/activin was upregulated. The study demonstrated that reduced circulating LH levels were due to a decrease in hypothalamic LHRH concentration and in LH pulsatility following tamoxifen treatment. The lack of effect on circulating FSH under the same experimental conditions was likely due to its modulation by inhibin and activin.

Hyperprolactinemia affects spermiogenesis in adult male rats.

The mechanisms underlying the antifertility effects of hyperprolactinemia have yet to be established in an appropriate experimental model. Hyperprolactinemia is a known side effect of fluphenazine, a broad spectrum, long-acting phenothiazine known to be dopamine type-D2 receptor antagonist. In our earlier study in adult male rats, we reported that fluphenazine at a dose of 3 mg/kg/day suppressed serum FSH but not testosterone (T) through increasing dopamine (DA) metabolism in the pituitary gland, within 60 days. Fluphenazine treatment affected sperm quality and male rats treated with fluphenazine sired fewer litters. The effects of fluphenazine-induced hyperprolactinemia on sperm quality appeared to be related to reduced FSH. We now report that FSH suppression enhanced the uptake of acridine orange (AO), a DNA intercalating, fluorescent dye by the fluphenazine-treated caput epididymal sperms with concomitant reduction in the uptake of thiol-specific monobromobimane (mBBr) fluorescent dye in vitro, suggesting greater accessibility of DNA intercalating dye to sperm chromatin and reduction in free sperm protein thiols. The concomitant increase in AO and decrease in mBBr fluorescence was suggestive of loose chromatin packaging in caput epididymal sperms after treatment with fluphenazine at 3 mg/kg/day for 60 days. The suppression in levels of protamine (P1) in caput epididymal sperms suggested that chromatin hypocompaction was due to reduced deposition of protamines in sperm chromatin. Reduction in testicular levels of cyclic adenosyl 3', 5' monophosphate response element modulator (CREMtau) and P1 further suggested that reduced deposition was indeed due to reduced synthesis. The concomitant reduction in testicular levels of transition protein 1 (TP1) and transition protein 2 (TP2) also suggested that hypoprotamination was due to reduced synthesis of these proteins crucial for facilitating P1 deposition. The effect appeared to have occurred at the level of translation of CREMtau, since its transcript levels were unaffected whereas those of TP1, TP2 and P1 and protamine were upregulated. The study led to the view that the effects of FSH suppression were manifest on the posttranscriptional modifications of CREMtau, as also on transcript repression of TP1, TP2, P1, which do the RNA- binding proteins bring about. Reduction in FSH did not decrease ABP expression in the testis, which has recently been implicated in the expression of transition protein 1 in vitro. However, a significant reduction was evident after fluphenazine treatment, in the immunoexpression of testicular cAMP, the mediator of FSH effects in the Sertoli cells and putative mediator of ABP effects in the spermatids. The study suggests that fluphenazine-induced hyperprolactinemia suppressed FSH and affected a putative cAMP-dependent mechanism underlying posttranscriptional modification of spermatidal genes involved in chromatin condensation, presumably by reducing the availability/secretion of ABP, a paracrine regulator of spermiogenesis in vitro.

Antifertility effects of fluphenazine in adult male rats.

The underlying mechanisms in human infertility associated with hyperprolactinemia have yet to be established. Hyperprolactinemia is a known side-effect of fluphenazine, a broad spectrum, long-acting phenothiazine known to be D2 dopamine receptor antagonist. Dose-related effects of fluphenazine decanoate were ascertained on the fertility of 60-day treated, adult male rats. Significant increase in the serum levels of prolactin and decrease in the levels of LH and FSH were seen at doses of 1-3 mg/kg/day. No effect was evident on the serum testosterone (T) and estradiol. The tissue levels of Inhibins were not affected. The weights of testes, epididymides, seminal vesicles, ventral prostate, adrenal and pituitary glands were not affected. Testicular histology showed sloughing indicating the sensitivity of this parameter to FSH deficiency. Mating occurred within 10 days of cohabitation in the control and 1-2 mg/kg/day treated groups but delayed in the 3 mg/kg/day treated group with a significant effect on potency. Implantation sites, litter size and fertility index were significantly reduced at 2-3 mg/kg/day doses of fluphenazine. No effects however were seen on sperm counts or motility whereas morphological changes were apparent in the acrosome. Chromatin decondensation in vitro was enhanced and sperm chromatin structure assay revealed DNA denaturation. Hypothalamic tyrosine hydroxylase levels were increased in 1-3 mg/kg/day dose range. Hyperprolactinemic males sired fewer pups as compared to controls. Hypothalamic tyrosine hydroxylase was upregulated at all the doses. The antifertility effects of fluphenazine-induced hyperprolactinemia appeared to be unrelated to testosterone (T). In addition, FSH decrease might have affected the intrinsic sperm quality and thereby reduced litter size.

Effect of oral tamoxifen on semen characteristics and serum hormone profile in male bonnet monkeys.

The effects of oral tamoxifen were studied at a dose of 0.4 mg/kg per day, on the serum hormones and semen parameters in adult male bonnet monkeys, for a period of 90 days. Honey was used as vehicle. Monkeys were treated with honey for 30 days, followed by tamoxifen from Day 30-120 (90 days). Thereafter the treatment was withdrawn until Day 150 of schedule. Blood samples were drawn at 12 and 24 clock hours at monthly intervals for the analysis of luteinizing hormone, follicle-stimulating hormone and testosterone. Semen samples were also collected for analysis once a month, from Day 0-150 of exposure. Tamoxifen treatment produced a transient but significant increase in circulating gonadotropins, at Day 90 of treatment schedule, corresponding to 60 days of treatment. Whilst serum testosterone levels were normal throughout treatment period, an increase was observed after 30 days of drug withdrawal. No effect of oral tamoxifen was evident on semen parameters, viz., volume, counts, morphology and motility. However, throughout the exposure period to honey, a significant increase was observed in sperm counts without any effect on testosterone levels. The present study suggests that oral tamoxifen has a transient antiestrogenic effect on the serum hormones and no effect on semen parameters of adult nonhuman primate males. It is concluded that bioefficacy of oral tamoxifen may have been reduced due to hepatic metabolism.

Temporal effect of tamoxifen on cytochrome P450 side chain cleavage gene expression and steroid concentration in adult male rats.

Adult male rats when treated with 0.4 mg tamoxifen (tam)/kg per day for 90 days show reduced circulating testosterone (T) and LH. The present study was designed to have an in depth understanding of tam induced androgen reduction in adult male rats. Adult male rats were orally administered 0.4 mg tam/kg per day for 30, 60 or 90 days and the temporal effects on intratesticular concentrations of pregnenolone (P(5)), progesterone (P(4)), T, 5 alpha-dihydrotestosterone (5 alpha-DHT) and estradiol (E(2)) were estimated. Control group rats were fed saline. Serum hormonal profile of LH, FSH, T and E(2) was also followed on these days. Testicular levels of cytochrome P450 scc mRNA transcripts on 30, 60 and 90 days of treatment with the same dose were quantitated by biplex RT-PCR using beta Actin as internal control followed by analysis using GelPro Analysis software.A significant reduction in intratesticular P(5), P(4), T, 5 alpha-DHT and E(2) was observed from day 30 of treatment. The P450 scc gene expression in the testis was reduced during treatment period from day 60 of treatment. This study demonstrates for the first time that tam reduces testicular pregnenolone biosynthesis through an effect on cholesterol transport and downregulation of P450 scc gene expression. In confirmation of the observed estrogenic effects of tam in this study, it is suggested that E(2) may have a role in cholesterol transport and testicular pregnenolone biosynthesis at the level of cytochrome P450 scc as shown by us.

Antifertility effects of estradiol in adult male rats.

The dose-related effects of estradiol 17-beta at the doses 0.1 pg, 10 microg, 100 microg, 200 microg, 300 microg, 400 microg, 1,000 microg/kg/day were determined on sperm motility, potency, fertility parameters, serum levels of LH, FSH, PRL and testosterone, weights of testes and accessory sex organs, weights of pituitary and adrenal glands. The drug was administered daily via sc route for a period of 60 days. Dose-related effects on fertility parameters of the estradiol-treated male rats were ascertained by allowing them to mate with normal cycling female rats. Estradiol at 0.1 microg/kg/day dose significantly reduced sperm motility with no effects seen on potency or fecundity, serum LH, FSH, PRL or testosterone, weights of testes and accessory sex organs while pituitary weight increased. Estradiol at 10 microg/kg/day dose significantly reduced motility, serum LH, FSH, weights of testes and accessory sex organs, while pituitary weight increased with no effects seen on potency, fecundity, PRL or testosterone. Estradiol at 100-1,000 microg/kg/day dose significantly reduced motility, potency and fecundity, serum LH, FSH and testosterone, weights of testes and accessory sex organs while serum PRL and the weights of pituitary and adrenal glands increased significantly. Histology of the testes revealed disorganization of the cytoarchitecture in the seminiferous tubules, vacuolation, absence of lumen and compartmentalization of spermatogenesis. Estradiol withdrawal, testosterone propionate at 100 pg/kg/day or antiestrogen (tamoxifen citrate) at 400 microg/kg/day prevented the histological changes. It is conduded that estradiol reduces sperm motility even at a low dose. Low doses (<10 microg/kg/ day) appear to maintain whilst high doses (>10 microg/kg/day) reversibly disrupt spermatogenesis. Prevention of disruption by testosterone or antiestrogen indicates crosstalk between androgen and estrogen receptors in Sertoli cells. Loss of potency and fecundity also suggests effects on crosstalk between these receptors in other male reproductive organs.

Effect of intermittent treatment with tamoxifen on reproduction in male rats.

AIM: To identify the antifertility effect of intermittent oral administration of tamoxifen in male rat. METHODS: Tamoxifen was administered orally at a dose of 0.4 mg x kg(-1) x d(-1) with an intermittent regime for 120 days. Treated and control rats were mated with cycling female rats on days 60, 90 and 120 of treatment. The mated males were sacrificed and the weights of reproductive organs were recorded, and the serum levels of LH, FSH, testosterone and estradiol estimated by radioimmunoassay. In the female rats, the numbers of implantation sites, corpora lutea, and numbers of normal and resorbed foetuses were recorded on d 21 of gestation. The potency, fecundity, fertility index, litter size and post-implantation loss were then calculated. RESULTS: The fecundity of male rats was completely suppressed by tamoxifen while the potency was maintained at the control level. The fertility index was significantly decreased. No viable litters were sired. Post implantation loss, indicative of non-viable embryos, was observed but was not significantly increased above the control level. The weights of the testes, epididymides, ventral prostate and seminal vesicles were significantly reduced. The blood LH and testosterone levels were significantly decreased, but not FSH and estradiol. CONCLUSION: Intermittent oral tamoxifen administration completely suppressed the fecundity of adult male rats with reserved potency.

Effect of tamoxifen on sperm fertilising ability and preimplantation embryo development.

Recent evidences point to a role of estrogens in males. We have earlier reported that tamoxifen, a synthetic non-steroidal antiestrogen, when administered to adult male rats, in the dose range of 0.04-0.4 mg/kg per day, reduced fertility. The reduced fertility was measured in terms of fertility index (a measure of the efficiency of the ovulated ovas to fertilise and implant), fecundity (siring ability) and litter size. The present study was done to investigate whether the reduction in fertility index was due to reduction in fertilising ability or increase in pre-implantation embryo loss. Also a dose related effect of tamoxifen from 0.02 mg to 2 mg/kg per day on the fertility of the male rats was studied. To study the fertilising ability, control and tamoxifen (0.4 mg/kg per day, the most effective dose) treated adult male rats were mated with normal cycling females and the females sacrificed at day 0-4 of gestation. Eggs fertilised/unfertilised were flushed from the oviduct/uterus and the number and types of eggs were noted. The index of fertilisation, a measure of the fertilising ability was determined. The studies demonstrate that the reduction in fertility is not due to decreased fertilising ability but because of the increased pre-implantation embryo loss as evident from an increase in number of abnormal eggs in the treated group with no change in index of fertilisation. A dose related decrease in fertility was observed. The present study suggests that tamoxifen at 0.02-2-mg dose is predominantly estrogenic in males and paternal factor/s sensitive to tamoxifen is involved in embryogenesis.

Effects of tamoxifen metabolites on fertility of male rat.

The effects of chronic oral administration of tamoxifen citrate, at a dose of 0.4 mg/kg/day, were compared to those of subcutaneous (s.c) administration of tamoxifen citrate, 4-hydroxy tamoxifen, N-desmethyl tamoxifen and intermittent oral tamoxifen administration on the fertility of the male rat and its post reversal progeny. The fertility parameters of 120 day-treated male rat sires from all groups and post reversal male F1 progeny of tamoxifen-treated sires were assessed. Chronic tamoxifen treatment via oral or s.c. routes reduced the fertility of the male rat, weights of accessory sex glands, serum luteinizing hormone, and testosterone levels without altering potency or sperm counts. However, antifertility effects of s.c. treatment were comparatively more consistent than those of oral treatment. 4-hydroxy and N-desmethyl tamoxifen failed to produce significant antifertility effects in the male rat. The antifertility effects of intermittent oral treatment were more sustained than those of chronic oral tamoxifen treatment. It is inferred that hepatic metabolism of tamoxifen interferes with its antifertility effects via oral route and that the parameters affected by chronic oral exposure in the male sires are completely reversed in progeny ensuing after an adequate period of drug withdrawal.

Effect of 5alpha-dihydrotestosterone implants on the fertility of male rats treated with tamoxifen.

In adult male rats, tamoxifen (TAM) reduces circulating levels of luteinizing hormone (LH) and testosterone (T) with no effect on follicle-stimulating hormone (FSH) and prolactin (PRL). It reduces the male rat's ability to inseminate the female (potency), as well as its siring ability (fecundity). The objective of the present study was to test whether androgen supplementation could reverse all or some of the observed effects of TAM. To obviate the effects of estrogen, the study was designed to evaluate the beneficial or deleterious effect of 5alpha-dihydrotestosterone (DHT), a 5alpha-reduced, nonaromatizable metabolite of T, on the reproductive functions of TAM-treated adult male rats. Adult male rats received either saline or TAM (0.2 or 0.4 mg per day p.o.) for 90 days. A group of TAM-treated rats was implanted with 6 mg DHT from day 50 to day 90. A third group of untreated animals was implanted with 0-, 1-, 3-, or 6-mg DHT implants for 90 days. Mating studies were done to assess the fecundity, potency, and fertility index at the end of the treatment. Weights of testes, pituitary, and accessory sex organs were recorded, and circulating levels of LH, FSH, PRL, T, and 17-beta-estradiol were estimated. DHT did not affect the fecundity or fertility index. TAM reduced fecundity, potency, and the fertility index. DHT implants improved the fertilizing ability of the TAM-treated male rat. This study discusses and reviews the role of T and 17-beta-estradiol in sperm-fertilizing potential in light of these observations.

Abnormalities in functional development of the Sertoli cells in rats treated neonatally with diethylstilbestrol: a possible role for estrogens in Sertoli cell development.

Diethylstilbestrol (DES) was administered neonatally (Days 2-12; 10 microg on alternate days) to rats, and developmental changes in Sertoli cell function were evaluated at 18, 25, and 35 days of age and compared to those observed in rats administered a GnRH antagonist (GnRHa; Days 2 and 5; 10 mg/kg) or a vehicle (controls). DES and GnRHa treatments resulted in similar reductions in both Sertoli cell numbers (40% for DES, 48% for GnRHa) and suppression of testicular growth at 18 and 25 days, though by 35 days the suppression was more pronounced (p < 0.001) in DES-treated animals. Plasma FSH levels were suppressed markedly at 18 and 25 days, but not at 35 days, in GnRHa-treated rats, whereas in DES-treated rats the FSH levels were suppressed significantly only at 35 days. Both treatments suppressed plasma levels of inhibin B, though this was more pronounced (p < 0.05) in DES- than in GnRHa-treated rats. In controls, Sertoli cell immunoexpression of inhibin alpha, sulfated glycoprotein-1 (SGP-1), and androgen receptor (AR) increased in intensity and changed to an adult, stage-dependent pattern by 25 days. In GnRHa-treated rats these changes were reduced in intensity but were similar to those in controls at 35 days. In DES-treated rats, the increase in intensity and stage-dependent pattern of immunoexpression of inhibin alpha, SGP-1, and AR were virtually absent at 25 days but were present by 35 days. Germ cell volume per Sertoli cell was reduced in GnRHa- and DES-treated rats compared with controls at 18 and 25 days but was significantly greater (p < 0. 001) in DES- than in GnRHa-treated rats at 35 days. The proportion of apoptotic to viable germ cells was increased (p < 0.01) in GnRHa- and DES-treated rats compared with controls at 18 and 25 days; but at 35 days, values in GnRHa-treated rats had declined to control values whereas those for DES-treated rats remained 10-fold elevated (p < 0.001). In adulthood, testis weight and daily sperm production were reduced by 43% and 44%, respectively, in GnRHa-treated rats, but spermatogenesis was grossly normal. Comparable changes were observed in approximately 25% of DES-treated rats, but the majority exhibited > 60% reduction in testis weight with many Sertoli cell-only tubules and very low daily sperm production. Taken together, these data are interpreted as providing evidence for direct modulation of Sertoli cell (maturational) development by DES.

Tamoxifen-induced light and electron microscopic changes in the rat testicular morphology and serum hormonal profile of reproductive hormones.

The effects of oral administration of tamoxifen at doses of 40 and 200 micrograms/kg/day on testicular histology, testicular ultrastructure and serum hormonal profile were studied. The drug was administered to adult male rats over a period of 90 days and the effect was assessed at 10-day intervals. The morphometry, microscopic structures of the testis, including ultrastructure and daily sperm production rate, were evaluated. The hormone profiles of luteinizing hormone (LH), follice-stimulating hormone (FSH), testosterone, and estradiol were studied. The testes from treated animals showed disorganization of tubular elements with increased intercellular space. At day 50, the changes were extensive including presence of phagosomes. Morphometric studies showed a reduction in the spermatid and spermatozoan population (69.3%) with no changes in tubular diameter. The mean Leydig cell area was significantly lowered at day 50, at both doses. The daily sperm production rate was reduced as compared with controls. An array of degenerative changes were revealed by ultrastructural studies. The changes were extensive at day 50 at both doses. The characteristic features were lost in most of the cells with phagolysosomes becoming abundant. The cytoplasm of the cells was dense with poorly defined cytoplasmic organelles. Circulating LH levels were not modified at the 40 micrograms/kg/day dose but at 200 micrograms/kg/day, LH levels were significantly decreased. Initial transitory rise in FSH was seen with both doses. Both doses of tamoxifen decreased testosterone levels. Changes in the circulating estradiol levels were inconsistent, and no apparent relationship between dose and days of treatment was observed. Thus, this study supports our thesis of tamoxifen as a potential male contraceptive agent.

Fetal and perinatal influence of xenoestrogens on testis gene expression.

The incidence of reproductive abnormalities in the male has been reported to have increased during the past 50 years. It has been suggested that these changes may be attributable to the presence of chemicals with oestrogenic activity in our environment. The aim of the experiments described in this chapter was to investigate the effects of acute exposure to high levels of xenoestrogens either indirectly during fetal life, or directly during neonatal life, on gene expression in the testis and pituitary. Fetal treatment involved administration of diethylstilbestrol (DES), 4-octylphenol (OP) or vehicle (oil, control) to pregnant rats on days 11.5 and 15.5 post coitum; fetuses were recovered on day 17.5. There was no difference between fetuses from control and treated mothers in either the overall histology of the testes or numbers of Leydig cells as determined by immunohistochemistry with an antibody directed against 3 beta-HSD. However there was a consistent and striking reduction in the amount of P450 17-a hydroxylase C17, 20 lyase (P450c17) and steroidogenic factor 1 (SF-1) detected by immunocytochemistry in testes from treatment groups given the higher doses of OP and DES. Oestrogen receptors (ER alpha) were present in the fetal leydig cells of all animals. Neonatal treatment involved direct injection of oil (control), DES, OP or Bisphenol A (Bis A) on days 2, 4, 6, 8, 10 and 12; pituitaries and testes were recovered on day 18. Testis weights and seminiferous tubule diameters were significantly reduced in animals treated with DES. In these same animals immunocytochemical localisation revealed that the amounts of FSH beta subunit and inhibin alpha subunit were reduced in their pituitaries and testes respectively. OP did not appear to have an acute, measurable effect on testis gene expression but a reduction in testis weight was noted in adult animals given the same treatment regime. The effects observed are consistent with negative feedback by oestrogens on pituitary production of FSH resulting in retarded maturation of seminiferous tubules and reduced Sertoli cell numbers. These studies have demonstrated that administration of high levels of oestrogens can affect gene expression in the testis early in life. However, the relevance of these findings to observations in man await a) a greater understanding of the physiological role(s) of oestrogens in normal males, b) an evaluation of the sources, routes of exposure, concentrations in vivo and bioavailability of xenoestrogens.

Effects of tamoxifen on the fertility of male rats.

The effects of oral administration of tamoxifen (a synthetic non-steroidal anti-oestrogen) at doses of 40, 200 or 400 micrograms kg-1 day-1 on the circulating concentrations of LH, FSH, prolactin, testosterone and oestradiol, weights of pituitary, testes, secondary sex organs and the fertility of adult male rats were determined. The drug was administered per os daily, for up to 90 days. The fertility of rats treated with tamoxifen for 60, 70, 80 or 90 days was assessed by allowing them to mate with normal female rats of proven fertility. Tamoxifen at 40 micrograms kg-1 day-1 reduced concentrations of testosterone in plasma but had no affect on LH, FSH, prolactin and oestradiol concentrations, and the weights of pituitary, testes, epididymides, ventral prostate and seminal vesicles. Tamoxifen at 40 micrograms kg-1 day-1 reduced potency, fecundity, the number of implantation sites, the fertility index and litter size. Tamoxifen at 200 and 400 micrograms kg-1 day-1 reduced the concentrations of LH and testosterone in plasma and the weights of testes and secondary sex organs compared with controls. Tamoxifen at 400 micrograms kg-1 day-1 was most effective in reducing the number of viable pups, the litter size (< or = 1) and the fecundity (20%). The potency of treated rats (a measure of the presence of an ejaculate) was significantly decreased when compared with controls, but copulation was apparently not affected as mated female rats showed a constant dioestrous phase. Histology of the testes revealed disorganization of the cytoarchitecture of the tubules with obliterated lumen.(ABSTRACT TRUNCATED AT 250 WORDS)

Assessment of bioactivity of WHO/NIH research standard for inhibin (code 86/690) using two separate pituitary cell-culture systems.

The Research Standard for inhibin, porcine (No. 86/690) distributed by the National Institute for Biological Standards and Control, U.K. for the bioassay of inhibin was tested for its bioactivity in vitro in two rat pituitary cell culture systems. The system A was obtained from pituitaries of 12 day old immature rats while system B was obtained from pituitaries of mature male rats. The inhibin preparation failed to inhibit basal secretion of FSH in the system A. Instead it stimulated the release of both LH and FSH. 1 ng LHRH induced release of LH was inhibited by 32, 80 and 43% by 0.1, 1 and 10 IU inhibin, respectively. 10 ng LHRH induced release of FSH was inhibited in a none-dose related manner and the maximum inhibition was by 10 IU inhibin (25%). The same dose of 10 IU inhibin stimulated LHRH-induced release of LH by 35%. In system B, 1, 10, 50, 100 and 200 IU inhibin suppressed basal secretion of FSH by 0, 44, 72, 70 and 48%, respectively, while LH was suppressed by 13, 24, 46, 22 and 21% respectively. The pattern of inhibition of 10 ng LHRH induced release of LH and FSH by inhibin was similar to its effect on basal secretion. A specific dose-related inhibition of FSH was not observed. Our data question the utility of the inhibin standard (86/690).

Temporal changes in the serum levels of gonadotrophins and testosterone in male rats bearing subcutaneous implants of 5 alpha-dihydrotestosterone.

This study has assessed the effect of s.c. implants of 5 alpha-dihydrotestosterone (DHT) on the blood levels of testosterone and gonadotrophins in intact and castrated adult male rats. The rats were bled via cardiac puncture at 1, 3, 7, 14, 21, 28, 35, 42, 49, 56, 63 and 70 days after DHT implantation. On days 28 and 49 post-implantation, rats were injected with LHRH (25 ng) and bled 15 min later. In intact rats bearing DHT implants, the serum levels of LH and testosterone were suppressed significantly with no significant changes in FSH levels. Ventral prostate, seminal vesicles and the pituitary were reduced significantly in weight when compared with controls with empty implants. DHT significantly inhibited LHRH-induced release of FSH in intact rats. In castrated rats, DHT implants inhibited the secretion of both LH and FSH, with a rise in serum DHT levels. DHT stimulated the LHRH-induced release of LH but inhibited FSH. DHT implants increased the weight of the seminal vesicles and ventral prostate but inhibited the weight of the pituitary when compared to castrated rats bearing empty implants. This study demonstrates specific inhibition of serum LH and testosterone by DHT implants in intact adult rats.

Cerebrospinal fluid and blood concentrations of luteinizing hormone, follicle stimulating hormone and prolactin following castration of adult male rats.

Comparative levels of LH, FSH, and PRL in the serum and cerebrospinal fluid (CSF) of adult male rats were studied at different periods following castration. Intact and sham-operated animals served as controls. Blood and CSF were collected at 1, 3, 7, 14, 21, 28, 35 and 46 days following castration. The CSF was collected via cisterna-magna puncture, while the blood was collected from abdominal aorta. Serum gonadotropins increased progressively beginning day 1 post-castration to reach maximum by day 35 or 46 post-castration. Sham operation and castration did not affect mean CSF, LH and FSH levels compared to intact controls. Analysis of the temporal pattern of serum and CSF gonadotropin levels following castration revealed significant positive correlation between CSF and serum LH (r = 0.58) and FSH (r = 0.64) levels respectively. The data suggest that CSF gonadotropins may be derived from systemic circulation. Serum PRL levels were not affected by castration, but CSF PRL levels were significantly reduced at days 28, 35 and 46 post-castration compared to intact controls. CSF PRL levels showed negative correlation with serum LH and FSH levels but failed to show a correlation with serum PRL levels. Hypothalamic norepinephrine turnover rate increased at days 28, 35 and 46 post-castration. Hypothalamic dopamine contents and turnover rates were reduced at days 21 and 28 post-castration. It is suggested that CSF PRL may have a role in the regulation of serum gonadotropins.

Diurnal variations and temporal coupling of bioactive and immunoactive luteinizing hormone, prolactin, testosterone and 17-beta-estradiol in adult men.

Diurnal variations and temporal coupling in the circulating levels of immunoactive and bioactive luteinizing hormone (LH) and prolactin (PRL), testosterone (T) and 17-beta-estradiol (E2) in plasma of 6 healthy men (mean age 33 years) were studied. Each hormonal profile was analyzed for circadian amplitude, acrophase and nadir. Acrophases for immunoactive LH and T were coincident and ranged between clock hours 1 and 5. Acrophase for bioactive LH ranged between 9 and 12 h and was coincident with nadir for T. Acrophase for E2 ranged between 15 and 18 h and was coincident with nadir for immunoactive LH (15-17 h). Acrophase for bioactive PRL and immunoactive PRL ranged between 20-23 and 23-4 h, respectively. The circadian amplitude for T showed a negative correlation coefficient with circadian amplitude of bioactive LH (alpha = -0.86) and positive correlation coefficient with circadian amplitude of immunoactive LH (alpha = 0.94). It is inferred that immunoactive LH may be a sensor of T concentration while bioactive LH may be actually involved in the feedback regulation of T secretion. It is suggested that PRL may have a key role in the regulation of LH secretion.