A role for inhibin in the control of follicle-stimulating hormone secretion in male rats

We examined the relationship of testosterone (T) and porcine follicular fluid (pFF) in the negative feedback control of FSH and LH secretion in adult male rats. Either at the time of castration (acute) or at least 30 days after castration (chronic), we implanted T-filled Silastic capsules, which were 2 mm, 10 mm, or 30 mm long; empty capsules (30 mm) served as controls. Seven days later, we injected either 0.15 ml of pFF or saline (i.v.), decapitated the rats 6 hours later, and collected trunk blood for subsequent serum analysis of FSH, LH, and T by RIA. In the acute groups, T implants suppressed the postcastration rises in plasma FSH and LH levels in a dose-dependent manner, with only the largest implant, 30 mm, able to return them to intact levels. PFF injection significantly suppressed FSH levels in intact and acute rats but had no effect on serum LH. In chronic rats, T therapy for 7 days suppressed plasma LH levels in a dose-dependent relationship, yet did not do so to plasma FSH levels. FSH levels were significantly higher in rats with the 30 mm T implants than in intact rats, but were significantly suppressed as compared to chronic controls. PFF significantly suppressed serum FSH levels in all chronic groups with the chronic controls showing the greatest amount of suppression. We conclude that the role for inhibin in the normal control of FSH secretion is that of a secondary modulator which is superimposed on, yet independent of, the steroid feedback mechanism. At any given moment this modulation is dependent upon the secretory activity of the FSH gonadotrope.     

Changes in gonadotropin secretion following complete or hemicastration in the adult rat.

The effect of sham castration, hemicastration or complete castration on gonadotropin and testosterone secretion was studied in adult male rats. Untreated control rats were autopsied 1, 10, 20, 30 and 40 days following assignment to treatment groups. Sham-castrated controls were autopsied 1, 2 and 3 days after surgery. Complete and hemicastrates were autopsied 1, 2, 3, 10, 20, 30 and 40 days after surgery. Serum levels of both FSH and LH were elevated by 24 h postcastration and the levels of both gonadotropins continued to rise throughout the course of the experiment. Serum levels of LH rose following hemicastration and remained above control values through day 30. Serum FSH levels were not significantly affected by hemicastration. Compensatory testicular hypertrophy was not observed in hemicastrated rats.     

Effects of gonadectomy and steroids on pituitary gonadotropin secretion in a frog, Rana pipiens

Secretory dynamics of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured at various times following gonadectomy in adult male grass frogs, Rana pipiens. Plasma levels and in vitro initial secretory rates of both LH and FSH increased significantly within 1 wk and remained elevated for 3-4 wk of castration. Pituitary FSH and LH content were unchanged. However, dissociation between the two gonadotropins (Gth) occurred thereafter: Secretion of FSH remained elevated for 70 days, but those of LH declined to control levels after 30 days. In vitro secretion of Gth from gonadectomized (gonadx) frogs declined progressively over time reaching control levels after 24 h incubation. The results indicate that elevated pituitary secretion contributes to the observed circulating LH and FSH levels in gonadx frogs, and that FSH and LH may be controlled independently. Replacement therapy with 17 beta-estradiol (E2) suppressed post-gonadectomy increases in plasma Gth and in vitro responses to GnRH, whereas 5 alpha-dihydrotestosterone (DHT) had little effect in vivo and augmented GnRH responses in long-term castrates. In vitro, E2 also inhibited, while 48 h of DHT treatment had no effect on GnRH responsiveness of pituitaries from gonadx frogs. The actions of these steroids were opposite to those typically observed in mammals (and birds), and support the hypothesis that E2 may contribute to seasonal testicular regression in ranid frogs.     

Effects of intermittent pulsatile infusion of luteinizing hormone-releasing hormone on dihydrotestosterone-suppressed gonadotropin secretion in castrate rams

The feedback effects of dihydrotestosterone (DHT) on gonadotropin secretion in rams were investigated using DHT-implanted castrate rams (wethers) infused with intermittent pulsatile luteinizing hormone-releasing hormone (LHRH) for 14 days. Castration, as anticipated, reduced both serum testosterone and DHT but elevated serum LH and follicle-stimulating hormone (FSH). Dihydrotestosterone implants raised serum DHT in wethers to intact ram levels and blocked the LH and FSH response to castration. The secretory profile of these individuals failed to show an endogenous LH pulse during any of the scheduled blood sampling periods, but a small LH pulse was observed following a 5-ng/kg LHRH challenge injection. Dihydrotestosterone-implanted wethers given repeated LHRH injections beginning at the time of castration increased serum FSH and yielded LH pulses that were temporally coupled to exogenous LHRH administration. While the frequency of these secretory episodes was comparable to that observed for castrates, amplitudes of the induced LH pulses were blunted relative to those observed for similarly infused, testosterone-implanted castrates. Dihydrotestosterone was also shown to inhibit LH and FSH secretion and serum testosterone concentrations in intact rams. In summary, it appears that DHT may normally participate in feedback regulation of LH and FSH secretion in rams. These data suggest androgen feedback is regulated by deceleration of the hypothalamic LHRH pulse generator and direct actions at the level of the adenohypophysis.     

Effect of castration on plasma concentrations of luteinizing hormone and follicle-stimulating hormone in adult Merino rams which were homozygous carriers or non-carriers of the Booroola fecundity gene

Before castration, the mean plasma concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) did not differ between FF and ++ Booroola rams. After castration, mean LH and FSH concentrations increased after 8 h, and for the next 14 days the rate of increase in FSH, but not LH, secretion was significantly faster in FF than in ++ rams (P less than 0.05). Mean FSH concentrations over this period were significantly higher in FF than in ++ rams (P less than 0.05). In both genotypes, the ranked FSH values did not significantly change their order over time, i.e. a significant within-ram effect was noted (P less than 0.05). Repeated-measures analysis of variance indicated a significant effect of genotype on mean FSH secretion (P less than 0.05) and a significant effect of sire in the FF (P less than 0.05), but not the ++ (P = 0.76), genotype. From Day 28 to Day 58 after castration, FSH and LH concentrations were variable and no overall increases in concentrations were observed. The mean concentrations of both hormones over this period were not related to genotype. There were no gene-specific differences in pulsatile LH secretion 14 weeks after castration. However, the mean LH, but not FSH, response to a bolus injection of 25 micrograms of gonadotrophin-releasing hormone (GnRH) was significantly higher in FF than in ++ rams (P less than 0.05) and this was not significantly affected by sire. These studies support the hypothesis that the F gene is expressed in adult rams, in terms of pituitary responsiveness to an injection of GnRH and to the removal of the testes, but it is not clear from this study whether the influence of sire is related to or independent of the apparent gene-specific differences.     

The acute stimulatory effect of estrogen on gonadotropin release in gonadotropin-releasing hormone-primed women

In order to prove the acute stimulatory effects of estrogen on pituitary gonadotropin release, we have performed the present experiments in 8 women with a hypergonadotropic state due to surgical castration or primary ovarian failure. They received gonadotropin releasing hormone (Gn-RH) for 12-21 h at the constant rate of 20 micrograms/h. In 5 of the women, estradiol-17 beta was concomitantly administered at the rate of 20 micrograms/h from 6 h after the start of Gn-RH infusion. Blood samples were collected frequently throughout the experiments for the analysis of LH, FSH and estradiol. In response to the sole stimulation of Gn-RH, remarkable and prompt rises in LH (313.5%), but to a lesser degree in FSH (194.2%), were observed within the initial 3 h, and their high levels were maintained throughout the experimental period. However, the additional administration of estradiol brought on a further sudden rise in both gonadotropins levels: 178.3% for LH and 163.5% for FSH within 2 h. These high levels were sustained during estradiol infusions. In 2 of them, blood samples were obtained for several hours after cessation of estradiol infusion. The circulating gonadotropin level dropped precipitously close to the baseline level within 3 h after estradiol infusions. Our data indicate that estrogen has an acute and strong augmentative effect on Gn-RH induced gonadotropin release in addition to its conventional negative and positive feedback effects.     

Opioidergic control of gonadotropin secretion in the female rabbit: divergent effects of morphine on secretion of follicle-stimulating hormone and luteinizing hormone

The nature of secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) was followed in female rabbits on a daily basis from age 36 to 60 days by sequential 5-min blood sampling over 1- to 2-h periods each day. Both LH and FSH were found to be secreted in a pulsatile manner. The mean LH pulse amplitude over the 25 days was 0.95 +/- 0.32 ng/mL and for FSH it was 10.15 +/- 1.11 ng/mL. Mean plasma LH levels were significantly increased from 1.46 +/- 0.08 ng/mL in 36 to 42-day-old rabbits to 1.89 +/- 0.12 ng/mL in 43 to 50-day-old rabbits and remained elevated from 50 to 60 days. FSH levels during the same periods also rose significantly from 14.93 +/- 0.79 to 19.57 +/- 2.05 ng/mL. To examine the influence of endogenous opioid peptides on the release of LH and FSH in 36 to 60-day-old female rabbits, morphine sulfate at 0.2, 0.5, 2.0, and 5.0 mg/kg was administered subcutaneously after 30 min baseline sampling, and blood was taken for another 60-120 min. Morphine at all doses and at all ages inhibited the amplitude and frequency of LH pulses but had no effect on FSH secretion. To determine whether the effects of morphine on LH secretion could be reversed with naloxone, females aged 82-114 days were used. Naloxone administered 1 h after morphine reversed the inhibitory effects of morphine, whereas the simultaneous administration of naloxone with morphine had variable effects but seemed to delay the LH increase.(ABSTRACT TRUNCATED AT 250 WORDS)     

Luteinizing hormone release by gonadotropin releasing hormone before and after castration in bulls

The magnitude of gonadotropin releasing hormone (GnRH) induced lutei nizing hormone (LH) release prior to castration, following castration, a nd during testosterone replacement in males, was compared, using 6 9-mon th-old Holstein bulls. Also, the effects of castration and testosterone replacement on patterns of episodic changes in serum LH were studied. Blood samples were collected at hourly intervals for 24 hours prior to castration, at 21 days after castration, and at 23 days postcastration a fter testosterone, 20 mg thrice daily, has been given for 24 hours. Each animal was given GnRH, 40 mcg iv, at 24 hours before castration, at 7 and 14 days after castration, and at 28 days postcastration following 6 days of testosterone treatment. GnRH caused LH release before and after castration. The LH increase was 2.5-fold at 14 days postcastratio n. Testosterone replacement did not reduce the magnitude of LH response to GnRH to precastration levels. The number of episodic increases in serum LH prior to castration averaged 3.7 daily and increased to 6.5 daily at 21 days after castration (p less than .05). The magnitude of increase in LH concentration in these epidsodic events was not affected by castration. Testosterone replacement failed to restore either the average number or change the magniture of LH increase above precastratio n levels. It was shown that LH is normally released episodically in bulls. The peaks of LH release were followed by increased testosterone in serum. Results suggest that LH release in bulls is controlled by gonadic factors other than testosterone.     

Age-dependent effect of Freund's adjuvant on 24-hour rhythms in plasma prolactin, growth hormone, thyrotropin, insulin, follicle-stimulating hormone, luteinizing hormone and testosterone in rats

The effect of Freund's adjuvant administration on 24-hour changes of plasma prolactin, growth hormone (GH), thyrotropin (TSH), insulin, follicle-stimulating hormone (FSH), luteinizing hormone (LH) and testosterone were studied in young (2 months) and aged (18 months) male Wistar rats. Rats were injected s.c. with Freund's adjuvant or adjuvant's vehicle and, 18 days later, they were killed at 6 different time intervals throughout a 24-hour cycle to measure circulating hormone levels by specific RIAs. Young rats receiving adjuvant's vehicle exhibited significant time-of-day-dependent variations in plasma TSH, LH and testosterone, with maximal levels at 1300 h, 0100 h and 1700 h, respectively. Prolactin and insulin levels, analyzed globally in a factorial ANOVA, showed significant time-of-day changes with maximal levels at 1300 - 1700 h and 2100 h, respectively. The daily rhythms in plasma LH and testosterone found in young rats were not longer observed in Freund's adjuvant-injected rats, while as far as TSH, a second peak was observed at 0100 h after Freund's adjuvant administration. Twenty-four hour rhythms in circulating TSH, LH and testosterone were blunted in old rats receiving either Freund's adjuvant or its vehicle. Aged rats exhibited significantly higher circulating levels of prolactin, and lower levels of GH, TSH, FSH and testosterone. The results indicate that secretion of prolactin, GH, TSH, FSH and testosterone are age-dependent, as are the responses of TSH, LH and testosterone to Freund's adjuvant administration.     

Feedback regulation of gonadotropic hormone secretion in neonatal pigs

The effect of castration and of administration of charcoal-treated porcine follicular fluid (pFF) containing inhibin-like activity on plasma concentration of gonadotropic hormones was studied in neonatal pigs. Plasma follicle-stimulating hormone (FSH) concentration averaged 25.1 +/- 1.5 ng/ml (mean +/- SEM) in 1-wk-old females and gradually declined to 20.2 +/- 0.7 ng/ml 6 wk later. Ovariectomy did not significantly influence plasma FSH concentration. In males, concentration averaged 8.0 +/- 0.7 ng/ml before castration but rose significantly within 2 days after castration. Injection of luteinizing hormone-releasing hormone (LHRH) did not influence plasma FSH concentrations in intact males, but did in females and in 7-wk-old males castrated at 1 wk. Plasma luteinizing hormone (LH) concentrations in 1-wk-old females (2.2 +/- 0.4 ng/ml) gradually declined and were not influenced by castration. Concentrations of plasma LH in 1-wk-old male piglets (2.8 +/- 0.7 ng/ml) were not significantly influenced by castration within 2 days but were significantly higher 6 wk later. LHRH induced a significant rise in plasma LH concentrations in all animals. Injection of pFF resulted in a decline of plasma FSH concentrations in intact and castrated males and in intact females, but did not influence plasma LH concentrations. These data demonstrate a sex-specific difference in the control of plasma FSH, but not in plasma LH concentration in the neonatal pig. Plasma FSH concentrations, but not plasma LH concentrations, are suppressed by testicular hormones in 1-wk-old piglets. Plasma FSH concentrations can be suppressed in both neonatal male and female pigs by injections of pFF.     

Increase in ovulation rate after treatment of ewes with bovine follicular fluid in the luteal phase of the oestrous cycle

Administration of charcoal-treated bovine follicular fluid to Damline ewes twice daily (i.v.) from Days 1 to 11 of the luteal phase (Day 0 = oestrus) resulted in a delay in the onset of oestrous behaviour and a significant increase in ovulation rate following cloprostenol-induced luteolysis on Day 12. During follicular fluid treatment plasma levels of FSH in samples withdrawn just before injection of follicular fluid at 09:00 h (i.e. 16 h after previous injection of follicular fluid) were initially suppressed, but by Day 8 of treatment had returned to those of controls. However, the injection of follicular fluid at 09:00 h on Day 8 still caused a significant suppression of FSH as measured during a 6-h sampling period. Basal LH levels were higher throughout treatment due to a significant increase in amplitude and frequency of pulsatile secretion. After cloprostenol-induced luteal regression at the end of treatment on Day 12, plasma levels of FSH increased 4-fold over those of controls and remained higher until the preovulatory LH surge. While LH concentrations were initially higher relative to those of controls, there was no significant difference in the amount of LH released immediately before or during the preovulatory surge. These results suggest that the increase in ovulation rate observed during treatment with bovine follicular fluid is associated with the change in the pattern of gonadotrophin secretion in the luteal and follicular phases of the cycle.     

Effect of vitamin A deficiency upon gonadotropin response to gonadotropin-releasing hormone

There is a monotypic change in basal serum gonadotropin levels following retinol treatment of chronically vitamin A-deficient (VAD) male rats. The present study was undertaken to investigate the hypothesis that the specific increase in serum follicle-stimulating hormone (FSH) represents a change in gonadotrope responsiveness to gonadotropin-releasing hormone (GnRH). To this end, a test dose of GnRH was given to VAD rats pre-, 5 days post-, and 10 days postreplacement of vitamin A (PVA). In VAD rats, basal serum FSH and luteinizing hormone (LH) levels were higher than those of controls. Increased LH/testosterone ratios, both in basal levels and in the secretory response to GnRH, suggested Leydig cell hyporesponsiveness in VAD animals. Both the FSH and LH responses to GnRH were maximal at 1 h, declining thereafter. Although the absolute increments in FSH and LH 1 h after GnRH in VAD rats were greater than in controls, the percent increase in FSH tended to be lower in VAD rats and to increase after vitamin A replacement. The specific enhancement of FSH release PVA became evident only when assessing total secretion of FSH and LH after GnRH. Luteinizing hormone response to GnRH increased PVA, but not significantly, while FSH secretion after GnRH increased both 5 and 10 days PVA, times during which basal FSH levels were also increasing. These changes in FSH secretion could not be attributed either to increases in endogenous GnRH or to changes in testosterone or estradiol levels. Basal serum androgen binding protein levels, elevated in VAD animals, did not respond to the acute increases in FSH after GnRH and remained high PVA, suggesting no acute change in Sertoli cell function. Thus, the PVA increase in FSH secretion unmasks a partial inhibition of the gonadotrope present in the retinol-deficient, retinoic acid-fed male rat.     

Short-term effects of vasoligation upon plasma follicle-stimulating hormone, luteinizing hormone, and prolactin in the adult rat: further evidence for a direct neural connection between the testes and the central nervous system

The purpose of these experiments was to determine whether bilateral vasoligation of adult male rats had any short-term effects upon plasma levels of follicle-stimulating hormone (FSH), luteinizing hormone (LH), and prolactin. Adult male rats (250-300 g) were either bilaterally vasoligated or sham vasoligated, and blood samples were obtained by cardiac puncture preoperatively and at 24 h and 7 days following surgery. Plasma levels of both FSH and LH were significantly (P less than 0.01) decreased at 24 h following vasoligation compared to preoperative levels and those of sham-operated controls. However, the response was differential since, at 7 days following vasoligation, plasma FSH was still significantly decreased while LH was returning to control levels. Conversely, plasma prolactin levels were significantly (P less than 0.01) increased at 24 h compared to preoperative values and those in sham-operated controls, and at 7 days prolactin had returned to preoperative control levels. Sham vasoligation did not significantly change plasma levels of FSH, LH, or prolactin at any of the time intervals investigated. These results provide further evidence that suggests that there may be a direct connection between the testis and central nervous system that may be involved in the short-term regulation of gonadotropin and prolactin secretion.     

Buserelin in a superovulatory regimen for Holstein cows. I. Pituitary and ovarian hormone response in an experimental herd

Two experiments were conducted with frequent blood sampling in standard superovulatory regimens using follicle stimulating hormone (FSH) and prostaglandin F(2) alpha (PGF) to study the effects of the gonadotropin releasing hormone analog, Buserelin, on changes in FSH, luteinizing hormone (LH), progesterone (P(4)) and estradiol (E(2)). In Experiment I, Buserelin (20 mug) was administered to a total of 28 dry Holsteins. One group was treated with Buserelin 36 and 60 h after PGF administration, a second group was treated 60 h after PGF, and a third group served as the controls. In Experiment II, 30 dry Holsteins received Buserelin (10 mug). One group was treated 48 h after PGF, a second group at 54 h after PGF, a third group 24 h after estrus was first observed and a fourth group was a control. The general pattern of a decrease in P(4) following PGF, an increase in E(2), the onset of estrus, an LH peak, and finally, an increase in P(4) in superovulated cows was observed. Buserelin consistently produced a sharp LH peak at 36 h when given 36 h after PGF. At later intervals, it produced either a major or minor peak depending upon whether a spontaneous LH peak had already occurred. There was too much individual cow variation in the interval from PGF to a spontaneous LH peak to consistently induce a uniform LH peak, except when Buserelin was given 36 h after PGF, which may be early for normal oocyte maturation. There was no treatment effect on FSH, and embryo recovery rate was unaffected by treatment (P>0.05).     

Differential effects of the perinatal steroid environment on three sexually dimorphic parameters of the rat brain

Gonadectomy of male rats was performed at 0, 6-7 (6h), 12-13 (12h), or 24 h postnatally in order to examine the influence of testosterone exposure on sexual differentiation of the brain. The indices examined were: the volume of the sexually dimorphic nucleus of the preoptic area (SDN-POA) and luteinizing hormone (LH) and follicle-stimulating hormone (FSH) titers following estradiol benzoate (EB) and progesterone (P) administration. Control animals were sham-operated at 0 h and gonadectomized at 29 days of age (sham). A decrease in the percentage of males with elevated plasma LH levels following P was found with increasing delay before gonadectomy. Significant (P less than 0.001) differences existed in the amplitude of plasma LH titers 5 h following P administration between sham, 0 h, and 6 h groups. Follicle-stimulating hormone was also elevated in all neonatally gonadectomized male groups following P administration, but there was no difference between the groups. Volume of the SDN-POA was significantly (P less than 0.001) smaller in all gonadectomized males when compared to that of sham-operated males, but no differences existed between males gonadectomized at the different hours postpartum. In female rats gonadectomized at 0 h (F0h), LH levels were elevated 5 h following P, but only to a magnitude of 36% of that of sham-operated controls (P less than 0.001). Volume of the SDN-POA of the F0h group was significantly reduced (P less than 0.05) when compared to that of sham females. Thus, in males, the presence of the tests prenatally may be responsible for the initiation of masculinization of LH release mechanisms and the SDN-POA, but both require further androgen exposure for their completion. In addition, the LH and FSH regulating systems show a differential sensitivity to the steroid hormone environment during development that shapes the animal's response to steroid as an adult.     

Selective release of follicle-stimulating hormone by 5 alpha-dihydroprogesterone in immature ovariectomized estrogen-primed rats

The effect of 5 alpha-dihydroprogesterone (5 alpha-DHP) on gonadotropin release was examined in the immature acutely ovariectomized (OVX) rat primed with a low dose of estradiol (E2). Treatment with various doses of 5 alpha-DHP given in combination with E2 increased levels of follicle-stimulating hormone (FSH) but had no effect on serum luteinizing hormone (LH). A single injection of a maximally stimulating dose of 5 alpha-DHP (0.4 mg/kg) stimulated increases in serum FSH at 1200 h and, 6 h later, at 1800 h. Pituitary LH and FSH content was dramatically enhanced by 1600 h and levels remained elevated at 1800 h. The administration of pentobarbital at 1200 h, versus 1400 h or 1600 h, prevented the increase in basal serum FSH levels at 1800 h, implying that the release of hypothalamic LH releasing hormone (LHRH) is modulated by 5 alpha-DHP. In addition, changes in pituitary sensitivity to LHRH as a result of 5 alpha-DHP were measured and a significant increase in the magnitude of FSH release was observed at 1200 h and 1800 h. Although the LH response to LHRH in 5 alpha-DHP-treated rats was not different from controls, the duration of LH release was lengthened. These results suggest that 5 alpha-DHP may stimulate FSH release by a direct action at the pituitary level. Together, these observations support the theory that 5 alpha-DHP mediates the facilitative effect of progesterone on FSH secretion and further suggests an action of 5 alpha-DHP in this phenomenon at both pituitary and hypothalamic sites.     

Reproductive toxicity with and without LHRHA administration during adjuvant chemotherapy in patients with germ cell tumors.

In order to evaluate the protective efficacy of an agonist of luteinizing hormone releasing hormone (LHRHA) on spermatogenic stem cells, we undertook a prospective study in patients with germ cell tumors. Following orchiectomy and unilateral lymph node dissection all patients received adjuvant chemotherapy consisting of 2 courses of PVB regimen (cisplatin, vinblastine and bleomycin). Six men were treated with LHRHA (d-Ser-(TBU)6 LHRH ethylamide) before, during and after PVB chemotherapy. Eight patients without LHRHA protection served as controls, receiving the identical chemotherapy. Follicle-stimulating hormone (FSH), luteinizing hormone (LH), and testosterone were within normal limits before therapy in all patients. In 6/6 protected patients, serum levels of FSH, LH and testosterone were effectively suppressed during pre-chemotherapeutic LHRHA administration. All protected patients showed elevated serum FSH levels and azoospermia after cessation of chemotherapy and LHRHA treatment due to germ and stem cell loss. Median FSH level and sperm density of the protected group normalized within 24 months after chemotherapy. In all unprotected patients elevated FSH values and azoospermia also occurred after chemotherapy. Likewise, median FSH level and sperm density normalized spontaneously in this group within 24 months after chemotherapy. Our results suggest completely reversible reproductive toxicity two years after 2 courses of adjuvant chemotherapy in all patients. Administration of LHRHA during chemotherapy seems to have no protective effects on germ cells since both groups developed reproductive toxicity. Furthermore, recovery time was identical in the protected and unprotected patients. FSH and LH could be used as diagnostic markers to assess the degree and duration of reproductive and endocrine gonadal toxicity after chemotherapy.     

Hormonal regulation of tissue plasminogen activator secretion and mRNA levels in rat granulosa cells

Granulosa cells from immature rats produce tissue plasminogen activator (tPA) in response to follicle stimulating hormone (FSH) or luteinizing hormone (LH) both in vitro and in vivo. We have used the in vitro system to investigate the level at which the hormonal induction of tPA is regulated. Within 12 h following FSH addition, a dramatic but transient increase in tPA secretion occurs for by 24 h secretion returns to basal levels. This pattern of enzyme induction is similar with LH, but the onset of the increase is delayed. When steady-state tPA mRNA levels are examined after hormone treatment, the results mirror those obtained if one measures enzyme activity; a large increase in tPA mRNA followed by a decrease to basal levels is observed with both hormones, and the lag in induction by LH is also apparent. These results demonstrate that the regulation of tPA activity by gonadotropins occurs at the level of the steady-state concentration of the mRNA. In the presence of cycloheximide, the induction of tPA mRNA by FSH or LH is not greatly affected, indicating that this phase of the response to gonadotropins does not require the synthesis of new protein. However, the decrease in tPA mRNA levels observed 24 h after FSH treatment is affected by cycloheximide, in that the drug delays the reduction in mRNA levels seen with hormone alone.     

Testosterone control of brain and anterior pituitary beta-adrenergic receptors

Orchidectomy of adult albino rats resulted in a quick, (approximately 70%) increase in the density of beta-adrenergic receptors in the anterior pituitary gland within the first day. There was a concurrent rapid increase in plasma levels of pituitary gonadotropins. The beta-receptor density continued to increase slowly for at least 16 days after castration, but it could be lowered significantly to the levels of sham-operated animals by treatment with testosterone (3 mg/kg/day) beginning on the fourth day after castration and continuing for 4 days. This treatment also completely reversed the elevation in plasma levels of luteinizing hormone (LH), and significantly reduced the circulating follicle-stimulating hormone (FSH) levels. Prolactin levels were not significantly altered by the treatments used in these studies. Most of the beta-adrenergic receptors induced by orchidectomy in the anterior pituitary were shown, using a beta 1-selective antagonist, practolol, or a beta 2-selective antagonist, IPS-339, to be of the beta 2-subtype. The density of the beta-adrenergic receptors in the cerebral cortex also increased significantly (10-24%) after castration, and returned to the levels of sham-operated animals following treatment with testosterone. No significant change in the density of the beta-adrenergic receptors in the hypothalamus resulted from either castration or testosterone replacement.     

Effects of a potent antagonist to gonadotropin-releasing hormone on male rats: luteinizing hormone is suppressed more than follicle-stimulating hormone

Previous work with female rats showed that serum levels of follicle-stimulating hormone (FSH) are suppressed by gonadotropin-releasing hormone (GnRH) antagonists less than are levels of serum luteinizing hormone (LH), suggesting a lesser dependency of FSH on GnRH stimulation. The differential regulation of LH and FSH is known to have some aspects that are sexually asymmetrical, and it was of interest to see if males also show differential gonadotropin suppressibility after injection of an antagonist to GnRH. Male rats were prepared for serial sampling 4 wk after castration. After a blood sample was removed at Time Zero, [Ac-3-Pro1, pF-D-Phe2, -D-Trp3,6]-GnRH (Antag) was injected subcutaneously in oil; doses were 0, 4, 20, 100, 500, and 2500 micrograms. Blood was sampled at 2, 5, 12, 24 and 36 h postinjection. All doses above 4 micrograms had lowered LH levels by 2 h, and LH remained suppressed for 12 to 24 h at the three higher doses. By contrast, serum FSH was unaffected by any dose at 5 h, and was only marginally suppressed by the highest doses thereafter. As in females, therefore, FSH secretion in male rats appears not to be as dependent on GnRH as is LH secretion.