Effects of progesterone on estrogen-induced gonadotropin release in male rhesus macaques

The effects of progesterone (P) on estrogen (E)-induced gonadotropin release were studied in 10 adult male rhesus macaques castrated more than 2 yr earlier. The intent was to determine whether physiological levels of P (approximately 400 pg/ml) found in the systemic circulation of intact males would block E-induced gonadotropin release and whether the responses of castrated males were similar to those of castrated females with and without pretreatment with 17 beta-estradiol (E2). Different doses of P were administered in Silastic capsules (0.3, 4.0, and 5.0 cm) implanted sc. A 0.3-cm implant maintained serum P levels at about 400 pg/ml (equivalent to physiological levels in intact males); 5.0-cm implants produced serum levels of about 4.0 ng/ml (similar to luteal phase levels in females). In male monkeys treated for approximately 3 weeks with E2, only the highest dose (approximately 4.0 ng/ml) of P blocked FSH induced by estradiol benzoate (E2B). LH was blocked in one third of the animals thus treated. The same P dose was ineffective in blocking E2-induced LH release in spayed females pretreated with E2, but did block FSH release. Gonadectomized males and females not treated beforehand with E2 released LH in response to an E2B challenge, but FSH was not elevated in the peripheral circulation under these experimental conditions. These results suggest that luteal phase levels of P block E2-induced FSH release in gonadectomized males and females. With the same treatment regimens, P blocks E2 action in some males, but all females responded to E2B by releasing LH. These data also suggest that estrogen priming is necessary for FSH, but not LH, release in adult rhesus macaques of both sexes. The prerequisite of E treatment for the induction of positive feedback appears to be associated with the level of gonadotropin suppression before E2B treatment.     

Monolayer cultures of gonadotrophs separated by velocity sedimentation: heterogeneity in response to luteinizing hormone-releasing hormone.

Isolated pituitary cells from 14-day-old male and female and adult male rats were separated into enriched populations of gonadotrophs by velocity sedimentation at unit gravity. The cells, collected from five gradient fractions, were established in monolayer culture. Hormone content and hormonal secretion in response to LHRH were measured after 3 days in culture. Stored FSH and LH declined during culture, but the relative differences between fractions and between animal groups were maintained. In all fractions, LHRH stimulated the release of both FSH and LH in a dose-response fashion. The secretory potential per gonadotroph changed with fraction and the pattern was highly characteristic for each animal group. In 14-day-old females, both FSH and LH secretion increased 20 times from the fraction with the smallest to the fraction with the largest gonadotrophs. In preparations from 14-day-old males, only the release of FSH consistently rose with gonadotroph cell size. With cells from adult males, FSH as well as LH release increased with cell size, but the pattern was different for each hormone. Secretion did not always correlate with the cellular content of hormone before stimulation. The present findings suggest that gonadotrophs isolated from animals in a different physiological or developmental status may retain in short term culture certain of their previous functional characteristics. There is evidence that the gonadotroph cell population is heterogeneous not only in terms of the magnitude of the response to LHRH but also in terms of the relative proportion of FSH and LH secreted. Changes in the relative proportion of certain variants of gonadotrophs may be a cellular basis for differential regulation of FSH and LH secretion by a single releasing hormone.     

Seasonal pattern of leutinizing, follicle-stimulating hormone, testosterone and progesterone in adult population of both sexes in the Jordan Valley

Differences were observed in hormonal levels between in both sexes of people living in Irbid City (620 meters above sea level) and in the Jordan Valley (360 meters below sea level). In addition, exercise was shown to differentially affect hormonal levels of both sexes at the above and below sea level locations. Serum levels of leutinizing hormone (LH) and testosterone (T) in adult male and serum levels of follicle-stimulating hormone (FSH) and progesterone (P) in adult female people were investigated in Irbid City and in the Jordan Valley during the years 1997 and 1998. The levels of these hormones were followed each month during this period. In males living in Irbid City, LH and T peaked from March through June, and in females at the same site, FSH and P also peaked from March through June. These data confirm the seasonal variation in sex hormones reported elsewhere in (wo)man and in other species. In males and females of the Jordan Valley, serum levels of LH, FSH, T and P were all higher than those of Irbid City throughout the year. Additionally, peaks of LH and T in male and FSH and P in female subjects in the Jordan Valley were observed from March through September. The high levels of these hormones and the extension of their peaks are suggested to be due to effects of the environmental factors of the Jordan Valley (high temperature, high barometric pressure) compared to those in Irbid City and other areas located at above sea level altitude.     

A comparison of changes in the peripheral plasma concentrations of luteinizing hormone and follicle-stimulating hormone in the rat.

Plasma FSH concentrations in rats have been determined by radioimmunoassay under a variety of experimental conditions to see whether any evidence could be obtained of an acute divergence in LH and FSH secretion rates which would support the idea of separate, specific hypothalamic releasing factors for these two hormones. During the normal ovarian cycle and after the administration of progesterone to female rats on the morning of the day of pro-oestrus increased secretion of both LH and FSH began simultaneously but FSH concentrations were later maintained or increased slightly while LHING EARLY PREGNANCY FSH concentrations were higher than at the corresponding stage of the cycle at a time when LH concentrations had been shown to be lower. Progesterone injected at the dioestrous stage of the cycle reduced both LH and FSH concentrations though the effect on LH was more marked. After ovariectomy at any stage of the oestrous cycle or on day 4 of pregnancy there was a rapid and significant increase in plasma FSH concentration which was quite different from the delayed increase in LH concentration observed in these animals. In contrast, the early increase in FSH concentration in male rats after castration was less than the increase in LH concentration. The final FSH concentration in castrated males was only about four times the basal level in contrast to the 10- to 15-fold increase in LH in males and both LH and FSH in females. Anovulatory adult females that had received 1-25 mg of testosterone propionate on day 4 of postnatal life showed the rapid and sustained increase in plasma FSH after ovariectomy that was seen in normal females. None of these results strongly support the idea that separate and specific hypothalamic releasing factors for LH or FSH are secreted in the rat although the differences in the early response to gonadectomy could be explained on this basis.     

Effects of starvation in rats on serum levels of follicle stimulating hormone, luteinizing hormone, thyrotropin, growth hormone and prolactin; response to LH-releasing hormone and thyrotropin-releasing hormone.

Adult male Sprague-Dawley rats averaging 300 g each were subjected to complete food removal for 7 days (acutely starved), 7 days complete food removal followed by 2 weeks of 1/4 ad libitum food intake (chronically strved), 7 days complete food removal and 2 weeks of 1/4 ad libitum intake followed by ad libitum feeding for 7 days (refed), or fed ad libitum throughout (controls). Serum LH, FSH, TSH, PRL, and GH levels were measured by radioimmunoassays for each group of rats. The in vivo response to the combination of synthetic LHRH and TRH also was tested in each group of rats. Circulating LH, TSH, GH, and PRL were significantly depressed in acutely and chronically starved rats, and FSH was lowered only in acutely starved rats. After 7 days of refeeding, serum levels of LH and FSH were significantly greater than in ad libitum fed controls, PRL returned to control levels, and TSH and GH increased but were still below control levels. After LHRH + TRH injection serum LH and TSH were increased significantly in all groups of rats, FSH and PRL rose in acutely but not in chronically starved rats, and GH was not elevated in any group. The increases in serum LH, FSH, TSH and prolactin in response to LHRH + TRH injection in acutely or chronically starved rats were equal to or greater than in the ad libitum fed controls. These data indicate that severe reductions in food intake result in decreased release of at least 5 anterior pituitary hormones, and this is due primarily to reduced hypothalamic stimulation rather than to inability of the pituitary to secrete hormones.     

A quantitative immunocytochemical study of the luteinizing hormone and follicle-stimulating hormone cells in the adenohypophysis of adult male rats and adult female rats throughout the estrous cycle

We investigated whether 1) the absolute or the relative numbers of LH and FSH cells change during the rat estrous cycle, 2) the percentages of gonadotrophs that contain LH and/or FSH change during the estrous cycle, and 3) gonadotrophs change in size during the rat estrous cycle. Groups of four female rats were decapitated at one of five different times during the estrous cycle. Four male rats were also decapitated. Serum concentrations of LH and FSH were determined by RIA. Paired horizontal flip-flopped or nonflipped paraffin sections were mounted from the dorsal, middle, and ventral portions of each pituitary gland. In each pair of sections, one was stained with a-rat LH-S4 and the other with a-rat FSH-S7 by the unlabeled antibody peroxidase-antiperoxidase method. All immunoreactive cells were counted. Photographs were taken from randomly chosen corresponding areas, and the cells were individually matched to determine the percentage that contained one or both hormones. Correction factors had to be used because in paired flip-flopped or nonflipped sections stained with the same antibody (a-rat LH-S4), not all of the stained cells found in one section were found in the other section. The absolute numbers of LH and FSH cells did not change throughout the estrous cycle. The ratio of LH cells to FSH cells in the pars distalis of female rats was also constant throughout the estrous cycle. In female rats, 75.2% of LH cells also contained FSH, while 99.4% of FSH cells also contained LH. In the male rats, 88.6% of LH cells also contained FSH, while 98.6% of FSH cells also contained LH. Similar results were obtained in paired flip-flopped sections stained with a-rat LH beta and a-rat FSH beta. Sequential staining of additional individual tissue sections with a-rat LH-S4 and then a-rat FHS-S7 or vice versa revealed the following. Staining of LH-stained tissue for FSH revealed less than 1% new cells, but staining of FSH-stained tissue for LH revealed a 8.7% increase in gonadotrophs in males and a 25.4% increase in females. The gonadotrophs in female rats did not change in size during the estrous cycle and were significantly smaller than the gonadotrophs in male rats. The results suggest that in normal adult rats: 1) virtually all FSH-containing cells contain LH, 2) about 25% of the gonadotrophs in females and about 11% of the gonadotrophs in males contain LH but not FSH, 3) the number of cells containing LH or those containing LH and FSH does not change during the estrous cycle, 4) gonadotrophs in female rats do not change in size during the estrous cycle and are smaller than the gonadotrophs in male rats, and 5) FSH release during the early morning of estrus, when the serum FSH concentration is elevated and the serum LH concentration is low, occurs from cells that contain both LH and FSH.     

Changes with age in levels of serum gonadotropins, prolactin and gonadal steroids in prepubertal male and female rats.

Radioimmunological determination of serum LH, FSH, and estradiol concentrations in prepubertal female rats demonstrates the temporal coincidence of increased serum levels of these hormones between days 9 and 21. Serum FSH and estradiol levels are continuously high during that time, whereas interindividual fluctuations in LH levels were enormous. No high LH, FSH, and estradiol levels were observed between day 21 and puberty, during which time serum prolactin and progesterone gradually increased. Serum testosterone in the female immature rats stayed uniformly low. It is suggested that increased serum estradiol levels in the presence of low prolactin levels (between day 10 and 20) act in a positive feedback fashion on the CNS-pituitary axis. The resulting increased gonadotropin levels are later (between day 20 and puberty) decreased by an inhibitory action of prolactin and/or progesterone on pituitary gonadotropin release. In male rats serum FSH and prolactin, which were low during the first 3 weeks, increased later to reach high levels during puberty. Serum LH was slightly elevated during the 2nd and 3rd week of life at which time serum progesterone also increased to reach the highest levels in the prepubertal period. Serum testosterone was higher in male than in female rats for the first 3 weeks of life; the difference between both sexes was significant but not striking. Between day 21 and the prepubertal period the testosterone levels were relatively low, but they increased again during puberty. Sex differences in androgen levels (measured with a less specific antibody) were more pronounced whereas estradiol levels in males showed the same pattern between birth and puberty as in the female littermates. These results suggest that not only testosterone but also other, not yet identified, androgens may be involved in the masculinzation of the brain.     

Assessment of luteinizing hormone and prolactin immunoactivity in Asian and African elephant urine using assays validated for serum

Analysis of serum hormones is useful for timing artificial insemination (Luteinizing hormone) and diagnosing pregnancy (prolactin) in elephants. However, these tests require blood collection, which is not tolerated by all animals, and is impractical for field studies. Thus, developing a means to obtain these measures noninvasively could improve species management. Matched urine and serum was collected from Asian and African elephants daily throughout the follicular phase and after administration of a GnRH analogue for LH determination, and in pregnant and nonpregnant females for prolactin analyses using immunoassays validated for elephant serum. Despite identifying robust increases in circulating hormone concentrations, no concomitant changes in urinary LH or prolactin immunoactivity was detected. Concentration of samples by centrifugal filtration or ethanol precipitation did not increase the ability to measure biologically relevant changes in endogenous urinary LH or prolactin immunoactivity. Sample matrix interference was ruled out following sufficient recovery of exogenous LH or prolactin added to samples, except for samples concentrated >35-fold where some interference was suspected. These results suggest that elephants either do not excrete native LH or prolactin in urine, or concentrations are too low to be measured accurately by standard immunoassay techniques that are valid for serum analyses. Thus, it does not appear feasible or economically viable to use these noninvasive tests for ovulation detection or for pregnancy diagnosis in elephants.     

Circannual variations in serum concentrations of pituitary, thyroid, parathyroid, gonadal and adrenal hormones in male laboratory rats

Seasonal effects were studied on basal levels of hormones in the serum of adult male Sprague-Dawley rats, which were born and raised under rigorously controlled laboratory conditions. Groups of 90-day-old rats were killed at monthly intervals by rapid decapitation. Significant fluctuations were observed throughout the observation period of 19 months in serum levels of TSH, prolactin, androgens, tri-iodothyronine and LH. Minor fluctuations were observed in serum levels of FSH, corticosterone, parathyroid hormone and thyroxine. The results indicate that male laboratory rats exhibit circannual and semi-annual fluctuations in serum levels of several hormones even though the animals were born, raised and maintained in constant laboratory conditions.     

THE TSH, FSH AND PROLACTIN RESPONSES TO CONTINUOUS INFUSIONS OF TRH AND THE EFFECTS OF OESTROGEN ADMINISTRATION IN NORMAL MALES

Four normal males received a constant infusion of 0.9% NaCl for 1 hr followed immediately by 500 μg of TRH infused over the same period. A rise in serum TSH was observed in all subjects while in three there was also a significant FSH response. The prolactin response, unlike that of TSH, was markedly pulsatile indicating that different mechanisms exist for the release of these two hormones from the pituitary after TRH. Circulating levels of LH were unaffected. Ethinyl oestradiol, 30 μg daily for 3 days, was administered to two of the subjects and the infusions were repeated. Both basal FSH and LH levels were depressed, as was the FSH response to the infusion of TRH. By contrast, however, the TSH response to thyrotrophin releasing hormone was enhanced after oestrogen. In one subject the basal prolactin levels were significantly higher while in both there was an augmented prolactin response to TRH, the pulsatile pattern of release being maintained.     

Sexual differences in the serotonergic control of prolactin and luteinizing hormone secretion in the rat

The effects of serotonin on PRL and LH release were investigated in female and male rats under different experimental conditions. At a dose of 5 mg/kg ip, serotonin increased serum PRL titers in intact males and in females during diestrus and estrus; the levels attained in the male rats were much higher than in the females. At a lower dose (2.5 mg/kg) the PRL-releasing effect of serotonin was only evident in male rats. Thus, we chose this dose for the following experiments to investigate the apparent sexual difference. To evaluate the importance of the hormonal status characteristic of male and female in conditioning the serotonin effect, an experiment was performed in gonadectomized rats, untreated or treated with estradiol benzoate (EB), or testosterone propionate (TP). In the three hormonal conditions the sexual difference was maintained: serotonin released PRL in males and failed to do so in females. However, if males were castrated within 24 h of birth, and females androgenized by a single perinatal injection of TP, the sexual difference in adulthood were reversed; thus, androgenized females responded to serotonin and males castrated at birth failed to do so. These results suggest that a male differentiated brain is more sensitive to the PRL-releasing effect of serotonin, irrespective of the hormonal environment of the rat. On the other hand, serotonin increased serum LH in female rats in estrus and in adult ovariectomized rats treated with EB; but not in females in diestrus or in ovariectomized rats, treated with TP or untreated. Neither did it modify serum LH titers in male rats whether intact, orchidectomized, or orchidectomized plus steroids. However, if male rats were castrated a few hours after birth and then treated in adulthood with EB, serotonin effectively released LH. Thus, two components, estradiol and a feminine differentiated brain, may be necessary for the facilitatory action of serotonin on LH release. Since no sex differences were observed in the increase of serum serotonin after the injection of 2.5 mg/kg of the drug, it can be discounted that the differences described for the endocrine effect of the drug could be due to different levels of circulating indolamine achieved in male and female rats. Taken together, our results indicate that serotonergic control of anterior pituitary secretion is sexually differentiated and that it presents individual characteristics for PRL and LH release.     

Prolactin releasing peptide (PrRP) stimulates luteinizing hormone (LH) and follicle stimulating hormone (FSH) via a hypothalamic mechanism in male rats

Prolactin releasing peptide (PrRP) was originally isolated as an endogenous hypothalamic ligand for the hGR3 orphan receptor. It has been shown to release prolactin from dispersed pituitaries harvested from lactating female rats and only at very high doses in cycling females. PrRP is reported to have no effect on prolactin production from dispersed pituitary cells harvested from males. The CNS distribution of this peptide suggested a role for PrRP in the control of the hypothalamo-pituitary axis. The aim of this study was to examine the actions of PrRP (1-31) on circulating pituitary hormones following intracerebroventricular (ICV) injection in male rats and to investigate the mechanism of PrRP's effect by measurement of hypothalamic releasing factors in vitro. In our experiments, PrRP (1-31) did not release LH, FSH, TSH, growth hormone or prolactin directly from dispersed male pituitary cells in vitro. We have shown for the first time that following ICV injection of PrRP (1-31) 5 nmol there was a highly significant simulation of plasma LH that began at 10 minutes and was maintained over the course of the experiment (at 60 minutes PrRP 5 nmol 2.2 +/- 0.2 vs. saline 0.5 +/- 0.1 ng/ml, p<0.001). Plasma FSH increased at 20 minutes following ICV injection (PrRP 5nmol 10.8 +/- 2.0 ng/ml vs. saline 5.1 +/- 0.5, p<0.01). Total plasma testosterone increased at 60 minutes post injection (PrRP 5nmol 9.2 +/- 1.6 vs. saline 3.5 +/- 0.6 nmol/l, p<0.01). There was no significant alteration in plasma prolactin levels. PrRP significantly increased the release of LHRH from hypothalamic explants in vitro (PrRP 100nmol/l 180.5 +/- 34.5% of the basal secretion, p<0.05). PrRP (100nmol/l) also increased the following hypothalamic peptides involved in the control of pituitary hormone release, vasoactive intestinal peptide (VIP) 188.1 +/- 24.6% and galanin 153.8 +/- 13.0% (both p<0.001 vs. basal secretion) but had no effect on orexin A secretion. These results suggest a role for PrRP in the control of gonadotrophin secretion acting via a hypothalamic mechanism involving the release of LHRH.     

In vitro pituitary responsiveness to gonadotropin-releasing hormone (LH-RH) in intact and castrated male and female rats

The in vitro response of pituitaries isolated from both normal and 18–21-day post-castration male and female intact rats to incremental doses of synthetic gonadotropin-releasing hormone (LH-RH) has been investigated. Intact male pituitaries released luteinizing hormone (LH) maximally at the smallest dose of LH-RH (0.1 ng/ml) whereas intact female pituitaries released LH in a dose-response fashion. FSH release from intact male pituitaries was considerably greater than that from intact female pituitaries. As with LH, intact male pituitaries appeared maximally stimulated at 0.1 ng/ml of LH-RH. Intact female pituitaries did not release FSH until a 10 ng/ml dose of LH-RH was used.Male and female castrate pituitaries were more susceptible to LH-RH-induced LH and FSH release than were their intact counterparts, although this was more pronounced with regard to LH release. In addition castrate male pituitaries were more sensitive to lower doses of LH-RH than were castrate female pituitaries, this being most pronounced regarding LH release. Castrate female pituitaries released less FSH at the 100 ng/ml dose than at the 10 ng/ml dose, possibly indicating inhibition at these higher doses.In addition, pituitary extraction and serum from normal and castrate male and female rats were examined for LH and FSH content. LH content of castrated rat pituitaries of both sexes was considerably greater than that of their intact counterparts, as expected. However, castrate male pituitaries contained significantly less FSH than intact male pituitaries, whereas the opposite was true for the female groups. Serum LH and FSH levels were increased in the castrate groups with no difference between sexes. Serum from intact males contained considerably more FSH than did the serum from intact females.     

Comparison of estimates of gonadotropin levels by isolated blood samples, integrated blood concentrations, and timed urinary fractions.

Gonadotropin levels in isolated blood samples, integrated plasma concentrations (IC), and timed urinary collections have been compared in 5 males with delayed puberty and 7 normal adult males. There was a significant correlation between urinary levels in 24-h collection and those in each of four shorter timed collections for both LH and FSH. Similarly, 24-h integrated plasma concentration and 4-h (0800--1200 h) integrated plasma concentration obtained on 10 additional subjects showed significant correlation. The 4-h integrated plasma concentrations correlated with single blood samples or the mean of three samples obtained at 0800, 1200, and 1600 h. These 4-h plasma samples also correlated significantly with all urine collections for FSH but only with the 2200--0800 h urine collection for LH. The study suggests that LH and FSH levels in urine samples collected over several hours correlate with 24-h urinary excretion and that levels in single blood samples estimate the 24-h plasma integrated concentration.     

Urinary excretion of immunoreactive luteinizing hormone-releasing hormone-like material in children correlation with pubertal development

Immunoreactive LRH (iLRH)-like material has been measured in extracts of urine from normal children and adolescents, adult men and women, and postmenopausal women. The urinary excretion of iLRH-like material was significantly greater in pubertal than in prepubertal subjects and in boys than girls at both stages of sexual maturation [prepubertal males, 3.26 +/- 0.49 ng/24 h (SE; n = 24); pubertal males, 5.94 +/- 1.36 (n = 12); prepubertal females, 1.14 +/- 0.21 (n = 19); pubertal females, 2.85 +/- 0.56 (n = 13)]. In adult males (n = 5) the urinary excretion of iLRH-like material was 7.8 +/- 1.3 ng/24 h, and in adult women in the follicular phase of the menstrual cycle (n = 8) it was 2.9 +/- 0.3. In five postmenopausal women the urinary iLRH-like content was 7.32 +/- 0.92 ng/24 h (P less than 0.01 relative to normal pubertal and adult women). In children the 24-h urinary excretion of iLRH-like material was positively correlated with chronological and bone ages, Tanner stage of genital (male) and breast (female) development, and the urinary excretion of LH and FSH in males. It did not correlate with the urinary excretion of either LH or FSH in females. Carboxymethylcellulose chromatography of extracts of urine from pubertal boys and girls, adult men and women, and postmenopausal women suggested that the iLRH-like material may be the 2-10 fragment of LRH rather than the intact decapeptide.     

Effects of tri-iodothyronine, thyroxine and isopropyl-di-iodothyronine on thyroid-stimulating hormone in serum and pituitary gland and on pituitary concentrations of prolactin, growth hormone, luteinizing hormone and follicle-stimulating hormone in hypothyroid rats

Replacement of the 3'-halogen of the tri-iodothyronine (T3) molecule by a propyl-group produces a thyromimetic analogue, 3'-isopropyl-3,5-di-iodo-L-thyronine (T2iPr), with high biological potency. A serum thyroid-stimulating hormone (TSH) suppression test with one single intraperitoneal injection of 3 or 30 nM-T3 or T2iPr or with 30 or 300 nM-thyroxine (T4) per kg body weight was performed on 56 adult male Lewis rats which were maintained for 3 weeks on an iodine-deficient diet containing 0.2% 6n-propyl-2-thiouracil (PTU). Blood was withdrawn from each rat by cardiac puncture 24 h before and 3, 7, 24 and 48 h after application of the iodothyronines. Raised serum levels of TSH, due to the treatment with PTU, were significantly reduced within 3 h of treatment with 30 nM-T3, 300 nM-T4, 3 or 30 nM-T2iPr and they remained low throughout the observation period. Treatment with 3 nM-T3, or 30 nM-T4 per kg body weight was less effective. Pituitary concentrations of growth hormone, TSH, prolactin and FSH were significantly reduced by the treatment with PTU. There was also a slight, but insignificant reduction of pituitary concentrations of LH. Treatment with T3, T4 or T2iPr stimulated the reaccumulation of growth hormone, TSH, prolactin, LH and FSH in the pituitary gland.     

Cortisol regulates secretion and pituitary content of the two gonadotropins differentially in female rats: effects of gonadotropin-releasing hormone antagonist.

To determine if LH and FSH respond to cortisol exposure the same way in females as they do in males, metestrous females were implanted with cholesterol or cortisol (F) subcutaneously, and either ovariectomized or left intact 4 days later. Tail vein injections of 1000 ng of GnRH in saline, or saline alone, were given 4.5, 23.5, or 47.5 h after the time of ovariectomy. Animals were killed 30 min after the injections at 5, 24, and 48 h after surgery. F attenuated the postovariectomy increase in serum LH at 48 h. F also suppressed GnRH-stimulated LH release 24 and 48 h after surgery in ovariectomized animals and in intact animals at 48 h. Pituitary content of LH was increased moderately by F at 5 h. These effects of F are similar to those seen in males. In contrast to LH, F increased serum FSH in intact females and suppressed levels in ovariectomized animals at 24 and 48 h, while inducing a remarkable increase in pituitary FSH content at all three times. These divergent effects of F on serum FSH (suppression in gonadectomized and stimulation in intact groups) were not seen in males, and the increase in pituitary FSH as a result of exposure to F was much more profound and reliable in females than in males. To determine if the F-induced increase in pituitary FSH was dependent on endogenous secretion of GnRH, intact metestrous females were implanted with either cholesterol or F pellets. Each implant group received sc injections of 100 micrograms GnRH antagonist or control injections every 48 h beginning at the time of steroid implantation. Animals were killed 5 days after implantation. The antagonist suppressed both serum and pituitary LH. F also suppressed serum LH levels, but had no effect on pituitary content of LH. Neither the antagonist nor F affected serum FSH. F greatly increased pituitary content of FSH in the presence or absence of GnRH antagonist. These data suggest that 1) LH responds to F treatment in a similar way in females and males; 2) pituitary FSH content is more sensitive to the enhancing effect of F in females than in males; 3) the ability of F to increase pituitary FSH in females is not dependent on GnRH.     

Effect of gonadectomy, season and the presence of female tammar wallabies (Macropus eugenii) on concentrations of testosterone, luteinizing hormone and follicle-stimulating hormone in the plasma of male tammar wallabies

Concentrations of FSH, LH and testosterone in plasma were measured in groups of adult male tammar wallabies before and after gonadectomy, and during the breeding and non-breeding seasons. Gonadectomy resulted in a rapid fall in plasma testosterone to undetectable levels by day 2, and significant increases in plasma LH and FSH levels. The concentrations of FSH, LH and testosterone did not change significantly between the non-breeding and breeding seasons in groups of male wallabies maintained in the absence of females. However, when male wallabies were associated with sexually mature females there were significant three- to fourfold increases in concentrations of LH and testosterone in plasma at the commencement of the breeding season. The observed increases in LH and testosterone were highly synchronized in the eight animals studied and occurred approximately 2 weeks before the synchronous onset of mating. Concentrations of FSH did not change significantly at this time.     

Effects of luteinizing hormone releasing hormone on plasma follicle-stimulating hormone and luteinizing hormone levels in the ferret.

Heterologous radioimmunoassays for FSH and LH were employed to examine the effect of synthetic LH-RH upon gonadotrophin secretion in the ferret. Intravenous injection of 4 microng LH-RH induced a surge of FSH and of LH secretion in male and in female animals. In intact and in castrated males, the rise of LH was much more marked than that of FSH. The gonadotrophin response to LH-RH was greater in anoestrous than in oestrous females; FSH secretion was not enhanced during oestrus. Ovariectomized females behaved as anoestrous females with respect to LH secretion, while FSH secretion remained unchanged. Treatment of ovariectomized females with progesterone did not alter the pattern of response to LH-RH, but oestradiol treatment depressed the reaction to match that seen in oestrous females. Repetitive injections of LH-RH induced repetitive surges of FSH and LH in anoestrous females, but only of LH during oestrus: slow i.v. infusion of LH-RH induced a sustained elevation of plasma LH levels both in oestrous and in anoestrous females; again FSH levels rose only in anoestrous females. Injection of synthetic TRH did not alter gonadotrophin secretion in corresponding groups of male or female ferrets.     

Diurnal variation of follicle stimulating hormone (FSH) in the male rat

The phenomenon of diurnal variation in secretion of FSH, LH and prolactin (Prl) has been investigated in adult male Wistar rats. When these animals were decapitated at 2 h intervals throughout the 24 h day, a highly significant elevation of serum FSH was observed at 12.30 and 14.30 h. No definite diurnal pattern was observed for LH and Prl. The basic FSH rhythm was found to persist in animals bled via an indwelling atrial cannula or by cardiac puncture. However, these techniques of blood collection were found to produce some variation in the timing of the surge. These observations suggest the existence of diurnal variation in the secretion of FSH in the adult male rat.