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PubMed1988

Evidence that hypothalamic neuropeptide Y secretion decreases in aged male rats: implications for reproductive aging.

The decrease in circulating testosterone and LH titer that occurs in aged male rats may in part be a consequence of decreased excitatory neurochemical signals that promote the episodic discharge of LHRH from the hypothalamus. In view of evidence that neuropeptide Y (NPY) stimulates the release and potentiates the action of LHRH on LH secretion, the present studies investigated age-related changes in the concentrations of NPY in individual hypothalamic nuclei and in the ability of hypothalamic tissues to release NPY in vitro. Compared with tissues of 2.5-month-old male rats, medial basal hypothalamic tissues of 13-month-old rats released significantly less NPY in response to K+ depolarization. In contrast, K+-evoked LHRH release from the same tissues was unimpaired. Aged male rats also exhibited markedly reduced concentrations of NPY in the median eminence and in the arcuate, medial preoptic, suprachiasmatic, paraventricular, dorsomedial, and ventromedial hypothalamic nuclei, which are sites of NPY perikarya and nerve terminal networks. These neurochemical changes occurred in association with decreased serum testosterone and LH levels. These findings demonstrate a widespread age-related decline in NPY levels and release in the hypothalamus, which may be responsible for the reduction in testosterone secretion and may contribute to the decline in reproductive function in aged male rats.

Aging↗
PubMed1989

Morphological and functional characterization of large antral follicles in three breeds of sheep with different ovulation rates.

Morphological and functional features of large ovarian follicles from three breeds of sheep, with different ovulation rates (Finnish Landrace N = 12, Finnish Landrace X Scottish Blackface N = 16, Merino X Scottish Blackface N = 16) were compared by integrating three techniques; ink labelling, in-vitro oestradiol production and morphological classification. The follicles were removed at two stages of the follicular phase, 1 (PG + 1) or 2 (PG + 2) days after PGF-2 alpha treatment and compared after monitoring their rates of growth with the use of ink labelling. After ovariectomy all follicles greater than or equal to 1 mm in diameter were dissected, and the 8 largest were incubated individually for 2 h to assess their ability to secrete oestradiol and testosterone. After incubation the follicles were processed for histological examination and checked for atresia. An analysis of the follicle population was based on in-vitro oestradiol secretion rates in all three breeds; an oestrogen-active population producing 500-8100 pg oestradiol/ml/h and an oestrogen-inactive population producing 0-499 pg oestradiol/ml/h. A comparison of the 3 approaches demonstrated agreement on 94.3 +/- 1.2% of occasions. Ink-labelling demonstrated that all follicles identified as oestrogen-active were increasing in size. Within oestrogen-active follicles significant correlations were detected between oestradiol production and testosterone production (r = 0.42), oestradiol production and granulosa cell number (r = 0.45) and between oestradiol production and mitotic index (r = -0.38). A regression model fitting breed, stage of atresia, granulosa cell number, in-vitro testosterone production and mitotic index demonstrated that granulosa cell number is a characteristic which contributes significantly to the variation of in-vitro oestradiol production in oestrogen-active and oestrogen-inactive follicles. There was no significant difference between breeds in the mean number of ink-labelled follicles growing from Day PG - 1 to Day PG + 1. There was a significant difference between the breeds in the number of ink-labelled follicles growing between Days PG + 1 and PG + 2 (Days 1 and 2 of the follicular phase), the number being similar to the ovulation rate for the breed. The majority of the oestrogen-active follicles had been recruited by Day PG - 1, although in the Finnish Landrace genotypes more than 30% were recruited on or after Day PG + 1 compared to less than 10% in Merino x Scottish Blackface ewes.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed2001

Changes in binding of iodomelatonin to membranes of Leydig cells and steroidogenesis after prolonged in vitro exposure to melatonin.

The aim of the present study was to investigate the effects of prolonged exposure to melatonin (MLT) on the binding of iodomelatonin to membranes of rat Leydig cells and the subsequent modulation of testosterone and cyclic adenocine monophosphate (cAMP) secretion from these cells by MLT itself. Leydig cells were Percoll-purified from adult rats and cultured in vitro with MLT (1--100 nmol/L) for 16 h. Binding assays with 2(125I)iodomelatonin were then performed; moreover, testosterone and cAMP secretion during an acute challenge with lutenizing hormone (LH) (20 mIU/mL for 3 h) was assayed by RIA. As a result of prolonged MLT administration, a decrease in maximum binding density (Bmax) and equilibrium dissociation constant (Kd) of the binding of 2(125I)iodomelatonin to purified cell membranes was noted. Higher testosterone and cAMP secretion during LH challenge were recorded in cells pre-incubated with MLT; notwithstanding, the inhibitory effect of acutely administered MLT on LH-challenged secretions was not only retained but also reinforced, as the IC50 was 30% lower in cells pre-treated with the higher concentration of MLT (100 nM). Cycloheximide administration (10 microg/mL for 16 h) did not prevent hyper-sensitization to LH challenge or to acute MLT administration on LH challenge. Pertussis toxin (180 ng/mL for 16 h) prevented hyper-sensitization to LH, but not to acutely administered MLT. Forskolin (10 nmol/L) administration abolished either phenomena. In conclusion, prolonged exposure to MLT modulates the secretion of testosterone by cultured rat Leydig cells. Although MLT receptors were reduced, hyper-sensitization to LH challenge and to acutely administered MLT on LH challenge were observed with the higher concentration of MLT. Reduction in intracellular cAMP as a result of prolonged administration of MLT, could be the primary cause of both phenomena. On the one hand, reduced cAMP could start re-arrangement of the G-proteins and thus LH-dependent adenylate cyclase sensitization. On the other hand, reduced cAMP could render the Leydig cells more responsive to MLT itself through a mechanism which does not involve G-protein re-arrangement.

Animals↗
PubMed1990

Immunocytochemical detection of prolactin or prolactin-like immunoreactivity in epididymis of mature male mouse.

Prolactin (PRL) binds to the testis of mice and rats where it increases the number of luteinizing hormone receptors, increases the binding of human chorionic gonadotropin (hCG) to LH receptors, and enhances testosterone synthesis and secretion. PRL also binds to the prostate and seminal vesicles of rats and humans where it increases organ weight and stimulates growth and uptake of testosterone. PRL binds to the epididymis of rats but the effect of PRL on this organ is unknown. In the present study, a standard immunoperoxidase (PAP) technique was used to detect the binding of endogenous and exogenous PRL or PRL-like peptides to the epididymis of the mature mouse. Throughout the epididymal duct, a positive reaction for peroxidase, suggesting PRL or PRL-like binding, occurred in the Golgi area of principal cells. In segment 1, positive reactions were also visualized in the perinuclear area and in the region located between the Golgi area and the apical surface of the principal cells (supra-Golgi area). In the corpus and cauda epididymidis, scattered entire principal cells were also positive. Throughout the epididymal duct, the reactions indicating the binding of exogenous PRL were slightly stronger than those testing for binding of endogenous peptides. The significance of such binding to the epididymis is uncertain but PRL may perform the same functions in epididymal principal cells as it does in the testis, prostate, and seminal vesicles.

Animals↗
PubMed2006

Behavioral and physiological responses to experimentally elevated testosterone in female dark-eyed juncos (Junco hyemalis carolinensis).

Testosterone mediates the expression of many fitness-related traits in male vertebrates and is thought to account for numerous sex differences in trait expression. Testosterone is also secreted by females; however, far less is known regarding its effects on female physiology and behavior. Using a bird species in which the effects of testosterone on males are well characterized, the dark-eyed junco (Junco hyemalis), we tested whether an increase in exogenous testosterone in females would alter the phenotypic expression of a suite of behavioral and physiological traits. We found that increased testosterone levels in female dark-eyed juncos led to decreased cell-mediated immune function and increased intrasexual aggression, hypothalamo-pituitary-adrenal (HPA) axis responsiveness, baseline corticosterone and corticosterone-binding globulin (CBG) levels. Furthermore, immunosuppression following testosterone implantation was negatively correlated with total and free testosterone but did not appear to be related to either total or free corticosterone. These results demonstrate that the phenotypic impact of elevated testosterone is not confined to males in dark-eyed juncos, and that the impact in adults can be similar in males and females. We discuss these results in the context of potential endocrine-immune interactions and the evolution of sexual dimorphism.

Aggression↗
PubMed1986

Gonadotropin-secreting pituitary adenoma with concomitant hypersecretion of testosterone and elevated sperm count. Treatment with LRH agonist.

Hypersecretion of both FSH and LH was demonstrated in a man with pituitary macroadenoma, who also presented elevated levels of blood testosterone and an increased sperm count. The patient underwent transsphenoidal surgery followed immediately by cranial irradiation. Immunocytochemical analysis of the tumour revealed the presence of FSH, LH, TSH and the alpha-subunit. Gel chromatography of the serum on Sephadex G-100 revealed immunoactive FSH, LH and the alpha-subunit which coeluted with the labelled standards of corresponding hormones. Blood levels of both gonadotropins and testosterone remained persistently elevated up to one year following surgical decompression of the tumour and radiotherapy. It was decided to treat this patient with sc administration of 100 micrograms D-Trp6-LRH biweekly. After 20 weeks, LRH-analogue treatment resulted in the reduction of serum FSH and LH levels and a diminishing in tumour size as assessed by computed tomography scan of the pituitary. This report shows that in a patient with clinically and biochemically documented gonadotropin-secreting adenoma, inducing a state of persistent gonadal hyperfunction, pituitary surgery and cranial irradiation failed to normalize the biochemical abnormality; however, therapy with D-Trp6-LRH agonist induced clinical, biochemical and radiologic improvement.

Adenoma↗
PubMed1984

Do testicular opiates regulate Leydig cell function?

beta-Endorphin is believed to be synthesized in testicular Leydig cells. To gain more information about the role of this and other endogenous opioid peptides in the testis, opiate antagonists (naloxone and nalmefene, 100 micrograms/testis) were administered intratesticularly to hemicastrated adult rats. Leydig cell function was evaluated by measurement of serum testosterone and testosterone production in vitro. Estimation of androgen binding protein (rABP) was used as an index of Sertoli cell function. Serum testosterone was reduced significantly by intratesticular administration of naloxone and nalmefene in treated animals. Systemic administration of these antagonists had no effect at the doses used. Testes from treated animals incubated in vitro with or without hCG produced significantly less testosterone than vehicle-treated control testes. Hemicastration reduced rABP synthesis and secretion; however, treatment with opiate antagonists did not alter the amount of this protein in the serum or epididymides of these rats. These observations suggest that endogenous testicular opiates modulate testosterone secretion by Leydig cells.

Androgen-Binding Protein↗
PubMed1988

In vitro synthesis and release of inhibin in response to FSH stimulation by isolated segments of seminiferous tubules from normal adult male rats.

The production of inhibin by isolated segments of seminiferous tubules from adult male rats cultured in vitro was investigated using a heterologous specific radioimmunoassay. Increasing lengths of tubules (5, 10, 20 and 40 cm) maintained in culture for 4 or 5 days produced increasing amounts of inhibin in vitro. A dose-dependent increase in inhibin production was observed after stimulation with ovine follicle-stimulating hormone (FSH)-s17 (0.1-1000 ng/ml). The tubule segments remain sensitive to FSH stimulation for up to 20 days of culture despite a progressive decline in basal inhibin production, resulting in an increase in the magnitude of the response to FSH stimulation between 0-5, 5-10 and 10-20 days of culture. In the presence of the protein synthesis inhibitor, cycloheximide (50 micrograms/ml), both basal and FSH-stimulated inhibin secretion are inhibited. Testosterone (10(-8)-10(-5) M) does not affect basal inhibin production, although inhibition of the FSH-induced production of inhibin occurred at only the highest dose of testosterone used (10(-5) M). These data demonstrate that the production of inhibin by segments of seminiferous tubules from adult male rats can be used to study the control of inhibin secretion.

Animals↗
PubMedDate not supplied

Pseudo-precocious puberty in a male patient and the melatonin-testosterone relationship.

We describe a 14 year-old boy with a pineal germ cell tumor which secreted beta HCG. Serum testosterone levels were markedly elevated with concomitant decreased LH secretion. 24-h serum melatonin levels were suppressed and lacked the normal nocturnal rise. Pineal radiation therapy was followed by tumor regression and the diminution of beta HCG stimulated testosterone, which in turn inhibited melatonin and LH. When beta HCG and testosterone were normalized after tumor radiation, a recovery of normal melatonin and LH secretory pattern occurred. These results indicate that circulating testosterone down-regulates pineal melatonin.

Adolescent↗
PubMed1997

Pulsatile patterns of melatonin secretion in patients with gonadotropin-releasing hormone deficiency: effects of testosterone treatment.

Recently, we have demonstrated that male patients with gonadotropin-releasing hormone (GnRH) deficiency had increased nocturnal melatonin secretion that decreased to normal levels during testosterone treatment. The purpose of the current study was to examine if the abnormally increased melatonin levels in these patients were associated with pulsatile secretory patterns, and, if these were modified during testosterone administration. Characteristics of nocturnal melatonin and luteinizing hormone (LH) secretion were compared in six normal young males, six males with idiopathic hypogonadotropic hypogonadism (IGD), and in six males with constitutional delayed puberty (DP). Patients were examined in the untreated state and following the administration of 250 mg testosterone enanthate/month for 4 months. Serum samples for melatonin and LH levels were obtained every 15 min from 19.00 hr to 07.00 hr in a controlled light-dark environment. Pulse detection and pulse characteristics were determined by the program ULTRA. In comparison with normal controls, untreated IGD patients showed significantly higher pulse frequency, lower relative increments and shorter half-life times for melatonin. Similar findings were observed in DP patients, although statistically of borderline significance. Treatment with testosterone normalized melatonin pulse characteristics in both IGD and DP patients. The secretory pattern of LH release in these patients was characterized by significantly higher relative and absolute increments and shorter half-life time without any significant change in the number of LH pulses. Taken together, these data suggest that melatonin is secreted in a pulsatile pattern in normal adult males and in male patients with GnRH deficiency. The abnormally increased nocturnal melatonin secretion observed in these patients may indicate that the pineal pulse generator is expressing an altered activity pattern within its normal capabilities. Testosterone administration normalized melatonin secretory patterns in IGD and DP patients. The lack of relationship between the pulsatile LH and melatonin secretory patterns suggest an independent signal for the nocturnal pulsatile melatonin and LH secretions.

Adolescent↗
PubMed1992

Somatic afferent stimulation-plasma corticosterone, luteinizing hormone (LH), and testosterone responses in aged male rats under anesthetization.

Our previous studies have demonstrated that somatic sensory stimulation can produce increases in secretions of corticosterone, luteinizing hormone (LH), and testosterone in young male Wistar rats of 13-22 weeks old even after emotional factors are eliminated by pentobarbital-anesthetizing of the subjects. In the present study, we examined the effects of somatic sensory stimulation on plasma corticosterone, LH, and testosterone using aged male Wistar rats (24-27 months old) under the same anesthetizing condition as employed in our previous studies. We compared the reflex responses in aged rats with those previously measured in young rats. Nociceptive mechanical stimulation of both hindpaws by pinching for 10 min significantly increased plasma corticosterone levels in aged rats. The magnitude and time-course of this response were equivalent to those in young rats. On the other hand, neither plasma LH nor testosterone levels were changed by nociceptive mechanical stimulation of the hindpaws of aged rats. This is in sharp contrast to the increase in both plasma LH and testosterone caused by the stimulation of young rats. These results indicate a functional dissociation induced by aging between the secretory responses of the anterior pituitary, testes on the one hand and the adrenal cortex on the other hand, to nociceptive somatic sensory stimulation. Aging does not alter corticosterone release from the adrenal cortex to nociceptive somatic sensory stimulation; however, LH secretion from the anterior pituitary and testosterone secretion from the testes to nociceptive somatic sensory stimulation are subject to dysfunction with aging.

Aging↗
PubMed1996

Adenohypophyseal-gonadal dysfunction in male haemodialyzed patients before and after subtotal parathyroidectomy.

The function of the adenohypophyseal-gonadal axis in haemodialyzed male patients is modified: the serum testosterone level is low, and the gonadotropin levels are increased. The pathogenetic role of secondary hyperparathyroidism in this disorder has not previously been defined. The area under the curve (AUC) and the secretion kinetics of testosterone, luteinizing hormone (LH), and follicle-stimulating hormone after administration of LH-releasing hormone were examined in 7 dialyzed men with secondary hyperparathyroidism (mean age 36.2, range 20-47 years) before and 3 and 6 months after parathyroidectomy (PTX). The operation was successful in all 7 patients, as intact parathyroid hormone declined markedly during both postoperative periods as compared with the values before PTX: 81 +/- (SEM) 34 and 138 +/- 57 ng/1 versus 965 +/- 116 ng/l (p < 0.01 and p < 0.0l). The testosterone AUC prior to PTX (63 +/- 115 nmol/l x min) and 3 months (-4 +/- 36 nmol/l x min) and 6 months after PTX (-62 +/- 69) did not differ significantly, as was the case with LH AUC (1,110 +/- 223 and 1,214 +/- 331 and 1,020 +/- 314 U/l x min, respectively) and follicle-stimulating hormone AUC (525 +/- 334 and 634 +/- 347 and 533 +/- 264 U/l x min, respectively). The secretion kinetics of all three hormones was atypical as compared with healthy men of similar age, but it did not change after PTX. There were no correlations between the sexual indicators and parathyroid hormone, 1,25(OH)2D3, calcium, or phosphate during the individual periods. These findings indicate that secondary hyperparathyroidism is probably not involved in the dysfunction of the adenohypophyseal-gonadal axis in dialyzed men.

Adult↗
PubMed1992

The in vitro perifused rat ovary: II. Role of oxygen tension in the whole and quartered ovary.

In vitro perifusion of whole ovaries raises questions about tissue viability and its effects on the observed ovarian steroid secretion. To assess effects of tissue degeneration, whole and quartered ovaries from pregnant mare serum gonadotropin (PMSG-) treated immature rats were perifused for 8 h, employing various levels of pO2. Histological examination of both the whole and quartered ovary showed signs of degeneration in centrally located follicles but not in follicles located near the surface. However, basal and gonadotropin-stimulated (luteinizing hormone plus follicle stimulating hormone) secretion of estradiol, testosterone and progesterone were not significantly different in the whole ovary whether in the presence of high or low pO2 (n = 8; p > 0.05). Similarly, although the quartered ovary secreted greater amounts of steroids than did the whole ovaries (p < 0.05, n = 8), pO2 levels did not affect the steroid output. We conclude that during in vitro perifusion, minimal oxygen supply is sufficient for ovarian steroidogenesis to proceed. In addition, although quartered ovaries displayed some evidence of tissue degeneration, they were more responsive in terms of steroid output per mg ovary than were whole ovaries.

Animals↗
PubMed1985

Progesterone and androgen secretion by isolated cultured bovine corpus luteum cells: effect of LH, hCG, PRL, estradiol 17beta and testosterone.

Primary cell cultures of bovine corpora lutea were used in order to examine their morphology and secretion of progesterone and androgen in vitro. The cells were grown as monolayers up to 6 days at 37 degrees C medium 199 supplemented with 10% calf serum. The concentration of progesterone and androgen was measured using appropriate radioimmunoassays [1,3] respectively. Luteal cells were cultured with addition of the following amounts of hormones: 100 ng LH, 10 i.u. hCG, 100 ng PRL, 150 ng Estradiol 17 beta and 150 ng Testosterone/ml of culture medium. The luteal cells also created considerable amounts of androgens. It was found that only estradiol added to the culture medium caused an increase in the level of testosterone. Progesterone secretion following the addition of hormones increased under the influence of LH, T, and E2 in statistically significant manner while hCG and PRL had no statistically significant effects.

Animals↗
PubMed1991

Testosterone stimulates reproductive behavior during autumn in mockingbirds (Mimus polyglottos).

Mockingbirds normally secrete little or no testosterone during the period of autumnal territoriality. To determine the behavioral effects of exogenously administered testosterone, 20-mm lengths of Silastic tubing filled with crystalline testosterone were implanted into free-living resident mockingbirds during the autumn. Control residents were given sealed empty implants. Focal animal sampling showed that T-implanted males sang significantly more than controls. Perhaps as a consequence, a significantly greater percentage of the T-implanted males acquired mates. Though nest building does not naturally occur in autumn, T-implanted males also showed significantly more nest building than control males. However, T-implanted males only built if there was a female in the territory, suggesting a synergy between the presence of testosterone and social cues provided by the female. Examination of the effects of testosterone on territorial aggression showed that despite the high levels of territorial activity common in this species in autumn, territorial fights were unaffected by the presence of testosterone. One aggressive call, known to function in fall territorial defense, was significantly decreased in T-implanted versus control males. The presence of fall testosterone appears to stimulate a number of reproductive activities in mockingbirds, leaving autumnal aggressive interactions either unchanged or decreased. We discuss the application of these data to the effects of testosterone on the mockingbird's reproductive behavior during the breeding season.

Animals↗
PubMed1987

Reciprocal inhibition of the long-acting luteinizing hormone releasing hormone agonist Buserelin and human chorionic gonadotropin in stimulating Leydig cell steroidogenesis.

The interference between human chorionic gonadotropin (hCG, Pregnyl, Organon 1500 IU i.m.) and the long acting LHRH agonist Buserelin (500 micrograms s.c.) in stimulating Leydig cell steroidogenesis was studied in 6 eugonadal men. Simultaneous administration of a single injection of the agonist (LHRH alpha) and hCG blunted the plasma testosterone response observed 24 h after LHRH alpha alone, enhanced the secretion of oestradiol without affecting 17-hydroxy-progesterone and aggravated the late steroidogenic block at the 17,20-lyase locus. As compared to hCG alone, combined LHRH alpha and hCG administration also decreased the maximum and 48 h testosterone increments and the testosterone production reflected by the area under the curve, enhanced the production of oestradiol and again aggravated the 17,20-lyase lesion. The data show that the long acting agonist LHRH alpha and hCG reciprocally inhibit their stimulatory effect on Leydig cell testosterone secretion probably by a suppressive effect of oestrogens on the conversion of C21- to C19-steroids. The mechanism underlying this reciprocal inhibition remains to be elucidated.

17-alpha-Hydroxyprogesterone↗
PubMed2006

Effects of testosterone on hormonal content and calcium-dependent basal secretion in female rat pituitary cells.

In vivo and in vitro effects of elevated androgens on agonist-induced gonadotropin secretion have been addressed previously. Here we investigated the effects of testosterone on hormonal content and basal (in the absence of agonists) hormone release in pituitary lactotrophs, somatotrophs and gonadotrophs from female rats. Furthermore we tested the hypothesis that testosterone action is dependent on the pattern of spontaneous and Bay K 8644 (a L-type calcium channel agonist) -induced calcium signalling. Mixed anterior pituitary cells were cultured in steroid containing or depleted media, and testosterone (1pM to 10nM) was added for 48h. Cells were studied for their spontaneous and Bay K 8644-induced calcium signalling pattern and total hormone levels (release and hormonal content). In lactotrophs, somatotrophs and gonadotrophs testosterone did not affect the pattern of spontaneous calcium signalling. Bay K 8644-induced calcium signalling and hormone release were not affected by testosterone. In both steroid-depleted and -containing medium, testosterone inhibited prolactin (PRL), luteinizing hormone (LH) and growth hormone (GH) cellular content and release in a dose-dependent manner, with IC(50)s in a sub-nanomolar concentration range. These results indicate that testosterone inhibits basal hormone release from lactotrophs, somatotrophs and gonadotrophs without affecting intracellular calcium signalling. This action of testosterone is not dependent on the presence of other steroid hormones.

3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethy↗
PubMed2001

Progesterone and testosterone in combination act in the hypothalamus of castrated rams to regulate the secretion of LH.

We tested the hypotheses that progesterone enhances the negative feedback actions of testosterone in rams and that this occurs through actions at the hypothalamus. In the first part of this study, blood samples were collected every 10 min for 12 h before and after 7 days of treatment (i.m.) of castrated Romney Marsh rams (n=5 per group) with vehicle, progesterone (4 mg/12 h), testosterone (4 mg/12 h) or a combination of progesterone (4 mg/12 h) and testosterone (4 mg/12 h). In the second part of this study the brains of four gonad-intact Romney Marsh rams were collected, the hypothalamus was sectioned and in situ hybridisation of mRNA for progesterone receptors conducted. After 7 days of treatment with vehicle or progesterone or testosterone alone, there were no changes in the secretion of LH. In contrast, treatment with a combination of progesterone and testosterone resulted in a significant (P<0.01, repeated measures ANOVA) decrease in mean plasma concentrations of LH, the number of LH pulses per hour and the pre-LH pulse nadir and a significant (P<0.01) increase in the inter-LH pulse interval. We found cells containing mRNA for progesterone receptors throughout the hypothalamus, including the preoptic area (where most GnRH neurons are located in sheep), the periventricular, ventromedial and arcuate nuclei and the bed nucleus of the stria terminalis. This study shows that progesterone is capable of acting centrally with testosterone to suppress the secretion of LH in castrated rams and that cells containing mRNA for progesterone receptors are located in the hypothalamus of rams in the vicinity of GnRH neurons.

Analysis of Variance↗