Interaction of season and estradiol in the regulation of gonadotropin secretion in the adult ram

1990 ◽  
Vol 68 (2) ◽  
pp. 150-156 ◽  
Author(s):  
Lee M. Sanford ◽  
Bernard Robaire
Keyword(s):  
Follicle Stimulating Hormone ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Gonadotropin Releasing Hormone ◽  
Control Groups ◽  
Gonadotropin Secretion ◽  
Scrotal Circumference ◽  
Lh Release ◽  
Mean Concentration ◽  
Gonadotropic Hormones

The effects of season and estradiol on the secretion of gonadotropic hormones in adult Dorset × Leicester × Suffolk rams were studied. Control groups of intact and castrate rams, and castrate rams given estradiol replacement (~ 11.5 pg/mL) via polydimethylsiloxane capsules (sc) were assessed for 1 year, beginning in August. Mean concentrations of luteinizing hormone (LH), follicle-stimulating hormone (FSH), and prolactin (PRL) were determined every 2 weeks for all three groups of rams and measurements of testosterone concentration and scrotal circumference were taken on the intact rams. Pulsatile LH release and the LH response to a 2-μg dose (iv) of gonadotropin-releasing hormone (GnRH) were assessed for all rams when the testes of intact rams were redeveloped (late October), regressed (early February, late April), and redeveloping (early August). Season directly affected LH-pulse amplitude, which increased only in the control castrate rams between February and April. In October, LH-pulse frequency was the same in both groups of castrate rams, while in April, frequency in the estradiol-treated castrate rams was suppressed to intact ram values. Pituitary responsiveness to exogenous GnRH did not change throughout the year in either of the castrate groups, but along with LH-pulse amplitude, it was increased in August in the intact rams. Although FSH secretion was 14-fold higher in the control castrate rams than in the intact rams, seasonal-directional changes in mean concentration were similar. FSH concentration in the estradiol-treated castrate rams was stable throughout the year. PRL secretion never differed between the control castrate and intact rams but was enhanced in the estradiol-treated castrate rams, particularly during long days.Key words: season, estradiol, gonadotropins, adult ram.

Changes in the characteristics of pulsatile luteinizing hormone secretion during the oestrous cycle and after ovariectomy and oestrogen treatment in female rats

1982 ◽  
Vol 94 (2) ◽  
pp. 177-182 ◽  
Author(s):  
Takashi Higuchi ◽  
Masazumi Kawakami
Keyword(s):  
Hormone Secretion ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Oestrous Cycle ◽  
Female Rats ◽  
Ovariectomized Rats ◽  
Luteinizing Hormone Secretion ◽  
Oestrogen Treatment ◽  
Serum Lh ◽  
Lh Release

Changes in the characteristics of LH secretory pulses in female rats were determined in different hormonal conditions; during the oestrous cycle and after ovariectomy and oestrogen treatment. The frequency and amplitude of the LH pulses were stable during the oestrous cycle except at oestrus when a pattern could not be discerned because of low LH concentrations. These were significantly lower than those measured during other stages of the cycle. Mean LH concentrations and LH pulse amplitudes increased with time up to 30 days after ovariectomy. The frequency of the LH pulse was unchanged 4 days after ovariectomy when mean LH levels had already increased. The frequency increased 10 days after ovariectomy and then remained stable in spite of a further increase in mean serum LH concentrations. Oestradiol-17β injected into ovariectomized rats caused a decrease in LH pulse amplitude but no change in pulse frequency. One day after treatment with oestradiol benzoate no LH pulse was detectable, probably because the amplitude was too small. A generator of pulsatile LH release is postulated and an oestrogen effect on its function is discussed.

Non-responsiveness of serum gonadotropins and testosterone to pulsatile GnRH in hemochromatosis suggesting a pituitary defect

1993 ◽  
Vol 128 (4) ◽  
pp. 351-354 ◽  
Author(s):  
Lise Duranteau ◽  
Philippe Chanson ◽  
Joelle Blumberg-Tick ◽  
Guy Thomas ◽  
Sylvie Brailly ◽  
...  
Keyword(s):  
Single Pulse ◽  
Serum Testosterone ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Gonadotropin Secretion ◽  
Pulsatile Gnrh ◽  
Serum Lh ◽  
Before And After ◽  
Gnrh Therapy ◽  
Lh Secretion

We investigated the potential pituitary origin of gonadal insufficiency in hemochromatosis. Gonadotropin secretion was studied in seven patients with hemochromatosis and hypogonadism, before and after chronic pulsatile GnRH therapy. Pulsatile LH secretion was studied before (sampling every 10 min for 6 h) and after 15-30 days of chronic pulsatile GnRH therapy (10-12 μg per pulse). Prior to GnRH therapy, all the patients had low serum testosterone, FSH and LH levels. LH secretion was non-pulsatile in four patients, while a single pulse was detected in the remaining three. Chronic pulsatile GnRH administration did not increase serum testosterone levels; similarly, serum LH levels remained low: neither pulse frequency nor pulse amplitude was modified. We conclude that hypogonadism in hemochromatosis is due to pituitary lesions.

Orchidectomy selectively increases follicle-stimulating hormone secretion in gonadotropin-releasing hormone antagonist-treated male rats

1995 ◽  
Vol 132 (3) ◽  
pp. 357-362 ◽  
Author(s):  
M Tena-Sempere ◽  
L Pinilla ◽  
E Aguilar
Keyword(s):  
Gnrh Antagonist ◽  
Follicle Stimulating Hormone ◽  
Hormone Secretion ◽  
Gonadotropin Releasing Hormone ◽  
Male Rats ◽  
Gonadotropin Secretion ◽  
Releasing Hormone ◽  
Treated Male ◽  
Lh Secretion ◽  
Stimulating Hormone

Tena-Sempere M, Pinilla L, Aguilar E. Orchidectomy selectively increases follicle-stimulating hormone secretion in gonadotropin-releasing hormone agonist-treated male rats. Eur J Endocrinol 1995;132: 357–62. ISSN 0804–4643 The pituitary component of the feedback mechanisms exerted by testicular factors on gonadotropin secretion was analyzed in adult male rats treated with a potent gonadotropin-releasing hormone (GnRH) antagonist. In order to discriminate between androgens and testicular peptides, groups of males were orchidectomized (to eliminate androgens and non-androgenic testicular factors) or injected with ethylene dimethane sulfonate (EDS), a selective toxin for Leydig cells (to eliminate selectively androgens) and treated for 15 days with vehicle or the GnRH antagonist Ac-d-pClPhe-d-pClPhe-d-TrpSer-Tyr-d-Arg-Leu-Arg-Pro-d-Ala-NH2CH3COOH (Org.30276, 5 mg/kg/72 hours). Serum concentrations of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) were measured 7 and 14 days after the beginning of treatment. We found that: in males treated with GnRH antagonist, orchidectomy or EDS treatment did not induce any increase in LH secretion; and orchidectomy, but not EDS treatment, increased FSH secretion in GnRH-treated males. The present results show that negative feedback of testicular factors on LH secretion is mediated completely through changes in GnRH actions. In contrast, a part of the inhibitory action of the testis on FSH secretion is exerted directly at the pituitary level. It can be hypothesized that non-Leydig cell testicular factor(s) inputs at different levels of the hypothalamic–pituitary axis in controlling LH and FSH secretion. Manuel Tena-Sempere, Department of Physiology, Faculty of Medicine, University of Córdoba, 14004 Córdoba, Spain

Responses of luteinizing hormone (LH) and follicle-stimulating hormone levels to exogenous gonadotropin-releasing hormone during the estrogen-induced LH surge in the ovariectomized rhesus monkey

1989 ◽  
Vol 67 (2) ◽  
pp. 135-139 ◽  
Author(s):  
Richard F. Weick ◽  
Vaclav Pitelka ◽  
David L. Thompson
Keyword(s):  
Luteinizing Hormone ◽  
Rhesus Monkey ◽  
Negative Feedback ◽  
Follicle Stimulating Hormone ◽  
Gonadotropin Releasing Hormone ◽  
Gonadotropin Secretion ◽  
Lh Surge ◽  
Releasing Hormone ◽  
Acute Response ◽  
Stimulating Hormone

Experiments were performed to study the responsiveness of the pituitary to gonadotropin-releasing hormone (GnRH) during the dynamic changes in gonadotropin secretion associated with the estrogen-induced luteinizing hormone (LH) surge in the ovariectomized (OVX) rhesus monkey. Silastic capsules filled with estradiol-17-β were implanted subcutaneously in ovariectomized rhesus monkeys, resulting in an initial lowering of circulating LH and follicle-stimulating hormone (FSH) concentrations followed by an LH–FSH surge. GnRH was injected intravenously just before estrogen implantation, during the negative feedback response and during the rising, the peak, and the declining phases of the LH surge. The LH and FSH responses during the negative feedback phase were as large as those before estrogen treatment (control responses). During the rising phase of the LH surge, the acute response to GnRH injection did not differ significantly from the control response, but the responses 60 and 120 min after injection were somewhat increased. During the declining phase of the LH surge, the pituitary was not responsive to exogenous GnRH, although LH probably continued to be secreted at this time since the LH surge decreased more slowly than predicted by the normal rate of disappearance of LH in the monkey. We conclude that an increased duration of response to GnRH may be an important part of the mechanism by which estrogen induces the LH surge, but we do not see evidence of increased sensitivity of the pituitary to GnRH as an acute releasing factor at that time.Key words: LH surge, GnRH, FSH, ovariectomized monkey.

scholarly journals Central Infusion of Agouti-Related Peptide Suppresses Pulsatile Luteinizing Hormone Release in the Ovariectomized Rhesus Monkey

Endocrinology ◽  
2005 ◽  
Vol 146 (2) ◽  
pp. 784-789 ◽  
Author(s):  
Nicolas R. Vulliémoz ◽  
Ennian Xiao ◽  
Linna Xia-Zhang ◽  
Sharon L. Wardlaw ◽  
Michel Ferin
Keyword(s):  
Pulse Generator ◽  
Third Ventricle ◽  
Reproductive Function ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Melanocortin Receptor ◽  
Central Administration ◽  
Related Peptide ◽  
Orexigenic Peptide ◽  
Lh Release

Abstract Agouti-related peptide (AGRP), an endogenous melanocortin receptor antagonist, is a powerful orexigenic peptide when infused centrally. AGRP and neuropeptide Y (NPY), another orexigenic peptide, are colocated within the same neurons in the arcuate nucleus. Both NPY and AGRP mRNA expression increases during food restriction, a condition that is known to suppress the GnRH pulse generator and reproductive function. Although NPY has been shown previously to suppress LH secretion in the ovariectomized monkey, data on AGRP are lacking. In this study, we examined the effect of AGRP infusion into the third ventricle on pulsatile LH release in five adult monkeys. The 8-h protocol included a 3-h intraventricular saline infusion to establish baseline pulsatile LH release, followed by a 5-h infusion of AGRP (83–132) [5 μg/h (n = 1) or 10 μg/h (n = 4)]. In separate experiments, each animal received an 8-h saline treatment as a control. Blood samples were collected every 15 min for LH measurements. Cortisol levels were measured every 45 min. AGRP infusion significantly decreased LH pulse frequency (from a baseline of 0.74 ± 0.07 pulse/h to 0.36 ± 0.12 during AGRP infusion; P < 0.01) and mean LH concentrations (to 41.1 ± 7.5% of baseline by h 5 of AGRP infusion; P < 0.001). LH pulse amplitude was not modified by AGRP treatment. AGRP infusion also significantly increased cortisol release, as previously reported. The data demonstrate that central administration of AGRP inhibits pulsatile LH release in the monkey and suggest that AGRP, like NPY, may mediate the effect of a negative energy balance on the reproductive system by suppressing the GnRH pulse generator.

scholarly journals Effect of Continuous Intravenous Administration of Human Metastin 45–54 on the Neuroendocrine Activity of the Hypothalamic-Pituitary-Testicular Axis in the Adult Male Rhesus Monkey (Macaca mulatta)

Endocrinology ◽  
2007 ◽  
Vol 148 (7) ◽  
pp. 3364-3370 ◽  
Author(s):  
Suresh Ramaswamy ◽  
Stephanie B. Seminara ◽  
Clifford R. Pohl ◽  
Meloni J. DiPietro ◽  
William F. Crowley ◽  
...  
Keyword(s):  
Adult Male ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
High Dose ◽  
Continuous Exposure ◽  
Continuous Administration ◽  
Marked Rise ◽  
Lh Release ◽  
G Protein Coupled

In agonadal juvenile male monkeys, continuous administration of human metastin 45–54 (hu metastin 45–54) leads to desensitization of its receptor, G protein-coupled receptor 54 (GPR54), and decreased LH. The present study extended this observation to the adult male monkey, a more preclinically relevant model in which robust activity in the hypothalamic-pituitary-testicular axis is present. Continuous iv infusion of hu metastin 45–54 at either 200 or 400 μg/h elicited a marked rise in circulating LH that peaked 2–3 h after initiation of treatment. Thereafter, levels declined, and by 24 h, LH in metastin 45–54-infused animals was similar to control. LH release in response to an iv bolus of hu metastin 45–54 (10–30 μg) during the final 3 h of continuous infusion was truncated or abolished (low and high peptide dose, respectively). GPR54 desensitization by the high-dose metastin 45–54 infusion was associated with compromised pituitary response to a bolus GnRH injection (0.3 μg). LH pulse amplitude and pulse frequency were markedly suppressed during high-dose metastin 45–54 treatment. Surprisingly, the fidelity of the relationship between circulating testosterone (T) and LH was distorted during the high-dose peptide infusion. Thus, for a given concentration of LH, T levels were invariably higher during the high-dose metastin 45–54 infusion than during vehicle, suggesting that the peptide may exert direct actions on the testis to amplify T production. These findings support the notion that GPR54 is desensitized by continuous exposure to ligand, and they raise the possibility of an intratesticular role of GPR54.

Determinants of the annual pattern of reproduction in mature male Merino and Suffolk sheep: responses to a nutritional stimulus in the breeding and non-breeding seasons

2003 ◽  
Vol 15 (1) ◽  
pp. 1 ◽  
Author(s):  
Maria J. Hötzel ◽  
Stephen W. Walkden-Brown ◽  
James S. Fisher ◽  
Graeme B. Martin
Keyword(s):  
Luteinizing Hormone ◽  
Breeding Season ◽  
Follicle Stimulating Hormone ◽  
Hormone Secretion ◽  
Pulse Frequency ◽  
Mature Male ◽  
Scrotal Circumference ◽  
Gonadotrophin Secretion ◽  
Gonadotrophin Releasing Hormone ◽  
Breeding Seasons

This study was designed to test whether an acute improvement in diet would increase gonadotrophin secretion and testicular growth in strongly photoperiod-responsive Suffolk rams and weakly photoperiod-responsive Merino rams in both the breeding (February–March) and the non-breeding (July–August) seasons. Mature rams (n = 5 or 6) of these breeds were fed a maintenance diet (0.9 kg chaff + 100 g lupin grain) or the same diet supplemented with 1.5 kg lupin grain for 42 days in each season. Lupin grain is a rich source of both energy and protein. Testosterone, luteinizing hormone (LH) and follicle stimulating hormone (FSH) were measured in plasma from blood sampled every 20 min for 24 h on Days −1, 12 and 35 relative to the change in feeding. In rams supplemented with lupins, body mass increased in both breeds in both seasons (P < 0.001). Scrotal circumference and LH pulse frequency increased with lupin supplementation in both seasons (P < 0.003) in Merinos, but only during the breeding season (P < 0.003) in Suffolks. Plasma FSH concentrations were affected by diet only during the breeding season, being elevated on Day 12 in lupin-supplemented rams of both breeds (P < 0.05). It was concluded that Merino rams exhibit reproductive responses to improved nutrition irrespective of time of the year, whereas Suffolk rams respond to nutrition only when the hypothalamic reproductive centres are not inhibited by photoperiod. Thus, Suffolks do respond to nutrition, just as Merinos do, but only when photoperiod allows. This difference between breeds appears to be a result of differences in the neuroendocrine pathways that control pulsatile gonadotrophin-releasing hormone secretion.

scholarly journals Cortisol Reduces Gonadotropin-Releasing Hormone Pulse Frequency in Follicular Phase Ewes: Influence of Ovarian Steroids

Endocrinology ◽  
2008 ◽  
Vol 150 (1) ◽  
pp. 341-349 ◽  
Author(s):  
Amy E. Oakley ◽  
Kellie M. Breen ◽  
Iain J. Clarke ◽  
Fred J. Karsch ◽  
Elizabeth R. Wagenmaker ◽  
...  
Keyword(s):  
Plasma Cortisol ◽  
Pulse Frequency ◽  
Follicular Phase ◽  
Gonadotropin Releasing Hormone ◽  
Gonadal Steroid ◽  
Elevated Plasma ◽  
Gonadotropin Secretion ◽  
Ovarian Steroids ◽  
Ovarian Cyclicity ◽  
Cortisol Increase

Stress-like elevations in plasma glucocorticoids suppress gonadotropin secretion and can disrupt ovarian cyclicity. In sheep, cortisol acts at the pituitary to reduce responsiveness to GnRH but does not affect GnRH pulse frequency in the absence of ovarian hormones. However, in ewes during the follicular phase of the estrous cycle, cortisol reduces LH pulse frequency. To test the hypothesis that cortisol reduces GnRH pulse frequency in the presence of ovarian steroids, the effect of cortisol on GnRH secretion was monitored directly in pituitary portal blood of follicular phase sheep in the presence and absence of a cortisol treatment that elevated plasma cortisol to a level observed during stress. An acute (6 h) cortisol increase in the midfollicular phase did not lower GnRH pulse frequency. However, a more prolonged (27 h) increase in cortisol beginning just before the decrease in progesterone reduced GnRH pulse frequency by 45% and delayed the preovulatory LH surge by 10 h. To determine whether the gonadal steroid milieu of the follicular phase enables cortisol to reduce GnRH pulse frequency, GnRH was monitored in ovariectomized ewes treated with estradiol and progesterone to create an artificial follicular phase. A sustained increment in plasma cortisol reduced GnRH pulse frequency by 70% in this artificial follicular phase, in contrast to the lack of an effect in untreated ovariectomized ewes as seen previously. Thus, a sustained stress-like level of cortisol suppresses GnRH pulse frequency in follicular phase ewes, and this appears to be dependent upon the presence of ovarian steroids. A sustained stress-like level of cortisol reduces GnRH pulse frequency in the follicular phase and appears to require the presence of ovarian steroids.

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