Pulsatile administration of gonadotrophin-releasing hormone stimulates, in oestrogen-treated anaesthetized ovariectomized ewes, a surge release of LH qualitatively and quantitatively different from that induced by oestradiol in conscious ovariectomized ewes

1988 ◽  
Vol 116 (1) ◽  
pp. 143-148 ◽  
Author(s):  
P. J. Wright ◽  
I. J. Clarke
Keyword(s):  
Plasma Concentrations ◽  
Lh Surge ◽  
Releasing Hormone ◽  
Treatment Regimens ◽  
Oestradiol Benzoate ◽  
Pulsatile Administration ◽  
Gonadotrophin Releasing Hormone ◽  
Induction Of Anaesthesia ◽  
Lh Secretion ◽  
Conscious Control

ABSTRACT The nature of the gonadotrophin-releasing hormone (GnRH) stimulus of the pituitary necessary for the oestrogen-induced plasma LH surge was studied in ovariectomized ewes. The sheep were treated with oestradiol benzoate (50 μg i.m.) at 0 h, and the hypothalamic contribution to the LH surge was blocked by pentobarbitone anaesthesia over the time during which the surge was expected (11–31 h). Pituitary responsiveness to exogenous GnRH (100 ng) administered i.v. in a pulsatile mode (once per hour or once per 20 min) over the period 15–30 h was assessed from plasma concentrations of LH. Neither of the GnRH treatments induced patterns of LH secretion similar to those seen in conscious ovariectomized ewes given oestrogen only. Plasma LH secretion in response to hourly GnRH pulses was less (P<0·01) than that associated with oestrogen-induced plasma LH surges in conscious control ewes. With pulses of GnRH administered every 20 min the amount of LH released was greater (P<0·05) than that in oestrogen-treated conscious control ewes. In contrast to the single surge induced by oestradiol in conscious ewes, GnRH pulses given every 20 min elicited phasic patterns of LH secretion consisting of two or three distinct surges. The failure of GnRH treatment to elicit an LH surge similar to an oestrogen-induced surge could reflect inappropriate GnRH treatment regimens, and/or inadequate priming of the pituitary with GnRH after induction of anaesthesia but before GnRH treatment. J. Endocr. (1988) 116, 143–148

Suppression of LH response to gonadotrophin-releasing hormone or oestradiol by ACTH(1–24) treatment in anoestrous ewes

1988 ◽  
Vol 118 (2) ◽  
pp. 193-197 ◽  
Author(s):  
H. Dobson ◽  
S. A. Essawy ◽  
M. G. S. Alam
Keyword(s):  
Plasma Concentrations ◽  
Suppressive Effect ◽  
Reproductive Efficiency ◽  
Adrenocorticotrophic Hormone ◽  
Releasing Hormone ◽  
Oestradiol Benzoate ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Baseline Values ◽  
Lh Secretion

ABSTRACT Stress is known to result in lowered female reproductive efficiency. The objective of this study was to examine how increased pituitary-adrenal activity may influence gonadotrophin release in anoestrous ewes. Various doses (0·06–1·0 mg) of a synthetic adrenocorticotrophic hormone (ACTH(1–24)) preparation were injected into ewes 30 min or 3 h before an i.v. injection of 500 ng gonadotrophin-releasing hormone (GnRH). The LH response to GnRH given 30 min after ACTH(1–24) was similar to that after GnRH alone, whereas the response 3 h after ACTH(1–24) was significantly lower, irrespective of the dose of ACTH(1–24). At 30 min and 3 h after ACTH(1–24) the concentrations of cortisol exceeded 50 nmol/l compared with baseline values of < 10 nmol/l. The effect of ACTH(1–24) on oestradiol-induced LH release was also examined. Those ewes receiving 0·8 mg ACTH(1–24) depot and 50 μg oestradiol benzoate simultaneously had a preovulatory-type increase in LH 14–20 h later, similar to when oestradiol benzoate was given alone. None of the ewes receiving an additional 0·8 mg ACTH(1–24) depot 10 h after oestradiol benzoate had increases in LH concentration. The cortisol concentrations in all ewes receiving either one or two injections of ACTH(1–24) were > 35 nmol/l at 10 h after the oestradiol injection. However, concentrations of progesterone increased from 0·9 ± 0·3 (s.e.m.) nmol/l at the time of the second ACTH(1–24) injection to 2·1 ±0·3 nmol/l after 2 h. In summary, it would appear that the suppressive effect of ACTH(1–24) on LH secretion induced by GnRH or oestradiol in the anoestrous ewe is not dependent on increased plasma concentrations of cortisol. J. Endocr. (1988) 118, 193–197

Infantile ovariectomy potentiates the stimulatory effect of oestrogen/progesterone on LH secretion in the rat

1985 ◽  
Vol 106 (1) ◽  
pp. 133-139 ◽  
Author(s):  
M. Wilkinson ◽  
R. Bhanot
Keyword(s):  
Inhibitory Mechanism ◽  
Releasing Hormone ◽  
Oestradiol Benzoate ◽  
Gonadotrophin Releasing Hormone ◽  
Prepubertal Rats ◽  
Lh Secretion

ABSTRACT Ovariectomy of prepubertal rats (9 days of age) eliminates the ability of the opiate peptide FK 33-824 to inhibit LH secretion when tested 19 days later. We have investigated whether this removal of opiate inhibition would modify the LH/FSH response to stimulation with oestradiol benzoate/progesterone priming. Ovariectomy of rats during infancy (9 days after birth) amplifies the stimulatory effects of these steroids on LH/FSH secretion when tested 19 days later. This amplification was not seen in rats ovariectomized before (day 24) or after puberty (day 43) and tested 19 days later. The pituitary content of LH/FSH does not appear to contribute to this phenomenon, though increased responsiveness to injected gonadotrophin-releasing hormone (GnRH) is clearly involved; ovariectomy at day 9 is considerably more effective than ovariectomy at day 24 of life in enhancing the response to GnRH. We conclude that infantile ovariectomy either removes, or prevents the development of, a hypothalamic inhibitory mechanism which normally modulates the responsiveness of the pituitary to stimulation with GnRH. J. Endocr. (1985) 106, 133–139

Effects of tamoxifen on concentrations of luteinizing hormone and follicle-stimulating hormone in the plasma of ovariectomized ewes

1983 ◽  
Vol 99 (1) ◽  
pp. 23-29 ◽  
Author(s):  
I. J. Clarke
Keyword(s):  
Plasma Concentrations ◽  
Tamoxifen Treatment ◽  
Similar Response ◽  
Lh Surge ◽  
Peripheral Plasma ◽  
Mediated Effects ◽  
Tamoxifen Citrate ◽  
Oestradiol Benzoate ◽  
Antagonist Action ◽  
Lh Secretion

The effects of tamoxifen on peripheral plasma concentrations of gonadotrophins were studied in ovariectomized ewes. First, ovariectomized ewes were injected (i.m.) with 10 mg tamoxifen citrate/day for 4 days which caused a significant reduction in plasma LH concentrations within 4 days and plasma FSH concentrations within 1 day of the commencement of treatment. Further groups of ovariectomized ewes were then injected (i.m.) with two injections of 10 mg tamoxifen citrate 6 h apart or 20 μg oestradiol benzoate (OB) or tamoxifen citrate plus OB or oil. Tamoxifen treatment caused a reduction in plasma LH and FSH concentrations within 6 h. In four of our ewes receiving OB, a surge in LH secretion was observed; a similar response was observed in two out of four ewes given the combination of tamoxifen citrate and OB. No LH surge was seen in ovariectomized ewes given tamoxifen alone. These results show that tamoxifen reduces plasma gonadotrophin levels in ovariectomized ewes suggesting it is an oestrogen agonist in the sheep pituitary gland. A partial oestrogen antagonist action of tamoxifen is similarly suggested by its ability to block the oestrogen-induced LH surge in some ovariectomized ewes. Since tamoxifen consistently lowers plasma gonadotrophin levels in ovariectomized ewes this could result from action via oestrogen receptors or by central nervous system, non-oestrogen receptor-mediated effects.

The oestrogen-induced surge of LH requires a 'signal' pattern of gonadotrophin-releasing hormone input to the pituitary gland in the ewe

1989 ◽  
Vol 122 (1) ◽  
pp. 127-134 ◽  
Author(s):  
I. J. Clarke ◽  
J. T. Cummins ◽  
M. Jenkin ◽  
D. J. Phillips
Keyword(s):  
Pituitary Gland ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Lh Surge ◽  
Releasing Hormone ◽  
Gnrh Secretion ◽  
Signal Pattern ◽  
Oestradiol Benzoate ◽  
Gonadotrophin Releasing Hormone ◽  
Baseline Values

ABSTRACT Two experiments were conducted with ovariectomized and hypothalamo-pituitary disconnected (HPD) ewes to ascertain the pattern of inputs, to the pituitary gland, of gonadotrophin-releasing hormone (GnRH) necessary for the full expression of an oestrogen-induced LH surge. The standard GnRH replacement to these sheep was to give pulses of 250 ng (i.v.) every 2 h; at the onset of experimentation, pulses were given hourly. In experiment 1, groups of sheep (n = 7) were given an i.m. injection of 50 μg oestradiol benzoate, and after 10 h the GnRH pulse frequency or pulse amplitude was doubled. Monitoring of plasma LH concentrations showed that a doubling of pulse frequency produced a marked increase in baseline values, whereas a doubling of amplitude had little effect on the LH response. In a second experiment, ovariectomized HPD sheep that had received hourly pulses of GnRH for 16 h after an i.m. injection of oil or 50 μg oestradiol benzoate were given either a 'bolus' (2·25 μg GnRH) or a 'volley' (500 ng GnRH pulses 10 min apart for 30 min, plus a 500 ng pulse 15 min later). Both groups then received GnRH pulses (250 ng) every 30 min for the next 13 h. Oestrogen enhanced the LH responses to the GnRH treatments, and the amount of LH released was similar in ovariectomized HPD ewes given oestrogen plus bolus or volley GnRH treatments and ovariectomized hypothalamopituitary intact ewes given oestrogen. These results suggest that the oestrogen-induced LH surge is initiated by a 'signal' pattern of GnRH secretion from the hypothalamus. Journal of Endocrinology (1989) 122, 127–134

Effects of gonadotrophin releasing hormone agonist treatment on oestrous cycle length and superovulatory response in maiden heifers

1995 ◽  
Vol 1995 ◽  
pp. 141-141
Author(s):  
L M Birnie ◽  
P J Broadbent ◽  
J S M Hutchinson ◽  
R G Watt ◽  
D F Dolman
Keyword(s):  
Luteinising Hormone ◽  
Antral Follicle ◽  
Follicle Development ◽  
Dominant Follicle ◽  
Releasing Hormone ◽  
Antral Follicles ◽  
Large Numbers ◽  
Pulsatile Administration ◽  
Gonadotrophin Releasing Hormone ◽  
Lh Secretion

Current variability in superovulatory response prevents the economical production of large numbers of high quality embryos and limits the use of embryo transfer. Pulsatile administration of GnRH (gonadotrophin releasing hormone) elicits pulsatile secretion of LH (luteinising hormone) while chronic treatment with a potent GnRH agonist reduces LH secretion. Using the latter, gonadotrophin-dependent preovulatory antral follicle development may be suppressed, resulting in a uniform cohort of small antral follicles in the absence of a dominant follicle which could then be superstimulated by exogenous gonadotrophin.

Plasma LH and testosterone responses to gonadotrophin-releasing hormone in adult red deer (Cervus elaphus) stags during the annual antler cycle

1988 ◽  
Vol 117 (1) ◽  
pp. 35-41 ◽  
Author(s):  
P. F. Fennessy ◽  
J. M. Suttie ◽  
S. F. Crosbie ◽  
I. D. Corson ◽  
H. J. Elgar ◽  
...  
Keyword(s):  
Red Deer ◽  
Plasma Concentrations ◽  
Reproductive Hormones ◽  
Sexual Cycle ◽  
Late Winter ◽  
Releasing Hormone ◽  
Antler Growth ◽  
Velvet Antler ◽  
Antler Cycle ◽  
Gonadotrophin Releasing Hormone

ABSTRACT Eight adult red deer stags were given an i.v. injection of synthetic gonadotrophin-releasing hormone (GnRH) on seven occasions at various stages of the antler cycle, namely hard antler in late winter, casting, mid-velvet growth, full velvet growth, antler cleaning and hard antler both during the rut and in mid-winter. The stags were allocated at random on each occasion to one of four doses, i.e. 1, 3, 10 or 95 μg GnRH. Blood samples were taken before GnRH injection and for up to 2 h after injection. Pituitary and testicular responses were recorded in terms of plasma LH and testosterone concentrations. There was an increase in plasma concentration of LH after the GnRH injection in all stags at all stages of the antler cycle. Dose-dependent responses of LH to GnRH in terms of area under the curve were apparent at all stages of the antler cycle. The lowest responses were recorded at casting, during velvet antler growth and at the rut sampling. The pattern of testosterone response reflected the inter-relationship of the antler and sexual cycles with very low testosterone responses occurring at casting and during velvet antler growth. The responses were higher at antler cleaning and then increased to a maximum at the rut before declining to reach their nadir at casting. The results are consistent with a hypothesis that the antler cycle, as a male secondary sexual characteristic, is closely linked to the sexual cycle and its timing is controlled by reproductive hormones. Low plasma concentrations of testosterone, even after LH stimulation, are consistent with the hypothesis that testosterone is unnecessary as an antler growth stimulant during growth. J. Endocr. (1988) 117, 35–41

scholarly journals Effect of androgen on Kiss1 expression and luteinizing hormone release in female rats

2017 ◽  
Vol 233 (3) ◽  
pp. 281-292 ◽  
Author(s):  
Kinuyo Iwata ◽  
Yuyu Kunimura ◽  
Keisuke Matsumoto ◽  
Hitoshi Ozawa
Keyword(s):  
Luteinizing Hormone ◽  
Arcuate Nucleus ◽  
Female Rats ◽  
Hormone Release ◽  
Lh Surge ◽  
Continuous Release ◽  
Ovulatory Dysfunction ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Lh Secretion

Hyperandrogenic women have various grades of ovulatory dysfunction, which lead to infertility. The purpose of this study was to determine whether chronic exposure to androgen affects the expression of kisspeptin (ovulation and follicle development regulator) or release of luteinizing hormone (LH) in female rats. Weaned females were subcutaneously implanted with 90-day continuous-release pellets of 5α-dihydrotestosterone (DHT) and studied after 10 weeks of age. Number of Kiss1-expressing cells in both the anteroventral periventricular nucleus (AVPV) and arcuate nucleus (ARC) was significantly decreased in ovary-intact DHT rats. Further, an estradiol-induced LH surge was not detected in DHT rats, even though significant differences were not observed between DHT and non-DHT rats with regard to number of AVPV Kiss1-expressing cells or gonadotrophin-releasing hormone (GnRH)-immunoreactive (ir) cells in the presence of high estradiol. Kiss1-expressing and neurokinin B-ir cells were significantly decreased in the ARC of ovariectomized (OVX) DHT rats compared with OVX non-DHT rats; pulsatile LH secretion was also suppressed in these animals. Central injection of kisspeptin-10 or intravenous injection of a GnRH agonist did not affect the LH release in DHT rats. Notably, ARC Kiss1-expressing cells expressed androgen receptors (ARs) in female rats, whereas only a few Kiss1-expressing cells expressed ARs in the AVPV. Collectively, our results suggest excessive androgen suppresses LH surge and pulsatile LH secretion by inhibiting kisspeptin expression in the ARC and disruption at the pituitary level, whereas AVPV kisspeptin neurons appear to be directly unaffected by androgen. Hence, hyperandrogenemia may adversely affect ARC kisspeptin neurons, resulting in anovulation and menstrual irregularities.

Inducing ovulation with oestradiol cypionate allows flexibility in the timing of insemination and removes the need for gonadotrophin-releasing hormone in timed AI protocols for dairy cows

2017 ◽  
Vol 29 (3) ◽  
pp. 468 ◽  
Author(s):  
R. M. Ferreira ◽  
H. Ayres ◽  
L. U. Gimenes ◽  
F. P. Torres ◽  
F. A. Lima ◽  
...  
Keyword(s):  
Dairy Cows ◽  
Pregnancy Rates ◽  
Holstein Cows ◽  
Device Removal ◽  
Releasing Hormone ◽  
Ovulatory Follicle ◽  
Oestradiol Benzoate ◽  
Gonadotrophin Releasing Hormone

The effects of addition of gonadotrophin-releasing hormone (GnRH) to a progesterone plus oestradiol-based protocol and timing of insemination in Holstein cows treated for timed AI (TAI) were evaluated. Cows (n = 481) received a progesterone device and 2 mg oestradiol benzoate. After 8 days, the device was removed and 25 mg dinoprost was administered. Cows were allocated to one of three (Study 1; n = 57) or four (Study 2; n = 424) groups, accordingly to ovulation inducer alone (Study 1; oestradiol cypionate (EC), GnRH or both) or ovulation inducer (EC alone or combined with GnRH) and timing of insemination (48 or 54 h after device removal; Study 2). In Study 1, the diameter of the ovulatory follicle was greater for GnRH than EC. Oestrus and ovulation rates were similar regardless of ovulatory stimuli. However, time to ovulation was delayed when GnRH only was used. In Study 2, cows treated with GnRH or not had similar pregnancy per AI (P/AI) 30 days (41.5% vs 37.3%; P = 0.28) and 60 days (35.9% vs 33.0%; P = 0.61) after TAI. TAI 48 and 54 h after device removal resulted similar P/AI at 30 days (40.3% vs 38.5%; P = 0.63) and 60 days (33.8% vs 35.1%; P = 0.72). Thus, adding GnRH at TAI does not improve pregnancy rates in dairy cows receiving EC. The flexibility of time to insemination enables TAI of a large number of cows using the same protocol and splitting the time of AI.

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