Effect of pulsatile infusion of gonadotrophin-releasing hormone on plasma oestradiol-17β concentrations and follicular development during naturally and artificially maintained high levels of plasma progesterone in heifers

1987 ◽  
Vol 112 (1) ◽  
pp. 77-85 ◽  
Author(s):  
R. G. Glencross
Keyword(s):  
Luteal Phase ◽  
Indirect Evidence ◽  
Follicular Development ◽  
Pulse Frequency ◽  
Oestrous Cycle ◽  
Plasma Progesterone ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Plasma Oestradiol

ABSTRACT To stimulate a follicular-phase pattern of pulsatile LH release, gonadotrophin-releasing hormone (GnRH; 5 μg) was infused (i.v.) hourly into heifers for periods of 5–11 days during the luteal phase of the oestrous cycle, and also when plasma progesterone levels were increased artificially by means of a progesterone-releasing intravaginal device. Plasma oestradiol-17β concentrations increased from basal (EEE 2·5 pmol/l) to preovulatory peak levels (20–30 pmol/l) during the first 3 days of GnRH treatment. They were maintained at these values before returning to basal levels within 24 h of cessation of infusion. This response occurred regardless of the source of progesterone (endogenous or administered). Follicular development was observed by ovarian palpation (per rectum) in some heifers at the time of maximum secretion of oestradiol-17β. There was no detectable cervical mucus secretion or oestrous behaviour during these periods of high oestradiol-17β levels and ovulation did not occur. Treatment with GnRH did not affect plasma progesterone concentrations or oestrous cycle length. The study shows that oestradiol-17β secretion and follicular development (and the accompanying oestrus and ovulation) are suppressed during the luteal phase of the cycle by high concentrations of plasma progesterone, and provides strong indirect evidence that such inhibition is associated with a reduction in the pulse frequency of LH release. J. Endocr. (1987) 112, 77–85

The antagonistic effect of exogenous LH pulses on FSH-stimulated preovulatory follicle growth in ewes chronically treated with a gonadotrophin-releasing hormone agonist

1990 ◽  
Vol 127 (2) ◽  
pp. 273-283 ◽  
Author(s):  
H. M. Picton ◽  
C. G. Tsonis ◽  
A. S. McNeilly
Keyword(s):  
Luteal Phase ◽  
Follicular Development ◽  
High Amplitude ◽  
Follicle Growth ◽  
High Concentration ◽  
Continuous Administration ◽  
Releasing Hormone ◽  
Low Concentrations ◽  
Gonadotrophin Releasing Hormone ◽  
The Mean

ABSTRACT The hypogonadotrophism model induced by the chronic administration of gonadotrophin-releasing hormone (GnRH) agonist was used to investigate the effects of different concentrations of FSH with or without LH pulses on the stimulation of follicular development in the ewe. Continuous administration of an agonist (buserelin) by osmotic minipump to thirty-six Welsh Mountain ewes from the early luteal phase for 5 weeks resulted in a sustained suppression of the plasma concentration of FSH and inhibited the pulsatile release of LH. The inhibition of gonadotrophin secretion was due to the desensitization and/or down-regulation of pituitary gonadotroph function, since the agonist-treated animals showed no response to a challenge of 1 μg GnRH. During week 6 of agonist treatment, ewes were infused with either 4-hourly pulses of ovine LH (9 μg/pulse), low concentrations of ovine FSH (3 μg/h) or high concentrations of FSH (9 μg/h) alone or with 4-hourly pulses of LH. After 5 days of gonadotrophin infusion, there was no difference between the mean number of follicles per ewe from the animals treated with LH alone, low concentrations of FSH with or without LH pulses or the high concentration of FSH alone compared with the mean number of follicles from control ewes on day 8 of the luteal phase. Infusion of the high concentration of FSH alone stimulated the development of an increased number of large oestrogenic follicles (follicles > 2·5 mm in diameter and secreting > 3·7 nmol oestradiol/h in vitro) compared with control ewes. The addition of high-amplitude LH pulses to the infusion of the high concentration of FSH prevented follicles developing beyond 2·5 mm in diameter, but doubled the number of small follicles (≤2·5 mm) present in the ovaries. These results show that normal follicular development can be induced by physiological concentrations of FSH alone in the absence of pulsatile LH release. The addition of high-amplitude LH pulses antagonized this stimulatory effect of FSH on follicle growth in the ewe. Journal of Endocrinology (1990) 127, 273–283

Effect of basal and pulsatile LH release on FSH-stimulated follicle growth in ewes chronically treated with gonadotrophin-releasing hormone agonist

1991 ◽  
Vol 128 (3) ◽  
pp. 449-456 ◽  
Author(s):  
H. M. Picton ◽  
A. S. McNeilly
Keyword(s):  
Gnrh Agonist ◽  
Follicular Development ◽  
Follicle Growth ◽  
Releasing Hormone ◽  
Normal Number ◽  
Stage Of Development ◽  
Normal Diameter ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Follicular Response

ABSTRACT Ewes chronically treated with gonadotrophin-releasing hormone (GnRH) agonist were used to investigate the importance of the peripheral concentration of LH in FSH-stimulated follicular development. Twenty-four Welsh Mountain ewes were treated with two agonist implants containing 3·3 mg buserelin. During week 6 of treatment all the ewes were given a 72-h continuous infusion of ovine FSH alone (3 μg/h) or FSH with large (7·5 μg)- or small (2·5 μg) amplitude pulses of ovine LH delivered at 4-hourly intervals. The importance of baseline LH throughout the FSH infusion was evaluated in six animals which were treated with a specific antiserum against bovine LH (LH-AS) 15–20 h before the start of FSH treatment. In the absence of LH-AS, infusion of FSH alone or with large or small pulses of LH stimulated the development of a normal number of small follicles (≤ 2·5 mm in diameter) and large follicles (> 2·5 mm in diameter). These follicles had normal diameter and steroid secretion compared with control ewes on day 8 of the luteal phase. In contrast, the animals pretreated with LH-AS developed no follicles > 2·0 mm in diameter but the number of small follicles per ewe was significantly (P < 0·05) increased. These results support the hypothesis that FSH in the absence of pulsatile LH release stimulates preovulatory follicular development in ewes treated with GnRH agonist. The follicular response to LH pulses of different amplitude is dependent on both the stage of development of the follicle and the peripheral concentration of FSH. The endogenous basal level of LH present throughout the FSH infusion is essential for FSH to induce follicle growth beyond > 2·5 mm in diameter. Journal of Endocrinology (1991) 128, 449–456

OESTRADIOL RECEPTORS IN THE RAT ANTERIOR PITUITARY GLAND DURING THE OESTROUS CYCLE: QUANTITATION OF RECEPTOR ACTIVITY IN RELATION TO GONADOTROPHIN RELEASING HORMONE-MEDIATED LUTEINIZING HORMONE RELEASE

1978 ◽  
Vol 76 (2) ◽  
pp. 211-218 ◽  
Author(s):  
K. K. SEN ◽  
K. M. J. MENON
Keyword(s):  
Pituitary Gland ◽  
Binding Sites ◽  
Anterior Pituitary ◽  
Anterior Pituitary Gland ◽  
Oestrous Cycle ◽  
Hormone Release ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Stimulation Of

Specific oestradiol binding to a receptor in nuclear and cytosol fractions of the rat anterior pituitary gland and pituitary responsiveness to gonadotrophin releasing hormone (GnRH) during the oestrous cycle have been studied. To accomplish this, both unoccupied and occupied oestradiol-binding sites in the cytosol and oestradiol-binding sites in the nucleus and total cell were measured during the oestrous cycle. The concentration of unoccupied and occupied sites and total oestradiol binding in the cytosol fluctuated during the cycle. At pro-oestrus, the concentration of cytosol receptor was diminished by about 40% and replenishment occurred during oestrus. On the other hand, a profound increase in concentrations of cellular and nuclear receptors occurred at pro-oestrus. Administration of GnRH significantly stimulated LH release at all stages of the cycle. The maximum stimulation of LH release by GnRH was observed at 13.00 h of pro-oestrus. From these studies, it is concluded that pituitary responsiveness to exogenous GnRH during pro-oestrus parallels the changes in the content of oestrogen receptors in the cytosol and nucleus.

Effect of graded doses of gonadotrophin-releasing hormone on serum LH concentrations in mares in various reproductive states: comparison with endogenously generated LH pulses

1986 ◽  
Vol 110 (1) ◽  
pp. 19-26 ◽  
Author(s):  
S. L. Alexander ◽  
C. H. G. Irvine
Keyword(s):  
Luteal Phase ◽  
Pulse Frequency ◽  
Follicular Phase ◽  
Hormone Release ◽  
Response Curves ◽  
Releasing Hormone ◽  
Serum Lh ◽  
Small Doses ◽  
Gonadotrophin Releasing Hormone ◽  
Log Linear

ABSTRACT Luteinizing hormone release induced by a range of small (3·3–33 μg) and large (300–500 μg) i.v. doses of gonadotrophin-releasing hormone (GnRH) was measured in acyclic (n = 4), luteal phase (n = 3) and follicular phase (n = 5) mares and compared with endogenously generated LH pulses in the same reproductive states. Extrapolation from log–linear dose–response curves showed that an LH pulse comparable to an endogenous one would be simulated by i.v. injection of 7·0 (n = 4) and 4·1 (n = 6) μg GnRH in luteal and follicular phase mares respectively; a much smaller dose than the 500 μg usually given clinically or experimentally. In acyclic mares (n = 4), LH pulses occurred too infrequently to be characterized. At small doses of GnRH the amount of LH released by the same dose was similar in all three reproductive states, although the steroid hormone milieu differed markedly. This implies that observed differences between states in mean (± s.e.m.) serum LH concentrations (0·7 ± 0·01, 1·2 ± 0·03 and 11·6 ± 0·33 (μg/l) in acyclic, luteal and follicular phase mares respectively) were produced by differences in GnRH pulse frequency and/or amplitude and not by steroid-mediated changes in pituitary response to GnRH. In acyclic, luteal and follicular phase mares, LH pulse frequency was: immeasurably low, 0·09 and 1·14 pulses/h respectively, which supports the important contribution of pulse frequency to determining mean LH concentration. The LH response to large doses of GnRH was significantly greater in the luteal than in the follicular phase, and was greater than the response to 33 μg in the luteal phase but not in the other two states. Thus, to a large but not to a small dose of GnRH, the pituitary appeared most responsive in the luteal phase. Therefore, in studies of the physiology of the hypothalamic-pituitary system, small doses of GnRH, which induce physiologically sized LH responses, may be preferred to large doses, which result in a level of stimulation to which the pituitary is never naturally exposed and to which it may respond in a non-physiological manner. J. Endocr. (1986) 110, 19–26

Proceedings: Variation in LH release in response to gonadotrophin-releasing hormone (GnRH) during the ovine oestrous cycle

Reproduction ◽  
1974 ◽  
Vol 36 (2) ◽  
pp. 474-475 ◽  
Author(s):  
R. Hooley ◽  
R. Baxter ◽  
W. Chamley ◽  
I. Cumming ◽  
J. Findlay
Keyword(s):  
Oestrous Cycle ◽  
Releasing Hormone ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

Corpus luteum life span and pituitary oestrogen and progesterone receptors in cyclic and gonadotrophin-releasing hormone-treated anoestrous ewes

2005 ◽  
Vol 17 (7) ◽  
pp. 721 ◽  
Author(s):  
C. Tasende ◽  
M. Rodríguez-Piñón ◽  
S. Acuña ◽  
E. G. Garófalo ◽  
M. Forsberg
Keyword(s):  
Luteal Phase ◽  
Luteinising Hormone ◽  
Binding Assay ◽  
Hormone Secretion ◽  
Progesterone Receptors ◽  
Oestrous Cycle ◽  
Inhibitory Effects ◽  
Releasing Hormone ◽  
Expected Time ◽  
Gonadotrophin Releasing Hormone

The present study investigated the pituitary oestrogen (ER) and progesterone (PR) receptor concentrations in ewes during the oestrous cycle in the breeding season (n = 19), and in anoestrous ewes treated with gonadotrophin-releasing hormone (GnRH) (n = 11) and anoestrous ewes treated with progesterone + GnRH (n = 11). The pituitary ER and PR concentrations at the expected time of ovulation and in the early and late luteal phases were measured by binding assay. The pattern of pituitary ER and PR concentrations in the progesterone + GnRH-treated ewes resembled the pattern found during the normal oestrous cycle, with ER and PR concentrations decreasing from the time of ovulation to the early luteal phase. In contrast, in ewes treated with GnRH alone, ER and PR concentrations increased in the early luteal phase, which may increase the inhibitory effects of steroid hormones on luteinising hormone secretion, ultimately leading to the development of subnormal luteal phases.

Plasma LH concentrations in the ewe in response to repeated injections of low doses of gonadotrophin releasing hormone during the follicular phase of the oestrous cycle

1984 ◽  
Vol 101 (3) ◽  
pp. 365-370 ◽  
Author(s):  
B. J. McLeod ◽  
W. Haresign
Keyword(s):  
Follicular Phase ◽  
Oestrous Cycle ◽  
Low Doses ◽  
Lh Surge ◽  
Releasing Hormone ◽  
Subsequent Cycle ◽  
Small Doses ◽  
Prostaglandin F ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone

ABSTRACT Oestrus was synchronized in 15 naturally cyclic ewes by the administration of a prostaglandin F2α analogue. Groups of five ewes were then treated i.v. with either small doses of gonadotrophin releasing hormone (GnRH; 125 or 250 ng/injection) or saline, at 2-h intervals from day 14 of the subsequent cycle until 24 h after the onset of oestrus. Treatment with GnRH induced episodic LH release which continued until the onset of a preovulatory LH surge. Mean plasma LH concentrations over this period were significantly (P< 0·001) higher in animals receiving 250 ng GnRH (2·44±0·11 μg/l) than in those receiving either 125 ng GnRH (1·17±0·06 μg/l) or saline (1·14±0·05 μg/l). However, GnRH treatment did not influence the timing of oestrus or mean ovulation rates. J. Endocr. (1984) 101, 365–370

Effect of gonadotrophin-releasing hormone agonist-induced suppression of LH and FSH on follicle growth and corpus luteum function in the ewe

1987 ◽  
Vol 115 (2) ◽  
pp. 273-282 ◽  
Author(s):  
A. S. McNeilly ◽  
H. M. Fraser
Keyword(s):  
Continuous Infusion ◽  
Corpus Luteum ◽  
Gnrh Agonist ◽  
Luteal Phase ◽  
Plasma Concentrations ◽  
Follicular Development ◽  
Similar Proportion ◽  
Simple Method ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone

ABSTRACT Continuous infusion of a gonadotrophin-releasing hormone (GnRH) agonist (buserelin) by osmotic minipump from day 1 of the luteal phase in five Welsh ewes resulted in a sustained suppression of plasma concentrations of FSH which increased three- to eightfold within 2 days after the end of infusion 29 days later. Plasma concentrations of LH increased three- to eightfold over the first 5 days of infusion and then became basal and non-pulsatile until 1 day after the end of infusion. Duration of the luteal phase and plasma concentrations of progesterone were not significantly different in control and treated ewes. Pulses of LH in control ewes were followed by increases in concentrations of progesterone in samples collected at 10-min intervals for 7 h on days 10 and 14 of the luteal phase. However, progesterone was also released in a pulsatile manner in the absence of LH pulses in both control and GnRH agonist-treated ewes. After natural luteolysis, no ovulation or corpus luteum function occurred in treated ewes up to 15 days after the end of treatment on day 29, even though oestrus, indicating follicular development and oestrogen secretion, had occurred 8–11 days after treatment ended. After 30 days of infusion the ovaries of GnRH agonist-treated ewes contained no follicles > 2·5 mm in diameter. In follicles of 1–2 mm in diameter the basal and LH-stimulated production of oestradiol and testosterone in vitro were similar in both control and GnRH agonist-treated ewes, and a similar proportion of these follicles was oestrogenic (> 370 mol oestradiol per follicle) in GnRH agonist-treated and control ewes. These results show (1) that progesterone secretion by the corpus luteum of the ewe can be sustained in the presence of basal concentrations but absence of pulsatile secretion of LH, and progesterone is released in a pulsatile manner whether or not LH pulses are present, (2) that follicular development beyond 2·5 mm in diameter in the ewe is dependent upon adequate stimulation by both LH and FSH and (3) that the continuous infusion of GnRH agonist is a simple method for providing reproducible suppression of LH and FSH and follicular development in the ewe to allow the study of gonadotrophin action on the ovary in vivo. J. Endocr. (1987) 115, 273–282

Luteal stage dependence of pituitary response to gonadotrophin-releasing hormone in cyclic dairy ewes subjected to synchronisation of ovulation

2005 ◽  
Vol 17 (8) ◽  
pp. 769 ◽  
Author(s):  
G. S. Amiridis ◽  
I. Valasi ◽  
I. Menegatos ◽  
C. Rekkas ◽  
P. Goulas ◽  
...  
Keyword(s):  
Luteal Phase ◽  
Luteinising Hormone ◽  
Prostaglandin F2α ◽  
Causative Factor ◽  
Releasing Hormone ◽  
Treatment Groups ◽  
Dairy Ewes ◽  
Lh Release ◽  
Gonadotrophin Releasing Hormone ◽  
Additional Sample

Possible hormonal aberrations precluding conception or maintenance of pregnancy in dairy ewes subjected to ovulation synchronisation were investigated in this study. The pituitary response to exogenous gonadotrophin-releasing hormone (GnRH) was tested at different luteal stages in 36 ewes. Oestruses were synchronised by using progestagen-impregnated sponges and the animals were randomly allotted into one of three treatment groups (A, B and C; n = 12 for each). Treatments commenced on Days 4, 9 and 14 of the new cycle (oestrus was defined as Day 0). Ewes were given two GnRH injections, 5 days before and 36 h after a prostaglandin F2α (PGF2α) injection, and the animals were inseminated 12–14 h after the second GnRH injection (modified OVSYNCH). For luteinising hormone (LH) determination blood samples were withdrawn from six ewes of each group at the time of GnRH administration, and 30, 90, 180, 270 and 360 min later. Progesterone was assayed in samples taken every other day starting from oestrus and for 17 days after the second GnRH injection, and in an additional sample collected on the day of insemination. After the first GnRH injection, the LH concentration was higher in Group C than in Groups B and A (mean ± s.d.: 64.8 ± 10.0 ng mL−1, 41.3 ± 3.7 ng mL−1 and 24.6 ± 9.0 ng mL−1, respectively; P < 0.05), whereas after the second GnRH injection a uniform LH release was found in all groups. PGF2α caused a significant decrease in progesterone (P4) concentration in all groups; however, at artificial insemination ewes that conceived had significantly lower P4 concentration in comparison with those that failed to conceive. As early as Day 5, pregnant animals had higher P4 concentrations than non-pregnant animals. Overall, 21 animals conceived (seven, nine and five ewes from Groups A, B and C, respectively). These results indicate that the proposed protocol is equally effective in inducing a preovulatory LH surge at any stage of the luteal phase, and that elevated P4 concentration along with a delayed P4 increase should be considered as a causative factor for inability to conceive.

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.

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