Effects of passively immunizing ewes against inhibin and oestradiol during the follicular phase of the oestrous cycle

1990 ◽  
Vol 125 (3) ◽  
pp. 417-424 ◽  
Author(s):  
G. E. Mann ◽  
B. K. Campbell ◽  
A. S. McNeilly ◽  
D. T. Baird
Keyword(s):  
Corpus Luteum ◽  
Passive Immunization ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Peptide Fragment ◽  
Lh Surge ◽  
Luteal Regression ◽  
Basal Concentration ◽  
Venous Plasma ◽  
Plasma Control

ABSTRACT Passive immunization was used to investigate the importance of inhibin and oestradiol in the control of FSH production during the follicular phase of the oestrous cycle in the sheep. Four groups of five mature Scottish Blackface ewes were injected with normal sheep plasma (control), antiserum to the 1–26α peptide fragment of porcine inhibin, antiserum to oestradiol-17β, or a combination of the two antisera, 24 h following cloprostenol-induced luteal regression. There was no difference in the concentration of LH in jugular venous plasma between the control and inhibin-immunized groups following the injection of normal sheep plasma or inhibin antiserum, with both groups exhibiting normal LH surges. In both the groups immunized against oestradiol, the basal concentration of LH rose by 25–30% (P<0.05) during the 96-h period following injection, while the LH surge and consequent formation of a corpus luteum was inhibited. In all three immunized groups there was a significant (P<0.001) rise in the concentration of FSH starting 3.8–4.8 h after the injection of antiserum. The duration of the rise was similar in the groups injected with oestradiol antiserum alone (43.6±12.8 h) or in combination with inhibin antiserum (40.6 ± 11.7 h), but was significantly (P<0.05) shorter in the group immunized against inhibin alone (17.0 ± 0.5 h). The rise in FSH was similar in the groups immunized against inhibin (142 ± 6%) or oestradiol (143±4%) alone, and was significantly (P<0.01) greater in the group injected with both antisera (195± 17%). These results provide evidence that both oestradiol and inhibin play a role in regulating the concentration of FSH during the follicular phase of the oestrous cycle, while reinforcing the hypothesis that inhibin is not involved in the regulation of LH production. Journal of Endocrinology (1990) 125, 417–424

Source of ovarian inhibin secretion during the oestrous cycle of the sheep

1989 ◽  
Vol 123 (2) ◽  
pp. 181-188 ◽  
Author(s):  
G. E. Mann ◽  
A. S. McNeilly ◽  
D. T. Baird
Keyword(s):  
Corpus Luteum ◽  
Luteal Phase ◽  
Venous Blood ◽  
Contralateral Side ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Secretion Rate ◽  
Antral Follicles ◽  
Luteal Tissue

ABSTRACT The source of inhibin secretion by the ovary in the sheep at different stages of the oestrous cycle was investigated by in-vivo cannulation of the ovarian veins. Twenty-four Scottish Blackface ewes were allocated to four groups of six ewes, i.e. those operated on during the luteal phase (day 10), and those operated on during the follicular phase 24–30, 36 and 60 h following an injection of 125 μg cloprostenol on day 10 of the luteal phase. Samples of jugular and timed ovarian venous blood were collected under anaesthesia before and after enucleation of the corpus luteum. Ovaries were then removed and follicles dissected out. Following injection of cloprostenol, luteal regression occurred as indicated by a fall in the secretion of progesterone. The concentration of inhibin in jugular venous plasma and its ovarian secretion rate were similar at all stages of the follicular phase and during the luteal phase. In contrast, the secretion rate of oestradiol rose from 2·68 ±0·73 pmol/min during the luteal phase to 8·70± 2·24 pmol/min 24 h after injection of cloprostenol (P<0·05). Following enucleation of the corpus luteum the secretion rate of progesterone fell from 809 ± 270 pmol/min to 86 ± 30 pmol/min (P<0·001). There was also a smaller, artifactual fall in the secretion rate of oestradiol following enucleation of the corpus luteum, which was of similar size to a fall seen in the secretion rate of inhibin. This resulted in a significant (P<0·001) fall in the ratio of progesterone to inhibin, while the oestradiol to inhibin ratio remained unchanged. The secretion rate of inhibin from ovaries containing luteal tissue was similar to that from the contralateral side without luteal tissue (1·41±0·30 compared with 1·32±0·30 ng/min), while ovaries with large antral follicles secreted significantly (P< 0·001) more inhibin than those with no follicles ≥3 mm (2·28 ± 0·36 compared with 0·25 ±0·06 ng/min). From these results we conclude that, in the sheep, large antral follicles are responsible for most, if not all, the secretion of inhibin by the ovary at all stages of the oestrous cycle, and that the corpus luteum secretes little or no immunoactive or bioactive inhibin. Due to the fact that, unlike inhibin, the secretion rate of oestradiol rises during the follicular phase of the cycle, when the concentration of FSH is suppressed, it seems likely that oestradiol rather than inhibin is the major ovarian factor modulating the change in FSH secretion seen at this stage of the oestrous cycle. Journal of Endocrinology (1989) 123, 181–188

Episodic secretion of inhibin into the ovarian vein during the follicular phase of the oestrous cycle in the ewe

1989 ◽  
Vol 122 (1) ◽  
pp. 287-292 ◽  
Author(s):  
A. S. McNeilly ◽  
D. T. Baird
Keyword(s):  
Plasma Concentration ◽  
Local Control ◽  
Venous Blood ◽  
Plasma Concentrations ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Ovarian Vein ◽  
Preovulatory Follicle ◽  
Luteal Regression ◽  
Merino Sheep

ABSTRACT Changes in the plasma concentration of inhibin were measured by radioimmunoassay in ovarian venous blood collected at 10-min intervals for 5-h periods between 16 and 21 h and 40 and 45 h after cloprostenol-induced luteal regression in six Finn–Merino sheep. Episodes of inhibin secretion occurred with an interpulse interval of 66 ± 5 min in both stages of the follicular phase. These changes in inhibin were unrelated to pulses of LH or oestradiol. There was no relationship with plasma concentrations of FSH, which did not change in a pulsatile manner. These results suggest that the release of inhibin by the preovulatory follicle(s) occurs in a pulsatile manner and is under local control by unknown factors. Journal of Endocrinology (1989) 122, 287–292

Evidence that the switch from negative to positive feedback at the level of the pituitary gland is an important timing event for the onset of the preovulatory surge in LH in the ewe

1995 ◽  
Vol 145 (2) ◽  
pp. 271-282 ◽  
Author(s):  
I J Clarke
Keyword(s):  
Pituitary Gland ◽  
Negative Feedback ◽  
Luteal Phase ◽  
Bolus Injection ◽  
Pulse Frequency ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Lh Surge ◽  
Small Rise ◽  
Lh Secretion

Abstract Experiments were performed to test the hypothesis that there is a negative feedback 'clamp' of ovarian hormones on the hypothalamus and pituitary gland during the follicular phase of the oestrous cycle that limits the secretion of GnRH and LH. GnRH secretion was monitored by sampling the hypophysial portal blood of ewes during the luteal phase of the oestrous cycle and either 24 h or 48 h after the induction of luteolysis by the injection of cloprostenol, a prostaglandin analogue. There was an increase in GnRH pulse frequency in the transition from the luteal to the follicular phase of the cycle. A reduction in the amplitude of GnRH pulses did not occur until 48 h after cloprostenol, suggestive of negative feedback at the level of the hypothalamus that is more profound in the latter part of the follicular phase. The responsivity of the pituitary gland to GnRH was monitored in ewes during the luteal phase of the oestrous cycle and 24 h or 48 h after cloprostenol. Injections of 250 ng or 1000 ng GnRH were given (i.v.) to ewes that had been anaesthetised to suppress endogenous secretion of GnRH and LH. Using the lower dose, the responses 48 h after cloprostenol were not significantly different from those in the luteal phase. With the higher dose of GnRH, a significant (P<0·05) increase in mean responsivity was seen 48 h after cloprostenol. There was, however, a marked variation in response, with some ewes showing profound increases in LH secretion in response to GnRH and others showing responses that were similar to those obtained during the luteal phase of the cycle. These data are interpreted to mean that the secretion of LH is 'clamped' during the follicular phase of the oestrous cycle and the 'clamp' is only released near the time of the preovulatory LH surge. To test whether or not a rise in GnRH input to the pituitary gland could over-ride the 'clamp' on the pituitary secretion of LH in the late follicular phase of the cycle, sheep were treated 40 h after cloprostenol with either a bolus injection of 500 ng GnRH or four pulses of 125 ng GnRH given at 10-min intervals. These treatments caused small elevations in LH secretion but did not always cause preovulatory LH surges. In some cases, a small rise in LH secretion was induced by GnRH treatments and levels of LH in plasma returned to baseline with the preovulatory LH surge occurring a few hours later. In one clear case, a bolus injection of GnRH induced an LH surge. The overall data from the GnRH-treated groups, however, indicated a significant delay in the onset of the LH surge which may have been due to perturbation of the subcellular mechanisms in the gonadotrophs. These data were interpreted to mean that the secretion of LH from the pituitary gland is inhibited up to very soon before the onset of the LH surge. The inhibitory factor could be oestrogen but could also be some other pituitary feedback hormone such as gonadotrophin surge-attenuating factor. It is concluded that the increase in the secretion of GnRH at the time of the onset of the LH surge is closely linked to an increase in the responsivity of the gonadotrophs to GnRH. The latter is not caused by the increase in the secretion of GnRH. Journal of Endocrinology (1995) 145, 271–282

EFFECTS OF HUMAN CHORIONIC GONADOTROPHIN ON THE RELEASE OF CYCLIC AMP AND PROGESTERONE FROM THE SHEEP OVARY AT DIFFERENT STAGES OF THE OESTROUS CYCLE

1978 ◽  
Vol 89 (1) ◽  
pp. 158-165 ◽  
Author(s):  
T. J. Weiss ◽  
P. O. Janson ◽  
K. J. Porter ◽  
R. F. Seamark
Keyword(s):  
Cyclic Amp ◽  
Corpus Luteum ◽  
Chorionic Gonadotrophin ◽  
Human Chorionic Gonadotrophin ◽  
Oestrous Cycle ◽  
Secretion Rate ◽  
Arterial Plasma ◽  
Venous Plasma

ABSTRACT The rate of release of cyclic AMP by sheep ovaries containing a corpus luteum was determined at different stages of the cycle before and up to 60 min after an intra-arterial (ia) injection of 500 IU human chorionic gonadotrophin (hCG). The median cyclic AMP concentration in arterial plasma and of ovarian venous plasma following hCG stimulation was 93.2 and 98.0 pmol/ml, respectively. The ovaries of ewes examined at Days 1 and 2 of the cycle showed no response to hCG, whereas in 2 sheep at Day 3, hCG caused a slight response, and in 13 sheep examined between Days 5–18, hCG caused a marked increase in cAMP release. In 5 of the sheep in which both ovarian veins were cannulated, only the ovary with a corpus luteum responded to hCG with an increased secretion rate of cyclic AMP and progesterone. The results indicate a lack of responsiveness in the newly formed corpus luteum to hCG.

THE EFFECT OF HYPOPHYSIAL STALK-SECTION ON THE CORPUS LUTEUM OF THE GUINEA-PIG

1971 ◽  
Vol 50 (4) ◽  
pp. 625-635 ◽  
Author(s):  
DOREEN V. ILLINGWORTH ◽  
J. S. PERRY
Keyword(s):  
Growth Rate ◽  
Guinea Pig ◽  
Corpus Luteum ◽  
Guinea Pigs ◽  
Oestrous Cycle ◽  
Corpora Lutea ◽  
Normal Cycle ◽  
Luteal Regression ◽  
Normal Regression ◽  
And Function

SUMMARY The effects of hypophysial stalk-section on the growth and function of the corpus luteum of the non-pregnant guinea-pig have been compared with the effects of hypophysectomy (as previously described) and with the effects of prolactin administered to hypophysectomized animals. Stalk-section soon after ovulation did not impair the growth of the corpora lutea nor their ability to secrete progesterone. Stalk-section before day 9 of the oestrous cycle prevented the normal regression of the corpora lutea; they continued to grow and 3 weeks after ovulation were as large as those of pregnant animals, or of non-pregnant hysterectomized guinea-pigs. The corpora lutea regressed irregularly during the following 2 weeks. When performed on, or later than day 9, stalk-section did not prevent luteal regression at the normal time. Administration of prolactin (10 i.u./day) to hypophysectomized guinea-pigs restored the growth-rate of the corpora lutea, which reached sizes comparable to those of the normal cycle, and those of stalk-sectioned animals, by 10 days after ovulation. Our results indicate that prolactin can have substantial luteotrophic activity in the guinea-pig.

Mobilization of LH secretory granules in gonadotrophs in relation to gene expression, synthesis and secretion of LH during the preovulatory phase of the sheep oestrous cycle

1995 ◽  
Vol 147 (2) ◽  
pp. 259-270 ◽  
Author(s):  
R J W Currie ◽  
A S McNeilly
Keyword(s):  
Electron Microscopy ◽  
Luteal Phase ◽  
Secretory Granules ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Single Type ◽  
Maximum Diameter ◽  
Northern Analysis ◽  
Mrna Levels ◽  
Lh Surge

Abstract Changes in LH secretory granules in pituitary gonadotrophs throughout the sheep oestrous cycle were determined by immunogold localisation of LH at ultrastructural level by electron microscopy. Oestrous cycles in Welsh Mountain ewes were initially synchronised with progestagen sponges and studies carried out in the subsequent cycle. Animals were allocated at random to six groups each of five animals, one killed on day 12 of the luteal phase and the other groups after prostaglandin (PG)-induced luteal regression at PG plus 18 h (early follicular phase), oestrus (PG plus 33·6±1·0 h), oestrus plus 9 h just before the preovulatory LH surge, 1 h after GnRH agonist-induced LH surge at PG plus 48 h (mid-LH surge) and oestrus plus 24 h, after the preovulatory LH surge. Blood samples collected throughout confirmed the pulsatile secretion of LH before and the timing in relation to the preovulatory LH surge. Pituitaries were dissected and processed for transmission electron microscopy and frozen for later extraction of mRNA. Only a single type of LH cell was present in the sheep pituitary. In the luteal phase, LHimmunopositive secretory granules were distributed throughout the cytoplasm in 80% of cells while in 20% of cells granules were polarised to the region of the cell next to a vascular sinusoid. The percentage of polarised cells increased during the follicular phase to 45% at oestrus, 75% at oestrus plus 9 h just before the LH surge and 90% in mid-LH surge. Cell size increased in parallel with polarisation. Gonadotrophs after the LH surge were almost totally devoid of LH granules but prominent LHβ immunoreactivity was observed in the rough endoplasmic reticulum. Analysis of granule diameters revealed a single class of granules with a maximum diameter of 300 nm. Polarised cells had significantly fewer 130–150 nm granules than non-polarised cells, suggesting preferential exocytosis of LH-containing granules of this size from polarised cells. Northern analysis showed that LHβ mRNA levels decreased from luteal through the follicular phase. These results suggest that the preovulatory LH surge in sheep is not related to a change in synthesis of LH but to a progressive recruitment of gonadotrophs into a releasing state, priming, as indicated by polarisation of secretory granules to the region of the cell next to the vascular system. Journal of Endocrinology (1995) 147, 259–270

Induction of the ovulatory LH surge in Asian elephants (Elephas maximus): a novel aid in captive breeding management of an endangered species

2009 ◽  
Vol 21 (5) ◽  
pp. 672 ◽  
Author(s):  
Chatchote Thitaram ◽  
Pornsawan Pongsopawijit ◽  
Saran Chansitthiwet ◽  
Janine L. Brown ◽  
Kannikar Nimtragul ◽  
...  
Keyword(s):  
Captive Breeding ◽  
Unique Feature ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Elephas Maximus ◽  
Asian Elephants ◽  
Lh Surge ◽  
Breeding Management ◽  
Gonadotrophin Releasing Hormone ◽  
Natural Mating

A unique feature of the reproductive physiology of Asian elephants (Elephas maximus) is the occurrence of two LH surges before ovulation, instead of one. An anovulatory LH (anLH) surge, the function of which is unknown, occurs consistently 3 weeks before the ovulatory LH (ovLH) surge that induces ovulation. Thus, the ability to induce an ovLH surge would be useful for scheduling natural mating or artificial insemination. The present study tested the efficacy of a gonadotrophin-releasing hormone agonist (GnRH-Ag) to induce LH surges during the follicular phase of the oestrous cycle, which resulted in varied LH responses, but generally none were as high as previously documented natural surges. Thus, for the ovulation-induction trials, nine females were administered 80 μg GnRH-Ag intravenously at three time periods during the oestrous cycle, namely the anovulatory follicular phase, the ovulatory follicular phase and the luteal phase. During the late anovulatory follicular phase, nine of 10 females (90%) responded with an immediate LH surge followed 15–22 days later by an ovLH surge or a post-ovulatory increase in progestagens. In contrast, despite responding to the GnRH-Ag with an immediate increase in LH, none of the females treated during other periods of the oestrous cycle exhibited subsequent ovLH surges. One cow got pregnant from natural mating following the induced ovLH surge. In conclusion, ovLH induction is possible using a GnRH-Ag, but only during a specific time of the anovulatory follicular phase.

Hormone production in vivo and in vitro from follicles at different stages of the oestrous cycle in the sheep

1992 ◽  
Vol 132 (2) ◽  
pp. 225-234 ◽  
Author(s):  
G. E. Mann ◽  
A. S. McNeilly ◽  
D. T. Baird
Keyword(s):  
Luteal Phase ◽  
Follicular Phase ◽  
Oestrous Cycle ◽  
Secretion Rate ◽  
Hormone Production ◽  
Luteal Regression ◽  
Follicle Diameter ◽  
Oestradiol Production

ABSTRACT This experiment was undertaken in order to investigate the production of inhibin, oestradiol and androstenedione by ovarian follicles at different stages of the oestrous cycle in sheep. Twenty-four Scottish Blackface ewes were allocated to four groups of six ewes, i.e. those operated on during the luteal phase (day 10), and those operated on during the follicular phase 24–30, 36 and 60 h after the induction of luteal regression by an injection of 125 μg cloprostenol on day 10 of the luteal phase. Samples of jugular and ovarian venous blood were collected under anaesthesia and ovaries were then removed and all follicles larger than 3 mm diameter dissected out and incubated in medium for 2 h. After injection of cloprostenol, luteal regression occurred as indicated by a fall in the secretion rate of progesterone. The ovarian secretion rate of inhibin was similar at all stages of the follicular phase and during the luteal phase while, in contrast, the secretion rate of oestradiol was significantly (P < 0·05) elevated in the group 24 h after injection of cloprostenol. There was good correlation between the in-vivo ovarian secretion rate and production rate during incubation in vitro for both inhibin (r = 0·57) and oestradiol (r = 0·60). When follicle diameter was compared with in-vitro hormone production there was good correlation for inhibin (r = 0·72) with larger follicles producing more inhibin, while the value for oestradiol was somewhat lower (r = 0·57) owing to the presence of large atretic follicles with low oestradiol production. Androstenedione production showed a lower correlation with follicle diameter (r = 0·39). When the four time periods were compared separately, there were significantly (P < 0·05) more follicles with high in-vitro oestradiol production (> 90 fmol/min) in the group at 36 h than in the other three groups, while inhibin release in relation to follicle size was similar in the four groups. Large oestrogenic follicles were responsible for 90% of the total oestradiol production during culture while only providing 55% of the total inhibin production, with large non-oestrogenic and small follicles contributing 33% and 12% of inhibin production respectively. From the results of this study we conclude that while oestradiol is mainly produced by the large oestrogenic follicles, a considerable amount of inhibin is also produced by large non-oestrogenic and small follicles. We also found that a lack of variation in inhibin secretion rate in the intact animal was paralleled by a lack of variation in the pattern of inhibin produced from individual follicles. Journal of Endocrinology (1992) 132, 225–234

The effect of active and passive immunization against oxytocin on ovarian cyclicity in ewes

1983 ◽  
Vol 103 (3) ◽  
pp. 337-344 ◽  
Author(s):  
D. Schams ◽  
S. Prokopp ◽  
D. Barth
Keyword(s):  
Corpus Luteum ◽  
Luteal Phase ◽  
Passive Immunization ◽  
Threshold Concentration ◽  
High Variability ◽  
Oestrous Cycle ◽  
Ovarian Cyclicity

Abstract. Active and passive immunization of ewes against oxytocin prolonged the luteal phase of the oestrous cycle, as evaluated by oestrus behaviour and determination of progesterone. Between the animals there was a high variability in response. In general animals with prolonged cycles had lower concentrations of free oxytocin. But in some animals oxytocin antibodies had no effect on cyclicity. Therefore, an individual minimal threshold concentration for oxytocin was presumed. In control or treated animals circulating oxytocin concentrations increased parallel with progesterone concentrations but decreased earlier during the mid luteal phase of the cycle. A new increase in oxytocin concentrations was only observed if a new corpus luteum was formed.

LYSOSOMAL FUNCTION IN THE CORPUS LUTEUM OF THE SHEEP

1968 ◽  
Vol 40 (3) ◽  
pp. 325-NP ◽  
Author(s):  
J. T. DINGLE ◽  
MARY F. HAY ◽  
R. M. MOOR
Keyword(s):  
Corpus Luteum ◽  
Functional Significance ◽  
Subcellular Fraction ◽  
Oestrous Cycle ◽  
Corpora Lutea ◽  
Lysosomal Function ◽  
Luteal Regression ◽  
Pregnant Sheep ◽  
A Cell

SUMMARY A subcellular fraction containing particles showing the characteristics of lysosomes has been isolated from the corpus luteum of the sheep. Histochemical and biochemical observations have demonstrated that the lysosomes increase in size and fragility late in the oestrous cycle. Similar changes were not found in the corpora lutea of pregnant animals. The observed increase in lysosomal fragility is one of the earliest changes associated with luteal regression, and is thought to be of functional significance in the involution of the lutein cells. The possible modification of lysosomal function by the production of a cell-specific lytic factor from the uterus of non-pregnant sheep is discussed.

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