Effects of luteolysis during late pregnancy on pituitary responsiveness to gonadotrophin-releasing hormone in the rat

1991 ◽  
Vol 128 (3) ◽  
pp. 411-418
Author(s):  
T. R. Koiter ◽  
G. C. J. van der Schaaf-Verdonk ◽  
G. A. Schuiling
Keyword(s):  
Plasma Concentrations ◽  
Control Level ◽  
Late Pregnancy ◽  
Ovariectomized Rats ◽  
Normal Delivery ◽  
Releasing Hormone ◽  
Oestradiol Treatment ◽  
Progesterone Treatment ◽  
Gonadotrophin Releasing Hormone ◽  
Series Of Experiments

ABSTRACT We investigated whether the increase in the gonadotrophin response to gonadotrophin-releasing hormone (GnRH) during the last days of pregnancy and the occurrence of parturition on day 22 of pregnancy in rats are due to the increase in the plasma concentrations of oestradiol-17β after luteolysis, which occurs around day 20. In a first series of experiments we studied the effects of s.c. implantation of two capsules containing oestradiol on basal and GnRH-stimulated secretion of LH and FSH before and after luteolysis. Before luteolysis, ovariectomy increased basal LH and FSH; oestradiol treatment prevented this increase partly (FSH) or completely (LH). Ovariectomy also lowered the LH response to the infusion of GnRH (100 ng/h). Oestradiol treatment, on the other hand, increased the LH and FSH responses of both intact and ovariectomized rats above the level in intact non-treated control rats. After luteolysis, ovariectomy increased basal FSH only. Treatment with oestradiol did not prevent the increase in basal FSH and ovariectomy diminished the LH response to GnRH infusion. Oestradiol treatment maintained the LH response in ovariectomized rats at the control level and increased the FSH responses of both intact and ovariectomized rats to a higher level than in control rats. Furthermore, the LH and FSH responses of the oestradiol-treated groups of intact and ovariectomized rats were higher after luteolysis than before. In a second series of experiments two capsules containing progesterone were s.c. implanted before or after luteolysis. Progesterone treatment suppressed the plasma concentration of oestradiol and the gonadotrophin responses to infusion of GnRH on the expected day of parturition in both groups of rats. Parturition was delayed only in the rats in which progesterone treatment had started before luteolysis. It was concluded that throughout pregnancy ovarian factors suppress basal FSH and that the increase in responsiveness to GnRH after luteolysis is due partly to an increase in oestradiol production and partly to an ovarian factor which augments the action of oestradiol. Furthermore, normal delivery does not require high plasma concentrations of oestradiol during the last day of pregnancy. Journal of Endocrinology (1991) 128, 411–418

HORMONAL REQUIREMENTS FOR THE MAINTENANCE OF OESTRADIOL-INDUCED INHIBITION OF UTERINE SENSITIVITY IN THE OVARIECTOMIZED RAT

1970 ◽  
Vol 46 (3) ◽  
pp. 341-346 ◽  
Author(s):  
K. P. MEYERS
Keyword(s):  
Subcutaneous Injection ◽  
Ovariectomized Rats ◽  
Ovariectomized Rat ◽  
Single Subcutaneous Injection ◽  
The Third ◽  
Oestradiol Treatment ◽  
Progesterone Treatment ◽  
Endometrial Scratching

SUMMARY Ovariectomized rats treated with 2·5 or 5·0 mg. progesterone daily received a single subcutaneous injection of 0·2 μg. oestradiol on the third day of the progesterone treatment. The deciduomal response to trauma by endometrial scratching was used to determine the degree of uterine sensitivity at various times after oestradiol. Uterine sensitivity was partially and then completely lost 36 and 48 hr. after oestradiol administration. The inhibition of uterine sensitivity persisted until 9 and 11 days after oestradiol when the animals received 2·5 and 5·0 mg. progesterone daily. Uterine sensitivity was completely inhibited on day 11 with doses of oestradiol from 0·2 to 0·05 μg. Withdrawal of progesterone treatment for 48 or 72 hr., but not for 24 hr., after oestradiol treatment restored uterine sensitivity. These results show that the oestradiol-induced inhibition of uterine sensitivity in the progestational endometrium is maintained by continuous progesterone treatment and that the duration of this effect is dependent on the dose of progesterone given.

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

Anti-fertility effects of oral medroxyprogesterone acetate in rabbits

1996 ◽  
Vol 8 (8) ◽  
pp. 1185 ◽  
Author(s):  
NO Oguge ◽  
GK Barrell
Keyword(s):  
Single Dose ◽  
Luteinizing Hormone ◽  
Medroxyprogesterone Acetate ◽  
Plasma Concentrations ◽  
Inhibitory Effect ◽  
Multiple Dosing ◽  
Releasing Hormone ◽  
Single Meal ◽  
Gonadotrophin Releasing Hormone ◽  
Hypothalamic Level

Studies on the anti-fertility effects of medroxyprogesterone acetate (MPA) were conducted in rabbits. The bioavailability of MPA and plasma concentrations of progesterone and luteinizing hormone (LH) after mating were monitored following a single meal containing MPA (1000 mg) in entire does (n = 4); the response to gonadotrophin-releasing hormone (GnRH; 250 ng) was also observed in MPA-treated, ovariectomized does (n = 6). The reproductive tracts of rabbits mated following MPA treatment were examined 28-30 h after mating. Another group of rabbits (n = 4) received a single dose of MPA on Days 1, 10 or 19 after mating or daily for five days from Day 24. After dosage with 1000 mg MPA, plasma concentrations of MPA were detectable for eight days. However, following multiple dosing (10 mg, 5 days) MPA was detectable in the plasma for two days. MPA reduced the rate of ovulation and suppressed the increase in plasma concentrations of progesterone and LH observed after mating for four days, but had no effect on the response to GnRH. When administered late in gestation, MPA caused the death of fetuses. These results demonstrate an inhibitory effect of MPA on ovulation, probably at the hypothalamic level, and impairment of gestation or parturition.

Effects of pituitary-gonadal suppression with a gonadotrophin-releasing hormone agonist on fetal gonadotrophin secretion, fetal gonadal development and maternal steroid secretion in the sheep

1994 ◽  
Vol 141 (2) ◽  
pp. 317-324 ◽  
Author(s):  
G B Thomas ◽  
A S McNeilly ◽  
F Gibson ◽  
A N Brooks
Keyword(s):  
Gnrh Agonist ◽  
Fetal Development ◽  
Plasma Concentrations ◽  
Gonadal Development ◽  
Maternal Circulation ◽  
Biodegradable Implant ◽  
Steroid Secretion ◽  
Releasing Hormone ◽  
Pituitary Glands ◽  
Gonadotrophin Releasing Hormone

Abstract In order to investigate the regulation of the hypothalamo-pituitary-gonadal axis during fetal development, sheep fetuses at day 70 of gestation were implanted subcutaneously with a biodegradable implant containing the longacting gonadotrophin-releasing hormone (GnRH) agonist, buserelin. The treatment of fetuses with a GnRH agonist throughout the last half of gestation (term=145 days) abolished the increase in plasma LH concentrations that was seen in 2-day-old control lambs in response to an injection of GnRH. This attenuated response was associated with corresponding reductions in the pituitary content of LH and FSH. Immunolocalization studies revealed that pituitary glands from newborn lambs implanted with a GnRH agonist during fetal development were devoid of immunopositive LH- and FSH-containing cells. At birth the testicular weights of GnRH agonist-treated ram lambs were significantly decreased by 40% when compared with controls. This was associated with a 45% reduction in the total number of Sertoli cells per testis. In newborn ewe lambs GnRH agonist treatment had no effect on ovarian weight or on the morphological appearance of the ovaries. GnRH agonist treatment had no effect on the plasma concentrations of progesterone and oestrone in the maternal circulation or on the length of gestation. These results show (1) that GnRH positively regulates the synthesis and secretion of gonadotrophins in the fetus, (2) that reduced fetal gonadotrophic support during the last half of gestation results in a reduction in testicular growth, and (3) that fetal gonadotrophins do not affect maternal steroid secretion. Journal of Endocrinology (1994) 141, 317–324

Use of a new drug delivery formulation of the gonadotrophin-releasing hormone analogue Deslorelin for reversible long-term contraception in male dogs

2003 ◽  
Vol 15 (6) ◽  
pp. 317 ◽  
Author(s):  
A. Junaidi ◽  
P. E. Williamson ◽  
J. M. Cummins ◽  
G. B. Martin ◽  
M. A. Blackberry ◽  
...  
Keyword(s):  
Slow Release ◽  
Semen Quality ◽  
Animal Health ◽  
Plasma Concentrations ◽  
Testicular Volume ◽  
Releasing Hormone ◽  
Detectable Range ◽  
Effect Of Treatment ◽  
Gonadotrophin Releasing Hormone

In the present study, we tested the effect of treatment with a slow-release implant containing the gonadotrophin-releasing hormone agonist DeslorelinTM (Peptech Animal Health Australia, North Ryde, NSW, Australia) on pituitary and testicular function in mature male dogs. Four dogs were treated with Deslorelin (6-mg implant) and four were used as controls (blank implant). In control dogs, there were no significant changes over the 12 months of the study in plasma concentrations of luteinising hormone (LH) or testosterone, or in testicular volume, semen output or semen quality. In Deslorelin-treated dogs, plasma concentrations of LH and testosterone were undetectable after 21 and 27 days, testicular volume fell to 35% of pretreatment values after 14 weeks and no ejaculates could be obtained after 6 weeks. Concentrations returned to the detectable range for testosterone after 44 weeks and for LH after 51 weeks and both were within the normal range after 52 weeks. Semen characteristics had recovered completely by 60 weeks after implantation. At this time, the testes and prostate glands were similar histologically to those of control dogs. We conclude that a single slow-release implant containing 6 mg Deslorelin has potential as a long-term, reversible antifertility agent for male dogs.

INTERACTION BETWEEN OESTROGEN AND GONADOTROPHIN-RELEASING HORMONE ON THE RELEASE AND SYNTHESIS OF LUTEINIZING HORMONE AND FOLLICLE-STIMULATING HORMONE FROM INCUBATED PITUITARIES

1976 ◽  
Vol 68 (1) ◽  
pp. 127-136 ◽  
Author(s):  
MARTA E. APFELBAUM ◽  
S. TALEISNIK
Keyword(s):  
Incubation Medium ◽  
Ovariectomized Rats ◽  
Spontaneous Release ◽  
Dose Response Relationship ◽  
Dual Effect ◽  
Releasing Hormone ◽  
Oestradiol Benzoate ◽  
Pituitary Glands ◽  
Gonadotrophin Releasing Hormone ◽  
Gland Content

SUMMARY The release and synthesis of LH and FSH were studied in adenohypophyses from ovariectomized rats incubated for a period of 4 h in flasks containing 1 ml Eagle's medium. One hemipituitary was used as the experimental gland and the other half served as a control. Glands from ovariectomized untreated animals showed a spontaneous release of LH and FSH and the amount of hormones released (per mg gland) by both the hemipituitaries was not significantly different. Also the content of the hormones at the end of the incubation period was similar in both halves. Gonadotrophin-releasing hormone (Gn-RH) added to the incubation medium stimulated the release of LH and FSH. A dose–response relationship was obtained between doses of 0·51 and 8·00 ng/ml medium. Although lower doses were required to increase the release of LH, the amount of FSH released was higher when expressed as a percentage of gland content. Pituitary glands from ovariectomized rats treated with 5 μg oestradiol benzoate 24 h before being killed showed an increase in sensitivity to Gn-RH, but the response decreased when oestrogen was injected 2 h before death. Also the addition of oestradiol-17β to the incubation medium inhibited LH and FSH release induced by Gn-RH. Gonadotrophin-releasing hormone increased the spontaneous synthesis of LH and FSH observed in the incubated pituitaries. This effect of Gn-RH was stimulated by the injection of oestrogen into the donor animals whereas administration of oestrogen into the medium enhanced the synthesis of LH and partially inhibited that of FSH. These results provide evidence for a dual effect of oestrogen on the release of LH and FSH induced by Gn-RH. They also show that synthesis of gonadotrophic hormones was favoured by oestrogen or by increased gonadotrophin release.

PARTURITION IN THE GUINEA-PIG; PLASMA LEVELS OF STEROID HORMONES, STEROID-BINDING PROTEINS, AND OXYTOCIN, AND THE EFFECT OF CORTICOSTEROIDS, PROSTAGLANDINS AND ADRENOCORTICOTROPHIN

1974 ◽  
Vol 63 (3) ◽  
pp. 557-570 ◽  
Author(s):  
D. V. ILLINGWORTH ◽  
J. R. G. CHALLIS ◽  
N. ACKLAND ◽  
A. M. BURTON ◽  
R. B. HEAP ◽  
...  
Keyword(s):  
Guinea Pig ◽  
Plasma Concentrations ◽  
Late Pregnancy ◽  
Maternal Plasma ◽  
Rapid Phase ◽  
Normal Delivery ◽  
Indwelling Catheters ◽  
Consistent Change ◽  
Significant Change ◽  
High Doses

SUMMARY Parturition in the guinea-pig is not preceded by any consistent change in the maternal plasma concentrations of progesterone, total unconjugated oestrogens or corticosteroids, or by a significant change in the concentration of progesterone-binding globulin (PBG). The onset of parturition was delayed by high doses of oestrogens (stilboestrol and oestradiol), but was not affected by oestriol or an antiserum raised against oestradiol. Premature parturition was achieved by the intra-carotid infusion of adrenocorticotrophin or prostaglandins (PGF2α, PGE2, I.C.I. 80,996) in conscious animals with indwelling catheters. I.C.I. 80,996, a potent analogue of PGF2α, induced parturition in all seven guinea-pigs treated; delivery occurred within 6 h of starting the infusion in six animals, and within 48 h in the seventh. The undesirable side-effects that accompanied treatment with PGF2α or PGE2 were not encountered with I.C.I. 80,996. Parturition induced experimentally resembled normal delivery but was not preceded by any significant change in the maternal levels of progesterone, total unconjugated oestrogens, corticosteroids, PBG or CBG in the circulation. Oxytocin was not detected until the delivery of the first foetus. Parturition was not induced by maternal or foetal injections of corticosteroids or dexamethasone. Earlier findings are confirmed that the foetal adrenal grows steadily throughout late pregnancy and, unlike the foetal lamb adrenal, undergoes no rapid phase of growth immediately before term. Foetal adrenal weight decreased relative to foetal body weight. The trigger for parturition in this species remains unidentified.

The significance of small pulses of gonadotrophin-releasing hormone

1987 ◽  
Vol 113 (3) ◽  
pp. 413-418 ◽  
Author(s):  
I. J. Clarke ◽  
J. T. Cummins
Keyword(s):  
Pulse Amplitude ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone ◽  
Series Of Experiments

ABSTRACT A series of experiments was conducted to ascertain the significance of 'small' pulses of gonadotrophin-releasing hormone (GnRH). In the first experiment, ovariectomized hypothalamo-pituitary disconnected (HPD) ewes were given 250 ng pulses of GnRH every 2 h for 1 week, 25 ng pulses every 2 h for 24 h, 25 ng pulses hourly for 24 h and then alternating hourly pulses of 25 and 250 ng. During the 25 ng pulses, LH was not detectable in plasma and FSH concentrations declined after 2 days. Following the 25 ng pulses, the resumption of 250 ng pulses led to exaggerated LH responses (mean ± s.e.m. pulse amplitude 18·7 ± 1·7 vs 10·2 ± 1·2 μg/l in the first week). In a second experiment, ovariectomized–HPD ewes were maintained on 250 ng GnRH pulses every 2 h for 1 week and were then given three 25 ng pulses mid-way between the 250 ng pulses. Samples of blood were taken over three 250 ng pulses without 25 ng insertions and over three pulses with insertions. The insertion of 25 ng GnRH pulses did not cause LH pulses in their own right and did not alter the LH responses to the 250 ng pulses. In a third experiment, 50 ng GnRH pulses were inserted between the 250 ng GnRH pulses, as in experiment 2; these 50 ng pulses caused small LH pulses and led to a reduction in the response of the LH pulse amplitude to the 250 ng pulses. The 'small' LH pulses which occurred in response to 50 ng GnRH compensated for the reduced responses to the 250 ng pulses. Hence, the integrated area under the LH curve and between successive 250 ng pulses remained the same, irrespective of the 50 ng insertions. From these data we conclude that 'small' GnRH pulses alone can sustain ongoing LH synthesis without release, leading to an accumulation of releasable LH, and that the insertion of 'small' GnRH pulses may modify the pattern of pituitary responsiveness to 'large' GnRH pulses. J. Endocr. (1987) 113, 413–418

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