scholarly journals Central administration of corticotrophin releasing hormone but not arginine vasopressin stimulates the secretion of luteinizing hormone in rams in the presence and absence of testosterone

1999 ◽  
Vol 162 (2) ◽  
pp. 301-311 ◽  
Author(s):  
AJ Tilbrook ◽  
BJ Canny ◽  
BJ Stewart ◽  
MD Serapiglia ◽  
IJ Clarke
Keyword(s):  
Arginine Vasopressin ◽  
Testosterone Propionate ◽  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Central Administration ◽  
Releasing Hormone ◽  
Adrenal Steroid ◽  
Reproductive Axis ◽  
Cortisol Levels ◽  
Lh Secretion

This study tested the hypothesis that central administration of corticotrophin-releasing hormone (CRH) and/or arginine vasopressin (AVP) will affect the secretion of LH in rams and that testosterone is necessary for these actions to occur. Plasma LH levels were measured in castrated rams during 1 h infusion of either 100 microliter vehicle/mock cerebrospinal fluid (CSF) or mock CSF containing 25 microgram CRH, 25 microgram AVP or 25 microgram of each peptide through guide cannulae into the third cerebral ventricle. These intracerebroventricular (i.c.v.) infusions were given to the castrated rams following injections (i.m.) each 12 h of oil or 8 mg testosterone propionate for 7 days. Blood samples were collected every 10 min for 4 h before i.c.v. infusion, during infusion and for 4 h following the infusion. Infusion of vehicle did not affect any endocrine parameters. In contrast, the plasma concentrations of LH and the amplitude of LH pulses were increased significantly during and following infusion of CRH, and this effect was not influenced by whether the castrated rams were treated with testosterone propionate or whether the CRH was administered in combination with AVP. Infusion of AVP alone did not affect LH secretion. The frequency of LH pulses and the plasma concentrations of FSH did not change with any of the i.c.v. treatments. The plasma concentrations of cortisol were significantly increased by CRH and AVP infusions. The plasma concentrations of cortisol achieved during and following i.c.v. infusion of CRH and AVP combined were greater than the concentrations achieved as a result of treatment with AVP alone but were similar to those with CRH. There was no effect of testosterone propionate on cortisol levels. These results show that CRH, but not AVP, is capable of acting either centrally or at the pituitary level to increase the secretion of LH in rams and these actions are not affected by testosterone. The stimulatory effects of CRH on LH secretion are to increase the amplitude of GnRH pulses and/or the responsiveness of the pituitary to the actions of GnRH with no effect on the frequency of GnRH pulses. The secretion of FSH in rams is not influenced by either CRH or AVP. The effect of CRH to increase LH pulse amplitude occurs in the face of increased cortisol levels, further reinforcing our belief that this adrenal steroid does not affect the reproductive axis in this species.

scholarly journals Suppression of the secretion of luteinizing hormone due to isolation/restraint stress in gonadectomised rams and ewes is influenced by sex steroids

1999 ◽  
Vol 160 (3) ◽  
pp. 469-481 ◽  
Author(s):  
AJ Tilbrook ◽  
BJ Canny ◽  
MD Serapiglia ◽  
TJ Ambrose ◽  
IJ Clarke
Keyword(s):  
Sex Steroids ◽  
Restraint Stress ◽  
Testosterone Propionate ◽  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Pulse Frequency ◽  
Blood Samples ◽  
Release Device ◽  
Lh Secretion ◽  
Female Sheep

In this study we used an isolation/restraint stress to test the hypothesis that stress will affect the secretion of LH differently in gonadectomised rams and ewes treated with different combinations of sex steroids. Romney Marsh sheep were gonadectomised two weeks prior to these experiments. In the first experiment male and female sheep were treated with vehicle or different sex steroids for 7 days prior to the application of the isolation/restraint stress. Male sheep received either i.m. oil (control rams) or 6 mg testosterone propionate injections every 12 h. Female sheep were given empty s.c. implants (control ewes), or 2x1 cm s.c. implants containing oestradiol, or an intravaginal controlled internal drug release device containing 0.3 g progesterone, or the combination of oestradiol and progesterone. There were four animals in each group. On the day of application of the isolation/restraint stress, blood samples were collected every 10 min for 16 h for the subsequent measurement of plasma LH and cortisol concentrations. After 8 h the stress was applied for 4 h. Two weeks later, blood samples were collected for a further 16 h from the control rams and ewes, but on this day no stress was imposed. In the second experiment, separate control gonadectomised rams and ewes (n=4/group) were studied for 7 h on 3 consecutive days, when separate treatments were applied. On day 1, the animals received no treatment; on day 2, isolation/restraint stress was applied after 3 h; and on day 3, an i. v. injection of 2 microg/kg ACTH1-24 was given after 3 h. On each day, blood samples were collected every 10 min and the LH response to the i.v. injection of 500 ng GnRH administered after 5 h of sampling was measured. In Experiment 1, the secretion of LH was suppressed during isolation/restraint in all groups but the parameters of LH secretion (LH pulse frequency and amplitude) that were affected varied between groups. In control rams, LH pulse amplitude, and not frequency, was decreased during isolation/restraint whereas in rams treated with testosterone propionate the stressor reduced pulse frequency and not amplitude. In control ewes, isolation/restraint decreased LH pulse frequency but not amplitude. Isolation/restraint reduced both LH pulse frequency and amplitude in ewes treated with oestradiol, LH pulse frequency in ewes treated with progesterone and only LH pulse amplitude in ewes treated with both oestradiol and progesterone. There was no change in LH secretion during the day of no stress. Plasma concentrations of cortisol were higher during isolation/restraint than on the day of no stress. On the day of isolation/restraint maximal concentrations of cortisol were observed during the application of the stressor but there were no differences between groups in the magnitude of this response. In Experiment 2, isolation/restraint reduced the LH response to GnRH in rams but not ewes and ACTH reduced the LH response to GnRH both in rams and ewes. Our results show that the mechanism(s) by which isolation/restraint stress suppresses LH secretion in sheep is influenced by sex steroids. The predominance of particular sex steroids in the circulation may affect the extent to which stress inhibits the secretion of GnRH from the hypothalamus and/or the responsiveness of the pituitary gland to the actions of GnRH. There are also differences between the sexes in the effects of stress on LH secretion that are independent of the sex steroids.

Pituitary-adrenal function in the immature ovine foetus

1995 ◽  
Vol 145 (3) ◽  
pp. 455-460 ◽  
Author(s):  
A C McFarlane ◽  
S Potocnik ◽  
M Towstoless ◽  
K Moritz ◽  
E M Wintour
Keyword(s):  
Body Weight ◽  
Arginine Vasopressin ◽  
Intravenous Infusion ◽  
Adrenal Function ◽  
Short Term ◽  
Releasing Hormone ◽  
Basal Cortisol ◽  
Cortisol Levels

Abstract Pituitary-adrenal responses to intravenous infusion of ovine corticotrophin-releasing hormone (oCRH) or arginine vasopressin (AVP) and to haemorrhage were examined in the ovine foetus prior to 90 days of gestation (term 145–150 days). In chronically cannulated foetuses (n=8), between 74 and 84 days of gestation, basal ACTH levels were less than 20 pg/ml while cortisol levels were 6·5 ± 1·5 nmol/l (mean±s.e m.). Intravenous infusion of oCRH (1 μg/h for 60 min) or AVP (1 μg/h for 60 min) significantly increased ACTH (P<0·05 for both treatments) and cortisol (P<0·01 for both treatments) levels, although the response to both hormones was modest. In acutely studied foetuses of a similar age (70–90 days of gestation, mean 82·0 ± 1·4 days, n=7), exteriorization and progressive haemorrhage significantly (P<0·05) elevated ACTH levels from 117·4 ± 32·1 pg/ml to a maximal value of 329·2 ± 112·8 pg/ml, the maximal ACTH response corresponding to the removal of a volume of blood equivalent to 6·6 ±1·2% of the pre-haemorrhage body weight. The present study has demonstrated that the ovine foetal pituitary, in vivo, is responsive to exogenous and endogenous stimuli by mid-gestation and, at this age, although basal cortisol levels are low, the foetal adrenal is capable of responding to elevated ACTH levels in the short term. Journal of Endocrinology (1995) 145, 455–460

Secretion rates and short-term patterns of gonadotrophin-releasing hormone, FSH and LH in the normal stallion in the breeding season

1988 ◽  
Vol 117 (2) ◽  
pp. 197-206 ◽  
Author(s):  
C. H. G. Irvine ◽  
S. L. Alexander
Keyword(s):  
Breeding Season ◽  
Venous Blood ◽  
Pulse Amplitude ◽  
Interpulse Interval ◽  
Statistical Testing ◽  
Pulse Interval ◽  
Apparent Difference ◽  
Releasing Hormone ◽  
Gonadotrophin Releasing Hormone ◽  
Lh Secretion

ABSTRACT Pituitary venous blood was collected by a painless non-surgical cannulation method from five ambulatory stallions at 5-min intervals for 5–6 h during the breeding season. In four adult stallions, statistical analysis showed that pulses of gonadotrophin-releasing hormone (GnRH) and LH were coincident (P <0·01), as were pulses of FSH and LH (P <0·05). Furthermore, the patterns of changes in concentration of FSH and LH were highly correlated in each of the four stallions. However, seemingly ineffective pulses of GnRH were also observed, with 28% of GnRH pulses failing to induce a significant gonadotrophin pulse. In the four adult stallions the amplitude of pituitary venous gonadotrophin pulses varied markedly but no correlation with GnRH pulse amplitude was observed. Peak secretion of FSH, but not LH, during pulses was correlated with the length of the interpulse interval. Consequently, the ratio of FSH to LH during peaks was least (P <0·02) when the interpulse interval was 30 min or less. Thus, differential FSH and LH secretion was achieved within a constant steroid milieu. Two stallions had regular contact with oestrous mares, and in these horses the secretion of GnRH and gonadotrophins occurred almost continuously with rapid, rhythmic pulses superimposed upon a tonic background. Mean (± s.d.) interval between GnRH pulses was 31·4 ± 9·8 min and 27·7 ± 10·1 min. This secretory pattern was not observed in the two stallions which had infrequent contact with oestrous mares, although the small numbers precluded statistical testing of this apparent difference. No GnRH pulses were observed in one of these stallions, while in the other mean (± s.d.) GnRH pulse interval was 45·0 ± 48·7 min, the large variance being partly due to rapid pulses during a period in which the stallion teased mares. The fifth stallion was pubertal, and GnRH and LH secretion occurred in 15 and 0% of samples respectively, while low levels of FSH secretion were observed in 37% of samples and jugular testosterone levels were immeasurably low. We conclude that there is a statistically significant synchrony between pulses of GnRH, LH and FSH in the pituitary venous blood of stallions. Furthermore, decreasing intervals between gonadotrophin pulses result in a significant reduction in secretion of FSH but not LH. J. Endocr. (1988) 117, 197–206

Plasma concentrations of adrenocorticotropin-related peptides after corticotropin-releasing hormone and vasopressin injections in sheep

1988 ◽  
Vol 119 (3) ◽  
pp. 391-396 ◽  
Author(s):  
P. Pradier ◽  
M. Dalle ◽  
C. Tournaire ◽  
P. Delost
Keyword(s):  
Body Weight ◽  
Column Chromatography ◽  
Arginine Vasopressin ◽  
Plasma Concentrations ◽  
Molecular Forms ◽  
Pituitary Cells ◽  
Plasma Samples ◽  
Corticotropin Releasing Hormone ◽  
Releasing Hormone ◽  
Simultaneous Injection

Abstract. Ovine corticotropin-releasing hormone (1 μg/kg body weight) and arginine vasopressin (1 μg/kg) were injected iv in sheep, both separately and in combination. Plasma were sampled just before and 5, 15 and 30 min after the injection. Adrenocorticotropin-related peptides were isolated by Sephadex G-50 column chromatography and measured by RIA. Cortisol and aldosterone were determined on the same plasma samples. Three molecular forms of immunoreactive ACTH (IR-ACTH) were isolated: 'big' (> 20 000 mol wt), 'intermediate' (= 8000 mol wt) and 'little' (= 4500 mol wt). Following CRH injections, the three molecular forms of ACTH were enhanced, particularly the 'little' form, whereas 'intermediate' IR-ACTH was highly and specifically responsive to AVP. After a simultaneous injection of CRH and AVP, additive increases occurred for 'intermediate' and 'little' IR-ACTH. The release of different molecular forms of IR-ACTH after stimulation by CRH or AVP of corticotrope cells suggests that ACTH-related peptides could be stored in different intracellular pools or secreted by different pituitary cells.

scholarly journals Hypersecretion of corticotrophin-releasing hormone and arginine vasopressin in hypothyroid male rats as estimated with push-pull perfusion

1998 ◽  
Vol 156 (2) ◽  
pp. 395-400 ◽  
Author(s):  
A Tohei ◽  
G Watanabe ◽  
K Taya
Keyword(s):  
Drinking Water ◽  
Median Eminence ◽  
Arginine Vasopressin ◽  
Plasma Concentrations ◽  
Male Rats ◽  
Releasing Hormone ◽  
In Vivo Release ◽  
The Relationship ◽  
Acth Release

The relationship between hypothyroidism and disturbance of the hypothalamo-hypophysial-adrenal axis was investigated using adult male rats. Hypothyroidism was produced by administration of 4-methyl-2-thiouracil (thiouracil) in the drinking water for 2 weeks. Hypothyroidism decreased adrenal weights to 57% of controls and plasma concentrations of corticosterone to 48% of controls. The changes in the weight of adrenals recovered to control levels by administration of thyroxine. The pituitary responsiveness to corticotrophin-releasing hormone (CRH) and arginine vasopressin (AVP) for ACTH release markedly increased in hypothyroid rats as compared with euthyroid rats. In vivo release of CRH and AVP in median eminence significantly increased in hypothyroid rats as compared with euthyroid rats. There were no significant differences in hypothalamic concentrations of CRH and AVP. These results indicate that hypothyroidism causes adrenal dysfunction directly and results in hypersecretion of ACTH mediated by increases in synthesis of CRH and AVP in the hypothalamus.

scholarly journals Stimulation of LH secretion in sheep by central administration of corticotrophin-releasing hormone

Reproduction ◽  
1997 ◽  
Vol 111 (2) ◽  
pp. 249-257 ◽  
Author(s):  
A. Caraty ◽  
D. W. Miller ◽  
B. Delaleu ◽  
G. B. Martin
Keyword(s):  
Central Administration ◽  
Releasing Hormone ◽  
Lh Secretion ◽  
Stimulation Of

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

scholarly journals Inhibition of the secretion of LH in ovariectomised pigs by sustained but not repeated acute elevation of cortisol in the absence but not the presence of oestradiol

1999 ◽  
Vol 163 (3) ◽  
pp. 477-486 ◽  
Author(s):  
AI Turner ◽  
PH Hemsworth ◽  
BJ Canny ◽  
AJ Tilbrook
Keyword(s):  
Acute Stress ◽  
Plasma Concentrations ◽  
Pulse Amplitude ◽  
Follicular Phase ◽  
Elevated Plasma ◽  
Acute Elevation ◽  
The Mean ◽  
The Impact ◽  
Lh Secretion ◽  
Prolonged Stress

Prolonged stress is known to impair reproduction. It has been proposed that reproduction will also be impaired when a severe acute stress occurs during a period of elevated plasma concentrations of oestradiol, such as during the follicular phase of the oestrous cycle. In this experiment, we hypothesised that repeated acute and sustained elevation of cortisol would suppress the secretion of LH in ovariectomised pigs and that these effects would be enhanced in the presence of oestradiol negative feedback. Cortisol (or vehicle) was administered 12 hourly to ovariectomised pigs (n=6/treatment) for 8 days in the absence of oestradiol treatment and for a further 8 days during treatment with oestradiol. Vehicle was administered to 'control' pigs, 10 or 20 mg cortisol was administered i.v. to pigs to produce 'repeated acute' elevation of cortisol and 250 mg cortisol was administered i.m. to pigs to give a 'sustained' elevation of cortisol. Both before and during treatment with oestradiol, plasma concentrations of LH were monitored on the day before treatment, on the 4th and 8th days of treatment and following an i.v. injection of GnRH at the end of the 8th day of treatment. The repeated acute elevation of cortisol did not impair any parameters of LH secretion (i.e. mean plasma concentrations of LH, pulse amplitude or frequency, pre-LH pulse nadir or the LH response to GnRH) in the absence or in the presence of oestradiol. In contrast, when the elevation of cortisol was sustained, the mean plasma concentrations of LH and the pre-LH pulse nadir were significantly (P<0.05) lower on the 8th day of treatment than on the day before treatment and on the 4th day of treatment. Nevertheless, no other parameters of LH secretion were affected and these effects only occurred in the absence (not in the presence) of oestradiol. In conclusion, cortisol needed to be elevated for more than 4 days to impair the secretion of LH, and oestradiol did not enhance the impact of cortisol on LH secretion in ovariectomised pigs.

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