Estradiol enables cortisol to act directly upon the pituitary to suppress pituitary responsiveness to GnRH in sheep

Pierce, B. N., Stackpole, C. A., Breen, K. M., Clarke, I. J., Karsch, F. J., Rivalland, E. T. A., Turner, A. I., Caddy, D. J., Wagenmaker, E. R., Oakley, A. E. and Tilbrook, A. J. 2009, Estradiol enables cortisol to act directly upon the pituitary to suppress pituitary responsiveness to GnRH in sheep, Neuroendocrinology, vol. 89, no. 1, pp. 86-97, doi: 10.1159/000151543.

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Title Estradiol enables cortisol to act directly upon the pituitary to suppress pituitary responsiveness to GnRH in sheep
Author(s) Pierce, B. N.
Stackpole, C. A.
Breen, K. M.
Clarke, I. J.
Karsch, F. J.
Rivalland, E. T. A.
Turner, A. I.ORCID iD for Turner, A. I. orcid.org/0000-0002-0682-2860
Caddy, D. J.
Wagenmaker, E. R.
Oakley, A. E.
Tilbrook, A. J.
Journal name Neuroendocrinology
Volume number 89
Issue number 1
Start page 86
End page 97
Total pages 12
Publisher S. Karger AG
Place of publication Basel, Switzerland
Publication date 2009-01
ISSN 0028-3835
1423-0194
Keyword(s) cortisol
luteinizing hormone
estradiol
hypothalamo-pituitary disconnection
Summary We have shown that cortisol infusion reduced the luteinizing hormone (LH) response to fixed hourly GnRH injections in ovariectomized ewes treated with estradiol during the non-breeding season (pituitary-clamp model). In contrast, cortisol did not affect the response to 2 hourly invariant GnRH injections in hypothalamo-pituitary disconnected ovariectomized ewes during the breeding season. To understand the differing results in these animal models and to determine if cortisol can act directly at the pituitary to suppress responsiveness to GnRH, we investigated the importance of the frequency of GnRH stimulus, the presence of estradiol and stage of the circannual breeding season. In experiment 1, during the non-breeding season, ovariectomized ewes were treated with estradiol, and pulsatile LH secretion was restored with i.v. GnRH injections either hourly or 2 hourly in the presence or absence of exogenous cortisol. Experiments 2 and 3 were conducted in hypothalamo-pituitary disconnected ovariectomized ewes in which GnRH was injected i.v. every 2 h. Experiment 2 was conducted during the non-breeding season and saline or cortisol was infused for 30 h in a cross-over design. Experiment 3 was conducted during the non-breeding and breeding seasons and saline or cortisol was infused for 30 h in the absence and presence of estradiol using a cross-over design. Samples were taken from all animals to measure plasma LH. LH pulse amplitude was reduced by cortisol in the pituitary clamp model with no difference between the hourly and 2-hourly GnRH pulse mode. In the absence of estradiol, there was no effect of cortisol on LH pulse amplitude in GnRH-replaced ovariectomized hypothalamo-pituitary disconnected ewes in either season. The LH pulse amplitude was reduced in both seasons in experiment 3 when cortisol was infused during estradiol treatment. We conclude that the ability of cortisol to reduce LH secretion does not depend upon the frequency of GnRH stimulus and that estradiol enables cortisol to act directly on the pituitary of ovariectomized hypothalamo-pituitary disconnected ewes to suppress the responsiveness to GnRH; this effect occurs in the breeding and non-breeding seasons.
Language eng
DOI 10.1159/000151543
Field of Research 110306 Endocrinology
Socio Economic Objective 970111 Expanding Knowledge in the Medical and Health Sciences
HERDC Research category C1.1 Refereed article in a scholarly journal
ERA Research output type C Journal article
HERDC collection year 2009
Copyright notice ©2009, S. Karger AG
Persistent URL http://hdl.handle.net/10536/DRO/DU:30019652

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