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Frequent Tail-tip Blood Sampling in Mice for the Assessment of Pulsatile Luteinizing Hormone Secretion
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Does cortisol inhibit pulsatile luteinizing hormone secretion at the hypothalamic or pituitary level?
Kellie M Breen1, Fred J Karsch
1Reproductive Sciences Program, University of Michigan, 300 N. Ingalls Building, Room 1101 SW, Ann Arbor, MI 48109-0404, USA.
Endocrinology
|October 25, 2003
Summary
Cortisol elevations suppress luteinizing hormone (LH) secretion in sheep by reducing pituitary responsiveness to gonadotropin-releasing hormone (GnRH), not by decreasing GnRH release from the hypothalamus.
Area of Science:
- Neuroendocrinology
- Reproductive Physiology
- Hormonal Regulation
Background:
- Glucocorticoids, like cortisol, are known to suppress pulsatile luteinizing hormone (LH) secretion.
- The precise neuroendocrine mechanisms underlying this suppression, specifically the site of disruption, remain incompletely understood.
Purpose of the Study:
- To investigate whether elevated cortisol inhibits LH secretion by suppressing gonadotropin-releasing hormone (GnRH) release or by reducing pituitary sensitivity to GnRH.
- To elucidate the neuroendocrine mechanisms of glucocorticoid-induced disruption of reproductive hormone secretion.
Main Methods:
- Two experiments were conducted in ovariectomized ewes.
- Measurement of LH and GnRH in pituitary portal and peripheral blood following cortisol administration.
- Assessment of pituitary responsiveness to exogenous GnRH pulses during cortisol elevation.
Main Results:
- Acute cortisol elevation rapidly suppressed LH pulse amplitude within 1 hour.
- Cortisol did not affect LH pulse frequency or GnRH secretion parameters.
- Cortisol significantly inhibited GnRH-induced LH pulse amplitude, indicating reduced pituitary responsiveness.
Conclusions:
- In ovariectomized ewes, cortisol suppresses pulsatile LH secretion primarily by inhibiting pituitary responsiveness to GnRH.
- The mechanism does not involve suppression of hypothalamic GnRH release.
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