ROLE FOR HYPOTHALAMIC ADRENERGIC RECEPTORS IN PREOVULATORY LH SURGE

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Coitus induces an increase in hypothalamic norepinephrine (NE) secretion that occurs several minutes prior to a preovulatory-like surge of gonadotropin-releasing hormone (GnRH)/luteinizing hormone (LH). To assess the causal relationship between NE and GnRH/LH release during coitus, we attempted to block the coitus-induced GnRH/LH surge by intrahypothalamic (ih) infusion of an `-adrenergic receptor blocker, prazosin. Intact female rabbits were subjected to push-pull perfusion for 7 h with continuous 10-min sample collections for perfusate GnRH and blood LH measurements. Mating with male partners occurred at the third hour and continuous ih prazosin was given between hours 2 and 7. Present data show that the magnitude of the coitus-induced GnRH/LH release was lower in prazosin-treated females as compared to that in the control group. However, prazosin did not completely abolish the GnRH/LH response to coitus. To this end, at least three interpretations can be offered (1) NE is not the only factor determining the coitus-induced GnRH/LH surge, (2) NE may also stimulate GnRH via `-adrenergic receptors located outside the mediobasal hypothalamus, and (3) the dosage of prazosin may be insufficient to block all `-adrenergic receptors within the mediobasal hypothalamus. We continue to explore these issues. Ultimately, the findings will aid understanding of brain functions during fertile and infertile reproductive stages.