SOCIAL REGULATION OF REPRODUCTIVE ENDOCRINOLOGY IN FEMALE MARMOSETS

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OBJECTIVE: To identify neuroendocrine mechanisms mediating the socially-induced suppression of ovulation in subordinate female marmosets utilizing push-pull perfusion of the pituitary stalk-median eminence. RESULTS Female common marmoset reproductive capacity is regulated by social status. Socially subordinate females show no ovarian activity and have low levels of pituitary gonadotropins. We successfully developed a push-pull perfusion technique to characterize gonadotropin-releasing hormone (GnRH) release in conscious female marmosets while simultaneously sampling luteinizing hormone (LH) from an indwelling jugular catheter. Since hypothalamic GnRH stimulates the release of the pituitary gonadotropin LH, we initially hypothesized that low acyclic LH in anovulatory subordinate females resulted from suppressed or diminished GnRH release. However, after successfully completing more than 30 push-pull perfusions, however, we found (1) GnRH release is not suppressed in subordinate females, and (2) dominant (mid-follicular) and subordinate females do not differ across any of nine parameters reflecting GnRH release. This suggests that rather than a dramatic hypothalamic deficit (typically associated with hypogonadotropic anovulation), socially suppressed fertility in subordinate marmosets appears to be mediated by a novel neuroendocrine mechanism(s), perhaps at the level of the pituitary. FUTURE DIRECTIONS We plan to continue using the push-pull perfusion paradigm in studying socially suppressed fertility in subordinate female marmosets by manipulating neuroendocrine factors that may alter pituitary responsiveness to GnRH and by examining the hypothalamic-pituitary response to estradiol challenges. KEY WORDS dominance, infertility, hypothalamus, pituitary, GnRH, LH, push-pull perfusion