Estrogen induction of LH release in the rhesus monkey

Abstract

Subcutaneous injections of estradiol benzoate in oil, resulting in a sustained elevation of circulating estrogen levels, induced LH discharges markedly similar to the spontaneous preovulatory LH surges observed during the normal menstrual cycle. Exogenous estrogen leading to high plasma estrogen concentrations for brief periods (less than 12 hr) was ineffective in this regard. The discharge of LH in response to estrogen administration was observed in cycling and in ovariectomized females but not in intact males or in lactating females. It is concluded that the “trigger” for LH discharge, in the rhesus monkey, consists of an effective increment in circulating estrogen levels which must be maintained for at least 12 hr and that this positive feedback action of the steroid is clearly operative only in nonlactating adult females. © 1971 by The Endocrine Society.