On the Mechanism of Prolactin Stimulation of Steroidogenesis

Abstract

Rescue of the rat corpus luteum was shown by Neill and his coworkers (1) to be prolactin (PRL) dependent. Morishige and Rothchild (2) were able to demonstrate effectively that the maintenance of pregnancy in the rat is virtually under PRL control for the first 6 days. In both instances (1,2), the PRL effect was mediated through increased secretion of luteal progesterone. Crisp has demonstrated more recently (3) that cultured rat granulosa cells, when maintained with PRL, secreted more progesterone than controls maintained in hormone-free medium. This observation was interpreted as a demonstration of the luteotropic action of PRL. In our attempts to understand the stimulatory action of PRL on luteal steroidogenesis, we have employed the technique of perifusion (continuous flow in vitro incubation) (4) together with the use of enzyme dispersed rat luteal cells taken at specific times in early pregnancy and pseudopregnancy (5-7). Our results indicate that during early pregnancy, progesterone secretion by dispersed luteal cells is stimulated most effectively by appropriate combinations of both LH and PRL (5-7). PRL alone maintained but did not stimulate progesterone secretion (5). The purpose of this presentation is to report recent findings related to PRL regulation of luteal steroidogenesis.