Gonadotropic Activation of Preovulatory Synthesis and Release of Progestin in the Rabbit

Abstract

Progesterone and 20α-hydroxypregn-4-en-3-one (β⁴-3-ketopregnene-20α-ol), an active progestin closely related in structure to progesterone, were measured in New Zealand white rabbit ovaries and ovarian vein blood by physicochemical methods described in detail. Coitus or the injection of ovulatory dosages of pituitary or placental gonadotropins caused marked elevations in progestin output. Single injections of other pituitary tropins were ineffective, with the exception of growth hormone, which stimulated the output of the steroids under certain conditions. The 20α-OH steroid (20α-hydroxypregn-4-en-3-one) was produced in quantities approximately 10-fold greater than progesterone. Increased output of both steroids was attended by a rise in the progestin content of the ovaries; the output could be attributed, therefore, to increased synthesis rather than to release from a preformed store. The amounts of both progestins released could be correlated positively with the size and maturity of the ovary. Their source appears to be the ovarian interstitial tissue: ovaries lacking corpora lutea and from which follicles had been removed by cauterization released approximately as much total progestin/hr/mg tissue as control ovaries with intact follicles.