Regulation of ovarian cholesterol esters: Evidence for the enzymatic sites of prostaglandin‐induced loss of corpus luteum function

The regulation of cholesterol ester synthetase and cholesterol esterase by prostaglandins and gonadotrophins in luteinized ovaries of the rat was studied. Prostaglandin F2α (PGF2α) depressed ovarian cholesterol esters by 75% (p<.025) within 48 hr. Hypophysectomy (APX) produced a similar effect; prolactin administration to this group maintained cholesterol esters at a higher level than in the APX group but the trophic effect of prolactin was abolished by simultaneous PGF2α treatment. Progesterone output in incubated ovarian slices was reduced 50% by PGF2α treatment in vivo (p<.005), an effect similar to that produced by APX. Prolactin administration in vivo maintained the ability of the incubated tissue to synthesize progesterone at an elevated rate in APX rats but simultaneous PGF2α treatment abolished this action of prolactin. Cholesterol ester synthetase activity was severely depressed (p<.005) by PGF2α treatment to animals with intact pituitaries, a decrease similar to that produced by APX alone. The effect of APX on synthetase activity was reversed by prolactin treatment but not when PGF2α was administered with prolactin. Esterase activity, also maintained by prolactin in APX animals (p<.005), was not affected to the same extent by PGF2α although a decrease in activity was produced in both the intact and the APX+ prolactin group by PGF2α (p<.10). However simultaneous administration of luteinizing hormone (LH) reversed the effect of PGF2α in the APX+ prolactin +PGF2α group on esterase activity. These data indicate that the luteolytic action of PGF2α is directly on the corpus luteum and this action appears to be mediated by a neutralization of prolactin activity. The loss in synthetase activity and to some extent in esterase activity, induced by PGF2α depressed ovarian cholesterol ester turnover and the availability of cholesterol for conversion to progesterone.