Metabolism of the Corpus Luteum During Luteolysis in the Pseudopregnant Rabbit1

Abstract

A number of parameters of luteal metabolism have been measured in rabbit corpora lutea at varying times after causing luteolysis by administration of LH during pseudopregnancy. Synthesis of progestins by corpora lutea in vitro decreased to 30% of control within 16 hr, and had ceased within 36 hr post-LH. No decrease in corpus luteum weight was observed until 36 hr post-LH. Luteal cholesterol ester concentration began to increase 36 hr post-LH. No change in incorporation of ¹⁴C from ¹⁴C-acetate into cholesterol occurred within 72 hr post-LH. Incubation of corpora lutea with labeled progesterone showed that the decrease in progestin synthesis was not due to increased catabolism. Activities of luteal cholesterol side-chain cleavage enzyme, 3²-hydroxysteroid dehydrogenase and cholesterol esterase were unchanged 36 hr post-LH. The increase in luteal cholesterol ester concentration during luteolysis correlated with a slight increase (41%) in total activity of cholesterol ester synthetase 36 hr post-LH. Luteal 3²-hydroxysteroid dehydrogenase was inhibited in vitro by 20±-hydroxypregn-4-en-3-one, but the concentrationof pregnenolone in incubated corpora lutea decreasedon lysis, and it was concluded that accumulationof 20±-hydroxypregn-4-en-3-one wasnot responsible for inhibition of steroid synthesis. It is proposed that functional luteolysis precedesstructural luteolysis in the rabbit, and that itoccurs by an unknown mechanism. (Endocrinology94: 509, 1974)