Initiation of Luteinization in Rabbit Graafian Follicles by DibutyrylCyclic AMPin Vitro12

We have used the technique of follicle incubation and autotransplantation to study the effects of cyclic AMP on the initiation of luteinization. Graafian follicles from estrous rabbits were everted to expose the granulosa cells to the incubation medium and incubated for 3 hr in Krebs-Ringer bicarbonate buffer plus glucose (KRB) either alone or with 10 ¼g/ml NIH-LH-S14, 8 or 12 mM cyclic AMP plus 1 mM theophylline, or 8 mM dibutyryl cyclic AMP (dbcAMP). Everted follicles incubated with KRB alone did not luteinize when autotransplanted beneath the kidney capsule althoughthe ovum was removed by this procedure. Follicles also failed to luteinize when incubated with cAMP plus theophylline. However, autotransplanted follicles which had been previously incubated with either LH or dbcAMP developed into corpora lutea as determined at laparotomy 7 and 12 days later. The incidence of luteinization was 67% and 63% forfollicles incubated with LH and dbcAMP respectively, and the ectopic corpora lutea initiated by these treatments were very similar in macroscopic and in histological appearances. On day 12, corpora lutea from several rabbits were removed from the kidney surface and incubated for 3 hr with 14C-pregnenolone. The formation of 14C-progesterone was quantitatively similar in both LH- and dbcAMP-initiated corpora lutea, indicating similarity in the activities of Δ5, 3β-hydroxysteroid dehydrogenase. This study demonstrates that removal of theovum is not sufficient in this system for the initiation of luteinization and supports the hypothesis that cAMP is a second messenger for LH in the process of luteinization.(Endocrinology95: 253, 1974)