Degradation of human choriogonadotropin in preovulatory rat granulosa cells and in follicular fluid.

The catabolism of human choriogonadotropin (hCG) in rat preovulatory granulosa cells and follicular fluid was studied in order to elucidate the mechanisms responsible for the removal of receptor-hCG complexes. Rats pretreated with pregnant mare serum gonadotropin (PMSG) were injected i.v. with 125I-labelled hCG with or without unlabelled hCG a few hours before the surge of endogenous preovulatory gonadotropin. The radioactive components of granulosa cells and of follicular fluid were characterized by filtration through Sepharose-6B gel. Granulosa cells catabolized receptor-bound 125I-hCG to hormone sub-units; however, the rate of catabolism in vivo was relatively slow. Receptor-125I-hCG complex also appeared in the follicular fluid. Binding of 125I-labelled hCG to receptor molecules of follicular fluid in vivo was time-dependent and it was inhibited by smaller amounts of unlabelled hCG than the binding, in vivo, of 125I-labelled hCG to the receptors of granulosa cells. Both follicular fluid and granulosa cell homogenate, in vitro, catabolized 125I-labelled hCG to hormone sub-units.