Theca is the Source of Progesterone in Experimentally Induced Atretic Follicles of the Hamster1

Phenobarbital blockade of ovulation for 3 days in the proestroushamster induces atresia of preovulatory follicles. In vitro incubations of the delayed preovulatory follicles with luteinizing hormone (LH) revealed that as the follicles approach the atretic phase (Day 3 ofdelay)theylose the ability to produce androstenedione (A) and estradiol (E2) but acquire the capacity to produce large quantities of progesterone (P) (Terranova, 1981b). This shift in steroidogenesis, from E2, to P, resembles those alterations in steroidogenesis during the preovulatory period in response to the LH/follicle-stimulating hormone (FSH) surge. The aim of the present study was to determine the sourceof P in the delayed follicle by in vitro incubation of theca and granulosa, separately, and to contrastand compare steroidogenesis ofthe delayed follicle with preovulatory follicles before and after the LH/FSH surge inthehamster.IncubationofthecawithLH on proestrusand eachday of delay(Days 1-3) revealedthatthecaisa primary source of follicular A and that 2-3 days of ovulatorydelayinducesa decline in the ability of thecato produce A in vitro. Concomitant with the decline in theca A production in vitro was an increaseinthecal P production. A similar shift from A to P production by theca in vitro was observed in preovulatory follicles exposed to an endogenous LH/FSH surge.Granulosacellsfrom proestrous follicles (before the LH surge) and from delayed follicles did not accumulate P in vitro. However after the LH/FSH surge granulosa cellsfrom nondelayed proestrous follicles produced large amounts of P in vitro.Granulosa cells aromatized more A to E2 on Days 1 and 2 ofdelaythannondelayedcontrols; however,by Day 3 of delayaromatizingactivity was reduced. These results indicate that theca is the major source of P in delayed follicles approaching the atretic phase; whereasin post-LH/FSH surge follicles both theca and granulosa cells produce significant quantities of P. In addition, ovulatory delay induced a significant decline in theca A production in vitro similar to that observed in preovulatory follicles after the LH/FSH surges.