An essential role for ovarian inhibin in pineal gland-mediated anestrus in Syrian hamsters

When transferred from long photoperiod (LP) to short photoperiod (SP), female Syrian hamsters exhibit depressions of follicle stimulating hormone (FSH) and follicular development, cessation of ovulation, and marked ovarian interstitial tissue hyperplasia. Pinealectomy prevents these effects of SP. The object of this study was to determine the role of inhibin in the regulation of FSH during SP‐induced anestrus. Adult LSH/SsLak hamsters maintained in LP (LD 14: 10 hr) were transferred to SP (LD 8: 16 hr) on the day of estrus, and groups of animals killed at either 16.00 hr on proestrus or 08.00 hr on estrus during each of five consecutive 4‐day estrus cycles after transfer. Groups of females that became anestrus in SP were killed either at 08.00 or 16.00 hr, 12 days after the last observed estrus discharge. Compared to LP controls, serum FSH levels on estrus increased significantly (P