Inhibin is present in the corpus luteum of pseudopregnant rats and can interact with progesterone to inhibit resumption of estrous cycles.

Abstract

The corpora lutea (CL) of ovaries of adult pseudopregnant (PSP) rats were stained by immunohistochemistry for inhibin alpha subunit using sheep alpha-chain1-27 antibody as a measure of inhibin content. Staining was light in estrous cycle CL (stage III), increased in Day 2 and Day 4 PSP CL and reached maximal density on day 6 PSP when both large cells and many small cells stained. Staining was decreased in CL from 8 and 10 day PSP. Granulosa cells of growing follicles showed light stain on days 8 and 10 of PSP. Adult female rats were treated for 5 days beginning at estrous cycle Stage III (cornified masses). In Experiment 1, three groups of rats were used: 1. implanted with 30mm progesterone capsules and injected with saline, 2. implanted with 30mm progesterone capsules and injected with 10 ng rh inhibin A daily, 3. implanted with empty capsules and injected with 10 ng rh inhibin A daily. Both groups of rats with progesterone implants had significantly slower return of cycling after removal of the capsules than did the rats injected with 10ng rh inhibin A alone. In Experiment 2, the same treatments were given except that 20ng of rh inhibin A (10ng 2x/day) was given to both inhibin treatment groups. Rats treated with progesterone and 20ng inhibin had a significantly slower return of cyclic activity (4.4 days) over that found in the other two treatment groups. We conclude that the absence of cyclic activity in PSP rats is possibly due to the secretion of both inhibin and progesterone by the CL.