Differential Changes in Inhibin A, Activin A, and Totalα -Subunit Levels in Granulosa and Thecal Layers of Developing Preovulatory Follicles in the Chicken1

Accumulating evidence implicates inhibins and activins as endocrine and local regulators of follicular development in mammals, and it was recently confirmed that inhibin/activin α and βA genes are also expressed in the avian ovary. To investigate the potential involvement of these proteins in the chicken ovary, thecal and granulosa layers of the four largest follicles (F1–F4) and the most recent post-ovulatory follicle were collected from hens (10/group) killed 4, 12, and 20 h before the expected time of F1 ovulation. Inhibin A and activin A concentrations of tissue extracts (expressed per mg DNA) were measured using validated two-site enzyme-linked immunosorbent assays; total immunoreactive inhibin α-subunit (ir-α) was also measured by heterologous RIA (Monash assay). Inhibin A and ir-α were largely confined to the granulosa layer, whereas activin A was much more abundant in the thecal layer. Granulosa inhibin A contents were similar in F4 and F3, but increased approximately 40-fold from F3–F1 (P < 0.000...