Follicle size class contributes to distinct secretion patterns of inhibin isoforms during the rat estrous cycle

The differential production of inhibins must be exquisitely controlled at the cellular level to ensure the secretion of the appropriate ligand at specific times during the reproductive cycle. The mechanisms underlying inhibin dimer assembly, processing and secretion are not well understood. Here we verify that the secretion of inhibin A and inhibin B from the granulosa cell is discordant during the estrous cycle: discordant production or secretion of the inhibins was not observed during the pregnant mare serum gonadotropin-induced cycle. We correlated the discordant production and secretion of inhibin A and inhibin B into the serum with distinct patterns of inhibin alpha- and beta-subunit colocalization during the cycle in granulosa cells. We determined that the discordant pattern of inhibin A and inhibin B during the rat estrous cycle is due to independent populations of antral follicles making inhibin B (small antral follicles) or inhibin A (large antral follicles).