Increase in Numbers of Gonadotropin Receptors on Granulosa Cells During Follicle Maturation

The binding of both human chorionic gonadotropin (hCG) and human luteinizing hormone (hLH) to a homogeneous population of isolated intact granulosa cells from increasingly mature porcine ovaan follicles has been studied. The number of receptor sites per granulosa cell increases 35-fold as the follicle enlarges, although cell size remains constant. This may explain the increased biologic responsiveness to gonadotropin of mature cells from large follicles. The affinity for both hormones, as determined by equilibrium dissociation constants, is high, and does not appear to change significantly as the cells mature. Comparison of dissociation constants, numbers of binding sites, and competitive inhibition between hCH and hLH, indicates that these two hormones probably interact with the same receptor on the granulosa cells.