Fig. 28. Diagram of the follicle-stimulating hormone (FSH) signal transduction pathway in granulosa cells of a dominant follicle. FSH interacts with a receptor protein that has seven transmembrane-spanning domains. The binding event is transduced into an intracellular signal by the heterotrimeric G proteins. The active &agr;Gstimulating (&agr;Gs -GTP) protein interacts with its effector protein, adenylate cyclase, to initiate cAMP formation. cAMP binds to and activates protein kinase A, which phosphorylates substrate proteins that stimulate transcription of the genes encoding P450AROM, 17β-hydroxysteroid dehydrogenase, and the luteinizing hormone and that activate mitosis and follicular fluid formation. (Adapted from Erickson GF: Polycystic ovary syndrome: Normal and abnormal steroidogenesis. In Schats R, Schoemaker J (eds): Ovarian Endocrinopathies: Proceedings of the 8th Reinier deGraaf Symposium. Park Ridge, NJ: Parthenon Publishing, 1994.)