Inhibins and activins inhibit and activate, respectively, the secretion of follitropin by the pituitary gland. Inhibins/activins are involved in regulating a number of diverse functions such as hypothalamic and pituitary hormone secretion, gonadal hormone secretion, germ cell development and maturation, erythroid differentiation, insulin secretion, nerve cell survival, embryonic axial development or bone growth, depending on their subunit composition. Inhibins appear to oppose the functions of activins. Induces somatostatin in the ciliary ganglion neurons and may play a role in regulating neurotransmitter phenotype. Dimeric, linked by one or more disulfide bonds. Inhibin A is a dimer of alpha and beta-A. Inhibin B is a dimer of alpha and beta-B. Activin A is a homodimer of beta-A. Activin B is a homodimer of beta-B. Activin AB is a dimer of beta-A and beta-B. Ciliary ganglion neurons. Levels are higher in the choroid than the iris. Levels increase in the iris from embryonic day 9 (E9) to E16 and in the choroid, levels are high from E9 to E14 but drop at E16. Belongs to the TGF-beta family.