Autoradiographic localization of gonadotrophin receptors in ovaries of the common carp, Cyprinus carpio L.

Binding sites for carp gonadotrophin have been located in carp ovaries using [125I]labeled gonadotrophin and autoradiography. The radioactive gonadotrophin was displaced from tissue by unlabeled gonadotrophin or carp hypophysial homogenate in a dose-dependent fashion. No binding of gonadotrophin was found in previtellogenic oocytes but binding appeared with the first indications of vitellogenesis. In the smaller vitellogenic oocytes binding was uniformly distributed in the follicular envelope, but in the largest oocytes binding was restricted to the interstitial tissue. In these more mature oocytes gonadotrophin was also found within the oocyte and appeared to migrate toward the nucleus. The relationship between binding location, steroidogenesis, and oocyte maturation is discussed. We found no evidence for specific binding of [125I]thyroxine under comparable conditions.