LOCALIZATION OF 2 GONADOTROPIN RECEPTORS IN THE SALMON GONAD BY IN-VITRO LIGAND AUTORADIOGRAPHY

Receptors for two salmon gonadotropins, GTH I and GTH II, were localiz ed by use of in vitro ligand autoradiography of coho salmon gonads at various stages of sexual maturation. The results in both sexes reveale d the presence of two types of GTH receptors: type I (GTH-RI), which i nteracts with both GTHs, and type II (GTH-RII), which interacts specif ically with GTH II. GTH-RI was found at all stages of spermatogenesis examined and was localized on cells that were most likely Sertoli cell s; however, it could not be determined whether GTH-RI was also localiz ed on Leydig cells. In contrast, GTH-RI was found only in Leydig cells in the testis from a spermiating fish. In the vitellogenic ovary, GTH -RI was localized in the thecal layer and intensely on granulosa cells ; in the preovulatory follicle, in contrast, GTH-RI was found in the t hecal layer and in interstitial connective tissue, but not in the gran ulosa layer. Among all the stages of oogenesis examined, only granulos a cells of the preovulatory follicle exhibited GTH-RII. The appearance of GTH-RII coincides well with the in crease in plasma levels of GTH II that occurs during final oocyte maturation and spermiation in coho salmon. The nature, distribution, and timing of appearance of these tw o receptors can explain, at least in part, the results of previous stu dies on steroidogenic activities of the two GTHs. The present study al so suggests the functional homology of salmon GTH I and GTH II to mamm alian FSH and LH, respectively, during gonadal development.