Autoradiographic localization of specifically bound 125I-labeled follicle-stimulating hormone on spermatogonia of the rat testis.

In a previous study, we used autoradiography to demonstrate specific FSH-binding sites on Sertoli plasma membranes in the basal compartment of rat seminiferous tubules. The present study was undertaken to determine whether spermatogonia in the rat testis also possess FSH-binding sites. Approximately 1 Mg [l25I]hFSH was administered as an intratesticular injection to 40-day-old rats that had been hypophysectomized 10 days earlier; a second group of rats received a 500-fold excess of cold hormone along with the [I25I]- hFSH, and served as a control for specificity of binding. Subsequently, all testes were perfused with a hyperosmotic fixative, which produces preferential shrinkage of spermatogonia and Sertoli cells in the basal compartment. The resulting separation of the cells from one another allowed us to determine whether spermatogonia were the source of any autoradiographic grains. In the absence of excess cold hormone, some grains were clearly localized to spermatogonial surfaces, although the majorit...