Inhibin: Evidence for Its Existence, Methods of Bioassay and Nature of the Active Material

Results are presented on the changes in serum FSH, LH and testosterone levels and in testis weight after efferent duct ligation, X‐irradiation or heating the testes, or injections of antiserum to testosterone. These results can only be explained by the existence of a feed‐back substance “inhibin”, which is produced by the seminiferous tubules and which regulates the secretion of FSH by the pituitary. Several bioassay methods have been developed for the detection of inhibin‐like activity and have been used to follow the purification of this activity, mainly from ram rete testis fluid proteins. The active material exhibits an apparent heterogeneity, with apparent molecular weights of 90 000, 20 000 and < 5000.