INHIBIN AND STEROID-RESPONSES TO TESTICULAR STIMULATION IN NORMAL MEN

Static measurements of immunoreactive inhibin have proved to be of lit tle relevance in the diagnosis of testicular disorders, To explore whe ther a dynamic evaluation of inhibin secretion might yield a more usef ul parameter of testicular function we compared the responses of inhib in with steroids to i.v. injections of pure follicle-stimulating hormo ne (FSH; 300 IU) or human chorionic gonadotrophin (HCG; 1500 IU) and o ral administration of the antioestrogen Tamoxifen (20 mg/day for 7 day s) in four normal fertile men, Blood was aspirated between 1 and 72 h after the injections and daily during Tamoxifen intake. Four controls were injected with physiological saline solution, An additional four m en were injected with pure FSH, and blood was taken after 24, 48 and 7 2 h, Injection of FSH was accompanied by nycthemeral variations of tes tosterone comparable with those observed in the controls. The concentr ation of inhibin showed similar nycthemeral variations but a significa nt increase was observed in all eight cases at 12 noon on days 2 and 3 after FSH injection, HCG injection resulted in the expected biphasic. response of testosterone, Inhibin displayed a pronounced increase 18 h after injection but the delayed response after 48 and 72 h was not o bserved. Tamoxifen intake increased testosterone but not inhibin, and caused a moderate and temporary increase of luteinizing hormone and FS H It was concluded that primary stimulation both of Leydig cells by HC G and Sertoli cells by FSH increase circulating inhibin. Comparison wi th the testosterone response suggests that the inhibin peak 18 h after BCG administration may reflect Leydig cell function, and that the del ayed response 48 and 72 h after FSH administration can be used as a pa rameter of Sertoli cell function.