Inhibin is released together with testosterone by the human testis.

The secretion of inhibin by the testis into the circulation was studied by measuring immunoreactive inhibin concentrations in spermatic vein blood samples drawn at 15 min intervals for 4 h. Mean spermatic vein inhibin levels were four times the levels in peripheral blood whereas spermatic vein testosterone (T) levels were 60-fold increased. Inhibin was released in well-defined pulses which coincided with episodes ot T release; both the duration and relative amplitude of inhibin and T pulses were similar. Inhibin pulses were undetectable in peripheral blood. These data suggest that the mechanism responsible for releasing T from the testis also stimulates inhibin release. This mechanism appears to involve LH and Leydig cells.