Evidence that in a physiological setting sertoli cell number is the major determinant of circulating concentrations of inhibin B in the adult male rhesus monkey (Macaca mulatta)

The relationship between changes in Sertoli cell number and function and ch anges in circulating inhibin B concentrations was investigated following un ilateral orchidectomy (UO) in the adult rhesus monkey. As expected, the 50% loss in Sertoli cells resulting from UO on day 0 was associated with a rap id and corresponding decline in plasma concentrations of inhibin B. The dec rease in inhibin B levels was sustained until the remaining testis was remo ved on day 44, at which time a compensatory 50% increase (P < 0.05) in the number of round spermatids was evident in the absence of a change in Sertol i cell number. Moreover, Sertoli cell number and inhibin B levels among ind ividual monkeys were highly correlated (r(2) = 0.65, P < 0.002). Round sper matid number and inhibin B, however, were poorly correlated (r(2) = 0.37, P < 0.04). These findings indicate that, in a physiological setting where th e negative feedback control system governing the adult primate testis is op erational, Sertoli cell number, rather than function, is the primary determ inant of circulating inhibin B levels.