Effects of Follicle-Stimulating Hormone on Inhibin Release by Different Testicular Compartments in the Adult Ram1

The aim of this study was to determine the bidirectional release of immunoreactive inhibin-α (irINH-α) by different testicular compartments in the adult ram and to assess the effects of FSH on the distribution of inhibin in the testis. Immunoreactive INH-α was measured by RIA in fluid samples collected concurrently from the three testicular compartments—the seminiferous tubules, the interstitium, and the vascular system—through catheters inserted surgically into the rete testis, testicular lymphatic duct system, and spermatic veins, respectively. Overall, the concentration of irINH-α in rete testis fluid was 25 times the level in testicular lymph and over 500 times the concentration in peripheral blood. The pattern of irINH-α concentration in rete testis fluid was inversely related to that in testicular lymph, but i.v. administration of FSH had a decoupling effect on this relationship by depressing inhibin concentration in testicular lymph without affecting inhibin levels in rete testis fluid. Nevertheless, increased flow of testicular lymph more than compensated for the transient fall in irINH-α concentration so that, overall, the total output of inhibin via the testicular lymphatic duct system (and the vascular system) increased significantly. No persistent or significant changes were observed in the flow rate of rete testis fluid or concentration of irINH-α in the fluid after administration of FSH. The time frame for the response of the testis to FSH is indicative of the involvement of a mediator. Electrophoretic analysis of serially collected testicular lymph samples consistently revealed an FSH-induced release of a series of proteins in the Mrrange of 30,000–32,000. These results point to an FSH-induced increase in vascular permeability as a major mechanism of inhibIn release by the outer compartment of the seminiferous epitheium.