Intratesticular hormone levels and the route of secretion of hormones from the testis of the rat, guinea pig, monkey and human

Abstract

Blood samples were obtained from the testes of rats, guinea pigs and Macaque monkeys and from normal men undergoing vasectomy reversal, in order to assess the comparative dynamics of hormone secretion. In each species, blood was sampled from a vein on the surface of the testis (testicular venous blood, TV), from a vein in the spermatic cord above the pampiniform plexus (spermatic venous blood, SV) and from a vein elsewhere in the body (peripheral venous blood, PV). Plasma concentrations of testosterone and inhibin were then determined by radioimmunoassay. In all species, testosterone secretion profiles were comparable, with concentrations being greatest in TV blood. SV concentrations were reduced by 40–60% compared with TV levels, with a significantly greater reduction in PV levels. Inhibin secretion varied significantly between species, with the rat being the only animal to show significant increases in inhibin concentrations from TV to SV blood. Inhibin secretion in the guinea pig was most comparable with that of the rat, although the increased SV levels fell short of being significant. Macaque and human profiles contrasted with those of the rat and guinea pig, with the greatest inhibin concentrations being found in TV blood. Levels in SV blood were reduced by some 40%, and PV levels were reduced significantly further. These differences may be due to the different position of the rete testis, and its relationship to the testicular vasculature, in these species. The sampling procedure described provides a defined set of testicular blood samples that could contribute important information of relevance to physiological and clinical studies of testicular function. Hormone concentrations in TV blood samples provide the most accurate indication of intratesticular levels, and the present study demonstrates that TV blood can be sampled with relative ease from a major vein on the surface of the human testis. The observation that testosterone and inhibin concentrations in TV blood were 10 or 250 times greater, respectively, than in PV blood in men, suggests that greater clinical use of this sampling procedure may be warranted when surgical intervention is taking place for other reasons, as this could give insight into the pathophysiology of the human testis.