INTRATESTICULAR HORMONE LEVELS AND THE ROUTE OF SECRETION OF HORMONESFROM THE TESTIS OF THE RAT, GUINEA-PIG, MONKEY AND HUMAN

Blood samples were obtained from the testes of rats, guinea pigs and M acaque monkeys and from normal men undergoing vasectomy reversal, in o rder to assess the comparative dynamics of hormone secretion. In each species, blood was sampled from a vein on the surface of the testis (t esticular venous blood, TV), from a vein in the spermatic cord above t he pampiniform plexus (spermatic venous blood, SV) and from a vein els ewhere in the body (peripheral venous blood, PV). Plasma concentration s of testosterone and inhibin were then determined by radioimmunoassay . In all species, testosterone secretion profiles were comparable, wit h concentrations being greatest in TV blood. SV concentrations were re duced 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 incre ases in inhibin concentrations from TV to SV blood. Inhibin secretion in the guinea pig was most comparable with that of the rat, although t he increased SV levels fell short of being significant. Macaque and hu man 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 significan tly 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 inform ation 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 ma jor vein on the surface of the human testis. The observation that test osterone and inhibin concentrations in TV blood were 10 or 250 times g reater, respectively, than in PV blood in men, suggests that greater c linical use of this sampling procedure may be warranted when surgical intervention is taking place for other reasons, as this could give ins ight into the pathophysiology of the human testis.