Dynamics of testosterone secretion by the rat testis: implications for measurement of the intratesticular levels of testosterone

Abstract

ABSTRACT Testosterone concentrations have been measured in testicular interstitial fluid (IF), and in blood plasma sampled from various parts of the rat testis and spermatic cord, to assess (1) the most accurate method for determination of the intratesticular levels of testosterone, and (2) the route of secretion of testosterone from the testis. In untreated adult rats, testosterone concentrations were highest in blood collected from veins on the surface of the testis (269·50 ± 30·63 (s.e.m.) nmol/l), but were reduced by 56% on average in blood collected from veins at the proximal end of the spermatic cord (123·06±24·75 nmol/l), and were reduced considerably in peripheral venous blood (4·55 ± 0·55 nmol/l). Similar changes occurred in adult rats in which steroidogenesis was either stimulated (by treatment with human chorionic gonadotrophin; hCG) or inhibited (by treatment with aminoglutethimide; AMG), and in rats of various ages during sexual maturation. The reduction in testosterone levels during passage of blood from the testis up the spermatic cord is probably due mainly to dilution by incoming arterial blood which transfers to venous blood via anastomoses in the spermatic cord. Venous-arterial transfer of testosterone in the cord contributed to this in only a minor way. Concentrations of testosterone in testicular IF were always greater than testicular venous concentrations in control, developing and hCG-stimulated rats, but were comparable in rats treated with AMG to suppress Leydig cell steroidogenesis. These and other results demonstrate that the method of drip-collection of IF results in over-estimation of the actual intratesticular levels of testosterone. However, the present study also suggests that testicular venous blood probably provides the most accurate indication of the concentrations of testosterone in IF (and therefore in the testis) at any given time. Journal of Endocrinology (1989) 122, 323–329