Testosterone Concentrating Mechanism in the Reproductive Organs of the Male Rat

Abstract

VASOACTIVE compounds injected into the spermatic vein of the rat, at levels which are inactive peripherally, have been observed to affect lateral pressure in the spermatic artery^1–3. Tritiated water infused into the spermatic vein was found in the spermatic artery in concentrations ten times higher than those in the femoral artery². If a product of an organ were transferred, in this fashion, from the effluent to the affluent circulation, that product would concentrate in the local circulation at higher levels than in the general circulation. This type of physiological concentrator could be of great importance in maintaining the concentration of a hormone in the local circulation when the target for the hormone was part of the same organ that produced it, as with the gonads. Testosterone is secreted and utilized by the testis. In fact high levels of testosterone can maintain spermatogenesis in the absence of gonadotrophins⁴. To determine if a testosterone concentrating mechanism existed in the reproductive organs of the male rat we conducted a series of experiments to measure concentrating effects on labelled and endogenous testosterone and to determine the site and extent of testosterone transfer in the local vasculature supplying the gonads. Techniques used for cannulation of the testis blood vessels, measurement of blood flow and collection of blood samples have been described elsewhere^1–3,5.