Comparison of androgen levels in ram rete testis fluid, testicular lymph and spermatic venous blood plasma: Evidence for a regulatory mechanism in the seminiferous tubules.

Abstract

Androgen levels were measured in fluids obtained from conscious adult rams through catheters in the rete testis, testicular lymphatic ducts, and internal spermatic vein. Comparisons were made between serial samples of rete testis fluid (RTF) and testicular lymph (TL) or spermatic venous blood plasma (SV), or between TL and SV. It was found that pre-injection levels of testosterone (T), as measured by radioimmunoassay, were similar in RTF and TL, but approximately two times higher in SV. Following i.v. injection of 1 or 2 mg/ram of LH or LH plus 5 mg FSH, the distribution of androgens among testicular compartments changed drastically. There was a pronounced elevation in the concentration of T in TL and SV, but a much smaller increase in 5α-dihydrotestosterone (DHT). In contrast, the concentration in RTF of T, DHT and androgen-binding protein (ABP), as determined by polyacrylamide gel electrophoresis, changed little. The concentration of T in peripheral blood plasma (PB) was always correlated with T levels in TL or SV. Injection of FSH alone apparently did not affect androgen concentrations peripherally or the distribution of androgens between testicular compartments. Nor did FSH appear to potentiate the steroidogenic effect of LH in PB, TL or RTF. Little change in T concentrations in RTF was observed during naturally occurring episodic changes in T levels in TL or SV. These results clearly demonstrate the very stable androgen milieu in the seminiferous tubules in the face of widely fluctuating T levels in adjacent testicular compartments and point to the existence in the seminiferous tubules of a regulatory mechanism that limits access of T to the tubular lumen.