INTRALUMINAL ANDROGEN BINDING-PROTEIN ALTERS H-3 ANDROGEN UPTAKE BY RAT EPIDIDYMAL TUBULES INVITRO

Previous experiments have shown that androgen binding protein (ABP) and androgens exist in high concentrations in the tissue and the lumen of the rat caput epididymis. The present experiments were performed to determine whether or not intraluminal APB affects tubule net uptake of androgens. Caput epididymal tubules were dissected into 2-cm segments, subjected to microperfusion into the tubule lumen, and incubated for 2.5 h in 35°C minimum essential medium (MEM) containing 2.0 ng tritiated testosterone (3H-T) per ml. 14C-polyethylene glycol [PEG] was included as a contamination marker. In the first series of experiments, caput tubules were perfused with a control, artificial perfusion (MKB) containing no ABP or fresh rat rete testis fluid (RTF), which is known to contain ABP. Tubules incubated while containing RTF took up 138% of the tritiated androgens taken up by control tubules. In the second series of experiments, tubules were perfused with fresh caput epididymal lumen content, MKB alone, MKB containing either 5.0 ng purified rat ABP/μl or 50 ng ABP/μl. Tubules incubated while containing perfused MKB took up only 47% of the tritiated androgens taken up by tubules containing perfused native lumen content. Increasing intraluminal ABP concentrations in the MKB medium increased 3H-androgen uptake in a stepwise fashion. Intraluminal ABP at a concentration of 50 ng/μl was associated with a 71% return of 3H-androgen uptake towards that amount of 3H-androgen taken up by tubules perfused with native lument content. Intraluminal ABP enhances net androgen uptake by caput epididymal tubules from their surrounding medium in vitro.