A high-affinity androgen-binding protein (ABP) in rat testis: evidence for secretion into efferent duct fluid and absorption by epididymis.

An androgen-binding protein (ABP) was detected in 105,000 × g supernatants of rat testis homogenates after removal of endogenous steroids by charcoal extraction. The ABP was identical to that previously demonstrated in highspeed supernatants of epididymis homogenates. When the exocrine secretion of the testis was blocked by ligation of efferent ducts, ABP increased in testis supernatant in proportion to the retention of testicular fluid while at the same time it disappeared from epididymis supernatant, first from the caput and later from the cauda. Treatment with large doses of testosterone did not alter the disappearance from epididymis. ABP disappeared almost completely from caput supernatant within three days after efferent duct ligation. When efferent ducts and corpus epididymidis were ligated simultaneously to block the flow of luminal fluid into and out of the caput, the disappearance of ABP from caput supernatant was only partially prevented. This finding suggested that a major portion of ABP is ei...