[ABP: the testicular protein that binds androgens].

ABP is a protein found in the testicular cytosol or secreted by Sertoli cells in the rete testis fluid. It has a high affinity for androgers and binds specifically 5 alpha-DHT and testosterone (but to a lesser extent). The binding capacity is saturable. ABP is measured by steady state polyacrylamide gel electrophoresis or by separation on dextran coated charcoal. ABP moves from testis to epididymis where its binding activity is totally or partially destroyed from caput to cauda epididymis. In some species (ram, bull, billy goat) but not in others (human, boar, stallion) ABP is present in the seminal plasma of the ejaculate. In some species like the rat, ABP is also secreted in the testicular blood stream by Sertoli cells through the basement membrane of the seminiferous tubules. ABP varies with age and with season. Its production is under separate endocrine control of FSH and testosterone and its transport from testis to epididymis is specifically controlled by FSH. Through its binding activity, ABP may play a role in spermatogenesis and epididymal sperm maturation by enhancing the local concentration of androgens around the germinal cells and the male gametes. However ABP is not present in some species, like the pig, although their spermatogenesis and epididymal sperm maturation are normal.