Recent approaches on the renin-angiotensin system in male reproduction

Abstract

The renin-angiotensin system, a complex biological system which is well known in the regulation of blood pressure has indeed multiple interaction with other regulatory system. Recently, several findings have also pointed to a possible involvement of this system in male reproductive function. High amounts of angiotensin converting enzyme (ACE), the main regulatory enzyme of this system, do not only occure within the human lung and kidney, but also in the male genital tract. In man, ACE occurs in two structurally dissimilar isoenzymes, a testicular and a serum form. Testicular ACE represents the C-terminal half of the lung enzyme with a molecular mass of 80 kDa and 701 amino acid residues. Testicular ACE is the product of a testis specific in RNA and is hormonally regulated depending on androgen. While ACE has been completely Characterized biochemically, its biological role is still unknown. In the rat, the highest ACE activities are found in the restis and epididymis. Increasing concentrations are observed from the caput to the cauda epidymis. However, differences seem to exist among various species, with highest ACE level in the mous testis and epididymis, lowest level in buffallo and rabbit. The observed gradient of ACE concentrations within the epididymis indicates that ACE may play a certain role in sperm maturation. Testicular ACE seems to be associated with membranes of spermatocytes. Studies of cattle semen demonstrtated that ACE is released from spermatozoa during incubation in capacitation medium.