Human seminal fluid contains significant quantities of prorenin: its correlation with the sperm density

The relevance of the tissue prorenin-renin-angiotensin system (PRAS) to male reproduction has been suggested by several investigators in the past. Although the presence of angiotensin converting enzyme in semen has been demonstrated, unequivocal evidence for the presence of prorenin and renin in the semen is not yet available. We have used a specific immunoradiometric assay based on an antibody directed against the pro-segment of the prorenin molecule to demonstrate that significant quantities of prorenin are present in human semen samples. Although semen is a rich source of proteases and protease inhibitors, the assay used by us, unlike the usual enzymatic renin assay, is not affected by such proteases, and their inhibitors. Furthermore, Western blotting data clearly demonstrated that prorenin is present in semen as a 48 kDa protein. In a majority of semen samples, the prorenin content was found to be several fold greater than that measured in EDTA-plasma samples. Interestingly, the level of prorenin was found to be directly proportional to the sperm density in semen samples. Our results suggest that seminal prorenin is produced locally within the male reproductive system, although its exact origin is yet to be defined, that a complete prorenin-renin-angiotensin system exists in human semen and that this system may be relevant to sperm function.