ABSTRACT
Monolayer cell cultures formed from the rat cauda epididymidis exhibited renin-like and angiotensin-converting enzyme (ACE) activities and contained immunoreactive angiotensin I (AI) and angiotensin II (AII). Renin-like activity, determined indirectly by radioimmunoassay of generated AI at a near-neutral pH of 6·0, was demonstrated in the cell lysate but was almost undetectable in the serum-free cell culture medium, suggesting that renin expression in epididymal cells is an intracellular phenomenon. In contrast, both AI and AII were detected in the cell lysate and cell culture medium. The level of AI was enhanced by pretreating the cells with the ACE inhibitor captopril (100 nmol/l). Incubating the cell monolayers with thoroughly washed sperm cells obtained from the intact cauda epididymides of rats increase (P < 0·01) the AII content of the cell culture medium, with a parallel decline (P < 0·01) in the AI concentration. However, adrenaline (0·23 μmol/l), which was found to stimulate electrogenic anion secretion by cell monolayers grown on pervious supports, was without effect on the renin-like activity or concentration of angiotensins.
The ACE activity in cells was confirmed by its strong dependence on chloride ion and its susceptibility to inhibition by captopril (100 nmol/l). Enzyme activity was significantly (P < 0·005) higher in the culture medium than in the cell lysate and cell membrane fragments. Angiotensinogen, which is obligatory for an intrinsic renin-angiotensin system, is present in epididymal cells. Presumably, it is synthesized and processed in the cell cytosol by intracellular renin.
These findings in cultured cells provide further evidence for a local renin–angiotensin system in epididymal tissue and suggest a possible role of endogenous AII in the regulation of epididymal function.
Journal of Endocrinology (1991) 131, 287–293
