Angiotensinogen expression by rat epididymis: evidence for an intrinsic, angiotensin-generating system

Previous studies have suggested the presence of an intrinsic renin-angioten sin system (RAS) in the rat epididymis with functions in epididymal activit y and sperm maturation. In the present study, the localization and expressi on of angiotensinogen, the component of the RAS which is indispensable for intracellular angiotensin generation, were investigated by immunochemistry, hybridization histochemistry and by reverse-transcriptase polymerase chain reaction (RT-PCR). Western blot analysis of protein from the epididymis co nfirmed the presence of angiotensinogen with the expected molecular mass of about 60 kDa, in agreement with results from other tissues. Immunocytochem istry showed the regional localization of immunoreactivity for angiotensino gen in the rat epididymis. In situ hybridization histochemistry further dem onstrated the expression of angiotensinogen mRNA by the epididymal epitheli um in a region-specific manner along the length of the rat epididymis. RT-P CR confirmed that the rat epididymis expresses angiotensinogen mRNA. On the other hand, mRNA of renin was not detected in the rat epididymis using Nor thern blot and RT-PCR analyses. The present study strongly supports the exi stence of an intrinsic, angiotensin-generating system based on locally form ed angiotensinogen as a precursor for angiotensin production. This epididym al RAS may have paracrine or autocrine roles in mediating the epididymal an d sperm functions. (C) 1999 Elsevier Science Ireland Ltd. All rights reserv ed.