Immunocytochemical localization of renin in the developing ovine fetus

The ontogeny of renin distribution in the outer cortical segments was studied by immunocytochemistry in two groups of ovine fetal kidneys; one set of fetal kidneys was obtained at 104-106 days (0.73 gestation, n = 6), and the other at 138-140 days (0.96 gestation, n = 6). Similar studies were performed in kidneys obtained from a lamb (2 weeks old) and from non-pregnant adult sheep, n = 4. Using rabbit anti-mouse renin antiserum that was proven to cross react with sheep renin and 0.033% 3',3'-diamino benzidine tetrachloride as a chromogen, immunoreactivity was found to be localized in the classical juxtaglomerular apparatus and the afferent arteriole in the immature fetuses, newborn lamb and adult sheep. In the mature fetuses a more extensive distribution was noted. Immunoreactivity was found in the afferent arteriole and the juxtaglomerular apparatus as well as other segments of the arterial vascular tree. These findings suggest that renal renin distribution in the lamb fetus is developmentally regulated. The results also correlate well with reports about renal cortical renin content and plasma renin activity at the stages studied. These observations further support the hypothesis that increased renal renin expression occurs in the fetus just prior to birth.