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; o ne set of fetal kidneys was obtained at 104-105 days (0.73 gestation, n=6), and the other at 138-140 days (0.96 gestation, n=6). Similar stu dies were performed in kidneys obtained from a lamb (2 weeks old) and from non- pregnant adult sheep, n=4. Using rabbit anti-mouse renin ant iserum 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 juxtaglo merular apparatus as well as other segments of the arterial vascular t ree. These findings suggest that renal renin distribution in the lamb fetus is developmentally regulated. The results also correlate well wi th reports about renal cortical renin content and plasma renin activit y at the stages studied. These observations further support the hypoth esis that increased renal renin expression occurs in the fetus just pr ior to birth.