RENIN AND RENIN MESSENGER-RNA IN PROXIMAL TUBULES OF THE RAT-KIDNEY

The present study was undertaken to assess the presence of renin enzym atic activity and renin mRNA in proximal tubules of rat kidneys, and t o determine the effect of converting enzyme inhibition (CEI) on proxim al tubule renin gene expression. Proximal convoluted tubules (PCT), pr oximal straight tubules (PST), outer medullary collecting ducts (OMCD) , and glomeruli (Gloms) were isolated by microdissection. Renin activi ty was measured in sonicated segments by radioimmunoassay. Renin mRNA levels were assessed using a quantitative PCR. Renin activity in PCT a veraged 51+/-15 mu GU/mm compared to 405+/-120 mu GU/ glomerulus. No m easurable renin activity was found in PST and OMCD. Renin activity in both glomeruli and tubules had the same pH optimum, between 7.0 and 7. 5, Renin mRNA was consistently detectable in cDNA prepared from PCT an d PST, although its abundance per mm tubule was about 1/500th that fou nd in one glomerulus. Renin mRNA was not detectable in OMCD. Tubular r enin PCR product identity was confirmed by restriction digestion. CEI administration increased glomerular renin activity and renin mRNA, but not proximal tubular renin. The absence of a stimulatory effect of CE I on proximal tubule renin gene expression suggests the operation of d ifferent intracellular signals in control of renin synthesis in the pr oximal tubule than in the vascular compartment.