Nonproportional changes in plasma renin concentration, renal renin content, and rat renin messenger RNA

The expression of the renin gene in rat kidneys was studied using mouse submaxillary gland renin complementary DNA. The length of rat renin messenger RNA (mRNA) was approximately 1600 nucleotides, similar to that of mouse submaxillary gland and kidney renin mRNA. Rat renin mRNA was quantified by a radiodensitometric complementary DNA hybridization assay. The effects of intense long-term stimulation and short-term inhibition of renin secretion on plasma renin concentration, renal renin concentration, and renin mRNA content were compared with those of controls. After 15 days of sodium depletion and captopril treatment, plasma renin concentration increased 46-fold, renal renin concentration only 1.5-fold, and renin mRNA content increased about threefold. Following a 1-hour infusion of angiotensin II in sodium-depleted and captopril-treated rats, plasma renin concentration decreased by 84% whereas no significant changes in either renal renin concentration or renin mRNA content were observed. These results show that sodium depletion and captopril treatment increase the level of renin gene transcription and renin biosynthesis. However, there are nonproportional changes in plasma renin levels, renal renin content, and its mRNA. These results suggest that newly synthesized renin is not stored in the kidney but is rapidly secreted into the blood. Short-term inhibition of plasma renin concentration by angiotensin II is most likely mediated by posttranslational mechanisms.