INCREASED C-TYPE NATRIURETIC PEPTIDE MESSENGER-RNA EXPRESSION IN THE KIDNEY OF DIABETIC RATS

To investigate the responsiveness of renal-synthesized C-type natriure tic peptide (CNP) to changes in water and electrolyte balance, we meas ured renal CNP mRNA levels, plasma CNP concentrations and urinary CNP excretion rates in streptozotocin-induced diabetic rats eating a norma l (0.26% NaCl) or low (0.04% NaCl) salt diet. Using reverse transcript ion-PCR followed by Southern blot analysis, we found that renal cortic al and medullary CNP mRNA levels were markedly enhanced in diabetic ra ts from the 14th day and remained enhanced with an accompanying elevat ion of urinary CNP excretion rates for the entire 60-day study period. All increases of renal CNP mRNA and urinary CNP excretion rates in di abetic rats were attenuated in low salt diet-treated diabetic rats as well as insulin-treated diabetic rats. These results demonstrate that renal CNP synthesis is enhanced in diabetic rats and the increase of r enal CNP mRNA is ameliorated by salt restriction and insulin treatment . These results imply that renal-synthesized CNP is responsive to the alteration of water and electrolyte homeostasis in diabetic rats.