REGULATION OF GLOMERULAR AND PROXIMAL TUBULE RENIN MESSENGER-RNA BY CHRONIC CHANGES IN DIETARY NACL

Renal adaptations to chronic changes in dietary NaCl and extracellular fluid volume involve both glomerular and tubular mechanisms that resu lt in preservation of glomerular filtration rate and modifications of renal tubular transport to secure external NaCl balance. Although the systemic renin-angiotensin system (RAS) mediates some of these respons es, the possible contributions of local glomerular and proximal tubule RASs in these adaptations have not been examined. Thus, in this study , glomeruli and proximal tubules were microdissected from rats adapted to high (4.0%)-, normal (0.5%), or low (0.01%)-NaCl diets, and renin mRNA was measured using quantitative competitive reverse transcription -polymerase chain reaction. After 4 days of the diets, glomerular reni n mRNA abundance was increased 100% by the low-NaCl diet (P < 0.05) an d suppressed 50% (P < 0.01) by the high-NaCl diet compared with contro ls. Renin mRNA in proximal tubules was stimulated 230% (P < 0.05) by t he low-NaCl diet and tended to be suppressed (68% decrease, not signif icant) by the high-NaCl diet. When the high-NaCl diet was continued fo r 2 wk, proximal tubule renin mRNA was suppressed by 89% (P < 0.05). T his study provides evidence that glomerular and proximal tubule renin transcript levels are regulated by chronic changes in dietary NaCl, su ggesting that local RASs contribute to the renal adaptations in respon se to chronic alterations in NaCl.