Renin gene expression in the aging kidney: effect of sodium restriction

The activity of the renin-angiotensin system as well as the ability of the kidney to retain sodium following salt restriction are reduced with age. The relationship between these age-related changes in renal function and the renin gene expression was presently investigated. The concentrations of renin and its mRNA were measured in kidney of 10- and 30-month-old control female WAG/Rij rats and of animals which were salt restricted for 4 days. In the senescent rats, the kidney renin concentration, like the plasma concentration of angiotensin II, was half that in adult rats. The intrarenal content of renin mRNA did not differ between 10- and 30-month-old animals, suggesting that the transcriptional rate of the renin gene is unchanged with age. During the early phase of adaptation to sodium depletion, the systemic angiotensin II concentration was not modified in either age groups. Four-days salt restriction did not significantly change the renal storage of renin. In contrast, this short term salt restriction induced a 2.3-fold increase in the renin mRNA in adult kidney, and a 1.9-fold increase in the senescent kidney. These data suggest that the age-related decrease in renal concentration of renin is linked to a modification in the rate of translation of renin mRNA, or to an alteration in the protein maturation. The difference in adaptation to the early phase of salt restriction with age should not be linked to changes in renin gene transcription, but more likely to a change in the tissue response to the local renin-angiotensin system.