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 wi th age. The relationship between these age-related changes in renal fu nction and the renin gene expression was presently investigated. The c oncentrations 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 sa lt restricted for 4 days. In the senescent rats, the kidney renin conc entration, like the plasma concentration of angiotensin II, was half t hat in adult rats. The intrarenal content of renin mRNA did not differ between 10- and 30-month-old animals, suggesting that the transcripti onal rate of the renin gene is unchanged with age. During the early ph ase of adaptation to sodium depletion, the systemic angiotensin II con centration was not modified in either age groups. Four-days salt restr iction did not significantly change the renal storage of renin. In con trast, 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 senesc ent kidney. These data suggest that the age-related decrease in renal concentration of renin is linked to a modification in the rate of tran slation of renin mRNA, or to an alteration in the protein maturation. The difference in adaptation to the early phase of salt restriction wi th age should not be linked to changes in renin gene transcription, bu t more likely to a change in the tissue response to the local renin-an giotensin system.