Inverse Regulation of Endothelin-1 and Nitric Oxide Metabolites in Tissue with Aging

Aging is an independent risk factor for cardiovascular and renal disease. The study reported here investigated whether aging affects endothelin-1 (ET-1) and tissue levels of the nitric oxide metabolites nitrite/nitrate in the kidney of rodents. Blood pressure was measured by the tail-cuff method, ET-1 protein was determined by radioimmunoassay/high-performance liquid chromatography (RIA/HPLC) and nitrite/nitrate was measured by ion-pairing chromatography. Compared to young male Wistar Kyoto rats (3 months of age), renal ET-1 protein levels in whole kidneys increased 3.6-fold at 24 months of age (from 70 +/- 9 to 253 +/- 43 pg/g tissue, p < 0.05, n = 6 each group). Similarly, renal ET-1 protein increased 1.7-fold in 18-month-old C57BL/6J mice as compared to 8-month-old adult animals (from 188 +/- 18 to 319 +/- 14 pg/g tissue, p < 0.05, n = 5-7). In female RoRo-Wistar rats (6, 18 and 33 months of age), tissue nitrite/nitrate levels in whole kidneys decreased with increasing age (from 232 +/- 25 to 130 +/- 6 micromol/l/g tissue, p < 0.05). Thus, aging in healthy rodents is associated with a marked upregulation of renal ET-1 protein content and a decrease in tissue nitrite/nitrate levels in whole kidneys, independent of blood pressure. Activation of the ET pathway with aging may promote the development of age-dependent diseases such as glomerulosclerosis, hypertension and atherosclerosis.