Increased angiotensin II receptor binding with age in isolated rat glomeruli

The current investigation was performed to determine whether there are changes in the renin-angiotensin system with increasing age in rats. Experiments were performed on male Sprague-Dawley rats (50 to 165 days old). There were no changes in plasma renin activity or angiotensin II concentrations, but the number of angiotensin II binding sites in isolated glomeruli increased with increasing age (r = 0.87, P less than 0.01). Since rat weight varies directly with age, we studied the possibility that the increase in receptor number was due to changes in glomerular morphometrics. In a separate group of experiments the diameter of isolated glomeruli was measured, and assuming spherical shape, glomerular volume and surface area were calculated. Glomerular diameter increased with age and weight of the rats (r = 0.99, P less than 0.001). There was a strong linear correlation between the changes in angiotensin II receptor number and glomerular surface area (r = 0.99, P less than 0.001). The number of receptors per unit surface area was independent of rat weight or age (1224 receptors/micron 2). To test the hypothesis that the apparent increase in glomerular angiotensin II receptor sites with increasing age was due to the shape of the glomerulus, additional binding studies were performed on membranes prepared from isolated glomeruli. There were no differences in the number of angiotensin II receptors in membranes from 63 and 112 day-old rats (888 +/- 115 vs. 925 +/- 128 fmol/mg). In additional experiments the effects of increasing age on angiotensin modulation of renal function were studied.(ABSTRACT TRUNCATED AT 250 WORDS)