The effect of age on beta-adrenergic receptors and adenylate cyclase activity in rat erythrocytes.

Beta-adrenergic receptors and catecholamine-sensitive adenylate cyclase activity were studied in erythrocytes obtained from rats 6 weeks, 6 months, and 15 months of age. Intact erythrocytes from 6 week old rats contained significantly more beta receptors (411 ± 31 sites/cell) than 6 month (328 ± 21) or 15 month old rats (335 ± 16), as determined by binding of [¹²⁵I] iodohydroxybenzylpindolol. Erythrocytes from 6 week old rats also contained significantly greater isoproterenol-sensitive adenylate cyclase activity (95.0 ± 9.4pmoles/10⁹ cells) than erythrocytes from 6 month (27.9 ± 3.3) or 15 month old rats (23.7 ± 3.6). The erythrocyte population of 6 week old rats was bigger (mean corpuscular volume = 62 ± 2μ^3/cell) than the older rat erythrocytes (47 ± 1μ³ and 48 ± 1μ³). When the data were expressed relative to a unit of cell volume, there was no difference in the density of beta receptors among all three populations but a progressive and significant fall in hormone-sensitive adenylate cyclase activity. In the rat erythrocyte, the age-related loss of adenylate cyclase activity is not accompanied by changes in β-receptor density.