Effect of age on acute regulation of beta-adrenergic responses in mononuclear leukocytes

We studied the acute regulation of beta-adrenergic receptors and cAMP production in mononuclear leukocytes from young and old human subjects. After one hour of supine rest, healthy young and elderly subjects had similar beta-adrenergic receptor density and cAMP responses to isoproterenol. After 10 min of standing, beta-adrenergic receptor density and cAMP response increased in the young subjects. Elderly subjects had a similar increase in cAMP responses after standing, but no change in beta-adrenergic receptor density. Lymphocyte subsets and percent monocytes were not altered by age or posture, suggesting that this was not an artifact of changes in cell populations. Incubation in vitro of cells from both groups with catecholamines, at concentrations comparable to those achieved in plasma after standing, resulted in enhanced isoproterenol-mediated cAMP responses, but no change in beta-adrenergic receptor density. These data suggest that acute regulation of adrenergic signaling is affected by age, mediated in part by catecholamines, and may be relevant in the study of acute cardiovascular regulation.