Effect of age and posture on human lymphocyte adenylate cyclase activity

1. A number of age-related changes have been reported in the catecholamine-adrenoceptor-adenylate cyclase system. Most of the data available on these alterations come from resting subjects; the response to acute stress may provide additional insights into the age effect on these responses. 2. We measured supine and 10 min upright plasma noradrenaline and lymphocyte adenylate cyclase activity in ten healthy elderly subjects (age 66-80 years) and seven healthy young subjects (age 27-34 years). 3. Isoprenaline stimulation of lymphocyte adenylate cyclase activity was not significantly different between supine and upright positions or between elderly and young subjects. There was a marked increase in forskolin-stimulated adenylate cyclase activity in the upright posture in both elderly and young subjects. The increment over supine levels was 70% in the elderly (P less than 0.025) and 73% in the young (P less than 0.05). This enhanced forskolin activity was not seen in two young subjects who became syncopal. 4. These data suggest that enhanced forskolin-stimulated adenylate cyclase activity occurs after 10 min of upright posture in both elderly and young subjects, and may be relevant to immediate blood pressure regulation. We were unable to demonstrate any age-related differences in these acute adrenergic responses.