Effects of age on cardiovascular responses to adrenaline in man

Whereas the effects of ageing on beta-receptor mediated responses have been extensively studied in vitro and in vivo using the beta-adrenoceptor agonist isoprenaline, little is known regarding ageing induced changes in responses to endogenous catecholamines. In the present study, we assessed age-related changes in cardiac responses to the endogenous beta-adrenoceptor agonist adrenaline and the influence of age-related changes in arterial baroreflex function on these responses.

Adrenaline alone was infused in 14 young subjects, age 30 +/- 2 years (eight males, six females), and 18 older subjects (six males, 12 females), age 60 +/- 2 years, and together with ganglionic blockade (trimetaphan) in seven young and 11 older subjects. Adrenaline was infused at 3-4 incremental rates, each rate for 8 min. Cardiac function was assessed by echocardiography.

Adrenaline alone, at infusion rates 20-160 ng kg-1 min-1 caused similar increases in heart rate in the two groups. In contrast, adrenaline caused larger increases in stroke volume, ejection fraction, cardiac index and systolic blood pressure and larger decreases in end-systolic wall stress and diastolic blood pressure in the young compared with older subjects. Older females exhibited the smallest increases in stroke volume index and ejection fraction. With concomitant ganglionic blockade, all above cardiovascular responses to adrenaline were similar in the young and older group. Plasma adrenaline increased similarly in the two groups.

We conclude that ganglionic blockade does not unmask an age-related decrease in cardiovascular responses to adrenaline (in contrast to isoprenaline). A concomitant ageing induced decrease in neuronal uptake (which applies to adrenaline, but not isoprenaline) may explain such a differential effect.