Differences in cardiovascular responses to isoproterenol in relation to age and exercise training in healthy men.

We conclude that there is an age-associated decline in heart rate, blood pressure, ejection fraction, and cardiac output responses to beta-adrenergic stimulation with isoproterenol in healthy men. Altered beta-adrenergic responses probably contribute to the reduced cardiac responses to maximal exercise that also occur with aging. Furthermore, intensive exercise training does not increase cardiac responses to beta-adrenergic stimulation with isoproterenol in either young or older men. The reduced beta-adrenergic response appears to be a primary age-associated change that is not caused by disease or inactivity.