Responsiveness to beta‐adrenergic receptor stimulation: the effects of age are cardioselective.

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Abstract
1 To examine the influence of age on beta‐adrenergic receptor mechanisms, we have observed the cardiovascular, bronchial and metabolic effects of an intravenous infusion of the beta‐adrenoceptor agonist terbutaline in healthy young and elderly female subjects (mean ages 20.9 and 72.1 years respectively). 2 There was a highly significant fall in systolic blood pressure in the elderly, in contrast to the rise in systolic pressure seen in the young subjects. A similar fall in diastolic pressure occurred in both groups, indicating comparable beta‐adrenoceptor‐mediated vasodilatation. The fall in mean arterial pressure was significantly greater in the old than in the young subjects. The increase in heart rate was significantly less in the elderly. 3 Changes in plasma glucose and potassium during the infusion were similar in the two groups. 4 The observed abnormality of myocardial sensitivity to beta‐adrenergic receptor stimulation, which is not associated with a generalized blunting of beta‐adrenoceptor mediated effects, may significantly impair autonomic cardiovascular regulation in the elderly.