Hemodynamic Effects of Epinephrine and Terbutaline in Normal Man

¹ From the Jane and Edward Shapiro Pulmonary Laboratory, Division of Pulmonary Disease, Department of Internal Medicine, Mount Sinai Medical Center, Miami Beach, Fla

The hemodynamic effects in normal man of the subcutaneous administration of 0.5 mg and 0.25 mg of epinephrine, an agent which stimulates -adrenergic and β-adrenergicreceptors, and of 0.5 mg and 0.25 mg of terbutaline, an agent with a more selective β₂-adrenergic activity in isolated organ preparations, and normal saline were assessed by a double-blind study using a modified Latin-square design. Noninvasive circulatory techniques were employed because of the large number of measurements and the five-hour duration of study for each agent. Instantaneous pulmonary capillary blood flow and calf blood flow were measured. Ten normal volunteers were studied in the supine position on alternate days. After a control period of one hour, the hemodynamic effects of these agents were studied over a four-hour period. Epinephrine and terbutaline had qualitatively similar actions. In terms of quantitative hemodynamic effects, 0.25 mg of terbutaline sulfate was equivalent to 0.5 mg of epinephrine hydrochloride. Terbutaline initially appeared to stimulate both β₁-adrenergic and β₂-adrenergic receptors, as evidenced by tachycardia, increased stroke volume associated with a fall in systemic vascular resistance, and an increase in calf blood flow. One to four hours after injection, the fall in systemic vascular resistance persisted, accompanied by an increased cardiac output related solely to tachycardia, since stroke volume had reached baseline values. Indirect evidence suggested that both terbutaline and epinephrine might have produced pulmonary vasodilatation; terbutaline appeared to give a longer duration of action.