1. We have studied whether the progressive rise in peripheral resistance observed in response to chronic intracoronary administration of dobutamine in conscious dogs could have resulted from extracardiac or non-β-adrenergic cardiac effects of the drug.

2. Six conscious dogs received dobutamine, 1.56 × 10−8 mol min−1 kg−1, intravenously for a 7 day period and seven conscious dogs were given dobutamine, 1.51 × 10−8 mol min−1 kg−1, into the left coronary artery under oral propranolol treatment for the same period while arterial pressure, cardiac output (electromagnetic flowmeter) and heart rate were measured.

3. Intravenous dobutamine produced no increase in arterial pressure, but a decrease in peripheral resistance and an increase in cardiac output which persisted until the end of the infusion.

4. With propranolol treatment intracoronary dobutamine induced no significant haemodynamic changes but a short-lasting increase in mean arterial pressure and peripheral resistance.

5. It is concluded that β-adrenergic cardiac effects of dobutamine are essential to the development of hypertension and increased peripheral resistance after prolonged intracoronary infusion of this drug.

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