Intracoronary injections of salbutamol demonstrate the presence of functional beta 2-adrenoceptors in the human heart.

To demonstrate the presence of functional cardiac beta 2-adrenoceptors in man, we studied the responses to intracoronary injections of salbutamol in three groups of six patients. We injected salbutamol, a selective beta 2-adrenoceptor agonist, into the right coronary artery to avoid peripheral vasodilator action and to stimulate the sinoatrial node directly. Salbutamol injections caused a sinus tachycardia. The same doses of salbutamol injected into the aortic root caused no change in heart rate, ruling out a systemic effect. The mean dose required to cause an increase in heart rate of 30 beats/min (IHR30) was 2.6 micrograms in the first group of six patients. In 12 other patients salbutamol was given after beta-blockade to confirm the beta 2-selectivity of the responses. Doses of practolol (beta 1-selective blockade) and of propranolol (beta 1- and beta 2-blockade) that had equal beta 1-blocking activity were used. In six patients who were given practolol, the mean IHR30 dose was 2.1 micrograms. In six patients who were given propranolol, the mean IHR30 dose was significantly greater at 64 micrograms (p less than 0.001, practolol vs. propranolol). This study demonstrates that direct cardiac beta 2-adrenoceptor stimulation in man has a positive chronotropic effect.