A review of the haemodynamic effects of labetalol in man.

1 Labetalol at a dose of 800 to 1600 mg daily inhibited isoprenaline-induced tachycardia and phenylephrine-induced elevation in arterial pressure in hypertensive subjects. The beta-adrenoreceptor effect was four times more potent than the alpha-adrenoreceptor effect. 2 Isoprenaline-induced tachycardia was more effectively blocked than isoprenaline-induced inotropism, thereby raising the possibility of a subselective effect on cardiac beta-adrenoceptors. 3 Labetalol reduced blood pressure in hypertensive subjects with no change in cardiac output in the supine or upright position and with marked inhibition of the heart rate and blood pressure response to treadmill exercise. 4 Labetalol administered in single doses to patients with stable, treated congestive heart failure impaired blood pressure support during exercise. 5 The unique adrenoceptor and haemodynamic effects of labetalol make it a potentially attractive drug for management of hypertension and other cardiovascular disorders.