The haemodynamic effects of labetalol under conditions of increased levels of circulating catecholamines.

Adrenaline was infused into normal volunteers to produce plasma adrenaline levels similar to those found in acute myocardial infarction. These infusions were performed after pretreatment with labetalol or placebo. Adrenaline produced an increase in systolic blood pressure, a decrease in diastolic blood pressure and an increase in heart rate. All of these haemodynamic effects were blocked by labetalol. In particular, no increase in diastolic blood pressure was seen as occurs during increased sympatho-adrenal activity in the presence of non-sensitive beta-blockade. Thus labetalol maintains a different haemodynamic profile from non-selective beta-blockade during increased sympatho-adrenal activity.