Circulatory effects of noradrenaline and adrenaline before and after labetalol.

Abstract

Two studies were carried out in the same six normal healthy males to compare the circulatory effects of exogenously infused noradrenaline and adrenaline before and after intravenous labetalol. 2 Noradrenaline before and after labetalol produced a similar pattern of circulatory change, namely dose related systolic and diastolic pressor responses accompanied by profound bradycardia and reduced cardiac output. 3 Labetalol competitively antagonized both the systolic and diastolic pressor effects of noradrenaline. 4 Adrenaline at low doses produced a diastolic depressor response accompanied by increases in heart rate and cardiac output. The highest dose also produced smaller increases in heart rate and cardiac output and diastolic pressure increased slightly. All doses provoked increases in systolic pressure.