The influence of the infusion of noradrenaline on plasma cortisol levels in man.

1. Noradrenaline was infused into normal resting male subjects for consecutive 20 min periods at 3, 7.5 and 15 microgram min-1. At the end of the 1 hr of noradrenaline infusion, total catecholamine levels were in the range 4-6 microgram l.-1, comparable with those observed in severe exercise. 2. At all rates of infusion there were marked elevations of arterial blood pressure leading to reflex reductions of heart rate. Blood flow in the foot was reduced but blood flow in the calf was unaffected. Following the infusion, blood pressure rapidly returned to normal but the heart rate was raised by some 15 beat min-1 higher than the preinfusion control for at least 90 min. 3. Plasma cortisol tended to decrease slightly during the noradrenaline infusion but in twelve out of seventeen experiments it began to rise 30-75 min after termination of the infusion, reaching values 5-15 microgram 100 ml.-1 higher than those at the end of the noradrenaline infusion. Simultaneous rises in plasma aldosterone level were observed in those experiments in which it was measured. 4. Because of the long delay in the onset of hypercortisolaemia it is suggested that this is initiated not by the noradrenaline levels per se but by some physiological readjustments to the rapid fall in plasma noradrenaline level when the infusion was discontinued. The nature of these changes was not determined. 5. It is concluded that the elevated levels of plasma noradrenaline observed during exercise are not responsible for the synchronous increases in cortisol secretion.