Circulating adrenaline and blood pressure: the metabolic effects and kinetics of infused adrenaline in man

Abstract

Six normotensive volunteers were infused with L-adrenaline [epinephrine, A] at 0.01, 0.03, 0.05, 0.075 and 0.10 .mu.g/kg per min; each increment lasted 10 min. Plasma A rose from 0.27 to 4.61 nmol/l, and there were dose-related increases in plasma renin activity, blood glucose, plasma cAMP and plasma free fatty acids, but not in plasma noradrenaline [norepinephrine, NA] and cGMP. Levels of circulating A previously noted in essential hypertensives had minimal cardiovascular effects. The secretion rate of A and its rate of clearance from the circulation were calculated from plasma samples taken during an hour-long infusion (0.083 .+-. 0.006 .mu.g/kg per min) of L-A in the same individuals. The secretion rate ranged from 1.40-6.01 nmol/min with a mean (.+-. SEM [SE of mean], 6) of 2.82 .+-. 0.76 nmol/min. Mean clearance (.+-. SEM, 6) was 9.41 .+-. 1.371/min and ranged from 4.86-14.61 l/min. The decline of plasma A following the infusion was biexponential. Plasma A is unlikely to be of primary importance in the elevation of blood pressure, either directly, via renin release or by NA release via presynaptic .beta.-receptors. Variation in clearance between subjects limits the use of plasma levels as an interindividual index of adrenal release of A. The relationship between sympathoadrenal activity and plasma A may be further perturbed by equilibration between the circulation and sites of tissue uptake. The lower levels of plasma A than of NA appear to be due to a slower rate of secretion and a higher rate of clearance from the circulation.