Metabolic heat production and cardiovascular responses to an incremental intravenous infusion of adrenaline in healthy subjects

Abstract

Increased circulating adrenaline causes a rise in metabolic heat production and well characterized cardiovascular changes. To further characterize these responses we measured metabolic heat production and cardiovascular responses during an incremental infusion of adrenaline (A) in ten healthy subjects (five male; aged 21 to 27 years) and in a placebo controlled (C) study. Plasma adrenaline was unchanged during C, but increased during A (baseline 0.2 nmol/l and low, intermediate and high dose 1.0, 1.9 and 3.1 nmol/l respectively). There was a stepwise increase in metabolic heat production during A (from baseline +0.19, +0.51 and +0.77 kJ/min) with a fall during C (-0.25 kJ/min). During high dose A, plasma adrenaline correlated with increments in metabolic heat production (p < 0.05). Heart rate increased (p < 0.01) and diastolic blood pressure decreased (p < 0.01) at low dose A, and systolic blood pressure increased during intermediate dose A (p < 0.01). Forearm blood flow increased during A and C, with a greater increase in the former during high dose A (p < 0.01). Toe blood flow and toe pulp blood velocity decreased during high dose A (p < 0.05), whereas, skin capillary blood velocity increased at low (p < 0.05) and fell at high (p < 0.01) dose A. In summary, adrenaline increases metabolic heat production and limb blood flow in a dose-dependent fashion. A small increment in plasma adrenaline causes a rise in skin capillary blood flow; and at higher plasma levels blood flow in skin capillaries and arteriovenous anastomoses falls.