Selective beta 1-adrenoceptor blockade and muscle thermogenesis.

Abstract

Muscle thermogenesis was measured by direct microcalorimetry in hypertensive patients randomly treated with either metoprolol or placebo. Samples from rectus abdominis were taken after muscle relaxation during surgery, which was accompanied by a significant increase in arterial plasma noradrenaline. Thermogenesis was significantly lower in the metoprolol group compared with both the hypertensives given (p less than 0.05), and a normotensive group without treatment (p less than 0.005). Metoprolol also provoked a significant fall in body temperature in comparison with the two other groups (p less than 0.01). In the hypertensives given placebo, heat production was inversely related to plasma adrenaline (r = -0.89), indicating a role of the sympatho-adrenal system in muscle thermogenesis. No such correlation appeared during metoprolol treatment. In the present acute stress situation it is suggested that muscle thermogenesis was decreased indirectly by metoprolol via blockade of beta 1-receptors in adipose tissue, causing a relative inhibition of lipolysis with diminished substrate supply to the muscles.