Role of beta adrenoceptors in metabolic and cardiovascular responses of cold exposed humans

Effect of a nonspecific beta adrenergic blocker - propranolol (40 mg per os ) on thermoregulatory responses of cold water immersed (12.5 degreesC) huma ns was studied. Propranolol attenuates resting and cold induced thermogenes is, rectal temperature, heart rate and systolic blood pressure, but increas es production of adrenaline and cortisol. Propranolol has no effect on the threshold body temperature for induction of cold thermogenesis and on centr al thermosensitivity. The following conclusions are drawn from consideratio n of the data presented: During the early phase of cooling (20 min after th e start of cooling) the thermogenesis mediated by beta adrenergic receptors may cover about 80% of the total metabolic increase induced by cold. After about 30 min of cooling the relative proportion of beta adrenergic thermog enesis starts to decline, reaching 20% of the total cold thermogenesis at t he end of cooling. It can be suggested from consideration of the data that, in man, the beta a drenergic receptors in the heart, blood vessels, adipocytes and muscles par ticipate in mediating effect of cold on cardiovascular and thermoregulatory responses. Furthermore, these data imply that human adrenergic thermogenes is is produced outside of the brown adipose tissue. Thus, physiological mec hanisms mediating adrenergic thermogenesis in humans appear to be different from those in small mammals. (C) 2000 Elsevier Science Ltd. All rights res erved.