Human nonshivering thermogenesis

Metabolic responses, skin temperatures and changes in heart rate and blood pressure were measured in a control group and in "polar swimmers" after inf usion of different doses of epinephrine, norepinephrine and isoprenaline. I n controls the highest infusion dose of isoprenaline (0.1 mu g min(-1) kg(- 1)) increased metabolic rate in normal humans by 36%, while the highest inf usion doses of epinephrine and norepinephrine (0.45 mu g min(-1) kg(-1)) in creased metabolic rate by 24%, only. In "polar swimmers" the epinephrine th ermogenesis was potentiated significantly, reaching about 45% of the basal metabolic rate. The norepinephrine and isoprenaline thermogenesis were not different from that of the control group. It is concluded that in humans th e epinephrine thermogenesis is probably located in muscles and in the white fat (Simonsen et al., 1992), and may be the principal mechanism of metabol ic adaptation to cold. It was calculated that the increased capacity of epi nephrine thermogenesis in cold exposed "polar swimmers" could theoretically shift the survival limit downwards to lower environmental temperatures by about 5 degrees C. (C) 1999 Elsevier Science Ltd. All rights reserved.