An assessment of human regulatory nonshivering thermogenesis.

To assess human thermoregulation independent of muscular activity, a method was developed exposing adult man not previously acclimatized to cold under simultaneous vasodilatation, resulting in a heat debt from the body. During exposure, a significant increase in oxygen consumption was found in two groups, the increases were 0.06 mmol . kg-1, . min-1 (41%) (range: 0.023--0.113) and 0.046 mmol . kg-1 . min-1 (30%) (range: --0.013--0.078), respectively. The change in plasma concentration of catecholamines showed a significant increase in noradrenaline of 4.58 nmol/l (300%) (range: 1.86--9.56), whereas adrenaline did not change measureably. The plasma concentration of non-esterified fatty acids (NEFA) showed a significant increase of 0.47 l mmol/l (96%) (range: 0.033 to 0.687), whereas the plasma concentration of glucose fell by only 0.3 mmol/l (6%) (range: 0.1--0.9). The results obtained by this method mirror findings from studies on small mammals acclimatized to cold, indicating that man without visible shivering and discomfort can increase heat production by an increased secretion of noradrenaline and by utilizing the fat stores in adipose tissue as the major substrate for this increased energy demand.