An Assessment of Human Regulatory Nonshivering Thermogenesis

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Abstract
To assess human thermoregulation independent of muscular activity, a method was developed in which adults not previously acclimatized to cold were subjected to cold and under simultaneous vasodilatation, resulted in a heat debt from the body. During exposure, a significant increase in O2 consumption was found in 2 groups; the increases were 0.06 mmol .cntdot. kg-1 .cntdot. min-1 (41%) (range: 0.023-0.113) and 0.046 mmol .cntdot. kg-1 .cntdot. min-1 (30%) (range: -0.013-0.078), respectively. The change in plasma concentration of catecholamines showed a significant increase in noradrenaline [norepinephrine] of 4.58 nmol/l (300%) (range: 1.86-9.56), whereas adrenaline [epinephrine] did not change measurably. The plasma concentration of non-esterified fatty acids (NEFA) showed a significant increase of 0.47 l mmol/l (96%) (range: 0.033-0.687), 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.