Metabolic and hormonal responses to exogenous hyperthermia in man

To study whether hyperthermia reproduces hormonal and metabolic responses seen in stress states such as mild infections, six normal male subjects underwent (i) a 3-h hot bath and (ii) a 3-h thermoneutral control period. During the hot bath body temperature rose by 1.2 +/- 0.03 degrees C (mean +/- SEM) and significant peaks of circulating growth hormone (56 +/- 9 vs 7 +/- 4 mU/l), adrenaline (310 +/- 34 vs 152 +/- 39 pmol/l), glucagon (19.2 +/- 4.3 vs 11.8 +/- 2.3 pmol/l) and cortisol were recorded together with slight hyperinsulinaemia (6.5 +/- 1.3 vs 5.3 +/- 1.0 mU/l, P less than 0.05). Hyperthermia was also accompanied by significant increases in circulating levels of free fatty acids (0.93 +/- 0.1 vs 0.46 +/- 0.1 mmol/l), 3-hydroxybutyrate (196 +/- 67 vs 50 +/- 18 mumol/l), glycerol (102 +/- 10 vs 48 +/- 5 mumol/l) and lactate. Blood alanine decreased and blood glucose remained constant. When an intravenous glucose tolerance test was performed during the last hour of hyperthermia signs of impaired first phase and enhanced second phase insulin responses were recorded. Calculated values for glucose disappearance also deteriorated (1.34 +/- 0.19 vs 2.04 +/- 0.50 %/min, P less than 0.05). We conclude that hyperthermia mimics most major metabolic and hormonal changes observed during mild infection and could provide a model to study these conditions.