[Hormonal response to cold during maximum oxygen consumption in the dog]

In dogs, acute exposure to severe cold (immersion 8-13 degrees C) induced a sustained shivering, a rapid increase in oxygen consumption (VO2) and a progressive colonic temperature fall. With a colonic temperature fall rate of 2-6 degrees C/h, VO2 reached a maximum value (VO2 max), which remained steady for more than 30 min. Under these conditions, we studied time-courses of plasma catecholamine, cortisol, insulin, T4, T3 and TSH concentrations, as well as of plasma glucose, FFA, lactic acid and K+ concentrations which can be considered to reflect the metabolic effects of these hormones. 15 min after the start of immersion, plasma epinephrine and norepinephrine were largely increased, plasma cortisol was moderately enhanced, while no change was observed in plasma insulin, T4, T3 and TSH concentrations. Plasma FFA, glucose, lactic acid and K+ were increased. 30 min after the start of immersion there was a change in evolution of plasma hormone concentrations whereas VO2 level remained steady. T4 concentration was decreased, cortisol did not change, noradrenaline tended to be higher, and epinephrine was increased. Simultaneously, a further rise was observed in glycemia and plasma K+ concentration. Negative correlations were found between colonic temperature and plasma epinephrine and between colonic temperature and plasma norepinephrine. Other plasma hormone concentrations did not seem to be affected directly by the colonic temperature fall. Each of these hormones may be involved in the mechanisms involved during exposure to a severe cold, but our data suggest that catecholamines play a major role.