Plasma catecholamine and metabolic changes during cooling and rewarming in dogs

A slow and progressive fall in colonic temperature occurred in dogs immersed in cold water (8-16 degrees C) when heat production reached a maximum value (CVO2 max). When moderate hypothermic dogs were placed in air (21 degrees C), they continued to shiver and progressively recovered a normal core temperature. Plasma epinephrine (E) and norepinephrine (NE) concentrations, metabolic rate (VO2), arterial and venous blood gas, pH, saturation and oxygen content values were compared, for the same colonic temperature, during cooling and during rewarming. Plasma lactic acid, glucose and free fatty acid (FFA) concentrations, were also measured under both conditions. 1) VO2 was lower during rewarming than during cooling. 2) Plasma NE decreased from maximal value observed during cooling but was still significantly higher than precooling control. During rewarming as well as during cooling a correlation was found between plasma NE and mixed venous oxygen saturation and between plasma NE and mixed venous oxygen content. 3) As NE, plasma E was lower during rewarming than during cooling but was still significantly higher than precooling control. During cooling an acidosis was observed and plasma E was significantly correlated with venous and arterial pH. 4) During rewarming: arterial acidosis disappeared, plasma lactate and glucose concentrations were lower and FFA were higher than during cooling. These results suggest that for the same degree of moderate hypothermia there was less involvement of the sympathoadrenal system during rewarming than during cooling. The simultaneous decrease in metabolic rate and the variations observed in blood pH and in plasma substrate concentrations suggest a relationship between the level of plasma catecholamine concentrations and metabolic adjustments associated with rewarming from hypothermia.