Influence of cold exposure on blood lactate response during incremental exercise.

This study examined the effect of acute exposure of the whole body to cold on blood lactate response during incremental exercise. Eight subjects were tested with a cycle ergometer in a climatic chamber, room temperature being controlled either at 24 degrees C (MT) or at -2 degrees C (CT). The protocol consisted of a step increment in exercise intensity of 30 W every 2 min until exhaustion. Oxygen consumption (VO2) was measured at rest and during the last minute of each exercise intensity. Blood samples were collected at rest and at exhaustion for estimations of plasma norepinephrine (NE), epinephrine (E), free fatty acid (FFA) and glucose concentrations, during the last 15 s of each exercise step and also during the 1st, 4th, 7th, and the 10th min following exercise for the determination of blood lactate (LA) concentration. The VO2 was higher during CT than during MT at rest and during nearly every exercise intensity. At CT, lactate anaerobic threshold (LAT), determined from a marked increase of LA above resting level, increased significantly by 49% expressed as absolute VO2, and 27% expressed as exercise intensity as compared with MT. The LA tended to be higher for light exercise intensities and lower for heavy exercise intensities during CT than during MT. The E and NE concentrations increased during exercise, regardless of ambient temperature. Furthermore, at rest and at exhaustion E concentrations did not differ between both conditions, while NE concentrations were greater during CT than during MT. Moreover, an increase off FFA was found only during CT.(ABSTRACT TRUNCATED AT 250 WORDS)

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.