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The Sympathetic Nervous System in Short-Term Adaptation to Cold,
LAVAL UNIV QUEBEC DEPT OF PHYSIOLOGY
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Rats were adapted to cold by 10-min exposure to -20C every hour during daytime for a total of 27 exposures over a period of 3 days. The significant delayed hypothermia observed in these adapted animals when exposed to severe cold -16C for 4 h was concomitant with only a 15 increase in oxygen consumption over control animals. While some protection against severe cold was observed in rats given 27 injections of 1 microgram thyroxine over a 3-day period, the same treatment with 30 microgram noradrenaline NA 100 g body weight had opposite effects. Urinary NA was increased during the second and third day of adaptation and the excretion during the 4-h test at -16C was significantly greater in the adapted then in the control group. No significant changes in adrenaline A excretion were observed during the adaptation period. However during the 4-h test at -16C, A excretion was four times greater in the control than in the adapted animals. These results could indicate emotional adjustments in animals adapted by intermittent exposures to severe cold IS adaptation. It might be suggested that adaptation by continuous exposure to moderate cold CM adaptation and IS adaptation are both related to catecholamine secretion in the case of CM adaptation an increased sensitivity to NA would prevail, whereas in IS adaptation a decreased A secretion could be a factor of some importance. Author
APPROVED FOR PUBLIC RELEASE