The effect of deep hypothermia on the secretion of thyroid hormones and cortisol and oxygen consumption in guinea-pigs.

Adult guinea-pigs were exposed to cold (-20 degrees C) to the point of deep hypothermia, and the heart rate (HR), rectal temperature (Tr) oxygen consumption (V02), serum concentrations of proteins, thyroid hormones (by T3 and T4 radioimmunoassays) and cortisol (by fluorometry) were determined and compared with those obtained from sham-exposed animals (22 degrees C) Vo2, and HR rose to a maximum in 1 h in the cold, but then declined in parallel to Tr for 2-3 h. The cold-exposed animals became unconscious after 2 h and developed cardiac failure in 4 h. At this time serum proteins and T3 concentrations were similar in the cold and sham-exposed animals. Serum T4 was significantly higher (P less than 0.01) in the cold-exposed animals than in the sham-exposed animals (45.0 +/- 4.2 nmol/l vs. 28 +/- 1.4 nmol/l). Similarly, the cortisol levels were higher in the cold-exposed animals (1.34 +/- 0.11 mumol/l vs. 0.26 +/- 0.03 mumol/l). Severe cold exposure for 4 h resulted in simultaneous activation of the thyroid gland and adrenal cortex preceded by an increase in oxygen consumption and a decrease in rectal temperature.