Body glucose as fuel in white rats exposed to cold: results with fasted rats

Abstract

Concentration of glycogen in liver and muscle of warm- and cold-acclimated rats was measured during fasting at 30 or 6 C. The biokinetics of glucose were then studied by priming and continuous infusion with C¹⁴-labeled glucose in 24-hr-fasted rats exposed to 30, 18, and 6 C. In warm-acclimated rats at 18 and 6 C there were higher rates of turnover and oxidation of glucose than at 30 C and the ratio of rates of oxidation to turnover increased, but glucose concentration in plasma, volume of distribution of glucose, and proportion of respiratory CO₂ derived from glucose remained constant in the three environments. Cold-acclimated rats at 6 C had higher values of glucose concentration in plasma, of volume of distribution of glucose, and a slightly higher rate of turnover of glucose than warm-acclimated rats at 6 C. Gluconeogenesis thus can satisfy the elevated glucose requirement in the cold, and the fasted rat increases its heat production by an increase in glucose oxidation proportionate to the increase in energy metabolism as does the nonfasted animal.