Abstract
The effect of thermal acclimation on fasting (96 h) -induced modifications in the substrate metabolism and sympathetic activity was studied in rats. The increase in body weight was smaller in cold-acclimated rats (5°C, 4wk) (CA) and heat-acclimated rats (33°C, 4wk) (HA) than that in warm controls (25°C) (WC) . Fasting-induced decrease in body weight was greater in CA, while it was smaller in HA as compared with WC. Blood glucose was lower in HA, and fasting decreased it in all groups to the same extent. Blood free fatty acids did not differ among the groups, and fasting increased it in all groups. Its increase was greater in CA. Plasma glycerol was higher in CA, and fasting increased it in WC, but not in CA and HA. Beta-hydroxybutyric acid was higher in CA, and fasting increased it in all groups. Its increase was greater in HA and smaller in CA. Urinary excretion of vanilmandelic acid did not differ among the groups, and fasting decreased it in all groups. Its decrease was smaller in CA, showing the higher excretion than in WC and HA. Urinary excretion of metanephrine + normetanephrine was higher in CA. Fasting did not affect it, and CA kept the higher excretion. These results indicate that the modified substrate metabolism and sympathetic activity by thermal acclimation may influence the fasting-induced changes in these indices.
