In vivo lipolytic effect of glucagon in warm-adapted and cold-adapted rats

In vivo effect of glucagon on blood-free fatty acid (FFA) concentration was investigated in rats adapted to 25 degree C and to 5 degree C. Intraperitoneal injection of glucagon in 100 or 25 mug/100 g body weight doses was followed by a triphasic response in blood FFA concentration: an immediate and marked rise at 5 min, a secondary depression at 60 min and a final rise at 120 to 240 min after the injectionss. For the 12.5 and 6.25 mug/100 g body weight injections, an initial increment was significantly lowered and no elevation at 240 min was observed. Concomitant elevations of blood glucose concentration were shown 5 min after glucagon injection of 100, 25, 12.5, and 6.25 mug/100 g body weight doses and their extents were not significantly different each other between these doses. However, rise in blood glucose level at 60 min was not seen at the 12.5 and 6.25 mug/100 g body weight doses. Blood lactate concentrations did not show any significant variations by the injections of glucagon. In fasting rats, glucagon at the 100 mug/100 g body weight dose caused similar increase in blood FFA as that in fed ones. In fed cold-adapted rats at 5 degree C glucagon at the dose of 100 mug/100 g body weight brought about similar effects in elevation of blood FFA level and its time-course as those in fed rats adapted to 25 degree C. However, under fasting condition cold-adapted animals exhibited greater increment in blood FFA level at 5 min than those adapted to 25 degree C, while an elevation of blood FFA at 240 min was not observed in the former animals. These results indicate for the first time an in vivo lipolytic action of glucagon in rats and further suggest an enhanced sensitivity to lipolytic action of glucagon in cold adaptation.