IN VIVO LIPOLYTIC EFFECT OF GLUCAGON IN WARM-ADAPTED AND COLD-ADAPTED RATS

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