Glucose intolerance in thyrotoxic rats: role of insulin, glucagon, and epinephrine

To elucidate the possible role of insulin, glucagon, and epinephrine on glucose intolerance in thyrotoxicosis, the secretion of insulin and glucagon in vivo (glucose, arginine, and epinephrine infusion tests) and in perfused pancreas and the hepatic action of insulin, glucagon, and epinephrine in perfused liver were investigated in experimental thyrotoxic rats (induced by thyroxine injection, 20 micrograms/kg sc, for 7 days). In thyrotoxic rats, fasting blood glucose (87 +/- 5 mg/dl, mean +/- SD) and plasma insulin (16 +/- 3 microU/ml) were significantly (P less than 0.001) higher than those in controls (74 +/- 5 mg/dl and 8 +/- 1 microU/ml), respectively. In glucose infusion test (0.5 g/kg iv), blood glucose, plasma insulin, and glucagon responses in thyrotoxic rats were not significantly different from those in controls. In arginine infusion test (5 mg/min for 20 min iv), the increments in blood glucose and plasma insulin after arginine in thyrotoxic rats were not significantly different from those in controls. Plasma glucagon response was almost the same in both groups. In epinephrine infusion test (100 micrograms/kg iv), the increments in blood glucose and plasma insulin in thyrotoxic rats were significantly greater than those in controls. In perfused pancreas, insulin and glucagon secretions in response to 16.7 mM glucose or 6.4 mM arginine in the presence of 5.5 mM glucose in thyrotoxic rats were not different from those in controls.(ABSTRACT TRUNCATED AT 250 WORDS)