Glucose tolerance and gastric emptying in thyrotoxic rats

To clarify the contribution of gastrointestinal function to impaired oral glucose tolerance in hyperthyroidism, gastric emptying rate and portal and peripheral blood glucose responses to intragastric or intraduodenal glucose administration were investigated in experimental thyrotoxic rats. Glucose absorption from perfused intestine of thyrotoxic rats was also examined. Thyrotoxicosis was induced by subcutaneous (SC) thyroxine injection (50 micrograms/kg/d) for seven days. In intragastric glucose tolerance test, although insulin and glucagon responses were not significantly altered, increments in portal and peripheral blood glucose were significantly higher in thyrotoxic rats than in controls at 30 minutes. This phenomenon was almost normalized by the preadministration of phentolamine (2 mg/kg SC). In intraduodenal glucose tolerance test, blood glucose, insulin, and glucagon responses were similar in thyrotoxic and control rats. Gastric emptying rate in thyrotoxic rats was significantly higher than that in controls at 30 minutes, and that was also normalized by phentolamine administration. Absorption of glucose from perfused intestine was similar in thyrotoxic and control rats. These results suggest that an altered glucose tolerance to intragastric glucose load in thyrotoxic rats may primarily be due to rapid gastric emptying induced by increased alpha-adrenoceptor responses, and that glucose absorption from small intestine was not increased in short-term thyrotoxic rats.