Effect of thyroidectomy and food intake on oral and intravenous glucose tolerances in rats.

I N A PREVIOUS STUDY of the effect of thyroidectomy on oral glucose tolerance, interpretation of the findings was complicated by the marked difference in size between thyroidectomized and normal control rats (I). It was demonstrated that age had a pronounced effect on the rate of intestinal absorption of glucose, but it was not ascertained if this was a direct effect of age or secondary to its effect on body size. The present experiments were planned so that thyroidectomized rats could be compared directly with body size controls of the same age. Body growth in normal rats was restricted by pair-feeding them to ad libitum-fed thyroidectomized rats. Other thyroidectomized rats were force-fed an increased amount of food in an attempt to maintain their body weight gain at the same rate as that in ad libitum-fed normal rats. Both oral and intravenous glucose tolerances were studied, the latter to eliminate any effect of intestinal absorption on the glucose tolerance test. Glucose tolerance in thyroidectomized rats was found to be impaired when determined by both the intravenous and oral tests. There was no effect of food intake on oral and intravenous glucose tolerances in thyroidectomized and normal rats.