Thyroidectomy and combined thyroxine-cortisol therapy. Their effects on blood sugar, serum immunoreactive insulin and free fatty acids during an oral glucose tolerance test

Summary

Blood sugar, serum immunoreactive insulin and free fatty acid responses to glucose stimuli during an oral glucose tolerance test in dogs in three experimental conditions (normality, untreated and thyroxine-cortisol treated hypothyroidism) have been studied. The basal levels of blood sugar, serum immunoreactive insulin ad free fatty acids remained unaffected by either the untreated or treated hypothyroid conditions. Thyroidectomy delayed both the onset of hyperglycemia following the oral glucose load and the return of blood sugar levels to baseline at the end of the test; these changes were completely reversible by the combined therapy. The grossly exaggerated serum insulin response to hyperglycemia found in the dogs after thyroidectomy was markedly reduced but not normalized by the combined therapy. Glucose induced a prompt and marked drop of the serum free fatty acid levels in the normal dogs, followed by a recovery period at the end of the test. In hypothyroid dogs, the fall was slower and less intense, and the recovery period was not observed. Combined thyroxine-cortisol administration improved only the recovery period, and the improvement was only partial. The foregoing results show the importance of the effects of both hypothyroidism itself and of secondary adrenocortical deficiency for the development of the disturbances of intestinal glucose absorption and insulin response to hyperglycemia found in dogs after thyroidectomy.