Serum Insulin and Free Fatty Acid Responses to Slow and Quick Graded Hyperglycaemias in Hypothyroid Dogs*

Hypothyroidism brought about a considerable alteration of the dynamics of serum insulin response to glucose. Early during the continuous stimulation, serum insulin levels were normal (A tests) or somewhat higher then normal (B tests). Late during the stimulation or, even, after interruption of glucose infusion quite an intense insulin response was tardi Iy observed, which was the major effect of hypothyroidism on the insulin response to continuous stimulation by glucose. These abnormalities of the serum insulin proftle were correct ed by thyroxine therapy. Serum free faUy acid levels of the thyroidectomized dogs fell during glucose infusion, whether significantly (A test) or not (B test), and no further rebound during the test period was observed. The basal values of serum free faUy acids of the thyroidectomized group hardly rose following thyroxine therapy; during the infusion, serum free faUy acids fell more intensely than in the untreated thyroidectomized dogs, but no further rebound despite the therapy was observed.