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

Abstract

The effects of thyroidectomy by radioiodine on blood sugar, serum immunoreactive insulin and serum free fatty acid levels in dogs, in the course of glucose infusion tests whether involving glucose priming-dose (B tests) or not (A tests) were studied.

The basal levels of blood sugar and serum insulin were not affected by hypothyroidism; circulating free fatty acids hadhardly risen. In the hypothyroid group, the blood sugar profiles curing both tests were somewhat higher than normal, and hyperglycaemia was maintained for longer. These abnormalities were restored by Thyroxine therapy.

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 than normal (B tests). Late during the stimulation or, even, after interruption of glucose infusion quite an intense insulin response was tardily observed, which was the major effect of hypothyroidism on the insulin response to continuous stimulation by glucose. The abnormalities of the serum insulin profile were corrected by thyroxine therapy.

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 tardily observed, which was the major effect of hypothyroidism on the insulin response to continuous stimulation by glucose. These abnormalities of the serum insulin profile were corrected by thyroxine therapy.

Serum free fatty 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 fatty acids of the thyroidectomized group hardly rose following thyroxine therapy; during the infusion, serum free fatty acids fell more intensely than in the untreated thyroidectomized dogs, but no further rebound despite the therapy was observed.

Key words

Glucose Infusion Test - Blood Sugar - Serum Immunoreactive Insulin - Serum Free Fatty Acids - Hypothyroidism - Dogs

1 The present study was partly reported in abstract from (XI Congreso Latinoamericano de Ciencias Fisiológicas, Mendoza, Argentina, July 29 - Agust 4, 1973; VIII Congreso Panamericano de Endocrinologia, Buenos Aires, Argentina, October 27 - November 2, 1974). The study was sponsored by the "Consejo Nacional de Investigaciones Científicas y Técnicas", Argentina, Res. Grant no. 2304-d.

1 The present study was partly reported in abstract from (XI Congreso Latinoamericano de Ciencias Fisiológicas, Mendoza, Argentina, July 29 - Agust 4, 1973; VIII Congreso Panamericano de Endocrinologia, Buenos Aires, Argentina, October 27 - November 2, 1974). The study was sponsored by the "Consejo Nacional de Investigaciones Científicas y Técnicas", Argentina, Res. Grant no. 2304-d.

2 Established Investigator at this Council.

3 Post-graduated Fellow, University of Buenos Aires, Argentina