Serum Insulin Response to Glucose Infusion in Hyperthyroid Dogs[*]

Abstract

The effect of hyperthyroidism on BS, serum IRI and FFA basally and during a GIT was studied in anesthetized dogs. They were given a glucose priming-dose (rapid, intravenous injection) immediately followed by an intravenous glucose infusion for one hour.

In hyperthyroid dogs under anesthesia, the basal BS and serum IRI levels were normal, but the serum FFA levels above those of the normals also under anesthesia.

During the GIT the BS levels followed those of the normals only over the first 30 min; thereafter, the glucose levels fell less than in the normals.

In normal dogs, a biphasic insulin response to glucose was observed; a serum IRI peak at 10 min and a plateau between 30 and 75 min were found. The insulin response of hyperthyroid dogs was less than in the normals throughout the GIT, while they showed no initial peak of response.

Circulating FFA values were low in normal dogs, remained unaffected by glucose administration and failed to rebound as hyperglycemia declined. In the hyperthyroid condition, serum FFA levels fell abruptly during and excessively rebounded after the maintained hyperglycemia.

We conclude that, in the dog, hyperthyroidism depresses the ability of tissues to take up large amounts of glucose from circulation, and impairs the insulin response to glucose, particularly the immediate response.

Key words

Glucose Infusion Test - Blood Sugar - Serum Immunoreactive Insulin - Serum Free Fatty Acids - Hyperthyroidism - Dog

1 The present studies have been reported in abstract form (VIII Congress, Intern.Diabetes Fedn., Brussels, July 15-20, 1973, Comm.No. 458) and sponsored by the "Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina" (Res.Grant No. 2304-d).

1 The present studies have been reported in abstract form (VIII Congress, Intern.Diabetes Fedn., Brussels, July 15-20, 1973, Comm.No. 458) and sponsored by the "Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina" (Res.Grant No. 2304-d).

2 Established Investigator, "Consejo Nacional de Investigaciones Cientifícas y Técnicas de la Repúlbica Argentina".

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