Studies on the Effect of Thyroxine Replacement Therapy on the Increased Insulin Response to Hyperglycemia in the Thyroidectomized Dog[*] [**]

Abstract

Serum immunoreactive insulin and free fatty acids as well as blood sugar levels in normal, untreated and thyroxinetreated (10 γ/kg body wt./d, for nine days) thyroidectomized dogs, both in the fasting condition and during an intravenous glucose tolerance test were measured.

Reversal of the tendency for serum immunoreactive insulin levels to be overnormal in thyroidectomized dogs in the postabsorptive condition was obtained through thyroxine therapy. It also fully corrected the overnormal serum immunoreactive insulin curve after glucose load in these animals.

Both treatments failed to affect the blood sugar basal values. Thyroidectomy hardly enhanced the mean blood sugar during the test (with no change in Conard's k constant), which was corrected by thyroxine therapy.

A moderate delay for serum free fatty acids to fall during the test from subnormal basal values was detected in the dogs after thyroidectomy; in this group, serum free fatty acids remained below base line until the test was over. Thyroxine therapy failed to correct these alterations.

Key words

Hypothyroid Dogs - Thyroxine Therapy - Serum Immunoreactive Insulin - Serum Free Fatty Acids - Blood Sugar - Intravenous Glucose Tolerance Test

1 This work was partially supported by the "Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina", Res.Grant No. 2304-C.

1 This work was partially supported by the "Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina", Res.Grant No. 2304-C.

2 This paper was partially presented at the Meetings of the XXV International Congress of Physiological Sciences, Munich, Germany, July 25-29, 1971.

3 Member of the "Carrera del Investigador Científico", Consejo Nacional de Investigaciones Científicas y Técnicas de la República Argentina.