FFA metabolism in thyroidectomized and normal dogs during rest and acute cold exposure.

Uniformly labeled (14C)glucose was infused iv at a constant rate into unanesthetized surgically thyroidectomized (THY) and normal dogs during the basal state at 22 degrees C and during cold exposure at 4–5 degrees C. 02 uptake, CO2 output, and plasma glucose levels were determined; from these rates of glucose turnover and oxidation were calculated. Comparison of THY with normal dogs shows that at a mean plasma glucose level of 103 mg/100 ml, a significantly lower glucose turnover rate was observed in THY dogs on the basis of a kg body weight, body surface area (m-2), but not per cal BMR. The same percentage of glucose turnover was immediately oxidized in THY and normal dogs, accounting for 16 and 15% of the total caloric expenditure, respectively. Acute cold exposure increased energy expenditure in both THY and normal dogs without a change in glucose level or turnover rate. However, the percentage of glucose turnover which was immediately oxidized as well as the amount of glucose oxidized increased significantly and proportionally to the increase in energy expenditure so that the percent of calories derived from plasma glucose oxidation remained the same as that observed during the control period.