Glucoregulatory function of thyroid hormones: evidence for an insulin-independent effect

The effect of hyperglycemia on glucose kinetics was investigated in normal and T4-treated miniature pigs. 1. T4-treatment increased basal plasma glucose (G) (+ 20%) and glucose turnover (+36%). 2. Glucose infusion (2 mg/kg x min) in controls increased insulin and glucose utilization (Rd), but decreased glucagon and hepatic glucose production (Ra). After T4-treatment glucose increased insulin, decreased glucagon and Ra but only a slight effect on G and Rd were observed. 3. Infusing glucose + somatostatin resulted in hyperglycemia in both groups due to an initial fall in Ra and Rd followed by an increase in Rd, where total Ra (endogenous + exogenous exceeded Rd. Glucose intolerance was more pronounced in controls, due to a T4-induced increase in Rd. During this non-steady state the increment in Rd per increment in G was calculated and showed 1.5 in controls and 2.5 after T4-treatment. These data give evidence that thyroid hormones increase glucose utilization during hypoinsulinemia.