Acute changes in biliary excretion of reverse triiodothyronine in rats after insulin-induced hypoglycemia: effect of glucose, verapamil, cycloheximide and actinomycin D

Institute of Experimental Endocrinology, Slovak Academy of Sciences, Bratislava.

Biliary excretion of reverse triiodothyronine (rT3) was estimated in rats during hypoglycemia induced by a 10-min infusion of 1 U of insulin (INS) and for the following 5 h. During that period an increase in biliary rT3 was found. This was seen also during the infusion of exogenous glucagon (10 micrograms in 1.2 ml of saline per 1 h for 5 h) given independently of INS. The infusion of glucose (1 g/kg per 50 min or 2 g/kg per 110 min) following INS infusion delayed the increase in rT3. The increase in rT3 was prevented by actinomycin D (1 mg/kg) when injected before (90 min), but not after (30 min) INS, and also by cycloheximide (2.5 mg/kg) injected immediately before INS. The same dose of cycloheximide also prevented a similar increase of rT3 during the infusion of exogenous glucagon. Verapamil (5 mg/kg divided into five doses per 4 h) blunted the increase of rT3. These data indicate that following INS injection counter-regulatory hormones may be responsible for the increased production of rT3; this altered metabolic activity apparently is dependent on protein synthesis.