Increase of biliary excretion of reverse triiodothyronine in rats during the infusion of neurotensin possibly resulting from the inhibition of iodothyronine 5'-monodeiodination.

Male rats weighing about 350 g were inserted polyethylene tubes into the bile duct and femoral vein under pentobarbital anaesthesia. After taking the first (control) 2-h bile sample the control group (n = 24) was infused saline for 4 h and the other group (n = 14) was infused neurotensin in a dose of 27 micrograms per animal per 4 h. The concentration of thyroxine (T4), triiodothyronine (T3) and reverse triiodothyronine (rT3) in the bile was estimated by radioimmunoassay. No significant differences between groups were found in the biliary excretion of T4 and T3, while the excretion of rT3 after the infusion of neurotensin was significantly increased which was not the case in controls. Since neurotensin is known to increase glycemia which effect might be or might not be mediated by glucagon, it may be suggested that these results bring an additional support for the previously reported coincidence between a prevailing effect of gluconeogenetic hormones and inhibition of iodothyronine 5'-deiodination in the liver.