Effect of adrenaline on biliary excretion of triiodothyronines in rats mediated by alpha1-adrenoceptors and related to the inhibition of 5’-monodeiodination in liver

Abstract

Biliary excretion of thyroxine (T4),3,5,3'-triiodothyronine (T3),3,3,5'-triiodothyronine (rT3) and diiodothyronines (3,3'-T2,3,5-T2 and 3',5'-T2) was estimated with the aid of radioimmunoassay in 3-4 subsequent 2-h samples of bile obtained from pentobarbital anesthetized rats through the tubing inserted in bile duct. The excretion of T3 was significantly decreased during 4-h infusion of 2400 ng/kg/min adrenaline in normal rats or during 6-h infusion of the latter dose in the animals preinjected with 2 micrograms T4. Moreover, the excretion of rT3 was significantly increased after the infusion of 1200 and 2400 ng/kg/min adrenaline. Such increase after 1200 and 2400 ng/kg/min adrenaline was prevented by a single dose of 10 mg/kg phentolamine (alpha 1-2-antagonist) and that after 2400 ng/kg/min adrenaline also by 2.5 mg/kg prazosin (alpha 1-antagonist) injected at the beginning of the infusion, but not by 6 mg/kg yohimbine (alpha 2-antagonist) injected every 60 min during 4-h infusion. In addition, increased rT3 excretion was found during the infusion of alpha 1-agonist methoxamine (1.5 mg/kg/4 h), while no such effect of the infusion of alpha 2-agonist azepexol (10 mg/kg/4 h) was observed. It may be suggested that the effect of adrenaline was mediated predominantly by alpha 1-adrenoceptors and that the observed changes in biliary excretion of T3 and rT3 were related to the inhibition of 5'-monodeiodination in the liver.

Thyroid Hormone Indices During Illness in Six Hypothyroid Subjects Rendered Euthyroid with Levothyroxine Therapy

“…Alternatively, interference of binding of thyroid hormones to thyroid binding globulin may contribute to lowering of concentrations of both T4 and T3 with a rise in T3 resin uptake (Afandi et al, 2000;Chopra et al, 1986;Oppenheimer et al, 1982;Chopra et al, 1979). Finally, the inhibition of the deiodinase as well as impaired hypothalamic pituitary axis with lowering of circulating TSH concentration have been attributed to rising stress hormones i.e., catecholamines, glucocorticoid, and glucagon (Duntas et al, 1999;Langer et al, 1989;Hidal and Kaplan, 1988;Kabadi and Premachandra, 1988;Langer and Foldes, 1988;Bianco et al, 1987;Faber et al, 1987;Kabadi and Premachandra, 1987;Silva and Larsen, 1986;Chopra et al, 1985;Langer et al, 1985;Kabadi et al, 1982). These hormones also appear to play a role in the interference in binding between thyroid hormones and their binding globulin attributed to elevation of circulating free fatty acids by promoting lipolysis (Afandi et al, 2000;Faber et al, 1987;Chopra et al, 1986;Chopra et al, 1985;Oppenheimer et al, 1982;Chopra et al, 1979).…”

Immediate and Dose-Response Related Increase of Biliary Excretion of Reverse Triiodothyronine after Propylthiouracil Administration

“…At a day of experiment polyethylene tubings were inserted into a bile duct and femoral vein under pentobarbital anesthesia. The bile was then continuously collected into preweighed vials containing methimazole and I or 2 h samples were taken for radioimmunoassay of T4, T3 and rT3 as previously described (Langer et al, 1988(Langer et al, , 1989. In Experiment 1 two groups of 7 rats each were used.…”

“…In our previous experiments (Langer et al, 1988(Langer et al, , 1989 we suggested that the acute increase in biliary excretion of rT3 reflected the acute inhibition of 5'deiodinase type Tin the liver and thus it may be employed as a useful marker of the activity of that enzyme in vivo. The aim of this study was to test this hypothesis with the aid of PTU.…”

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

“…Exogenous administration of hormones that counterregulate hypoglycemia acutely increases biliary rT3 excretion (5)(6)(7). In the present study we have evaluated the effect of endogenous counter-regulatory hormones whose secretion was stimulated by acute insulininduced hypoglycemia to expand these studies.…”

“…Biliary excretion of rT3 increases after a single iv injection of salicylate (2) as well as after short-term (4-5 h) intravenous infusion of linoleic acid (3), propylthiouracil (4), adrenaline and methoxamine (5), glucagon, vasopressin, angiotensin II (6) and neurotensin (7). As certain variations in biliary excretion of iodothyronines in rats after various interventions occur earlier than those in serum, monitoring of biliary iodothyronines is a useful technique for the in vivo study of acute changes of liver iodothyronine metabolism.…”