[Role of norepinephrine in the regulation of thyroid gland functional activity in rabbits]

By collecting in situ the blood flowing from the thyroid, the authors have demonstrated that noradrenaline injected in a dose 1 microgram/kg into rabbit thyroid artery enhanced triiodothyronine secretion without changing thyroxin secretion. This process was inhibited by prazosin, an alpha-adrenoblocker, in a dose 1 microgram/kg, injected 5 min before noradrenaline, but not by propranolol, a beta-adrenoblocker. Phenylephrine, an alpha-adrenergic agonist, in a dose 1 microgram/kg, injected into the thyroid artery, influenced thyroid hormone secretion similarly as noradrenaline. The T3/T4.100 ratio taken as an indicator of T4 thyroid conversion increased under the effect of noradrenaline injection after prazosin. Thus, in our experiment noradrenaline activated thyroid function via stimulation of alpha-adrenoceptor system. Hence, catecholamines are capable of directly influencing thyroid functional activity.