Liberation of thyreotropin, thyroxine and triiodothyronine in the controllable and uncontrollable stress and after administration of naloxone in rats

The aim of this study was to investigate whether controllable stress, in which the animal can avoid a stressor, and uncontrollable stress, in which the animal can not avoid its influence change the activity of the endocrine pituitary-thyroid axis and whether these changes are modified by naloxone--the antagonist of opioid receptors. The experiments were carried out on rats using electric foot shock as a stressor and the concentration of thyreotropin, thyroxine and triiodothyronine in the blood was determined with radioimmunoassay. The uncontrollable stress caused the inhibition of secretion of the hormones mentioned above, but the controllable stress did not influence their secretion. Naloxone administered centrally to lateral ventricle of the brain decreased the inhibitional influence on the pituitary-thyroid axis. The obtained results suggest that change of pituitary-thyroid axis activity during the stress depends not only on the stressor but also on the animal's abilities to control that stressor.