The Influence of Stress Conditions on the Uptake of 131i by the Rat Thyroid

Abstract

The uptake of 131I by the thyroid of the rat has been investigated under various conditions of stress.The acute change always consists in a considerable reduction of the rate of uptake of 131I irrespective of the nature of the stress. This acute inhibition in the uptake of 131I is independent of the anterior pituitary lobe, since it occurs in the normal and hypophysectomized animal alike. It is also independent of the presence of the adrenals. The inhibition of the uptake of 131I by the thyroids occurs in vivo only; their ability to take up 131I in vitro is not impaired.All the acute changes seen under stress conditions can be readily reproduced by treatment with adrenaline, which shows the same inhibitory effect on normal and hypophysectomized animals, the action being equally transitory.It is suggested that the acute changes in thyroid function seen under stress conditions are entirely independent of the anterior pituitary and are caused by increased release of vasoconstrictor substances.An increased uptake rate of 131I by the thyroid was seen 24 hr after the acute stress. This was thought to be caused by a compensatory increase in the secretion of thyrotrophic hormone by the anterior pituitary.It has been reported previously [Haigh, Reiss & Reiss, 1954] that the rate of uptake of 131I by the human thyroid during the first hour after intravenous injection of this tracer may be considerably decreased in conditions of severe mental tension. This state was shown to be only transitory, since the thyroids of the investigated subjects showed a normal or even increased 24-hr uptake rate if their function was not other¬ wise disturbed. It was suggested that this initial inhibition of 131I uptake might be due to an increased concentration of vasoconstrictor substances in the blood. Supporting evidence was provided by preliminary experiments carried out on rabbits under Nembutal anaesthesia in which the uptake slope was completely flattened after intravenous infusion or injection of adrenaline.The investigations described in this paper were undertaken with the object of analysing the reaction of the thyroid to different stress conditions. A further purpose was to clarify and differentiate between the roles played by the pituitary, the adrenal and vasoconstrictor substances in the response of the thyroid to stress. METHODSThe rats used in this study were of the Wistar (Portón) strain. They were fed on Parkes' diet no. 41, and kept in a thermo-regulated room at 70 + 5°F. Hypophys¬ ectomy was performed by the paratracheal route and adrenalectomy by the dorsal route. 2i J. Endoc.

Responses of Hypophysectomized Rats to Stress

“…These changes comprise a decrease in uptake of32P by the thyroid and an increased uptake by the adrenal. The reduction in uptake of 32P by the thyroid gland parallels the decreased uptake of 131I which has been previously described as occurring under similar conditions [Badrick et al 1954]. These changes would seem to indicate an inhibition of thyroid function.…”

“…In a preceding paper [Badrick, Brimblecombe, Reiss & Reiss, 1954] conditions of acute stress were shown to reduce the 131I uptake of the rat thyroid. This reduction occurred very soon after stress and was independent of the anterior hypophysis, since intact and hypophysectomized animals reacted alike.…”

Thyroid Function in Experimental Streptococcal Pneumonia in the Rat

“…From the observations of Brown-Grant et al (28) it has been inferred that severe physical stress may reduce the responsiveness of the thyroid gland to TSH, and depress pituitary TSH output as well. Even in the hypophysectomized animal, severe physical stress has been shown to reduce thyroid activity (29), suggesting the participation of local metabolic or vascular factors independent of TSH. Similar factors probably are operative in the thyroid inhibition associated with infection.…”

The effect of exogenous and endogenous adrenaline on the uptake of radio‐iodine by the thyroid gland of the rabbit

“…In view of the work presented here it is clear that the role of the adrenal medulla must be considered when evaluating these findings. Badrick, Brimblecombe, Reiss & Reiss (1954), have also emphasized the importance of vascular factors in their findings of reduced 13II uptake by the rat thyroid in acute 'stress'. In their discussion, however, they prefer to attribute their findings to the release of 'vasoconstrictor substances', and not to adrenaline as they were able to elicit the response in adrenalectomized animals.…”