No 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.

No abstract

The uptake of radioiodine by the human thyroid 24 hr after a tracer dose of 25 \g=m\c. has been measured by means of a toroidal counter with a high sensitivity not critically dependent on the relative position of the source. The distribution of the 24 hr uptake values for males and females is given. Values of the sum of the 24 hr uptake and the 24 or 48 hr urinary excretion of radioiodine have been determined, and are shown to be distributed about a mean of 91 % of the dose. With this information it has been possible to replace excretion measurements by uptake measurements in the computation of the thyroid index It described previously [Haigh & Reiss, 1950;Reiss, Haigh, Hemphill, Maggs, Reiss & Smith, 1952]. The new index I \ m=' \ t has the same dimensions as It, but the respective scales of thyroid activity, although similar, are not interchangeable. The I \ m=' \ t values appear less susceptible to accidental errors.In some cases a discrepancy has been found between the rate of uptake of radioiodine during the 1st hr following the injection and the 24 hr uptake value, a low rate of uptake being accompanied by a 24 hr absolute uptake which was at least normal. This may be due to the mobilization of vaso-constrictor substances in the patient during the 1st hr. These anomalies occurred chiefly in patients suffering from some kind of anxiety neurosis.Most methods of assessing thyroid activity with radioiodine are concerned with the behaviour of inorganic 131I. Attention is usually centred on a single parameter, this being most frequently the uptake by the gland or the urinary excretion of 131I. It is surprising that, so far as we are aware, few attempts have been made experimentally to relate these two variables. Absolute measurements of the radioiodine taken up by the thyroid have been made by many workers [In general, the various methods involve a degree of technical skill which, in our opinion, makes them unsuitable for routine investigation of large numbers of patients, and in many cases require much greater doses of radioiodine than we are prepared to give. For a diagnostic test it is always important to use the minimum amount of radioactive material, and bearing in mind that a dose of, say, 25 µ . of 131I in a normal case results in a radiation dose to the thyroid of 30 to 40 r, it is difficult to justify doses of 100/200 µ . commonly used for absolute uptake measurements. By using the toroidal counter [Haigh, 1951], which combines high sensitivity with a measure of indepen¬ dence of the geometrical position of the source, these objections may be largely overcome, and in this way we have examined the relation between the absolute uptake and excretion of radioiodine. This information has enabled us to dispense with urine measurements in our particular method of measuring thyroid function [Reiss et al. 1952].

A method of estimating thyroid function with carrier-free radio-iodine which provides an arbitrary numerical scale of thyroid activity is described. It is suitable for investigating borderline thyroid dysfunction.The results on over 500 psychiatric patients are given in the form of histograms, and arbitrary limits of normality are defined on the basis of these results.While there is usually a correlation between the tracer method and the basal metabolic rate, cases exist in which increased thyroid activity, determined by the radio-active method, is associated with normal or subnormal B.M.R. and vice versa. This is explained as a disturbance of the sensitivity of body tissues to thyroid hormone.The significance of under-sensitivity to thyroid hormone and related problems is discussed, and the importance of considering peripheral sensitivity of the tissues of the body in evaluating an abnormal thyroid activity is emphasized.