The Importance of the Thyroid in Maintaining an Adequate Production of Heat during Exposure to Cold

نویسنده

  • GORDON C. RING
چکیده

It is well known that there is increased activity of the thyroid during prolonged exposure to cold (see Ring, 1939, for references) and that thyroidectomiaed animals do not survive as well as normal animals under such conditions. Yet cold does not bring about a large increase in activity of the thyroid since a sojourn of three weeks in a refrigerator at 2 to 4 degrees centigrade increases the basal metabolism of rats only 10 or 15 per cent. The total metabolism while the animals are in the refrigerator must be about three times the basal level (see Benedict and MacLeod, 1929, and Swift and Forbes, 1939). Therefore the rise in basal metabolism due to increased thyroid activity accounts for no more than 3 to 5 per cent of the total output of heat required by the rat under such severe conditions. These facts have caused us to wonder whether the direct effect upon basal metabolism might really be of minor importance. It is possible that the greatest value of the thyroid lies in sensitizing the response to epinephrine (Goetsch effect). To test this possibility, the calorigenic response to epinephrine under varying conditions of thyroid activity has been measured. This included a study of the response to epinephrine after prolonged exposure to cold. In the course of these observations, it was found that the maximal metabolic response to cold as well as the response to epinephrine was potentiated by thyroxin. METHOD. Male rats weighing about 200 grams were selected for these experiments. The basal metabolism was determined by using the apparatus previously described (Ring, 1940). The oxygen consumption was recorded during the four hours prior to the injection of the gelatin preparation of epinephrinel and for six hours thereafter. Periods of quiet were selected for calculating the oxygen consumption. A few measurements of the respiratory quotients using the Haldane principle have been made to be sure that the caloric expenditure may be satisfactorily estimated by determining oxygen consumption alone. In studying the response following prolonged exposure to cold, rats were kept in individual cages in the refrigerator for three weeks. After they were returned to normal room temperature, a number of the rats were given ordinary drinking water but some were given water containing NaI (0.75 mgm. per cc.) in order to bring about a more rapid return of the basal metabolism to normal (see Ring, 1941). At weekly intervals, the basal metabolism and the calorigenic response to epinephrine were measured. These responses were compared with those obtained in normal rats, thyroidectomiaed rats and rats injected with thyroxin.

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تاریخ انتشار 2004