Changes in thyroid activity at low atmospheric pressures and at high altitudes, as tested with I131.

Abstract

The activity of the thyroid gland of rats was observed by measuring the uptake of 131I in the living animal over a period of several days. The method is described in detail, and the importance of iodine contained in the diet or applied to the skin, in affecting the results, is stressed. Reduction of the atmospheric pressure to 250 and 380 mm Hg decreases the uptake of 131I. The lower the pressure, the less iodine is concentrated in the thyroid. Under natural conditions a small decrease of thyroid activity at an altitude of 3450 m (490 mm Hg) can be noticed, but not at 2010 m altitude (592 mm Hg). The depression of the thyroid is temporary; after some days 131I is taken up again with normal velocity. At low atmospheric pressure (below 480 mm Hg) the body temperature decreases, but this, too, is restored to normal in 3–4 days. The adaptation of thyroid activity to low atmospheric (oxygen) pressure may play an important part during acclimatization to high altitudes. The mechanism underlying the alteration in thyroid function and, in particular, the relation between the thyroid and adrenocortical activity is discussed. It is suggested that the increased adrenocortical activity and the decrease of thyroid activity observed at low oxygen or atmospheric pressure may be inter-connected.