Effect of Hypoxia and High Altitude on Thyroidal Iodine Metabolism in the Rat1

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Abstract
In order to study the effects of hypoxia on thyroidal iodine metabolism, chambers were designed to maintain reduced concentrations of O2 at ambient barometric pressures. The resulting partial pressures of O2 simulated 15, 000-18, 000 feet altitude. Rats were kept in this environment for 7-9 days before they were injected with I131 -and killed. Thyroid weight was reduced only in the hypoxic animals previously fed a low iodine diet. Histology and radioautography suggested a "resting" gland in the hypoxic groups. The thyroidal accumulation of I131 - was decreased in the hypoxic animals in most experiments. The percentage of I131 - in the thyroidal homogenates was increased only in the iodine-deficient hypoxic groups. Chromatographic (collidine: H2O : NH3) analysis of pancreatin digests of these homogenates showed a marked decrease in T4-I131 and T3 - I131 with a rise in DI131 T. Studies carried out at 1, 3, 5, 7 and 37 days after groups of rats were transported to the summit of Pikes Peak, Colorado (14,100 ft) substantiated this finding. PBI, PBI131, and conversion ratio were all reduced in the hypoxic animals. The data are interpreted as showing a depression of various aspects of thyroidal iodine metabolism in hypoxic rats. A block in the iodination of tyrosine and in the coupling reaction is postulated.

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