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Study of the Pituitary-Thyroid Functions at High Altitude in Man

^* Department of Endocrinology, Postgraduate Institute of Medical Education Research, Chandigarh Army Hospital, Delhi Cantt Delhi Cantt., India
^{* *} Army Hospital, Delhi Cantt, and the Defence Institute of Physiology and Allied Sciences Delhi Cantt., India

Correspondence to: Professor G. K. Rastogi FRCP, Chief of Endocrinology, Postgraduate Institute of Medical Education & Research, Chandigarh, India.

The alterations in serum levels of T₃, T₄, TSH and TBG, TSH response to 100 µg iv TRH, and urinary excretion of T₃ and T₄ were studiedin 8 healthy men at sea level (SL), on days 1, 2, 4, 8 and 16 after arrival by air at high altitude (3, 700 m, HA), and during days 5 to 7 after their return to SL. No significant alterations in serum levels of TSH and TBG or TSH response to TRH were observed during exposure to HA or on return to SL. There was, however, an acute elevation in both serum total T₃ and T₄. Serum total T₃ from amean basal ± SE value of 128 ± 13ng/dlincreased to 320 ± 18 on day 1 and remained significantly elevated at 225 ± 48 up to day 8 after arrival at high altitude. Similarly serum total T₄ increased from basal level of 9 ± 0.92 ug/dl to15.2 ±1.2 and remained elevated till day 16 and it was 11 ± 1.19 µg/dl during days 5 to 7 after return to SL. The urinaryexcretion of both T₃ and T₄ was decreased. These changes perhaps were theresult of complex physiologic adjustments on acute exposure to high altitude, like shrinkage of the T₃ and T₄ distribution pools, altered binding capacities of tfiyroid hormones binding proteins, and a reduction in clearance of thyroid hormones from the plasma compartment; and were probably not suggestive of an enhanced thyroid activity. Their actual significance in high altitude adaptation in man is not clearly understood.

Received March 8, 1976.

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