EFFECTS OF HIGH-ALTITUDE AND COLD-EXPOSURE ON RESTING THYROID-HORMONECONCENTRATIONS

This study examined the effect of high altitude and cold exposure on t hyroid hormone status during a mountaineering expedition. There were 1 5 males participating in an expedition to climb Mt. McKinley, AK. Rest ing blood samples were collected and analyzed for thyroid-stimulating hormone (TSH), total (T)-free (f) thyroxine (T4), triiodothyronine (T3 ), reverse T3 (rT3), and cortisol. Measurements were made on three occ asions: baseline in the continental U.S. one week pre-expedition (PRE- I), baseline in Alaska immediately pre-expedition (PRE-II), and immedi ately upon descent post-expedition (POST). Statistical analysis indica ted that no significant trial PRE-I vs. PRE-II (p > 0.05) differences occurred. Significant (p < 0.05) reductions, however, occurred from PR E-II to POST expedition in TSH, TT3, and fT3. Also rT3 and cortisol in creased significantly PRE-II to POST while TT4 and fT4 were unchanged. The increase (Delta = POST minus PRE-II) in cortisol was negatively c orrelated with the decrease (Delta) in TSH (r = -0.52, p = 0.05) and T T3 (r = -0.49, p < 0.06). Moreover, the reduction in TT3 was inversely correlated with the rT3 increase (Delta comparison, r = -0.66, p < 0. 01). The findings demonstrate that the resting concentrations of thyro id hormones are disrupted by a mountaineering expedition, specifically an environmental stress-related ''low T3 condition'' seems to develop . These changes would seem to be related to an impaired peripheral con version of T4 to T3, possibly brought about by elevations in the circu lating cortisol levels.