Journal of Applied Physiology, Vol 53, Issue 2 313-315, Copyright © 1982 by American Physiological Society
Altitude-induced changes in plasma thyroxine, 3,5,3'-triiodothyronine, and thyrotropin in rats
J. M. Connors and L. G. Martin
We have studied the thyroid function of high-altitude-acclimated (6,900 m
for 5 wk) and nonaltitude-acclimated control (198 m) rats. After 5 wk of
high-altitude exposure the plasma concentrations of both thyroxine (T4) and
triiodothyronine (T3) were lower than those in control rats (4.7 +/- 0.3
vs. 3.3 +/- 0.2 microgram/dl and 96 +/- 5 vs. 74 +/- 6 ng/dl,
respectively). The plasma thyrotropin (TSH) concentration was elevated in
the high-altitude-acclimated rats compared with controls (52 +/- 4 vs. 29
+/- 3 micrograms/dl, respectively). Gross anatomical (thyroid wt/body wt)
and histological observations of thyroid tissue were consistent with
elevated plasma TSH concentrations. These results suggest that the fall in
the plasma concentrations of T4 and T3 during acclimation to severe hypoxia
is due to a primary block of thyroid secretion and not to a fall in plasma
TSH levels.
