AJP - Endocrinology and Metabolism, Vol 254, Issue 6 E733-E739, Copyright © 1988 by American Physiological Society
Pituitary and peripheral hormone responses to T3 administration during Antarctic residence
H. L. Reed, J. A. Ferreiro, K. M. Mohamed Shakir, K. D. Burman and J. T. O'Brian
Department of Medicine, Naval Hospital, Bethesda, Maryland 20814-5011.
Very little is known regarding hormonal adaptation in human subjects who
are exposed to the extremes of temperature and light that are found in
polar latitudes. We have previously reported a 50% elevation in the serum
thyrotropin (TSH) response to thyrotropin-releasing hormone (TRH), a fall
in serum total triiodothyronine (T3) and free T3 (fT3), and no change in
serum total thyroxine (T4) or free T4 (fT4) after 42 wk of Antarctic cold
exposure. To differentiate between central and peripheral mechanisms that
may lead to these changes, we report the effect of sequentially increasing
oral doses of T3 (Cytomel) on serum T3 and fT3 levels and on the resultant
attenuation of the TSH response to TRH in nine men before, during, and
after 42 wk residence in Antarctica. Serum T3 values basally and following
the administration of 25, 50, and 75 micrograms/day of T3 were lower after
42 wk of cold exposure (151 +/- 4, 160 +/- 8, 189 +/- 10, and 222 +/- 14
ng/dl, respectively, compared with control values of 160 +/- 7, 178 +/- 7,
202 +/- 9, and 251 +/- 19 ng/dl, respectively, P less than 0.05). Likewise,
the fT3 values measured after these three increasing T3 doses were also
lower after 42 wk of cold exposure. The pituitary response to TRH was
attenuated by each T3 regimen (48 +/- 6, 68 +/- 4, and 77 +/- 4% decreases
in the control period), and this suppression was not different after 20 and
42 wk of Antarctic residence.(ABSTRACT TRUNCATED AT 250 WORDS)
