In:
Canadian Journal of Physiology and Pharmacology, Canadian Science Publishing, Vol. 71, No. 12 ( 1993-12-01), p. 904-909
Abstract:
The present study was conducted to investigate day–night variations of plasma thyroid hormone and energy substrate levels in rats after acclimation to heat loaded for several hours at a fixed time per day. The heat-acclimated rats were exposed to an ambient temperature of 33 °C for 5 h in the last half of the dark phase for 16 consecutive days, while the control rats were kept at 24 °C for the same period. After completing the schedule, plasma levels of triiodothyronine (T 3 ), free T 3 (FT 3 ), thyroxine (T 4 ), free T 4 (FT 4 ), cortisol, triglyceride, nonesterified fatty acid, total protein, and glucose were measured at 3-h intervals between 00:00 and 18:00 (dark phase, 03:00–15:00). The plasma levels of T 3 and FT 3 of the heat-acclimated rats were higher than those of the controls in the last half of the dark phase. Similar differences were observed for T 4 and FT 4 levels. The plasma cortisol level was consistently higher in the heat-acclimated rats than in the control rats. There were no particular differences in energy-substrate levels between the two groups at any time of the day. These results indicate that heat exposure at a fixed time per day alters the pattern of day–night variations of plasma thyroid hormone levels in rats. It is noteworthy that the plasma levels of thyroid hormones, especially T 3 and FT 3 , increased during the period when the rats had been previously exposed to heat.Key words: triiodothyronine, thyroxine, cortisol, energy substrate, circadian rhythm.
Type of Medium:
Online Resource
ISSN:
0008-4212
,
1205-7541
Language:
English
Publisher:
Canadian Science Publishing
Publication Date:
1993
detail.hit.zdb_id:
2004356-9
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