Regulated hypothermia in the hypothyroid rat induced by
administration of propylthiouracil.
Yang, Ying, and Christopher J. Gordon.
Neurotoxicology Division, National Health and Environmental Effects
Research Laboratory, U.S. Environmental Protection Agency, Research
Triangle Park, North Carolina 27711, Visiting scientist, Institute of
Food Safety Control and Inspection, Ministry of Public Health,
Beijing, China
APStracts 3:0413R, 1996.
Propylthiouracil (PTU), an antithyroidal drug which reduces serum
thyroxine (T4) and triiodothyronine (T3), is presumed to lower core
temperature (Tc) by impairing metabolic thermogenesis. However, it is
not understood why PTU-treated animals cannot use behavioral and
other thermoeffectors to maintain normal Tc . Male rats were
administered PTU in drinking water (0.05 mg/ml) while the following
parameters were measured: (i)Tc and motor activity (MA) recorded by
radiotelemetry for 24 hr at ambient temperatures (Ta) of 10 to 30 oC;
selected Ta, MA, and Tc in a temperature gradient; and Tc, MA, and
grooming behavior during exposure to heat stress (Ta=34.5 oC) for 2
hr. PTU reduced serum levels of T4 and T3 by 95 and 60%,
respectively. Tc decreased after 3 days of PTU treatment; a 0.5 oC
decrease in Tc persisted throughout the PTU treatment. PTU rats
exposed to Ta's of 10 to 30 oC maintained a consistent hypothermic Tc
during the light phase; however, a deficit in the stability of Tc at
night was noted when exposed to 10 oC. In the temperature gradient,
PTU rats selected warmer Ta's but their Tc was maintained at the same
hypothermic levels as observed at fixed Ta's of 15 to 30 oC. Heat
stress caused Tc of control rats to increase to 39 oC, whereas Tc of
the PTU rats was maintained below 38 oC. The regulation of Tc at
hypothermic levels over a wide range of Ta's and when housed in a
temperature gradient indicates that chronic PTU induces a state of
regulated hypothermia.
Received 23 July 1996; accepted in final form 5 November 1996.
APS Manuscript Number R431-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 31 December 1996