Cold stress or a pyrogenic substance elevates thyrotropin-releasing hormone levels in the rat hypothalamus and induces thermogenic reactions.
Both thyrotropin-releasing hormone (TRH) levels in the hypothalamus and thermoregulatory responses were assessed in rats after they had been equilibrated to each of three ambient temperatures (Ta: 8, 22 and 30 degrees C) tested. Cold exposure, in addition to elevating TRH levels in the hypothalamus, led to increased metabolism and cutaneous vasoconstriction in rats at Ta = 8 degrees C. In contrast, heat exposure resulted in decreased metabolism and cutaneous vasodilatation in rats accompanied by no change in hypothalamic TRH levels at Ta = 30 degrees C. In addition, rats were chronically implanted with a cerebroventricular cannula to allow administration of the pyrogenic substance polyriboinosinic acid-polyribocytidylic acis (Poly I:C) into the brain at Ta = 22 degrees C. Intracerebroventricular administration of Poly I:C, in addition to elevating hypothalamic TRH levels, produced a fever with a latency of onset of about 30 min. The fever induced by Poly I:C was brought about by increased metabolism and cutaneous vasoconstriction in rats. The results suggest that either cold stress or Poly I:C injection elevates TRH levels in rat hypothalamus and thus induces thermogenic reactions.
Lin
M T
MT
Department of Physiology, National Cheng Kung University Medical College, Tainan, Taiwan, Republic of China.
Wang
P S
PS
Chuang
J
J
Fan
L J
LJ
Won
S J
SJ
D000818:Animals; D001833:Body Temperature Regulation / Q000187:drug effects; D003080:Cold Temperature; D007031:Hypothalamus / Q000032:analysis* / Q000187:drug effects; D007276:Injections, Intraventricular; D008297:Male; D011070:Poly I-C / Q000494:pharmacology*; D011749:Pyrogens; D051381:Rats; D011919:Rats, Inbred Strains; D012867:Skin / Q000098:blood supply; D013312:Stress, Physiological / Q000503:physiopathology*; D013973:Thyrotropin-Releasing Hormone / Q000032:analysis*; D014661:Vasoconstriction
D011749:Pyrogens; D013973:Thyrotropin-Releasing Hormone; D011070:Poly I-C