It has been suggested that
hypothermia induced in rabbits by
As2O3 3 mg/kg (i.v.) depends mostly on the blocking of the thermo-regulatory center. The relationship between
hypothermia induced by
As2O3 and brain monoamine levels in rabbits was investigated. To clarify the mechanism of the
hypothermia, the influence of pretreatment with several agents on As2O3-induced
hypothermia and on monoamine levels in the hypothalamus was examined. The core temperature was measured by inserting the thermister probe into the rectum and
noradrenaline(NA), 5-hydroxytryptamine(5-HT) and 5-hydroxyindoleacetic acid(5-HIAA) levels in the hypothalamus were estimated fluorometrically. Pretreatment with
p-chlorophenylalanine(PCPA),
alpha-methyl-p-tyrosine(
alpha-MPT) or 5-hydroxytryptophan(5-HTP) did not inhibit the
hypothermia induced by
As2O3 but did decrease NA levels in the hypothalamus. On the contrary, pretreatment with
barbital sodium,
pheniprazine, 1-DOPA and 1-tyrosine significantly inhibited the
hypothermia or exhibited the
hyperthermia. As2O3-induced
hypothermia in rabbits was followed by a decrease in NA levels and an increase in
5-HT levels in the hypothalamus. On the other hand, when the
hypothermia induced by
As2O3 was inhibited by pretreatment with
barbital sodium,
pheniprazine, 1-DOPA and 1-tyrosine, both NA and
5-HT levels in the hypothalamus were significantly increased. These results suggest that As2O3-induced
hypothermia is due to a decrease in NA levels and inhibition of the
hypothermia is due to an increase in NA levels, in the rabbit hypothalamus.