[Studies on As2O3-induced rabbit hypothermia and brain monoamines (author's transl)]

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.