Effects of methacholine and acetylcholine on metabolic, respiratory, vasomotor and body temperature responses in rabbits.

Abstract

Central administration of methacholine and acetylcholine each produced a dose-dependent hypothermia in conscious rabbits at room temperature (22 degrees C) and below. At room temperature, hypothermia in response to methacholine and acetylcholine was due to decreased metabolism and increased heat loss (both an increase in ear skin blood flow and in respiratory evaporative heat loss). In the cold (4 degrees C), hypothermia was brought about by a decrease in metabolic heat production and an increase in respiratory evaporative heat loss. However, in the heat (32 degrees C), central administration of methacholine and acetylcholine each produced a dose-dependent hyperthermia in rabbits. The hyperthermia was due to a decrease in both ear skin blood flow and respiratory evaporative heat loss. Furthermore, the effects of methacholine of acetylcholine on body temperature was antagonized by pretreatment with atropine.