Effects of methanol on autonomic thermoregulation of rats at different ambient temperatures

To measure the effect of methanol on autonomic thermoregulation, male Fischer rats were injected intraperitoneally with saline or 1 or 3 g/kg methanol (20% w/v in saline). The rats were then placed in a chamber, set at an ambient temperature (Ta) of 5, 15, 25, or 35 degrees C, for 60 min while total activity, metabolic rate (MR), evaporative water loss (EWL), and dry thermal conductance were measured. After 60 min, the rat was removed from the chamber and colonic temperature (Tc) was measured. The rats developed a significant hypothermia following the 3 g/kg dosage of methanol at Ta's from 5 to 25 degrees C, while the change in Tc at 35 degrees C was not significant. Total activity decreased following 3 g/kg methanol at Ta's from 15 to 35 degrees C. At a Ta of 25 degrees C, MR was at basal levels and methanol had no effect, but at the other Ta's, where MR was elevated, methanol caused a significant reduction in MR. EWL and thermal conductance were elevated at 35 degrees C in control rats, and methanol reduced EWL at this Ta while it had no effect on conductance at this or any other Ta. These data suggest that the methanol-induced hypothermia and its depressive effect on activity and MR were related. The effect of methanol on the heat loss effectors (EWL, conductance) was not significant or was in the direction of heat conservation. Thus, methanol exposure leads to a significant hypothermia in rats by an inhibitory action on heat production pathways.