Lowering of body core temperature by exposure to a cold environment and by a 5-HT1A agonist: effects on physiological and psychological variables and blood serotonin levels.
The present study was designed to compare the effects of a pharmacologically induced decrease in body core temperature to the effects observed with lowering of body temperature by exposure to a cold environment. Our special interest was the involvement of 5-HT in thermoregulatory responses. Sixty healthy male volunteers were randomly assigned to one of the following conditions: exposure to normal ambient temperature (28 degrees C) and placebo, exposure to cold ambient temperature (5 degrees C) and placebo, or normal ambient temperature and 10 mg of the partial 5-HT1A agonist ipsapirone. As indicators of physiological responses to lowering of body temperature, tympanic temperature, skin temperature, EMA, metabolic rate, and heart rate were monitored and saliva cortisol levels and peripheral 5-HT concentrations were determined. In addition, ratings on ambient temperature, thermal discomfort, and feelings of irritability were obtained. While lowering of body core temperature was associated with marked counterregulations (decrease of skin temperature, increase in EMA and metabolic rate) and feelings of discomfort, this was not observed with ipsapirone. An increase in cortisol levels was primarily observed in the ipsapirone group and was not reflected by respective changes in whole blood or platelet 5-HT indicating that brain and platelet 5-HT are not related.