Naunyn-Schmiedeberg's archives of pharmacology
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Naunyn Schmiedebergs Arch. Pharmacol. · Mar 1997
Comparative Study Clinical Trial Controlled Clinical TrialComparison of the effects of high ambient temperature and clonidine on autonomic functions in man.
The effects of two interventions, high ambient temperature, a sympathetic activator, and clonidine, a centrally acting sympatholytic drug, were compared on a number of autonomic functions. Eight healthy male volunteers participated in four weekly sessions. Each session was associated with one of the following treatments: placebo (physiological saline infused intravenously over 10 min) at 20 degrees C; clonidine hydrochloride (1.5 micrograms kg-1 in 10 ml infused intravenously over 10 min) at 20 degrees C; placebo at 40 degrees C; clonidine at 40 degrees C. ⋯ These result indicate that while the effects of the heat stressor are consistent with an increase in sympathetic activity, and most of the effects of clonidine are consistent with a decrease in sympathetic activity, only two functions (body temperature and heart rate) were affected in opposite directions by the two interventions. Indeed physiological antagonism between the two interventions could be demonstrated on body temperature and heart rate only, and there was no evidence for an interaction between the effects of the two variables on any of the other indices of autonomic activity. The failure of clonidine to affect two sympathetically mediated functions, carbachol-evoked sweating and physiological finger tremor, under either temperature condition, indicates that central alpha 2-adrenoceptors cannot be involved in the regulation of these functions.