Anticholinergic drugs: effects on oxygen consumption and energy expenditure

Premedication has been shown to affect both oxygen consumption (VO2) and energy expenditure (EE). The metabolic responses to anticholinergic drugs have not been studied. In this study the effects of anticholinergic drugs on VO2 and EE (calculated from the measured rates of VO2 and carbon dioxide production [VCO2]: EE [kcal/d] = 3.581 x VO2 [L/d] + 1.448 x VCO2 [L/d] - 32.4) were measured in six healthy female volunteers. They were given intramuscular atropine (15 micrograms/kg), glycopyrrolate (8 micrograms/kg), scopolamine (8 micrograms/kg), and placebo in a random double-blind cross-over design. The consecutive sessions were at least 1 wk apart for each subject. VO2 and EE were measured using an indirect calorimetry (Deltatrac). Cardiovascular responses were assessed using standard noninvasive monitoring. Plasma drug concentrations were analyzed using a sensitive modification of radioreceptor assay. Subjective responses were measured with visual analog scale (VAS). Atropine and glycopyrrolate induced a significant increase in heart rate with a simultaneous decrease in pressure rate quotient (PRQ), while scopolamine caused a significant decrease in heart rate with a simultaneous increase in PRQ. Scopolamine significantly decreased both VO2 and EE, whereas glycopyrrolate increased VO2. Atropine had no significant effect on metabolic variables. Only scopolamine induced sedation in this study. In conclusion, atropine, glycopyrrolate, and scopolamine differ not only in their cardiovascular and central nervous system effects, but also in their effects on metabolism.