Attenuation of the Baroreceptor Reflex by Propofol Anesthesia in the Rat

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Abstract
The effect of the intravenous (i.v.) short acting anesthetic propofol on baroreflex control of heart rate (HR) was examined in normotensive rats. Propofol was infused at a fixed rate of 9 mg/kg/h immediately after a bolus dose of 10 mg/kg. Blood pressure (BP) was maintained with a plasma substitute. Conscious rate were used for comparisons. Reflex HR responses were recorded after i.v. doses of the pressor agent phenylephrine and the depressor agent sodium nitroprusside. Baroreceptor reflex parameters were determined by sigmoidal computerized curve-fitting. Propofol produced tachycardia at rest and atropine increased HR only moderately. In addition, a limitation in the bradycardiac response to artificial BP increases (lower plateau) was shown. This set of data indicated a vagal depression. The sympathetic component of the baroreflex was equally affected, since the maximal tachycardia resulting from artificial BP decreases (higher plateau) was shifted toward lower values. A marked diminution of the baroreflex gain resulted from the reduced activity of both vagal and sympathetic components. The mechanism for this decrease in the baroreflex-dependent total autonomic effector output (HR range) probably reflects the interaction of propofol with the baroreceptor pathways.