THE EFFECT OF PENTOBARBITAL-ANESTHESIA ON THE AUTONOMIC NERVOUS-SYSTEM CONTROL OF HEART-RATE DURING BARORECEPTOR ACTIVATION

This study determined the influence of pentobarbital anesthesia on the autonomic nervous system control of baroreceptor mediated reflex bradycardia in the rat. Reflex bradycardia was elicited by phenylephrine-induced hypertension in conscious and pentobarbital anesthetized (PA) rats before and after sympathetic blockade with the beta-1 receptor antagonist atenolol or parasympathetic blockade with the peripherally acting muscarinic receptor antagonist methyl-atropine. Reflex bradycardia was significantly decreased by pentobarbital anesthesia. Cardiosympathetic blockade produced equivalent relative decreases in baroreflex gain in conscious and PA rats. In contrast, parasympathetic nervous system blockade with methyl-atropine produced relatively less inhibition of baroreflex gain in the PA rat compared with the conscious rat. These results suggest that pentobarbital anesthesia decreases baroreflex gain by inhibiting vagally mediated reflex bradycardia.