Bupivacaine inhibits baroreflex control of heart rate in conscious rats

Background: Because exposure to intravenously administered bupivacaine may alter cardiovascular reflexes, the authors examined bupivacaine actions on baroreflex control of heart rate in conscious rats. Methods: Baroreflex sensitivity (pulse interval vs. systolic blood pressure in ms/mmHg) was determined before, and 1.5 and 15.0 min after rapid intravenous administration of bupivacaine (0.5, 1.0, and 2.0 mg/kg) using heart rate changes evoked by intravenously administered phenylephrine or nitroprusside. The actions on the sympathetic and parasympathetic autonomic divisions of the baroreflex were tested in the presence of a muscarinic antagonist methyl atropine and a β-adrenergic antagonist atenolol. Results: Within seconds of injection of bupivacaine, mean arterial pressure increased and heart rate decreased in a dose-dependent manner. Baroreflex sensitivity was unaltered after administration of 0.5 mg/kg bupivacaine. In addition, 1 mg/kg bupivacaine at 1.5 min depressed phenylephrine-evoked reflex bradycardia (0.776 ± 0.325 vs. 0.543 ± 0.282 ms/mmHg, P < 0.05) but had no effect on nitroprusside-induced tachycardia. Bupivacaine (2 mg/kg), however, depressed reflex bradycardia and tachycardia (phenylephrine, 0.751 ± 0.318 vs. 0.451 ± 0.265; nitroprusside, 0.839 ± 0.256 vs. 0.564 ± 0.19 ms/mmHg, P < 0.05). Baroreflex sensitivity returned to prebupivacaine levels by 15 min. Bupivacaine (2 mg/kg), in the presence of atenolol, depressed baroreflex sensitivity (phenylephrine, 0.633 ± 0.204 vs. 0.277 ± 0.282; nitroprusside, 0.653 ± 0.142 vs. 0.320 ± 0.299 ms/mmHg, P < 0.05). In contrast, bupivacaine did not alter baroreflex sensitivity in the presence of methyl atropine. Conclusions: Bupivacaine, in clinically relevant concentrations, inhibits baroreflex control of heart rate in conscious rats. This inhibition appears to involve primarily vagal components of the baroreflex-heart rate pathways.