Abstract
The blocking (endoanesthetic) effects of lidocaine (Xylocaine) and benzonatate (Tessalon) on cardiac ventricular, non-medullated endings were tested in cats. Lidocaine was found to cause an effective and long-lasting partial blockade of the cardiovascular reflex responses to stimulation of the ventricular receptors. This effect was obtained at plasma concentrations of 2.5-4.7 microgram/ml, which is within the concentration range seen in patients with myocardial infarction treated with lidocaine because of its antiarrhythmic properties. Tessalon also markedly attenuated the reflex response, normally obtained when the ventricular receptors are excited, but the effect was very shortlasting when doses, producing no side effects, were used. Recordings of impulse traffic from the left ventricular receptors showed that the impaired reflex responses after lidocaine and Tessalon were due to a blockade at the receptor level. Thus both the receptor response to ventricular distension and to injection of protoveratrine (Bezold-Jarisch reflex) was markedly attenuated after infusion of lidocaine (2-4 mg/kg) or a bolus injection of Tessalon (0.2-1 mg/kg).
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