Cardiac nerve blockade by infusion of procaine into the pericardial space of conscious dogs

Abstract

A technique was developed to produce acute, reversible cardiac nerve blockade (CNB) in the conscious dog by infusion of 2% procaine into the pericardial (PC) space. During CNB, reflex changes in heart rate (HR) in response to intravenous bolus injections of phenylephrine (100 micrograms) and nitroglycerin (300 micrograms) and the reflex tachycardia and hypotension after a 50-micrograms bolus injection of veratridine into the left atrium were abolished. In response to CNB, HR increased from 79 +/- 10 to 142 +/- 10 beats/min and mean arterial pressure (MAP) increased from 101 +/- 5 to 117 +/- 6 mmHg. Baseline values for plasma arginine vasopressin (AVP), plasma renin activity (PRA), and plasma norepinephrine (NE) were unchanged by CNB, but there was a small increase in plasma cortisol levels (1.4 +/- 0.3 to 2.3 +/- 0.3 micrograms/dl) during CNB. There was no significant change in the baseline levels of any of these hormones during PC infusion of 0.9% saline. To control for the possibility that procaine leaked into the systemic circulation, identical amounts of procaine were infused intravenously. Systemic administration of procaine caused a rise in MAP but had no effect on HR and did not alter plasma levels of AVP, PRA, NE, or cortisol. The relationship between plasma osmolality and plasma AVP, as well as the drinking response to a 60-min infusion of hypertonic NaCl, was unaltered by CNB. We conclude that PC procaine infusion is an effective technique for producing acute, reversible blockade of the cardiac nerves in the conscious dog.