Cholinergic-sympathetic interactions in the left atrium and left ventricle of conscious dogs

The extent of cholinergic-sympathetic interaction in the heart was examined in the resting control state and after isoproterenol stimulation in eight conscious dogs. Sonomicrometer crystals and solid-state pressure transducers were implanted in the left atrium and the left ventricle to evaluate mechanical function while heart rate was held constant by atrial pacing. Edrophonium (0.5 mg/kg i.v.) was given as a single dose at rest and during increased sympathetic tone produced by continuous infusion of isoproterenol (0.08 μg/kg/min). In the control state, edrophonium administration caused no change in left ventricular dP/dt, fractional shortening or velocity of contraction, but produced significant (P < .001) decreases in left atrial fractional shortening and contraction velocity. During isoproterenol infusion there were significant increases in dP/dt, the velocity of contraction and fractional shortening in both left atrium and ventricle (P < .001). Administration of edrophonium during this increase in inotropic state produced significant (P < .01) decreases in left ventricular dP/dt, fractional shortening and contraction velocity. Moreover, after edrophonium, left atrial fractional shortening and velocity of contraction were decreased to values that were significantly (P < .001) less than control. Thus, cholinergic stimulation caused selective depression of left atrial systolic function at rest and depression of both left atrial and ventricular function during sympathetic stimulation.