Influence of atrial mechanoreceptors upon the sympathetic efferent activity elicited during a cardiogenic chemoreflex in the dog

Abstract

Two different cardiogenic reflexes were studied for their effects upon the activity recorded from the thoracic cardiac nerves of 7 chloralose-anesthetized dogs. Sympathetic efferent activity in 5 right and 7 left anterior ansa multifiber preparations was quantitatively analyzed. A cardiogenic hypertensive chemoreflex was induced by administration of serotonin (100 μg/ml, 2 ml) into the left atrium before, during and after inflation of balloons in the right and/or left atrial appendages. Balloon inflations alone resulted in heart rate increases of 5–20 bpm but arterial blood pressure, pulse pressure and end diastolic pressure were not significantly affected. Control serotonin-induced efferent discharges were 174 ± 10% (mean ± S.E.M.) of resting activity with a duration of 5.2 ± 0.4 s. During inflation of both atrial balloons, the serotonin-induced efferent discharges were 165 ± 14% (N.S.) of resting activity with a duration of 7.8 ± 0.7 s ( P < 0.011). Following release of the balloons, the serotonin-induced discharges were 152 ± 17% (N.S.) of resting activity with a duration of 4.9 ± 0.4 s (N.S.). These results suggest that afferent signals from atrial mechanoreceptors can act to increase the duration but not the total intensity of the efferent sympathetic discharges elicited during a cardiogenic chemoreflex.