Left atrial receptors in arterial baroreflex control of heart rate.

We have studied the influence of left atrial receptor stimulation on arterial baroreflex control of heart rate with a view to determine the role of cardiac efferent sympathetic and parasympathetic pathways in any interaction observed. Experiments were performed on anaesthetized, artificially ventilated, and thoracotomised cats and dogs. The sensitivity of baroreflex heart rate response was found to be higher in dogs as compared to cats. Both the sympathetic and parasympathetic effects contributed to the reflex chronotropic effects observed during changes in mean arterial blood pressure. The reflex tachycardia response during left atrial receptor stimulation was more pronounced in dogs than in cats. Stimulation of left atrial receptors caused slight inhibition of the baroreflex tachycardia response and potentiation of the bradycardia response.