The effects of distension of the pulmonary vein-atrial junctions upon peripheral vascular resistance.

1. Small balloons were inserted through the left pulmonary veins so as to lie at the pulmonary vein-left atrial junctions.2. Distension of the balloons caused a reflex increase in heart rate. The afferent path was in the vagus nerves and the efferent path was in the cardiac sympathetic nerves.3. Only small and variable changes in vascular resistance in a perfused hind limb accompanied the increase in heart rate when a steady state had been reached.4. In about half of the experiments a transient vasodilatation was observed in the perfused hind limb, occurring immediately after distension of the pulmonary vein-atrial junctions and lasting about 22 sec.5. The transient dilatation was due to a decrease in sympathetic vasoconstrictor nervous activity.6. Stimulation of left atrial receptors causes an increase of sympathetic nervous activity to the heart but does not cause a corresponding increase in sympathetic nervous activity to the hind limbs.