Involvement of the reflex increase in heart rate in the differences in urinary responses to stimulation of atrial receptors in dogs with different blood volumes.

The effect of increasing heart rate by increasing the rate of atrial pacing in the absence of any reflex effects from atrial receptors, by cooling the vagi to 12 degrees C, was studied in two groups of dogs with different blood volumes. In one group of nine dogs with a high blood volume increasing heart rate, by an amount similar to that reflexly obtained in response to stimulation of atrial receptors, resulted in significant increases in urine flow and sodium excretion; in another group of eight dogs with a low blood volume similar increases in heart rate did not result in a diuresis or natriuresis. The findings suggest that the effects of an increase in heart rate in combination with differences in blood volume could contribute to the previously reported differences in the urinary responses that result from stimulation of atrial receptors in dogs with different blood volumes.