Abstract
1. Urinary responses to stimulation of atrial receptors have been found to be greater in dogs with a high blood volume than in dogs with a low blood volume. Two groups of dogs with different blood volume were examined by distending a large balloon in the left atrium, to stimulate atrial receptors and find out whether the increase in atrial receptor discharge was different in the two groups of dogs. 2. The relationship between atrial receptor discharge and left atrial pressure was determined in twenty-six fibres studied in four dogs with a high blood volume and sixteen fibres studied in three dogs with a low blood volume. 3. The slope of the relationship representing the increase in atrial receptor activity during increases in left atrial pressure, and the activity at each left atrial pressure, were significantly greater in dogs with a high blood volume than in dogs with a low blood volume. 4. This study has shown that the atrial receptor discharge and their responses to increases in left atrial pressure are greater in dogs with a high blood volume than in those with a low blood volume.