The effects of vasopressin on the diuretic response to left atrial distension.

1. The diuretic response to left atrial distension was studied during infusion of saline or during infusion of vasopressin at four different dose rates.2. During infusion of saline left atrial distension caused an increase in free water clearance and an increase in osmolal clearance.3. During infusion of vasopressin at a rate of 0.025 m-u./kg.min and 0.1 m-u./kg.min there was no statistically significant increase in free water clearance during left atrial distension but there were variations in free water clearance in individual experiments.4. During infusion of vasopressin in doses of 0.4 m-u./kg.min and 1.0 m-u./kg.min changes in free water clearance were dependent upon changes in osmolal clearance indicating that these doses of vasopressin provided a maximum antidiuretic effect.5. Infusion of vasopressin had no effect on the increase in osmolal clearance which occurred in response to left atrial distension.6. The results allow the view that a part of the diuretic response to left atrial distension could depend upon a decrease in the concentration of antidiuretic hormone in the circulating blood.