Release of natriuretic factor from rat heart-lung preparation by atrial distension

The hypothesis that an increase in blood volume results in the release of an atrial natriuretic factor (ANF) via atrial stretch was examined using an isolated rat heart-lung preparation. The heart lung preparation was perfused with a fluorocarbon emulsion for two periods of 20 min. During the first period the venous return reservoir was placed at a level of 1-2 cm above the right atrium [low central venous pressure (low CVP)] and at a level 7-12 cm above the heart (high CVP) for the second period. The perfusate used for each period was collected and saved for later analysis of natriuretic activity using anesthetized rats as a bioassay. Samples of either low or high CVP perfusate were infused into the abdominal aorta of the assay rats while urine was collected from a bladder catheter. A 3-min infusion of the high CVP perfusate at a rate of 0.5 ml/min resulted in an increase in urine flow from 10 to 28 microliter/min (P less than 0.01), sodium excretion from 0.14 to 1.34 mueq/min (P less than 0.01), and potassium excretion from 0.17 to 0.81 mueq/min (P less than 0.01). Infusion of the low CVP perfusate failed to produce a significant diuresis, natriuresis, or kaliuresis. These results are consistent with the hypothesis that ANF may be a hormone involved in the control of blood volume.