EFFECT OF LOADING RIGHT ATRIAL AND VENTRICULAR RECEPTORS ON STIMULATED AVP, ACTH, AND RENIN SECRETION IN AWAKE DOGS

The goal of this study was to test the hypothesis that increasing or d ecreasing the load on baroreceptors in the right heart influenced the secretion of arginine vasopressin (AVP), adrenocorticotropic hormone ( ACTH), and renin during a state of sustained arterial hypotension. The hypothesis was tested in chronically instrumented conscious dogs prep ared with inflatable cuffs around the pulmonary artery (PA) and the th oracic inferior vena cava (IVC). In one protocol (n = 5), mean arteria l pressure was reduced 10 or 20% below control by constriction of the PA, a maneuver that caused a fall in left atrial pressure (LAP) and an increase in right atrial pressure (RAP). Plasma AVP, ACTH, atrial nat riuretic peptide (ANP), and plasma renin activity (PRA) all increased (P < 0.05) in response to constriction of the PA. Reducing RAP to cont rol by constriction of the IVC during maintained constriction of the P A had no effect on MAP, LAP, plasma AVP, ACTH, or PRA, but plasma ANP fell significantly. In a separate protocol (n = 4), constriction of th e IVC was used to reduce MAP 10 or 20% below control, and this led to significant decreases in both LAP and RAP and increases in plasma AVP, ACTH, and PRA. RAP was then increased above control by constriction o f the PA without altering either MAP or LAP. Raising RAP from a level that was 6.3 +/- 1.3 mmHg below control to 3.5 +/- 1.0 mmHg above cont rol had no effect on plasma AVP, ACTH, or PRA. These results show that , against constant reductions in MAP and LAP, acute changes in RAP ove r a 9-mmHg range have no effect on plasma AVP, ACTH, or PRA. Therefore , in contrast to the potent inhibitory effect of loading left atrial r eceptors on secretion of AVP, ACTH, and renin, we conclude that barore ceptors on the right. side of the heart have minimal influence on the secretion of AVP, ACTH, and renin in conscious dogs.