Regulation of plasma ANF after increases in afterload in conscious dogs

Although atrial stretch is the primary stimulus for atrial natriuretic factor (ANF) secretion, hormones may directly affect ANF secretion or may indirectly influence ANF by changing left ventricular afterload, thereby altering atrial stretch. To determine whether direct effects are important for the release of ANF in vivo, we measured changes in plasma ANF and in atrial wall function in the conscious dog after the administration of vasopressin, angiotensin II, and phenylephrine and by mechanically increasing left ventricular afterload by partial aortic occlusion. Injections of phenylephrine, angiotensin II, and arginine vasopressin (AVP) that were chosen to cause similar changes in systemic arterial pressure resulted in similar changes in atrial pressure and diameter. Maximum V wave atrial wall stress increased to 283 +/- 12, 311 +/- 41, 327 +/- 24, and 277 +/- 22 g/cm2 for AVP, angiotensin, phenylephrine, and occlusion, respectively, and plasma ANF increased to 242 +/- 81, 248 +/- 62, 299 +/- 95, and 190 +/- 53 pg/ml. There were significant linear correlations between left ventricular afterload and left atrial pressure, and each method for increasing left ventricular afterload shifted the position to the left on an atrial pressure-diameter, compliance curve, by a similar degree. Thus changes in left ventricular afterload result in changes in atrial wall function and similar changes in plasma ANF. No hormonal-specific increase in plasma ANF was found in conscious dogs after increases in afterload.