Acute saline loading in normal and bilaterally atrial-resected conscious dogs

Acute isotonic saline volume loads (400 ml) were intravenously administered to conscious, renal-denervated dogs before and after bilateral removal of the atrial free walls and atrial appendages to determine the role of atrial-mediated hormonal factors in the renal excretory response. In one group of dogs (n = 11), the volume was given in 10 min; in another group (n = 5), the volume was given in 30 min while arginine vasopressin (AVP) was infused to maintain plasma AVP at a fixed, normal level (3 pg/ml). Sodium and water excretion, mean arterial pressure, and plasma hormone levels were determined before and for 5 h after volume loads. Atrial resection resulted in a 40-50% reduction of sodium and water excretion in both groups during the first 2 h after volume expansion. The blunted renal excretory responses could not be explained by differences in arterial pressure, renal sympathetic nerve activity, or by hormonal differences of plasma immunoreactive atrial natriuretic factor (iANP), plasma AVP, plasma renin activity, or plasma aldosterone. Plasma iANP was not significantly increased by the volume load in either the normal or atrial-resected state. Atrial-resected dogs exhibited normal plasma levels of iANP. The data indicate the presence of an unidentified diuretic and natriuretic substance, which is released with volume expansion from either the cardiac atria or via the central nervous system, and that the release of this factor is removed by atrial resection.