Left atrial pressure and sodium balance in conscious dogs on a low sodium intake

Summary 10 conscious chronically prepared dogs were used. After recovery from thoracotomy (catheter into the left atrium, nylon purse string around the mitral annulus) they were kept chronically on a low sodium intake (<0.5 meq Na/kg bw daily). On 51 days left atrial pressure (LAP) was increased for 60 min about 10 cm H₂O once daily by tightening the purse string (distension period: DP). During DP urine volume (\(\dot V\)) increased about threefold, and sodium excretion (E _Na) about sixfold. The amount of renal sodium loss on the days when LAP was increased exceeded the daily intake considerably. The application of DOCA (15 mg i.m.) did not diminishE _Na during DP and 60 min thereafter. During DP heart rate increased by about 70 b/min and mean arterial blood pressure increased by about 15 mm Hg. The data suggest that stimulation of intrathoracic receptors by a reversible mitral stenosis augments renal sodium excretion even in a state of a highly stimulated tubular sodium resorption.