Left atrial pressure and postprandial diuresis in conscious dogs on a high sodium intake

5 conscious, well trained, female dogs kept on a high sodium intake (14 meq Na/kg bw) were used to measureeft atrial pressure (LAP), urine volume ( $\dot V$ ), sodium and potassium excretion (U_Na $\dot V$ , U_K $\dot V$ ) as well as plasma osmolality (P_osm) before and up to 180 minafter food intake. The dogs were fitted with a catheter in the left atrium (thoracotomy). In all experiments (n=23) LAP increased postprandially (pp) above fasting controls. The mean peak increase range from 4 to 6 cm H₂O and was observed as early as 61–80 and as late, as 161–180 min pp. Increase in LAP was closely correlated to V which rose from 36±28 to 160±51 ul/min·kg. pp $\dot V$ was also correlated to pp U_Na $\dot V$ which increased from 4.8±3.3 to 34.0±8.5 ueq/min·kg. The pp increase in LAP and its close relation to pp $\dot V$ and pp U_Na $\dot V$ emphasize the assumption that intrathoracic receptors are involved in the regulation of body fluids.