ATRIAL PRESSURE AND POSTPRANDIAL VOLUME REGULATION IN CONSCIOUS DOGS

Conscious, chronically instrumented dogs (n=24; left and right atrial catheter, electromagnetic flow probe around the left renal artery, carotid loop) were used in 97 expts. to study mechanisms mediating postprandial (pp) excretion of sodium and water up to at least 180 min after food intake. The dogs were kept under standardized conditions and maintained on a high (14.5 mmol Na/kg b.w./day) or a low (0.5 mmol Na/kg b.w./day) sodium intake diet (HSI, LSI) which was given once daily in the morning. In HSI dogs left atrial pressure (LAP) increased from a fasting control value of 0.2 kPa (2 cm H2O) to 0.7 kPa (7 cm H2O) (120-180 min pp), right atrial pressure from 0.0 kPa (0 cm H2O) to 0.3 kPa (3 cm H2O). 25% of the sodium intake were excreted up to 180 min pp. There was a highly significant positive correlation between pp sodium excretion (UNaV) and pp LAP. UNaV was not related to pp increase in renal blood flow (RBF) and glomerular filtration rate (GFR). Fractional sodium excretion increased from a fasting control value of 0.6% to more than 4% in HSI dogs and from 3.3% to more than 7% in an adrenalectomized HSI dog. DOCA did not diminish UNAV in HSI dogs. In LSI dogs, RBF and GFR increased pp, LAP did not change pp. No substantial increase in UNaV was observed. The close correlation between pp UNaV and pp LAP in HSI dogs supports the hypothesis that intrathoracic vascular receptors are involved in the mediation of volume regulation by stimulation of still unknown natriuretic mechanisms which operate on the tubular level in the presence of high mineralocorticoid activity. © 1979 Springer-Verlag.