Contribution of peripheral pooling to the renal response to immersion in the dog

The present investigation evaluated the renal and hemodynamic responses to head-out water immersion in dogs. Dogs were immersed in the vertical (seated) position in a 34 degrees C bath. Urine flow (V), osmolar clearance (Cosm), free water clearance (CH2O), sodium excretion (UNa+V), potassium excretion (UK+V), GFR, effective renal plasma flow (ERPF), central venous pressure (CVP), and cardiac output (CO) all increased significantly during immersion. This response was unchanged by bilateral cervical vagotomy or by deoxycorticosterone acetate and antidiuretic hormone administration. The control values of these dogs were low and indicated a state of peripheral vascular pooling which was readjusted to normal by the immersion maneuver. The renal and hemodynamic values during the period of immersion were similar to values of a group of dogs which were recumbent in air. Furthermore, when the latter group of dogs were tilted head down 19 degrees, there was no further increase in any of the measured parameters. These data are consistent with the view that water immersion in the upright dog simply redistributes blood volume back to that level seen in the recumbent dog, a position which is more natural for this species.