Evidence that decreased cardiac output is not the stimulus to sodium retention during acute constriction of the vena cava.

It has been proposed that the antinatriuresis during constriction of the TVC is due to a decrease in CO. We have compared the effect on sodium excretion of comparable reductions in CO by three separate methods: TVC constriction, PA occlusion, and LV infarction. Dogs were studied during 10% of body weight saline loading and again after TVC constriction, PA occlusion, or LV infarction. CO fell 26 to 31% in all groups; sodium excretion was not significantly altered after PA occlusion (474 to 533 micronEq/min.) or LV infarction (587 to 609 micronEq/min.) but fell significantly after TVC constriction (504 to 271 micronEq/min.). Renal and systemic hemodynamoderate reduction of CO per se does not cause sodium retention. PA and TVC dogs had comparable increments in vena caval pressure but opposite changes in RVEDP; 4 to 0.9 mm. Hg (TVC) and 0.5 to 9.1 mm. Hg (PA).