ON MAINTENANCE OF PROPER OSMOLALITY AND VOLUME OF BODY FLUIDS .2. DIURETIC EFFECT OF HYPOTONIC SALINE GIVEN INTO A PERIPHERAL VEIN INTO PORTAL VEIN OR BY MOUTH IN DOG

The diuretic effect of 0.45% saline infused alternately into the portal vein, into a peripheral vein and given by mouth (at the same speed) was studied in unanaesthetized (trained) dogs. Saline was infused into the portal vein by means of implanted catheters, through which blood samples could be drawn. When compared with the intravenous infusion, there is an earlier and stronger diuretic response during intraportal infusion. Oral administration of 0.45% saline has the strongest diuretic effect of all three routes. Urinary sodium excretion and osmotic clearance increase more during oral administration and intraportal infusion of 0.45% saline than during intravenous infusion. The results are interpreted as positive evidence of an osmoregulatory mechanism localised between the intestine and the hepatic veins. This mechanism may play a major role in the homeostatic control of extracellular fluid volume since it is located where excessive fluid intake could first be observed. The results also provide evidence of the importance of the intestinal wall in this mechanism. © 1969 Springer-Verlag.