Response to Rapid Water, Sodium and Dextran Loads of Intact Ringer's-Infused Unanesthetized Dogs

Abstract

In Ringer's-infused unanesthetized intact dogs, rapid intravascular injections (200 cc) caused an enhanced diuresis, regardless of injection site. Injection of Ringer's solution induced an immediate and sustained increment of H2O, Na and total solute diuresis. These changes were correlated with increases in venous pressure, reductions in hematocrit and in plasma oncotic pressure (except in the dextran experiments). They were not correlated with patterns of GFR, RPF, plasma Na and total solute, filtered electrolyte load, blood pressure of heart rate. Injection of 3.75% glucose-in-water induced a sustained increment of H2O diuresis, with only a transient or no increase in Na and total solute diuresis. Injection of 6% dextran-in-water induced a complex, variable response, with sustained enhanced diuresis of H2O, Na and total solutes in some experiments. It is suggested that two adjustments, volume and composition homeostatic correction, are operative, the former immediate, the latter delayed (possibly hormonal). It is further suggested that the former is a response to circulating intravascular volume expansion, possibly ‘sensed’ by stretch and/or pressoreceptors.