Control of renal function in isovolemic hemodilution or in vagotomized, infused rats

In male Sprague-Dawley rats cardiac output (CO) was increased 0.16 ml/min x g body weight and inulin clearance was increased 2.2 ml/min x g kidney weight either by isovolemic hemodilution with 6% albumin solution or by isohemic expansion to 133% of control blood volume. Despite similar changes in CO and glomerular filtration (GFR), hemodilution caused a much smaller rise in renal excretion at a much later time than did volume expansion. Therefore, in addition to simultaneous changes in CO and GFR and afferent factor indicating a state of expanded extracellular fluid volume was required for normal diuresis and natriuresis. This might have been mean central venous pressure (CVP). In further experiments, volume expansion in vagotomized or non-vagotomized rats led to nearly identical changes in water-, sodium- and potassium excretion in both groups. The only other measured parameter that showed identical behaviour in the two groups was CVP. It was concluded that CVP is an important contributor to body fluid control mechanisms even after vagotomy.