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·g body weight and inulin clearance was increased 2.2 ml/min°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 an 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\((\overline {CVP} )\). 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\(\overline {CVP} \). It was concluded that\(\overline {CVP} \) is an important contributor to body fluid control mechanisms even after vagotomy.