The effect of acute spinal cord section upon the renal response to intravascular volume expansion.

Abstract

Data have been presented recently which show abolition of the diuretic and natriuretic response to acute intravascular volume expansion in the chronic spinal dog. Since these experiments indicate that salt and water homeostasis can be achieved solely through spinal pathways, experiments were done in the acute spinal preparation to determine if the reported abolition of natriuresis and diuresis in the chronic preparation was related to interruption of spinal pathways per se or to a long term effect of the procedure. Dogs were anesthetized and creatinine clearance (GFR), and sodium and water excretion determined. The spinal cord was then sectioned at the C8 level and intravascular volume expanded with 6% clinical dextran (30 ml/kg). The determinations were then repeated after urine flow had achieved a new steady state. Seven of the ten dogs studied showed a significant increase in sodium and water excretion following dextran infusion. However, both responses were attenuated compared to a previously studied group of intact dogs. The remaining three animals showed a decrease in urine flow, sodium excretion and GFR despite volume expansion. These experiments indicate that spinal pathways are not the sole determinants of intravascular volume control.