Sodium conservation and control of glomerular filtration rate

¹ Department of Physiology, University of Oregon Medical School, Portland, Oregon

Experiments on dogs were designed to study the role of glomerular filtration rate (creatinine clearance, C_Cr) in sodium homeostasis. Dogs were studied on a normal Na intake (salted) and after Na had been removed from the diet (unsalted). In both instances C_Cr was estimated before and after rapid expansion of extracellular fluid volume (ECF) with glucose, mannitol, or NaCl solutions. Before expansion of ECF, C_Cr showed no consistent change relating to Na-deficiency as such. Following expansion of ECF, C_Cr increased in dogs with normal intake of Na and decreased (or increased less) in nine out of ten comparisons in dogs with no Na in the diet. The percentage change in C_Cr elicited by ECF expansion correlated positively with change in plasma Na concentration and inversely with change in plasma potassium concentration, except following NaCl solution infusion or the inclusion of K in glucose infusions. Decreased C_Cr following ECF expansion in dogs with no Na in the diet was tentatively ascribed to intrarenally evoked vasoconstriction consequent to the loss of intracellular K from some undefined site.