Glomerular filtration effects of acute volume expansion: Importance of chloride

Glomerular filtration effects of acute volume expansion: Importance of chloride. The present studies were done to determine the effect on GFR of acute volume expansion (AVE) using solutions of various sodium salts and to explore if degree of tubuloglomerular feedback (TGF) activation plays a role in any GFR differences. Free-flow micropuncture and inulin clearance studies were combined to investigate anesthetized Munich-Wistar rats expanded to 10% body weight with isotonic solutions of NaCl, Ringers bicarbonate (RB), NaHCO3, Na acetate (NaAc) and Na2SO4 as well as euvolemic controls. In the clearance studies, AVE yielded per gram kidney weight GFR's greater than control (1009 ± 51 µl/min) in the NaCl and RB (chloride expanded) groups (1397 ± 89 and 1389 ± 64) µl/min, respectively, P < 0.05 vs. control) but not in the NaHCO3, NaAc, and Na2SO4 (non-chloride expanded) groups. Proximal minus distal single nephron GFR determinations (P-D), an estimate of the degree of TGF, were less than control 13.2 ± 24 nl/min) in the NaCl and RB groups (4.1 ± 0.7 and 5.3 ± 1.9 nl/min, respectively, P < 0.05 vs. control) but were not significantly different from control in any of the non-chloride expanded groups. Early distal (ED) fluid flow correlated positively with P-D in all groups. ED chloride concentration but not TCO2 nor osmolality correlated with P-D for all groups. The correlation was negative for control and chloride expanded groups and positive for non-chloride expanded groups. We conclude 1.) AVE with chloride, but not non-chloride, solutions results in whole kidney GFR's greater than control due at least in part to greater inhibition of TGF by chloride expansion; 2.) ED chloride is correlated with opposite effects on TGF in chloride versus non-chloride AVE. We propose that this difference in TGF activation relates to characteristic intrarenal hormonal environments created by these different models of AVE in which the TGF mechanism is enacted