The renal blood flow and the glomerular filtration rate of anaesthetized dogs during acute changes in plasma sodium concentration

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Abstract
The effects of acute changes in plasma Na concentration (PNa) on renal blood flow (RBF) and glomerular filtration rate (GFR) were studied in anesthetized greyhounds. Saline was infused at a constant rate (0.1 ml kg-1 min-1) either into a renal artery or into a systemic vein. Plasma Na concentration was altered by varying the Na concentration of the infused saline from 0.154 to 0.077, 0.616 or 1.232 M. Blood pressure (BP), packed cell volume (PCV), concentration of plasma solids (PS) and the plasma concentration of H+ [H+] and K+ (PK) were measured but no attempt was made to contain their fluctuation. An infusion of hypertonic saline into a renal artery usually led to an ipsilateral increase in RBF for 5-15 min, followed by a progressive fall. Over-all, mean values of RBF fell with PNa throughout the range studied (120-190 m-mole l-1). Glomerular filtration rate rose with PNa to reach maximal values at PNa levels of 140-160 m-mol l-1, but fell thereafter. The combined fall in RBF and GFR, without change in filtration fraction, at PNa values above 160 m-mole l-1 is consistent with an alteration in afferent arteriolar resistance. The fall in GFR despite a rise in RBF noted when PNa was reduced below 140 m-mole l-1 requires an additional explanation. Renal blood flow was independent of PK; it was inversely related to [H+] and directly related to PS. Glomerular filtration rate was independent of PCV and PK. It was also inversely related to [H+] and directly related to PS up to a value of 6 g 100 g-1 plasma, after which the relationship was reversed. These results suggest that the renal vascular responses to acute changes in PNa may be mediated in part, at least, by concurrent change in PS and [H+].