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

1. The effects of acute changes in plasma Na concentration ( P Na ) on renal blood flow (RBF) and glomerular filtration rate (GFR) were studied in anaesthetized 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 . 2. Blood pressure (B.P.), packed cell volume (PCV), concentration of plasma solids (PS) and the plasma concentration of H + and K ( P K ) ions were measured but no attempt was made to contain their fluctuation. 3. 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 P Na throughout the range studied (120‐190 m‐mole l. −1 ). Glomerular filtration rate rose with P Na to reach maximal values at P Na levels of 140‐160 m‐mole l. −1 , but fell thereafter. The combined fall in RBF and GFR, without change in filtration fraction, at P Na 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 P Na was reduced below 140 m‐mole l. −1 requires an additional explanation. 4. Renal blood flow was independent of P K ; it was inversely related to [H + ] and directly related to PS. Glomerular filtration rate was independent of PCV and P K . 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 P Na may be mediated in part, at least, by concurrent change in PS and [H + ].