Effect of potassium deficiency on papillary plasma flow in the rat

Chronic potassium (K⁺) deficiency has been shown previously to cause a reduction in solute content in the renal papilla, an effect that is potentially important as a contributing factor to the concentrating defect seen in this circumstance. The cause of the decrease in papillary solute content has not been adequately explained. Because alterations in the blood flow rate through the renal papilla may affect the solute content of the papilla, the present experiments examined the effect of chronic K⁺ deficiency on papillary plasma flow (PPF) in the rat. PPF was measured by the radioactive albumin accumulation technique. Sprague-Dawley rats were fed identical quantities of water and either a normal or a K⁺-deficient diet for 21 days. Total GFR in the control rats, 1.7 ± 0.17 (SE) ml/min, was similar to that in K⁺-deficient rats, 1.4 ± 0.14 ml/min (P > 0.1). Total [³H]PAH clearance was also comparable in the two groups, i.e., 4.4 ± 0.47 in control and 4.7 ± 0.45 ml/min in K⁺-deficient rats (P > 0.6). PPF was significantly lower in K⁺-deficient rats, 19.7 ± 1.1 ml X min^-1 X 100 g^-1, than in control rats, 59.8 ± 1.6 ml X min^-1 X 100 g^-1 (P < 0.001). The decrease in PPF in the K⁺-deficient rat may reflect a reduction in perfusion to the juxtamedullary nephrons, thereby resulting in a diminution in both solute delivery and blood flow to the papilla.