SODIUM-LITHIUM COUNTERTRANSPORT ACTIVITY AS A DETERMINANT OF DETERIORATION OF GLOMERULAR FUNCTION IN IGA NEPHROPATHY

We measured Na+/Li+ CT in 16 IgA nephropathy patients. Records were re viewed (mean observation period 5.5 years) for serial measurements of blood pressure (BP), urinary protein excretion, GFR (Cr-51-EDTA) and p lasma creatinine. Na+/Li+ CT correlated with the slope of the plot of GFR versus time (r(s) = -0.66, p = 0.005) systolic BP at diagnosis (r( s) = 0.62, p = 0.011) and both systolic and diastolic BP at the end of follow-up (r(s) = 0.69, p = 0.003, and r(s) = 0.56, p = 0.023). A dia stolic blood pressure(DBP) greater than or equal to 95 mm Hg was assoc iated with a faster rate of GFR decline (rate of change of GFR: -0.40 vs. -0.14 ml/min/month, p = 0.07; for DBP greater than or equal to 95 vs. <95 mm Hg, respectively). In a multiple regression analysis with t he rate of decline of GFR as dependent variable, Na+/Li+ CT emerged as a significant and independent determinant of the rate of fall of GFR (beta coefficient -1.56, SE beta 0.49, p = 0.006) and explained 52.7% of the variation in the GFR fall. Higher activities of Na+/Li+ CT are significantly associated with an increased rate of deterioration of re nal function in IgA nephropathy; part of this effect could be mediated by higher blood pressure values.