Normotensive hyperreninemia in systemic lupus erythematosus. An indicator of tubular dysfunction

High plasma renin activity (PRA) was found in 16 of 42 randomly selected nonuremic systemic lupus erythematosus (SLE) patients. Mild hypertension was present in 3 of the 16.6 high-PRA and 10 normal-PRA patients were admitted to a metabolic ward. Salt restriction produced a disproportionate rise in both PRA and aldosterone, a decrease in glomerular filtration rate (GFR) and a slightly greater negative sodium balance in the group with high PRA. Potassium excretion was less than intake in both groups. Balance studies were performed in 6 additional high-PRA patients before and during indomethacin administration (150 mg/24 h). PRA and aldosterone were markedly suppressed by indomethacin. UnaV was significantly greater than in the control period despite of the 28% reduction in GFR. These results suggest that high PRA is secondary to impaired distal tubular sodium reabsorption. Such a defect could be responsible for the relatively low frequency of hypertension in lupus nephritis.