ERYTHROCYTE NA-K-CL COTRANSPORT ACTIVITY IN LOW RENIN ESSENTIAL HYPERTENSIVE PATIENTS - A NA-23 NUCLEAR-MAGNETIC-RESONANCE STUDY

The Na-K-Cl cotransport activity in red blood cells from essential hyp ertensive men with low (n = 8, mean age 42 +/- 4 years) or normal reni n activity (n = 4, mean age 43 +/- 3 years), and in normotensive men w ith normal renin activity (n = 7, mean age 38 +/- 4 years) has been ev aluated by means of a recently developed Na-23 nuclear magnetic resona nce (NMR) method. Sodium efflux was determined by relating the resonat ing frequency of the NMR signal from extracellular sodium to sodium co ncentration in the presence of the shift reagent Dy(PPP)(2)(7-). The m aximum Na+ efflux driven by cotransport (V-max) was measured in Na+-lo aded erythrocytes in the presence of ouabain to block the Na-K-Cl pump activity. A significant difference (P < 0.05) was found in V-max valu es of low renin patients (0.70 mmol/h/L cells, range 0.40 to 0.90 mmol /h/L cells) as compared with normotensive controls (0.39 +/- 0.08 mmol /h/L cells) and normal renin hypertensives (mean 0.49 +/- 0.04 mmol/h/ L cells). In conclusion, this study showed an increased activity of th e Na-K-CI cotransport in red blood cells from low renin hypertensive m en as compared with normal renin hypertensives and normotensives.