Interaction in hypertensive man between sodium intake, converting enzyme inhibitor (enalapril), plasma renin and blood pressure control.

Sixteen patients with hypertension entered a study in which the effects of enalapril were compared with sodium restriction, with the two in combination and with placebo using a balanced randomized double-crossover design. Each patient had four treatment phases of two weeks, duration which comprised a 2 x 2 factorial design as well as an initial period on sodium restriction and enalapril placebo. All patients received a reduced sodium diet and sodium intake was altered by slow Na tablets. Increasing sodium intake raised blood pressure similarly whether patients were receiving enalapril or its placebo. Enalapril lowered blood pressure to a similar extent in patients on either a low and high sodium intake. The combination of a low sodium intake and enalapril was additive and there was no interactive effect between the two therapies whether assessed by a linear or a logarithmic method. Plasma renin was increased by enalapril and lowered by increased sodium intake. These effects were additive and there was no interactive effect. Neither the initial plasma renin nor the rise in renin predicted which patients would respond to enalapril. Enalapril was an effective antihypertensive agent and its blood pressure-lowering effect and that of sodium restriction were additive.