Renin Unresponsiveness and the Effects of Oxprenolol, Methyldopa and Spironolactone in Patients with Essential Hypertension

Plasma renin activity (PRA), supine, erect and post-frusemide (1 mg/kg IV) was studied in 51 patients with previously untreated essential hypertension and their age- and sex-matched normotensive controls. Supine PRA, and the rise in PRA in response to the erect posture and frusemide, were significantly less in hypertensives compared to controls. When the hypertensives were arbitrarily divided into lower, mid, and upper subgroups according to supine PRA, the renin responsiveness was similar in each subgroup but significantly less in hypertensives compared to controls, subdivided in the same way. This does not support the existence of a separate "low renin" subgroup. The low supine PRA and reduced response to stimulation appears to be a feature of patients with essential hypertension. Thirty-nine of these hypertensives entered a double-blind cross-over drug trial of oxprenolol, methyldopa and spironolactone. All three drugs were equally effective in lowering the systolic and diastolic blood pressures in all three renin subgroups. Spironolactone caused a greater fall in systolic pressure in the lower renin group than in the other groups. Oxprenolol was the best tolerated drug, with only 5% of patients withdrawing due to side-effects compared to 13% on spironolacone and 29% on methyldopa.