To the Editor.—
The recent COMMENTARY by Vertes, "Clinical Use of Renin Determinations" (230:1279, 1974), was quite informative. However, one statement on page 1280 implied that minoxidil is a drug that produces renin inhibition. There is now ample evidence to demonstrate that minoxidil will produce definite increases in plasma renin activity.1,2 Velasco found that minoxidil administration increased plasma renin activity from about 1.21±0.28 to 8.58±2.83 ng/ ml/hr. When propranolol was given concomitantly with minoxidil, plasma renin activity still increased in comparison with control values, but the activity on combined treatment, 3.63±1.05 ng/ml/hr, was much lower than that seen with minoxidil alone.Thus, it appears that minoxidil produces an increase in plasma renin activity similar to that seen with other vasodilator antihypertensive agents including hydralazine (Apresoline),3,4 diazoxide (Hyperstat),5,6 sodium nitroprusside (Nipride),7 and thiazide diuretics.8 Spironolactone (Aldactone) also appears to produce an increase in plasma renin activity.