Hypotensive effect of O-[3-(tert, butylamino-2-hydroxypropoxy]-benzonitrile hydrochloride (bunitrolol, Kö 1366) was examined by intravenous administration of 5 mg to 20 cases of essential hypertension and by longterm oral administration of 15-30 mg to 27 cases of essential hypertension. 2. It was found that bunitrolol given either i.v. or p.o., produced a significant decrease of systolic, diastolic and mean blood pressure at rest. 3. Inhibitory effect of bunitrolol on exercise-induced increase of blood pressure was remarkable, while there was little inhibitory effect on the cold pressor-induced one. 4. Bunitrolol decreased blood pressure and lowered plasma renin activity in high renin hypertensive patients, suggesting that the hypotensive mechanism based, at least in part, on its capacity of inhibiting renin secretion. 5. However, the main hypotensive mechanism of bunitrolol seemed, in the case of i.v. use, related to the cardiac inhibitory action. Regarding the hypotensive mechanism of this drug in the long-term use, further investigation will be required.
