Effects of several beta-blocking agents on the development of hypertension in spontaneously hypertensive rats

Antihypertensive effects of chronic oral administration of adrenergic beta-blocking agents were assessed in SHR. Propranolol, pindolol, oxprenolol, atenolol and labetalol were used as beta-blockers and the effects of these compounds on the blood pressure and the heart rate were compared with those of hydralazine, a representative vasodilating antihypertensive agent. Propranolol, oxprenolol and atenolol produced a definite decrease in the heart rate; the development of hypertension was retarded. Pindolol produced antihypertensive effects only after a longer period of administration and such were associated with insignificant decrease in heart rate. With a shorter period of administration the drug produced only an insignificant fall of blood pressure with practically no change in the heart rate. With labetalol, a beta-blocker with alpha-blocking action, a fall of blood pressure appeared earlier and was of greater magnitude. Hydralazine produced a definite antihypertensive effect, which appeared immediately after administration and was associated with a tachycardia. In pithed rats, only pindolol produced a definite fall of blood pressure. On the basis of these findings, possible mechanisms of antihypertensive effects of beta-blockers were discussed.