[Antihypertensive action of adrenergic beta-receptor blockers and its effect on the entire sympathetic outflow in spontaneously hypertensive rats].

Three kinds of beta-adrenoceptor blocking agents were orally administered to spontaneously hypertensive rats (SH rats) from 5 to 13 weeks of age, and their effects on the development of hypertension and on peripheral sympathetic nervous system were investigated. In SH rats treated with the vehicle (2% Tween 80) for 8 weeks, systolic blood pressure increased from 132 +/- 1.3 to 179 +/- 2.7 mmHg (n = 10). Treatment with propranolol (2 X 50 mg/kg/day p.o., n = 8), pindolol (2 X 15 mg/kg/day p.o., n = 8) and D-32 (2 X 15 or 2 X 50 mg/kg/day p.o., n = 9) for 8 weeks slightly but definitely depressed the aforesaid development of hypertension, and their average reduction in systolic blood pressure was approximately 15 mmHg. In the pressor response to electrical stimulation of pre-ganglionic sympathetic nerves, there was not any difference between SH rats treated with vehicle and beta-adrenoceptor blocking agents (propranolol and D-32). P.o. administration of guanethidine or phentolamine, however, caused a slight hypotension and produced a significant reduction in the pressor response to electrical stimulation. SH rats treated with propranolol showed a leftward shift of the pressor response curve not to norepinephrine but to angiotensin II as compared with that obtained from vehicle treated SH rats. This phenomenon is probably due to the decreased renin release by the prolonged-treatment with drug. On the basis of these results, we could not obtain any clear evidence that the antihypertensive action exerted by beta-adrenoceptor blocking agents resulted from some interference with the function of the peripheral sympathetic nervous system.