HEMODYNAMIC EFFECTS OF BETA-ADRENERGIC BLOCKADE WITH PINDOLOL, OXPRENOLOL, PROPRANOLOL AND BUFETOLOL HYDROCHLORIDE IN ESSENTIAL HYPERTENSION

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Hemodynamic studies (using ¹³¹I-labeled albumin [RISA]) were performed before and 5 and 42 weeks after the oral administration of pindolol (av. 30 mg/day), oxprenolol (av. 216 mg/day), propranolol (av. 75 mg/day) or bufetolol hydrochloride (av. 30 mg/day) in 40 patients with essential hypertension. Responders to the antihypertensive actions of short-term (5 weeks) pindolol or bufetolol showed a reduction in total peripheral resistance (pindolol, from av. 2622 to 2022 dyne·sec·cm^-5·m²; befetolol, from av. 3301 to 2620, p<0.05), without significant changes in cardiac index, while hypotensive actions of propranolol or oxprenolol appeared to be due mainly to a decrease in cardiac output (propranolol, from av. 4.03 to 2.99 L/min/m²; oxprenolol, from av. 3.97 to 3.29 L/min/m²), although the decrease in cardiac output was not significant. In long-term (42 weeks) oxprenolol therapy, antihypertensive effects seemed to be related to reduced cardiac output and a readaptation of peripheral resistance to chronic reduction of cardiac output was not always observed. Circulation time was determined in 9 patients with oxprenolol therapy and 8 with pindolol therapy by the measurement of the arrival time in the cerebral hemisphere of the intravenously injected radioisotope. The patients with oxprenolol therapy showed significant prolongation in circulation time (short-term administration, av. 6.6 to 8.4 sec; long-term administration, av. 6.6 to 9.2 sec, p<0.05), while no prolongation was observed in pindolol therapy. These results suggest that hemodynamic responses to beta-blocking agents are not uniform and that the antihypertensive actions of beta-blockers depend on the effects on both cardiac output and peripheral vascular resistance.