Abstract
1 Haemodynamic changes during the onset of the antihypertensive action of pindolol, 10 mg twice daily, and propranolol, 80 mg three times daily, were studied for 24 h in two groups of 10 patients with uncomplicated essential hypertension.
2 Baseline haemodynamics were not different between the two groups.
3 Pindolol, with considerable intrinsic sympathomimetic activity (ISA) exerted its maximal antihypertensive efficacy within 3-4 h after dosing (-15 ± 3%, mean ± s.e. mean, P < 0.001). This effect was maintained for 24 h.
4 After propranolol, which is devoid of ISA, arterial pressure fell more gradually, but after 24 h the two drugs shared an equal antihypertensive effect.
5 Cardiac output rose after pindolol by 16 ± 5% (P < 0.01). It decreased transiently by 16 ± 6% (P < 0.01) 1-4 h after propranolol. At that time vascular resistance had risen by 18 ± 5% (P < 0.001).
6 The onset of the antihypertensive action of the two drugs was associated with reductions in vascular resistance. Since reflex vasoconstriction did not occur after pindolol, vascular resistance was always lower on this drug than on propranolol (-29 ± 4%, P < 0.001 vs -15 ± 5%, P < 0.01).
7 Cardiac filling pressures, pulmonary artery pressure and pulmonary vascular resistance did not change after pindolol but they rose after propranolol.
8 During the onset of the vasodilator and antihypertensive effects of the two β-adrenoceptor blockers heart rate, stroke volume and cardiac output rose, despite cardiac β-adrenoceptor blockade, suggesting a reduction of parasympathetic tone and an increase in venous return.
9 Thus, haemodynamic changes after administration of β-adrenoceptor blockers are much more complex, than would be expected from their ancillary properties and the effects of cardiac β-adrenoceptor blockade.
Keywords: β-adrenoceptor blockers, cardiac output, vascular resistance, hypertension, pindolol, propranolol
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Selected References
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