Abstract
1 Eleven β-adrenoceptor blocking agents (propranolol, oxprenolol, penbutolol, carteolol, bupranolol, bufetolol, pindolol, atenolol, metoprolol, acebutolol and labetalol) were orally administered to 144 patients with essential hypertension for 5 weeks to assess their antihypertensive effects. In addition haemodynamic responses were measured non-invasively using radioactive iodinated human serum albumin.
2 In a second study central haemodynamic changes in response to intravenous injection of propranolol (0.4 mg/kg) were assessed in 21 untreated patients with essential hypertension and compared with those induced by short-time therapy with propranolol, acebutolol or pindolol.
3 During short term (5 weeks) oral therapy all the antagonists with the exception of pindolol and carteolol, showed a tendency to reduce heart rate. The effects on blood pressure were not uniform and for each drug a subgroup of responders (defined as those showing 10 mmHg or more reduction of mean arterial blood pressure) was separately analysed.
4 The responders to antihypertensive therapy showed a wide spectrum of haemodynamic responses. The results would be compatible with the hypothesis that in addition to the reduction in cardiac output, the β-adrenoceptor blockers lower blood pressure by at least one, as yet unknown, mechanism leading to a reduction in total peripheral resistance.
5 The antagonists tested demonstrate a variety of ancillary properties and some differences were apparent between the haemodynamic responses to the different drugs. Cardioselective β-adrenoceptor blockers caused a significant decrease in cardiac index; however no significant change in total peripheral resistance was observed. These effects may be attributable to their weak vascular β-adrenoceptor blockade.
6 In the case of labetalol the additional α-adrenoceptor blocking activity of the drug was reflected by a fall in total peripheral resistance resulting from blockade of the vasoconstrictor effects of neuronal noradrenaline.
7 Pindolol, because of its pronounced ISA, showed qualitative differences from the other antagonists, its antihypertensive effects being accompanied by significant falls of total peripheral resistance and increases in cardiac output.
8 During short term (5 weeks) oral therapy with propranolol, acebutolol or pindolol no marked central haemodynamic changes occurred and in particular, no significant increase in cardiopulmonary blood volume was detected.
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Selected References
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