Effects of (+) and (-)-propranolol on the responses of the human isolated basilar artery to cerebrospinal fluid obtained from patients with subarachnoid haemorrhage and cerebral arterial spasm.

1. The human isolated basilar artery has been used as a model to investigate the aetiology of cerebral arterial spasm associated with rupture of intracranial aneurysms. 2. The isolated artery is contracted by 5-hydroxytryptamine, noradrenaline, six prostaglandins and cerebrospinal fluid from patients with ruptured aneurysms and cerebral arterial spasm. 3. These contractions are reversed by (+/-)--, (+)-- and (--)-propranolol in concentrations known to produce local anaesthetic effects on isolated frog sciatic nerve; the (+) isomer was 2.5 to 10 times more potent (-)-propranolol in antagonising all contractions. 4. As the two isomers are known to have similar local anaesthetic potency but (-)-propranolol has greater beta-adrenoreceptor blocking effects we conclude that the antagonistic effects described do not involve beta-adrenoreceptor blockade. 5. The data indicate that propranolol may be of clinical use in reversing cerebral arterial spasm.