Role of adrenergic neurone blockade in the hypotensive action of propranolol.

1. Propranolol, in doses of 25-100 mug/kg, blocks contractions of the nictitating membrane to nerve stimulation but not to injected noradrenaline.2. This adrenergic neurone blocking action of propranolol is antagonized by amphetamine.3. It is also reversed by raising the dose of propranolol to amounts exceeding 0.5 mg/kg.4. Still larger amounts potentiate the responses of the nictitating membrane to both submaximal stimulation of the cervical sympathetic nerve and to injected noradrenaline.5. The (+) isomer of propranolol produced adrenergic nerve blockade and some degree of hypotension without blocking cardiac beta-adrenoceptors.6. The relevance of adrenergic neurone blockade to the hypotensive effect of propranolol is discussed.