β‐Adrenoceptors mediate inhibition of [3H]‐acetylcholine release from the isolated rat and guinea‐pig trachea: role of the airway mucosa and prostaglandins

Abstract

Rat or guinea pig isolated tracheae were labelled with [3H]‐choline to measure evoked tritium outflow, which reflects neuronal release of [3H]‐acetylcholine. Tritium outflow was evoked either by electrical stimulation of the extrinsic vagal nerve (rat tracheae) or by 27 mm potassium (guinea pig tracheae). In rat tracheae isoprenaline (0.01, 0.1 μm) inhibited evoked [3H]‐acetylcholine release, whereas β‐adrenoceptor‐selective agonists (fenoterol, formoterol, salbutamol) were ineffective. The inhibitory effect of isoprenaline was abolished under the following conditions: (i) presence of propranolol (1 μm) or of the β‐selective antagonist CGP 20712 A (0.1 μm); (ii) removal of the mucosa at the ..