ELECTROPHYSIOLOGICAL CHARACTERISTICS OF TENSION RECEPTORS IN THE ABOMASAL ANTRUM OF SHEEP

Unitary impulse activity from tension receptors in the abomasal antrum in sheep anaesthetized with chloralose was studied with concurrent me asurements of isometric tension in the antral wall, intraluminal press ures and electromyography (EMG). Rhythmical background activity had a close correlation with intraluminal pressure changes and usually a clo se correlation with local increases in EMG activity and isometric tens ion. Impulse frequencies increased, but were not sustained, following changes from isotonic to isometric conditions. Tension receptors were excited by transmural compression, by antral distension and by local i ntra-arterial injections of acetylcholine (2.5-25 mug), pentagastrin ( 10-20 mug), 5-hydroxytryptamine (1-20 mug), adrenaline (10 mug) cholec ystokinin-8 (1-5 mug) or bradykinin (0.5-20 mug), and by systemic inje ctions of bethanecol (5-1000 mug). Local intra-arterial perfusions of atropine (50 mug) and hexamethonium (100 mug) did not abolish spontane ous antral movements or affect the enhanced impulse activity evoked by acetylcholine or 5-hydroxytryptamine. Most antral tension receptors w ere excited by increases in antral tension or passive distension; they therefore functioned 'in series' with the muscularis externa. The dis charges of three tension receptors were 'off-loaded' early during the contraction evoked by local injections of pentagastrin (10-20 mug).