ACTIONS OF PUTATIVE TRANSMITTERS IN THE CHICKEN VAGUS NERVE/OESOPHAGUS AND REMAK NERVE/RECTUM PREPARATIONS

Abstract

1 Histamine (0.02–0.1 μg/ml) contracted the chicken rectum preparation. This effect was antagonized by mepyramine (0.01 μg/ml) but not by hyoscine (0.02 μg/ml). 2 5-Hydroxytryptamine (0.05–0.25 μg/ml) relaxed the rectum preparation and at higher concentration produced a biphasic response. These responses were not antagonized by methysergide (0.01 μg/ml), and the relaxation was not antagonized by tetrodotoxin (0.1 μg/ml) or a combination of propranolol (0.05 μg/ml) and phentolamine (0.1 μg/ml). 3 Neither mepyramine (0.1 μg/ml) nor methysergide (0.01 μg/ml) antagonized the contractions produced by nerve stimulation in vagus nerve/oesophagus and Remak nerve/rectum preparations. 4 5-Hydroxytryptamine (2 μg/ml) in the presence of methysergide (0.01 μg/ml), inhibited the contractions produced by nerve stimulation in Remak nerve/rectum and vagus nerve/oesophagus preparations. 5 Adenosine, adenosine 5′-phosphate (AMP), adenosine 5′-diphosphate (ADP) and adenosine 5′-triphosphate (ATP), in order of decreasing potency, produced slow contractions in most oesophagus preparations. The action of ATP in this preparation was antagonized by tetrodotoxin (0.1 μg/ml), hyoscine (0.1 μg/ml) and strychnine (5 μg/ml). 6 Desensitization of the vagus nerve/oesophagus preparation to ATP did not produce any antagonism of the contractions to nerve stimulation. 7 Adenosine and AMP produced relaxations and ADP and ATP contractions in the rectum preparation. ATP was about 100 times as potent as ADP in producing fast contractions which were not antagonized by tetrodotoxin, hyoscine or strychnine. 8 Desensitization of the Remak nerve/rectum preparation to ATP resulted in the contractions to nerve stimulation and acetylcholine being inhibited to the same extent. 9 Prostaglandin E₂ produced slow contractions in the oesophagus and rectum preparations which were not antagonized by tetrodotoxin (0.1 μg/ml). Polyphloretin phosphate (10 μg/ml) antagonized spontaneous movements and responses to prostaglandin E₂ in the rectum but not the oesophagus. 10 Neither polyphloretin phosphate (60 μg/ml) nor indomethacin (20–100 μg/ml) antagonized the contractions produced by nerve stimulation in vagus nerve/oesophagus (with hyoscine in the bathing solution) and Remak nerve/rectum preparations. 11 These experiments seem to exclude histamine, 5-hydroxytryptamine, adenosine and its nucleotides and prostaglandin E₂ as possible motor transmitters in synapses and neuromuscular junctions in the chicken vagus nerve/oesophagus and Remak nerve/rectum preparations.