The action of physostigmine and the distribution of cholinesterases in the chicken oesophagus

Actions of putative transmitters in the chicken vagus nerve/oesophagus and Remak nerve/rectum preparations

1 Histamine (0.02-0.1 mug/ml) contracted the chicken rectum preparation. This effect was antagonized by mepyramine (0.01 mug/ml) but not by hyoscine (0.02 mug/ml).2 5-Hydroxytryptamine (0.05-0.25 mug/ml) relaxed the rectum preparation and at higher concentration produced a biphasic response. These responses were not antagonized by methysergide (0.01 mug/ml), and the relaxation was not antagonized by tetrodotoxin (0.1 mug/ml) or a combination of propranolol (0.05 mug/ml) and phentolamine (0.1 mug/ml).3 Neither mepyramine (0.1 mug/ml) nor methysergide (0.01 mug/ml) antagonized the contractions produced by nerve stimulation in vagus nerve/oesophagus and Remak nerve/rectum preparations.4 5-Hydroxytryptamine (2 mug/ml) in the presence of methysergide (0.01 mug/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 mug/ml), hyoscine (0.1 mug/ml) and strychnine (5 mug/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 E(2) produced slow contractions in the oesophagus and rectum preparations which were not antagonized by tetrodotoxin (0.1 mug/ml). Polyphloretin phosphate (10 mug/ml) antagonized spontaneous movements and responses to prostaglandin E(2) in the rectum but not the oesophagus.10 Neither polyphloretin phosphate (60 mug/ml) nor indomethacin (20-100 mug/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 E(2) as possible motor transmitters in synapses and neuromuscular junctions in the chicken vagus nerve/oesophagus and Remak nerve/rectum preparations.

Myogenic peristalsis in isolated preparations of chicken oesophagus

1. Nicotine, 20 mug/ml, briefly and partially blocked the longitudinal contractions of a chick vagus nerve-oesophagus preparation to nerve stimulation, but potentiated them in the presence of hyoscine, 10 mug/ml.2. Strychnine, 20 mug/ml, antagonized the longitudinal contractions of the chick oesophagus to nerve stimulation, though not to acetylcholine or 5-hydroxytryptamine. Hyoscine, 10 mug/ml, enhanced the nerve-blocking action of strychnine.3. These observations suggest that in the vagus nerve of the chicken, hyoscine either blocks certain types of fibre selectively or interacts with pharmacological receptors for strychnine and nicotine.4. Tetrodotoxin, 1 mug/ml, propranolol, 40 mug/ml, cocaine, 200 mug/ml, or strychnine, 100 mug/ml, which render autonomic nerves inexcitable, potentiated the spontaneous movements of isolated preparations of chicken oesophagus at normal intra-luminal pressure; they also potentiated peristaltic response to increased intra-luminal pressure.5. These observations suggest that the preparations contain intramural nerves that inhibit the musculature.6. Peristalsis in the chicken oesophagus was unaffected by nicotine, 20 mug/ml, tubocurarine, 20 mug/ml, hyoscine, 10 mug/ml, phentolamine, 1 mug/ml, propranolol, 0.5 mug/ml, mepyramine, 1 mug/ml, methysergide, 0.1 mug/ml, and morphine, 20 mug/ml. It was produced in preparations of chicken oesophagus after removal of the mucous membrane. Papaverine, 20 mug/ml, inhibited the peristalsis and had a spasmolytic action in the musculature.7. These observations suggest that the peristalsis in isolated preparations of chicken oesophagus is dependent solely upon myogenic contractility.

A hyoscine-resistant contraction of isolated chicken oesophagus in response to stimulation of parasymphathetic nerves

1. Contractions of the chicken isolated oesophagus or separated external muscle produced by stimulation of the vagus and descending oesophageal nerves were abolished by hyoscine (1-100 mug/ml.) if the duration of stimulation was less than 5 sec, but prolonged stimulation produced delayed contractions not antagonized by hyoscine.2. The contractions to nerve stimulation were abolished by nerve section but not by bretylium, hexamethonium or tubocurarine.3. In decerebrate chickens, intravenous hyoscine abolished the contractions of the oesophagus produced by nerve stimulation, but previous intravenous injection of hyoscine into chicks did not prevent subsequently isolated oesophageal preparations from contracting to nerve stimulation.4. Prolonged nerve stimulation of an isolated oesophageal preparation did not produce a contraction from a piece of isolated guinea-pig ileum or post-crop chick oesophagus suspended in the same organ-bath.5. It seems possible that small amounts of a slow contracting substance were released from the stimulated nerves together with acetylcholine.