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The longitudinal muscle of an isolated Remak nerve-rectum preparation from the chicken responded to nerve stimulation with a contraction or, when the tone of the preparation was raised by acetyl-fi-methylcholine (11 0 mM), with a contraction followed by a relaxation. The relaxation of the preparation was unaffected by hexamethonium, antagonized by bretylium, blocked by a combination of propranolol and phentolamine at specific concentrations and was absent or diminished in reserpinised preparations. The contraction was abolished by hexamethonium or tubocurarine and was partially antagonized by hyoscine.Remak's nerve consists of fibres of coeliac and sacral origin [Nolf, 1934]. The effect of autonomic blocking drugs on responses of the chicken isolated rectum to stimulation of Remak's nerve has been investigated to ascertain whether a hyoscine-resistant contraction, as observed in the chicken isolated oesophagus [Hassan, 1969], occurs in an aboral part of the alimentary tract of the domestic fowl. METHODSDrugs. Acetyl-f-methylcholine chloride, bretylium tosylate, hexamethonium bromide, (-) hyoscine hydrobromide, (-) noradrenaline bitartrate, phentolamine mesylate, (+) propranolol hydrochloride, reserpine and (+) tubocurarine hydrochloride were used. Reserpine was dissolved in 20 per cent (w/v) aqueous ascorbic acid and used on the same day. Concentrations of drugs in the text and figures refer to final concentrations in the organ-bath.Chick Remak nerve-rectum preparation. Chicks (Brown Leghorn) aged 1 to 3 weeks were decapitated and bled. The whole rectum together with the Remak nerve and adjoining blood vessels (Fig. 1) was removed and its contents washed out with Krebs solution [Krebs and Henseleit, 1932]. The Remak nerve and caudal mesenteric vein were tied with cotton and freed along 0 5 to 1.0 cm of their length from the caecal end ofthe rectum. The Remak nerve-rectum preparation with open ends was mounted in a 40 ml. organ-bath filled with Krebs solution at 350C and gassed with 5 per cent carbon dioxide in oxygen, responses of the longitudinal muscle being recorded isotonically with a load of 1 to 2 g on the lever. The nerve was stimulated through platinum electrodes with square wave pulses (1 msec, 20 Hz, 5 to 10 V), the stimuli being applied for periods of 15 to 60 sec at 5-15 min intervals. In experiments where relaxations of the longitudinal muscle were recorded the bathing solution contained acetyl-6-methylcholine (11.0 mM) to raise the tone. Preparations were rested for at least 30 min before commencement of an experiment.Guinea-pig hypogastric nerve-vas deferens and vagw.3 nerve-oesophaguw preparations.

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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 jLg/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 postcrop 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.In the anaesthetized fowl contractions of the oesophagus, crop, proventriculus and gizzard produced by stimulation of the vagus and descending oesophageal nerves are abolished by hyoscine or atropine (Hassan, 1967). The present paper describes experiments in which the isolated oesophagus responded to stimulation of these nerves with contractions resisting complete block by hyoscine. A preliminary report of the pharmacological characteristics of the hyoscine-resistant contraction of the chicken isolated oesophagus was communicated to the British and Scandinavian Pharmacological Societies Summer Meeting; it was concluded that hyoscine added to the organ-bath did not reach receptors responding to acetylcholine released from the nerves (Hassan, 1968). Further evidence suggests, however, that a slow contracting substance is released from the nerves together with acetylcholine, thus accounting for the resistance of the contraction to complete block by hyoscine.