Spontaneous and evoked release of neurotransmitter substances in the longitudinal muscle of the anterior mesenteric artery of the domestic fowl.

1. Changes in length of the longitudinal muscle of the anterior mesenteric artery of the domestic fowl (LMAMA) were recorded isotonically.2. The actions of physostigmine and hyoscine suggest that the tone of the LMAMA is dependent on a resting release of acetylcholine within the tissue.3. Catecholamines inhibited the contractions obtained in response to stimulation of cholinergic nerves; this was a beta-receptor effect. After beta-receptor blockade, noradrenaline, but not isoprenaline, weakly facilitated the effects of stimulating cholinergic nerves.4. In the presence of hyoscine, nicotine relaxed preparations of the LMAMA in which the tone had been raised with barium chloride. These relaxations were considered to be due to a release of catecholamine probably from sympathetic nerves.