NON-CHOLINERGIC AND NON-ADRENERGIC MECHANISMS IN THE CONTRACTION AND RELAXATION OF THE CHICKEN RECTUM

Mechanical responses produced in isolated chicken rectum by nerve stimulation were subjected to a pharmacological analysis to determine the nerves involved. Stimulation of Remak's nerve caused biphasic responses, consisting of an initial, short-lasting contraction and a subsequent, long-lasting relaxation. A similar pattern of responses was observed following coaxial stimulation of intramural nerves. The contraction was unaffected by atropine and hyoscine, and also insensitive to α-adrenoceptor blockers. The relaxation was reduced in duration but not in amplitude by β-adrenoceptor blockers, and still observed in preparations from reserpinized animals. These results suggest the presence of non-cholinergic excitatory innervation and nonadrenergic inhibitory innervation in the chicken rectum. Changing the stimulating sites and sectioning some of the side branches of Remak's nerve extending to the gut revealed that the excitatory nerve fibers appear to reach the rectal wall preferentially via the lower side branches. The smooth muscle of the dorsocaudal region appears to receive more excitatory innervation, since the largest contraction was found in muscle strips taken from the rectal wall where the side branches terminated when field stimulation was applied to the anal end of these strips.