Efferent sympathetic nervous control of rectal motility in the cat

The sympathetic nervous control of rectal motility was studied in anesthetized cats. Division of the sympathetic nerves, i.e. the hypogastric nerves and the lumbar colonic nerves and alpha-adrenergic blockade reduced rectal tone indicating that these nerves are tonically active. Efferent electrical stimulation of the nerves at high intensities caused an immediate and sustained contraction which was inhibited after phentolamine but unaffected by hexamethonium suggesting a direct alpha-adrenergic effect on the rectal smooth muscle. However when prevailing rectal tone was high beta-adrenergic inhibitory responses unaffected by hexamethonium were observed. In addition the hypogastric nerves seem to convey cholinergic excitatory fibres to the rectum. The results imply that the sympathetic nerves are integrated in the nervous regulation of rectal motility in a fashion similar to the nervous control of the internal anal sphincter.