The vagal control of the ileo-cecal sphincter in the cat

In acute experiments on chloralosed cats the effect of efferent cervical vagal stimulation on a flow through the ileo-cecal sphincter (ICS) was studied. The motor activity of the jejunum, ileum and large intestine adjacent to the sphincter was recorded simultaneously. Vagal stimulation caused a decrease in the transphincteric flow and increased motor activity in the ileum. Increased motor activity in the proximal colon was recorded only occasionally. When the vagal nerves were stimulated during continuous splachine stimulation the transsphincteric flow was decreased although the tone and motility of the ileum was suppressed. Furthermore, guanethidine (1-3 mg/kg b.w.) blocked or suppressed the effect of vagal stimulation on the transsphincteric flow while the excitatory response of the proximal colon was greatly enhanced. This indicates that the reduction of the transsphinctteric flow following vagal stimulation was at least partly due to a direct effect of the vagal nerves on the sphincteric muscle and not to a squeezing effect of that part of the colonic wall that surrounds the sphincter. Atropine (0.1 and 1 mg/kg b.w.) blocked all responses to vagal stimulation. Thus, both guanethidine and atropine blocked the vagally induced contraction of the ICS. Relaxation to the ICS was never obtained by vagal stimulation even when the tone of the sphincter had been increased by infusion of noradrenaline.