Evidence of reflexive beta adrenergic motor stimulation in the canine stomach and small intestine.

Studies in our laboratory have confirmed the previous observations that adequate electrical stimulation of either the left or right central vagus nerves in the dog after bilateral vagectomy produces relaxation of the stomach and small intestine. On the other hand, central vagal stimuli delivered to dogs that were either chronically reserpinized or were premedicated with the alpha adrenolytic phenoxybenzamine resulted in increased segmenting activity of these two organs. These excitatory responses were abolished by bilateral section of the sympathetic chains and could be reproduced by electrically stimulating the chains. The excitatory effects of either central vagal stimulation, peripheral sympathetic stimulation or intravenous isoproterenol administration could be abolished by dichloroisoproterenol. It was also determined that isoproterenol produced a tonic contraction of the separated muscularis mucosa which was distinguishable from a relaxation of the muscularis externa. It is suggested that a sympathetic pathway exists which is excitatory to the stomach and small intestine and that these excitatory effects are mediated by beta adrenergic neurotransmitters. The results further suggests that the beta excitatory reflex response is mediated by the muscularis mucosa as the target effector system.