Neuronal control of the pyloric sphincter of the guinea-pig

The pyloric sphincter (PS) controls gastric emptying and prevents the reflu x of duodenal content into the stomach. Neuronal pathways and reflexes cont rolling the guinea-pig PS were physiologically investigated in isolated pre parations. Simultaneous intracellular or extracellular and tension recordin gs from PS circular muscle with electrical and stretch stimulation were use d. Electrical stimulation evoked an initial small contraction followed by a relaxation with a corresponding inhibitory junction potential (IJP) then a second large contraction with a corresponding excitatory junction potentia l (EJP). Hyoscine (1 mu mol L-1) blocked the first contraction, and reduced the second contraction and EJP by 52.5% and 61%, respectively. These respo nses were further reduced by the NK2 antagonist, MEN10627 (1 mu mol L-1), a nd the NK1 antagonist, SR140333 (1 mu mol L-1). N-nitro-L-arginine (100 mu mol L-1) and apamin (0.5 mu mol L-1) blocked the relaxation and the IJP. Du odenal electrical stimulation evoked an EJP, whereas antral stimulation evo ked an IJP followed by a small EJP. All were blocked by hexamethonium (100 mu mol L-1). Duodenal stretch evoked tetrodotoxin-sensitive reflex contract ions and membrane depolarization with action potentials in the PS. Thus, PS enteric motor neurones receive inputs from the duodenum and the stomach. T here are stretch-sensitive ascending excitatory reflex pathways from the du odenum to the PS.