The effects of cysteamine on neurogenic responses in the stomach and small intestine of the rat.

The actions of the duodenal ulcerogen cysteamine in different regions of the rat stomach and small intestine were investigated utilizing isolated gut-bath preparations. Applied cysteamine caused concentration-dependent contractions of forestomach strips, primarily by direct actions at cholinergic muscarinic sites on the longitudinal muscle, and to a lesser extent indirectly via stimulation of intrinsic cholinergic motor nerves. In contrast to its gastric actions, applied cysteamine evoked nerve-mediated relaxations of segments of whole duodenum, jejunum and ileum. These actions were concentration-dependent and due to stimulation of the non-adrenergic, non-cholinergic (NANC) inhibitory nerves. In addition, cysteamine selectively inhibited nicotinic and GABA-ergic stimulation of the NANC inhibitory nerves, as well as electrically evoked cholinergic contractions. The interactions of cysteamine with the NANC inhibitory nerves appears to be via sites distinct from nicotinic or GABA receptors, and may have involved toxic effects.