GABA-related actions in isolated in vitro preparations of the rat small intestine.

Longitudinal organ bath preparations of the rat duodenum, jejunum and ileum were tested for their responsiveness to GABA-receptor agonists. The GABAA-receptor agonists, GABA and 3APS, induced non-adrenergic, non-cholinergic relaxations and/or contractions, although the magnitude and type of response varied depending upon the region tested. All regions relaxed to applied GABA or 3APS, however the jejunum and ileum also responded with cholinergic contractions. These relaxant and contractile actions were neurogenic and sensitive to blockade by the GABA antagonists bicuculline or picrotoxinin, and desensitization to either agonist. The GABAB-receptor agonist baclofen, caused a reduction in electrically evoked cholinergic contractions. These inhibitory actions of baclofen were insensitive to bicuculline or picrotoxinin. Taken together, these results show that GABA-ergic actions in the rat small intestine are mediated by two pharmacologically distinct neural receptor populations, the GABAA and GABAB sites, the distribution and sensitivity of which differ along the length of the small intestine.