Abstract

The effects of fluoxetine, a serotonin reuptake inhibitor, were studied in the isolated rat small intestine. Electrical field stimulation (EFS) triggered relaxant and/or contractile responses that were sensitive to tetrodotoxin and fluoxetine at 1.0-10.0 mu M. In 0.1 mM hexamethonium-treated tissues, fluoxetine (1.0 mu M) induced a relaxant response at 10.0 Hz, while it decreased the attenuation of the contractile responses to EFS. In PCPA pretreated rat jejunum and ileum, 1.0 mu M of fluoxetine induced a greater relaxation response to EFS and significantly attenuated the contractile responses to EFS (10.0 Hz) in the duodenum. In a separate experiment, the application of reboxetine (1.0-10.0 mu M), a norodrenergic reuptake inhibitor, reduced the contraction and increased the relaxation responses to EFS at 10.0 Hz in most regions. In the presence of hexamethonium (0.1 mM) the application of 10.0 mu M reboxetine reduced contractile responses to ESF while enhancing the relaxant responses to EFS at 10.0 Hz. The data suggest that the effects of fluoxetine appear to be related to the selected region of the intestine and may contribute to a better understanding of the serotonergic and cholinergic transmitter mechanisms involved in ileal activity and the gastrointestinal discomfort associated with the clinical use of fluoxetine.