5-HT4 receptor antagonism potentiates inhibition of intestinal allodynia by 5-HT3 receptor antagonism in conscious rats.
Acute levels of distension were applied by balloon to the colo-rectal region in conscious rats and visceromotor responses observed as abdominal muscle contraction; the threshold was typically between 10-40 mmHg. In saline-pretreated rats, the selective 5-HT3 (granisetron) and 5-HT4 (SB-207266) receptor antagonists had no effects on the visceromotor thresholds. 5-Hydroxytryptophan 10 mg/kg, subcutaneously (s.c.) decreased the distension threshold, indicating mechanical allodynia. This increased sensitivity was dose-dependently inhibited by granisetron but was unaffected by SB-207266 100 microg/kg, s.c., a dose which maximally and selectively antagonizes at 5-HT4 receptors. However, this dose of SB-207266 potentiated the inhibitory activity of submaximally-effective doses of granisetron, reducing the ED50 from 0.83 to 0.02 microg/kg, s.c., but without changing the maximum response or the bell-shaped nature of the dose-response curve for granisetron. These data suggest that 5-HT4 receptor activation enhances the ability of 5-HT3 receptor activation to induce intestinal allodynia.[1]References
- 5-HT4 receptor antagonism potentiates inhibition of intestinal allodynia by 5-HT3 receptor antagonism in conscious rats. Smith, M.I., Banner, S.E., Sanger, G.J. Neurosci. Lett. (1999) [Pubmed]
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