Relaxation induced by serotonin and sumatriptan in isolated guinea pig gallbladder strips

The effects of 5-hydroxytryptamine (5-HT) and sumatriptan were investigated on isolated guinea pig gallbladder strips. While 0.1 muM-50 mM of 5-HT exh ibited contractile and/or relaxant effects in quiescent preparations, the s ame concentrations of sumatriptan did not. On the other hand, carbachol-pre contracted tissues were relaxed by the same amounts of 5-HT and sumatriptan in a concentration-dependent manner. The relaxant responses to 5-HT were n ot antagonized or changed by tetrodotoxin, indomethacin, capsaicin, NG-nitr o-L-arginine (L-NOARG), GR55562 [(+/-)-propranolol, 3-[3-(N,N-dimethylamlin o)propyl]-4-hydroxy-N-[4-(pyridin-4-yl)phenyl]benzamide], S(-)-propranolol, methysergide, ketanserin, tropisetron, GR113808 ([1- [2-(methylsulphonylam ino)ethyl] -4-piperidinyl]methyl-1-methyl-1H-indole-3-carboxylate maleate s alt), pargyline, and fluvoxamine. The relaxant responses to sumatriptan wer e antagonized by GR55562 but not by S(-)-propranolol, These results suggest that 5-HT and sumatriptan cause relaxation in carbachol-precontracted isol ated guinea pig gallbladder strips by yet undefined mechanisms.