In vitro effects of 5-hydroxytryptamine and cisapride on the circular smooth muscle of the jejunum of horses.
OBJECTIVE
To determine effects of cisapride and 5-hydroxytryptamine (5-HT) on the jejunum of horses.


METHODS
Jejunal muscle strips from 8 horses.


METHODS
Muscle strips were suspended in isolated muscle baths. Isometric stress responses to 5-HT and cisapride, with and without specific antagonists, were determined.


RESULTS
Muscle strips incubated with atropine and tetrodotoxin responded to 5-HT and cisapride with an increase in contractile force. The 5-HT caused a concentration-dependent increase in contractile amplitude, with a maximum response (Emax) of 1,151+/-214 g/cm2 and a molar concentration that induces contractile force equal to 50% of maximum response (EC50) of 0.028+/-0.002 microM. Prior incubation with the 5-HT2 antagonist ketanserin decreased the Emax (626 +/-147 g/cm2) and potency (EC50, 0.307+/-0.105 microM) of 5-HT Prior incubation with the 5-HT3 antagonist tropisetron decreased the efficacy (Emax, 894+/-184 g/cm2) to 5-HT Cisapride also caused a concentration-dependent increase in contractile amplitude, with an Emax of 331+/-82 g/cm2 and an EC50 of 0.302+/-0.122 microM. Prior incubation with ketanserin decreased the Emax (55+/-17 g/cm2) and potency (EC50, 0.520+/-0.274 microM) of cisapride.


CONCLUSIONS
Stimulatory effects of 5-HT and cisapride on circular smooth muscle of equine jejunum are mediated primarily through a noncholinergic effect. The effects of 5-HT are mediated, at least partially, by 5-HT2 and 5-HT3 receptors, whereas the effects of cisapride are mediated primarily by 5-HT2 receptors. This may impact treatment of horses with postoperative ileus.
Nieto
J E
JE
Department of Veterinary Surgical and Radiological Sciences, University of California, Davis 95616, USA.
Snyder
J R
JR
Kollias-Baker
C
C
Stanley
S
S
D000818:Animals; D001285:Atropine / Q000494:pharmacology; D020117:Cisapride / Q000494:pharmacology*; D004357:Drug Synergism; D006736:Horses; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007537:Isometric Contraction / Q000187:drug effects*; D007583:Jejunum / Q000187:drug effects / Q000502:physiology*; D007650:Ketanserin / Q000494:pharmacology; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology*; D012702:Serotonin Antagonists / Q000494:pharmacology*; D013779:Tetrodotoxin / Q000494:pharmacology; D000077526:Tropisetron
D007211:Indoles; D012702:Serotonin Antagonists; D012701:Serotonin; D013779:Tetrodotoxin; D000077526:Tropisetron; D001285:Atropine; D007650:Ketanserin; D020117:Cisapride