Abstract

Prokinetic benzamides (e.g., cisapride) enhance gastrointestinal motility and transit. In vitro studies on the guinea pig ileum suggest that their effect is mediated via serotonergic 5-hydroxytryptamine (5-HT4) receptors, resulting in a facilitation of cholinergic neurotransmission. However, most in vivo studies have been performed on the canine stomach. Therefore, our aim was to determine whether the findings obtained on the guinea pig ileum can be extrapolated to another species and another organ. Does a benzamide facilitate cholinergic neutrotransmission on strips of the canine stomach in vitro? If so, does the benzamide exert its effect via a serotonergic 5-HT4 mechanism? Longitudinal muscle strips with adhering myenteric plexus were isolated from the canine stomach and were electrically stimulated at submaximal frequencies resulting in a mean contractile response of 16 +/- 7% of the response to methacholine (10(-6) M). Atropine and tetrodotoxin (both 3 x 10(-7) M) abolished the contractile responses, whereas hexamethonium (10(-4) M) had no effect. Cisapride (3 x 10(-7) M) enhanced the contractile responses from 14 to 70% (59 +/- 5% increase). 5-HT (3 x 10(-7) M) similarly enhanced the responses from 12 to 72% (58 +/- 5% increase). Cisapride induced a sustained enhancement throughout the duration of the experiment; in contrast, the effect of 5-HT subsided in about 90 min. Single-concentration administration of cisapride (10(-8)-10(-6) M) and 5-HT (10(-9)-3 x 10(-7) M) resulted in EC50 values of 1.0 (0.8-1.4) x 10(-7) M for cisapride and 1.3 (0.8-2.1) x 10(-8) M for 5-HT. Methiothepin and methysergide (both 3 x 10(-7) M; 5-HT1-receptor antagonists), ketanserin and LY 53857 (both 3 x 10(-7) M; 5-HT2-receptor antagonists), granisetron (3 x 10(-7) M; 5-HT3-receptor antagonist) or ICS 205-930 (3 x 10(-7) M; 5-HT3-receptor antagonist and in addition 5-HT4-receptor antagonist at 3 x 10(-6) M) did not reduce the responses to both cisapride and 5-HT. 1-(1-Naphthalenyl)piperazine (10(-6) M; 5-HT-receptor antagonist in the rat gastric fundus) significantly reduced the increase by 5-HT (24 +/- 7%; 7-31%) but had no effect on the cisapride (3 x 10(-7) M)-induced increase (69 +/- 4%; 8-77%).(ABSTRACT TRUNCATED AT 400 WORDS)