Effects of erythromycin on the propulsive motility of upper gastrointestinal tract in rats

The differences between the postprandial mixing or propulsion and the interdigestive motility of the gastrointestinal (GI) tract are already known. Earlier studies showed dose-dependent differences in the effects of erythromycin on interdigestive motility. The various GI side-effects (vomiting, diarrhoea) also suggest that there are different effects of erythromycin on the GI motility. The aim of our study was to examine postprandially the propulsive effects of different doses of erythromycin on the movement of intraluminal contents in the upper GI tract of the rat. The animals were fasted for 24 h before the experiments but water was given freely. The rats received 1.5 ml 1.5% methylcellulose painted with 0.05% phenol-red intragastrically (test solution). Erythromycin(E. lactobionate) was given intravenously at doses of 0.05, 0.1, 0.25, 0.5, 1.0 and 5.0 mg/kg 15 min before the administration of a test solution. The animals were sacrificed 20,60 and 120 min after administration of methylcellulose, when the distance between the front of the painted intraluminal contents and the pylorus was measured and expressed as a percentage of the total length of small intestine. The phenol-red content in the stomach and small intestine was measured spectrophotometrically and the gastric emptying was calculated from the ratio of the measured total and intestinal phenol-red content. Our results showed that the small doses of erythromycin (0.1 and 0.25 mg/kg) accelerated gastric emptying after 20 min but did not change significantly the propulsive motility of upper small intestine; however, large doses of erythromycin (1.0 and 5.0 mg/kg) decreased gastric emptying and upper GI motility after 20 and 60 min. In summary, the prokinetic action of small doses of erythromycin was demonstrated, but its effecttime on GI motility is short and the ratio of the stimulating and inhibitory doses is 1:10. This paper was presented at the Section of IUPHAR GI Pharmacology Symposium on ’Biochemical pharmacology as an approach to gastrointestinal disorders (basic science to clinical perspectives)‘, October 12-14, 1995, Pécs, Hungary.