Erythromycin and its derivatives with motilin-like biological activities inhibit the specific binding of 125I-motilin to duodenal muscle.

Erythromycin, one of the macrolide antibiotics, and its derivatives had been found to mimic actions of exogenous motilin, a gastrointestinal peptide hormone. We found that some of the macrolide compounds inhibited the specific binding of 125I-motilin to rabbit duodenum muscle at 15 C in a dose-dependent fashion. The inhibitory activity of several macrolides examined did not relate to their antibacterial activity but to their motilin-like activity. A 50% inhibition by EM536, a non-antibacterial erythromycin derivative with the highest motilin-like activity, was obtained at 3-40 nM and little higher than that of non-radioactive motilin (5-6 nM) under the present conditions. The results suggest that erythromycin and its derivatives mimic physiological actions of motilin by acting as agonists for a motilin receptor.