Biotransformation of reproterol in the intestinal tract of the rat

The major metabolite of reproterol (Broncho-spasmin) in rat feces is 2-[3-theophyllinyl(7)-propyl]-4,6,8-trihydroxy-1,2,3,4-tetrahydroisoquinoline. It was also found in the bile of orally or intravenously dosed rats in the form of glucuronides. The biotransformation of an oral dose of reproterol to this metabolite occurred mostly in the cecum-colon section of the intestinal tract. Experiments in antibiotic treated rats showed no significant effect of the treatment on the extent of metabolite formation. This metabolite was also formed by incubation of reproterol with cecum-colon homogenates under aerobic as well as anaerobic conditions. The pharmacological action after an oral dose must be attributed to reproterol absorbed as intact form, since the metabolite is inactive.