IDENTIFICATION OF RACTOPAMINE HYDROCHLORIDE METABOLITES EXCRETED IN RAT BILE

1. Rats dosed orally with 2.85+/-0.30mg [C-14]ractopamine HC1 [(1R,3R ), no]-methyl]([U-C-14]benzenemethanol)hydrochloride] containing 1.44 +/-0.15 mu Ci radioactivity excreted 58+/-7% of the administered radio activity in the bile within 24h. Absorption and excretion of radioacti vity was rapid as 55% of the administered radiocarbon was excreted int o the bile during the first 8-h collection period.2. Radioactivity exc reted in rat bile was partitioned by XAD-2 column chromatography and r everse-phase hplc into at least seven different crude metabolite fract ions; metabolites representing approximately 76% of the biliary radioa ctivity were isolated and identified from four of the crude metabolite fractions. 3. Approximately 46% of the biliary radioactivity was iden tified as a sulphate-ester, glucuronic acid diconjugate of ractopamine . Identification was based on H-1-nmr and negative-ion FAB-ms spectros copy. Enzymatic and chemical hydrolysis of the sulphateester followed by co-chromatography of the hydrolysis products with synthetic ractopa mine mono-glucuronides, established the site of sulphation at the C-10 ' phenol (phenol attached to carbinol) and glucuronidation at the C-10 phenol (phenol attached to methylpropyl amine) of ractopamine. 4. A m etabolite representing approximately 6% of the biliary radioactivity w as identified as a ractopamine mono-sulphate conjugate by using mass s pectral and H-1-nmr techniques. Sulphate was conjugated at the C-10' p henol of ractopamine and was not stereospecific. 5. Approximately 25% of the biliary radioactivity was identified as ractopamine mono-glucur onides. The major site of glucuronidation was at the C-10 phenol, but ractopamine glucuronidated at the C-10' phenol was also present.