Metabolites of alprenolol were isolated and identified in dog, guinea-pig and rat liver microsomes by means of g.l.c.-mass spectrometry and comparison with synthetic reference compounds. 2. The compounds were chromatographed as n-butylboronate derivatives, giving a series of diagnostic ions in the mass spectral fragmentation, which was elucidated by using stable isotopes. 3. Alprenolol was metabolized by aromatic ring hydroxylation, oxidation of the allylic function, and degradation of the isopropylaminopropanol side-chain. Alprenolol and four metabolites were quantified by h.p.l.c. and batch extraction techniques based on radioactivity measurements. 4. Five metabolites were detected in rat and guinea-pig liver microsomes and four in the dog. A species variation in the biotransformation of the allyl function in alprenolol was observed. The metabolite formed by oxidation of the allyl double bond was detected in significant amounts in the guinea-pig, and was also formed in the rat but could not be detected in dog liver microsomes.
