Comparative metabolism of dietary terpene, p-cymene, in generalist and specialist folivorous marsupials

The urinary metabolites of the monoterpene, p-cymene, were studied in three marsupial species: a generalist herbivore, the brushtail possum (Trichosur us vulpecula), and two specialist folivores, the greater glider (Petauroide s volans) and the ringtail possum (Pseudocheirus peregrinus), as well as in the laboratory rat (Rattus norvegicus). Each animal was dosed, intragastri cally, with single doses of p-cymene (0.37 mmol/kg and/or 1.49 mmol/kg). Ur ine and feces were collected for two 24-hr periods. Quantitative analysis o f urinary metabolites by extraction, gas chromatography, and mass spectrome try gave a mean recovery of 64% (range 52-74%) of the administered dose in 48 hr for the four species, No fecal metabolites were found. A species-spec ific pattern of metabolite excretion was evident and reflected the natural occurrence of p-cymene (and terpenes in general) in the diet. If the metabo lites excreted are grouped according to the total number of oxygen atoms ad ded (one to four), then the rat excreted metabolites encompassing all degre es of oxidation, but predominantly a monooxygenated metabolite. The brushta il possum excreted metabolites having two, three, and four oxygen atoms add ed. The ringtail possum and greater glider only excreted metabolites with t hree or four oxygen atoms, Conjugation played a significant role in the exc retion of oxidized metabolites in only the brushtail possums and the rat, T hese findings indicate that species encountering terpenes, such as p-cymene , in their normal diet have developed efficient oxidation pathways to elimi nate them. This oxidative efficiency could also reduce the necessity for su bsequent conjugation of metabolites which minimizes further demands on a nu tritionally limited diet.