Ascorbic acid turnover and excretion in two arboreal marsupials and in laboratory rabbits

Rates of turnover and routes of excretion of 1-14C-ascorbic acid were compared among laboratory rabbits and two species of arboreal marsupials. Ringtail possums (Pseudocheirus peregrinus) exhibited higher blood ascorbate levels than either brushtail possums (Trichosurus vulpecula) or rabbits, as well as greater pool sizes, shorter half-times and higher total entry rates of ascorbic acid. These differences were due partly to the high ascorbic acid content of Eucalyptus foliage, the ringtail's diet; when the dietary contribution of ascorbate was taken into account, endogenous entry rates (i.e. 'synthesis') were not significantly different among species. The main excretory route of 14C from 1-14C-ascorbate was expired CO2 in all three species. Estimates to total pool size of ascorbate by isotope dilution were higher than those by tissue analysis. This was considered to be due to excretion of 14C during equilibration of injected 1-14C-ascorbate with the body pool.