Serum vitamin A esters are high in captive rhesus (Macaca mulatta) and marmoset (Callithrix jacchus) monkeys

We showed previously that hepatic vitamin A concentrations of captive rhesus monkeys (Macaca mulatta) are subtoxic to toxic, with livers exhibiting stellate cell hypertrophy and hyperplasia. Although marmoset (Callithrix jacchus) livers are also high in vitamin A, no stellate cell irregularities were observed. To further characterize the effects of high dietary vitamin A from preformed sources, stored serum samples were analyzed from monkeys used for biomedical research and housed at the Wisconsin Primate Research Center. The monkeys had been fed commercially available monkey diets, providing vitamin A (as retinyl acetate) at levels exceeding NRC recommendations by a factor of four. The serum from both rhesus and marmoset monkeys had total serum vitamin A (retinol, retinyl esters and metabolites) within the expected range for both species, i.e., 1.44 +/- 0.34 and 1.41 +/- 0.72 micromol/L serum for rhesus and marmoset monkeys, respectively. However, high serum retinyl ester concentrations as a percentage of total serum vitamin A were present in both species, 12 +/- 5.1% (range, 5.5-23%) for rhesus and 27 +/- 14% (range, 10-57%) for the marmosets. Serum retinol concentrations were normal, i.e., 1.21 +/- 0.28 (rhesus) and 0.92 +/- 0.43 micromol/L (marmoset), compared with published values.