Insensitivity of dogs to the effects of nonspecific bound vitamin A in plasma.

Retinol bound to its specific carrier, the retinol-binding protein, is known to be the physiological way vitamin A is transported in blood. Unspecific, lipoprotein-bound vitamin A has so far only be reported under the condition of hypervitaminosis A. In this investigation vitamin A concentrations in dog plasma are reported (2300 ng/ml), showing for the first time a species which, under physiological conditions, transports most of its vitamin A in plasma as retinyl esters (70%) associated with lipoproteins. This phenomenon might indicate that dogs are less sensitive to the effects of nonspecific delivery of vitamin A than other species. This can open new aspects in retinoid research, especially with regard to hypervitaminosis A - an undesirable side effect of the beneficial use of retinoids in dermatology and oncology.