Influence of vitamin A on formation and excretion of end products of nitrogen catabolism in chicks.

The effect of vitamin A deprivation at different stages, and of dosing with different levels of the vitamin of some parameters of protein catabolism was examined in chicks. Plasma uric acid and plasma urea were increased in vitamin A deficiency. Dosing with vitamin A caused a decrease in the plasma uric acid concentration only in deficient chicks which received the higher dosing level (3000 mug retinol equivalent), whereas plasma urea concentration increased in all cases after dosing. Nitrogen retention and uric acid excretion were not changed in chicks in the first stages of vitamin A deficiency, but excretion of urea was increased in comparison to pair fed chicks. Liver xanthine dehydrogenase (XDH) and kidney arginase were both increased even in the first stages of vitamin A deficiency. The increase in XDH activity was shown to be partially due to the stress of overnight fat caused by pair feeding, whereas this factor had no part in the increase of the kidney orginase. Dosing with vitamin A had almost no effect on the plasma vitamin A of chicks fed a high dietary level of the vitamin (9000 mug/kg) while there was a clear response in control chicks (fed 900 mug/kg) or deficient ones.