Effect of age on the levels of retinol and retinyl esters in blood plasma, liver and kidney of dogs.

The effect of age on plasma levels and tissue distribution (liver, kidney) of retinol and retinyl esters was studied in dogs from birth to the age of 18 months. In newborn dogs vitamin A in plasma was low and increased within four weeks to levels found in adult dogs. At four weeks retinyl esters (stearate > palmitate) dominated over retinol in plasma. Liver levels increased over 400 times from 10 micrograms/g at birth within six months. At all times retinyl esters represented the majority of vitamin A (> 70%). In kidneys, highest levels were observed not before 18 months after birth. Results indicate obvious quantitative and qualitative differences concerning vitamin A accumulation in plasma and tissue possibly associated with changes from fetal development to suckling stage and later to the uptake of feed.