Transport of esterified retinol in fasting human blood.

The transport of retinyl palmitate in postabsorptive human blood has been investigated. For this purpose, lipoproteins were isolated from fasting serum of normal subjects as well as of patients with various diseases. The serum retinyl palmitate values of these individuals ranged from 2.0-30.3 micrograms/100 ml, with a mean value of 7.6 micrograms/100 ml. In the 14 human subjects investigated, 68.1% of the recovered retinyl palmitate was associated with the VLDL fraction and 28.9% with the LDL fraction. Nevertheless, the individual pattern of retinyl palmitate distribution among VLDL and LDL differed considerably within this group. No esterified retinol, however, was detected in the HDL as well as in the nonlipoprotein fraction (d greater than 1.21 g/ml) of human serum. It is concluded that the transport of esterified retinol in fasting blood is not restricted to chylomicron remnants. Nevertheless, in humans the serum transport of retinyl palmitate is preferentially mediated by lipoproteins of the VLDL fraction.