Figure 2.

Retinoid transport in the form of retinyl esters. Dietary retinoid, in the form of retinol, retinyl esters, and provitamin A carotenoids, are absorbed in the small intestine, where they are packaged into chylomicrons and secreted into the lymphatic system. Retinyl esters in chylomicrons undergo lipolysis and remodeling while traversing the circulation. From there, retinyl esters may take one of two paths—(I) they may either be hydrolyzed into retinol (via the actions of LPL), which may be taken up by peripheral tissues (in rodents, 25-33% of chylomicron retinyl ester is delivered directly to peripheral tissues); or (II) they may be transported to the liver (in rodents, 66-75% of chylomicron retinyl ester is transported to the liver). Retinyl esters are stored in the liver. The liver can secrete some retinyl ester bound to VLDL into circulation. Upon metabolism of VLDL, some retinyl esters may be found in LDL or transferred to high density lipoprotein (HDL). Retinyl esters bound to these lipoprotein particles may also be taken up into peripheral tissues.