Morphology of the release of vitamin A-containing lipid droplets by perisinusoidal lipocytes in the rat liver.

Abstract

Vitamin A-containing lipid droplets in perisinsoidal lipocytes (or fat-storing cells) of rat liver were found to be exocytotically released from the cells in the form of a 'lipid droplet-protein complex' following intraportal injection of retinol (17, 33, 67 or 100 micrograms). Intraportal injection of retinol produced varied numbers and sizes of vacuoles with a limiting membrane in perisinusoidal lipocytes. The substance within the vacuoles exhibited a meshwork-like configuration in sections from slices incubated in a medium for revealing acid phosphatase activity or the corresponding control medium, and was immunoreactive to retinol-binding protein and proteinaceous in nature. The occurrence and number of the vacuoles depended on the dosage of injected retinol, being greatest at a dosage of 100 micrograms of retinol and becoming progressively less at dosages of 67, 33 and 17 micrograms. The vacuoles appeared to be formed by vacuolization of cisternae of the rough endoplasmic reticulum. Little or no esterase activity was found in lipid droplets in perisinusoidal lipocytes before the intraportal injection of retinol, but after the injection lipid droplets which had fused with the vacuoles became strongly positive for this enzyme activity. This suggests that hydrolysis of retinyl esters may occur in the process of complex formation in perisinusoidal lipocytes.