title: Effect of particle size and lipid composition of bovine blood high density lipoprotein on its function as a carrier of beta-carotene.
abstract: As part of a study on the influence of dietary lipids on vitamin transport and metabolism in lactating cows, we have examined the beta-carotene content and other properties of fractions of the high-density lipoprotein (HDL, density 1.05-1.16 g/ml) of bovine blood. Our purpose was primarily to explain previous results indicating that feeding cows polyunsaturated lipids alters the properties of the HDL and increases the concentration of beta-carotene in the blood but not in the milk. Fractions of HDL of different particle size were prepared by gel-filtration chromatography and the particle diameters measured by electron microscopy. We found that large HDL particles contain more beta-carotene per unit weight than small particles. Furthermore the HDL from cows fed lipid-rich diets with a high proportion of linoleic-acid residues, which had been protected against microbial degradation in the rumen, had a high percentage of HDL particles with large diameters. The blood from these cows had a higher concentration of beta-carotene than before feeding polyunsaturated lipids, but their milk had a lower concentration. We suggest that HDL is the main store of beta-carotene in bovine blood. Moreover the concentration of beta-carotene in blood is increased by feeding polyunsaturated lipids largely because of the increase in the percentage of large HDL particles, which contain more beta-carotene. The effect on the concentration of beta-carotene in milk implies that the transfer mechanism is less efficient as a result of feeding polyunsaturated lipids. This lower efficiency may be due in part to the higher percentage of large HDL particles.
mesh_terms: D000818:Animals; D002338:Carotenoids / Q000097:blood*; D002417:Cattle; D004041:Dietary Fats; D005227:Fatty Acids / Q000302:isolation & purification; D005260:Female; D007774:Lactation; D008075:Lipoproteins, HDL / Q000302:isolation & purification / Q000378:metabolism*; D008970:Molecular Weight; D011247:Pregnancy; D011485:Protein Binding; D019207:beta Carotene
chemical_list: D004041:Dietary Fats; D005227:Fatty Acids; D008075:Lipoproteins, HDL; D019207:beta Carotene; D002338:Carotenoids