Parenteral beta-carotene administration to cows: effect on plasma levels, lipoprotein distribution and secretion in the milk.

Beta-carotene has been considered to have a positive effect on fertility. Therefore the effect of a parenteral administration (intravenous or intramuscular) of beta-carotene on plasma levels, its distribution among the lipoprotein fractions and its secretion in the milk was investigated in cows. A single parenteral administration of beta-carotene resulted in a marked increase in total beta-carotene in the blood. Low density lipoprotein (LDL)-bound beta-carotene increased rapidly in the initial phase and then remained rather constant. The proportion bound to the high density fraction (HDL), however, increased continuously, reaching maximum levels parallel to the total plasma concentration. Beta-carotene administration had no effect on vitamin A levels in plasma, but caused an increase of beta-carotene and vitamin A in milk. The results show that the parenteral administration of beta-carotene is not only an effective way to increase its blood plasma level but also results in a binding of beta-carotene to its physiological carrier--the lipoproteins. Beta-carotene is therefore supplied to peripheral target tissue by the same carriers as those when beta-carotene is administered orally. The availability of beta-carotene for peripheral tissues is further supported by the increase in beta-carotene in milk, as well as by the increase in vitamin A in milk which points to a local conversion of beta-carotene into vitamin A in the mammary gland.