BIOAVAILABILITY OF CHOLINE AND CHOLINE ESTERS FROM MILK IN RAT POPS

Previously, we had shown that human milk and infant formulas contained choline, phosphocholine (PCho), glycerophosphocholine (GPCho), and ph osphatidylcholine (PtdCho). The relative bioavailability of these chol ine-containing compounds in milk has not previously been studied. Usin g a rat pup model, infant formula (S.M.A.(TM), Wyeth-Ayerst) containin g either [C-14-methyl]-choline chloride (C-14-Cho) [C-14-methyl]-PCho, [C-14-methyl]-GPCho), or [L-alpha-dipalmitoyl-C-14-methyl]-PtdCho was fed intragastrically by a single intubation into 15-day-old postnatal rat pups. Label from the water-soluble metabolites of choline (cholin e, phosphocholine, and glycerophosphocholine) appeared rapidly within blood and liver reaching peak levels within 1 to 5 hr, and label in br ain continued to increase for more than 24 hr. Label from the lipid so luble metabolite, phosphatidylcholine, took much longer to appear in b lood and liver (5 to 8 hr) and label remained elevated in blood for at least 24 hr. Label in brain continued to increase for more than 24 hr , but always remained lower than that attained after treatment with th e labeled water-soluble choline metabolites. The liver is a major stor age site for choline metabolites, and provides a sensitive indicator o f dietary choline status. In liver, a large portion of the label deriv ed from the water-soluble choline metabolites was in the form of betai ne at 4 hr post dose. At the same time, most of the the PtdCho-derived label was still present as PtdCho in liver. At 24 hr after dose, most of the label derived from choline and PCho in liver was present as be taine (85%) and PtdCho (15%), label derived from GPCho was found as be taine (54%), PtdCho (15%), PCho (11%), GPCho (2%), and choline (18%). Label derived from PtdCho was found as betaine (13%) PCho (2%), and Pt dCho (85%). We conclude that 15-day-old postnatal rat pups can absorb the various choline compounds in milk. Choline and PCho appear to be e ssentially identical in their absorption and metabolic fate. GPCho and PtdCho have different rates of absorption and/or metabolism Thus, we conclude that there are significant differences in bioavailability, ti ssue uptake and metabolism among the choline compounds that are presen t in milk.