Previously, we had shown that human milk and infant formulas contained choline, phosphocholine (PCho), glycerophosphocholine (GPCho), and phosphatidylcholine (PtdCho). The relative bioavailability of these choline-containing compounds in milk has not previously been studied. Using a rat pup model, infant formula (S.M.A.(TM), Wyeth-Ayerst) containing 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 (choline, phosphocholine, and glycerophosphocholine) appeared rapidly within blood and liver reaching peak levels within 1 to 5 hr, and label in brain continued to increase for more than 24 hr. Label from the lipid soluble metabolite, phosphatidylcholine, took much longer to appear in blood 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 the labeled water-soluble choline metabolites. The liver is a major storage site for choline metabolites, and provides a sensitive indicator of dietary choline status. In liver, a large portion of the label derived from the water-soluble choline metabolites was in the form of betaine 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 betaine (85%) and PtdCho (15%), label derived from GPCho was found as betaine (54%), PtdCho (15%), PCho (11%), GPCho (2%), and choline (18%). Label derived from PtdCho was found as betaine (13%) PCho (2%), and PtdCho (85%). We conclude that 15-day-old postnatal rat pups can absorb the various choline compounds in milk. Choline and PCho appear to be essentially 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, tissue uptake and metabolism among the choline compounds that are present in milk.
