The absorption, distribution and excretion of 1- and 2-[14C]palmitoyl triacyglycerols in the rat

Human breast milk is rich in 2-palmitoyl 1,3 unsaturated triacyglycerols and during the neonatal period, when milk is the sole source of nutrients, their role could be particularly important. Betapol is a novel triacylglycerol mix resembling human breast milk in its high palmitic acid content and positional distribution. The total fat absorption from Betapol has been shown to be higher than fat from conventional infant milk formulas and closer to human breast milk in infants. However, the relative fate of purified palmitic acid esterified to glycerol in the 1-, 3- and 2-positions in neonatal and young animals has not previously been established. Therefore, the fate of orally administered 1-[1-14C]palmitoyl, 2,3 dioleoyl glycerol ([14C]POO) and 1,3 dioleoyl,2-[1-14C]palmitoyl glycerol (O[14C]PO) was investigated in suckling and weanling rats using liquid scintillation counting of tissues and expired air and whole-body autoradiography. The results obtained indicate that orally administered [14C]POO and O[14C]PO are extensively absorbed from the gut, probably either as palmitic acid or as a palmitoyl glyceride in both suckling and weanling rats. Radioactivity initially concentrated in brown fat with apparent migration to the white fat of weanling rats by 96 h. Levels of 14C were low in blood, brain and other tissues. Excretion of 14C was mainly by expiration of CO2 (approximately 72% in 96 h), indicating β-oxidation as a major route of metabolism. Urine and faeces accounted for only approximately 6% of the excreted radioactivity. The design and size of the experiment did not allow tests of statistical significance between the absorption and excretion of OPO and POO to be conducted. However, the absorption, distribution, β-oxidation and excretion appeared to be similar.