GLYCEROPHOSPHOCHOLINE AND PHOSPHOCHOLINE ARE THE MAJOR CHOLINE METABOLITES IN RAT MILK

Choline is a constituent of cell membranes, surfactant and acetylcholi ne and is also a major source of methyl groups for the regeneration of methionine from homocysteine. Previous analyses of rat, human and bov ine milk measured only choline, phosphatidylcholine and sphingomyelin. Choline-containing compounds in milk from rats lactating for 15 d wer e measured by HPLC and gas chromatograph-mass spectrometry. In additio n to the previously reported choline metabolites, substantial concentr ations of glycerophosphocholine (3.7 mmol/L) and phosphocholine (653 m umol/L) were also detected. At 1 h after oral administration of [methy l-C-14]choline to lactating rats, the major labeled metabolites were p hosphocholine (91% of label in milk) and betaine (9%). Twenty-four hou rs after the dose, glycerophosphocholine was the major labeled metabol ite (69% of label in milk). Rat mammary epithelial cells, in primary c ulture, synthesized and secreted phosphatidylcholine, phosphocholine, glycerophosphocholine and betaine. Thus, the mammary gland was able to synthesize the choline metabolites found in milk, but these metabolit es may not be derived exclusively from uptake from maternal blood. We have established that the total choline concentration in rat milk is s evenfold higher than previously reported, with >80% present as glycero phosphocholine and phosphocholine.