Choline and C1 metabolism pathways intersect at the formation of
methionine from
homocysteine. Hepatic
S-adenosylmethionine (
AdoMet) concentrations are decreased in animals ingesting diets deficient in
choline, and it has been suggested that this occurs because the availability of
methionine limits
AdoMet synthesis. If the above hypothesis is correct, changes in hepatic
AdoMet concentrations should relate in some consistent manner to changes in hepatic
methionine concentrations. Rats were fed on a
choline-deficient or control diet for 1-42 days. Hepatic
choline concentrations in control animals were 105 nmol/g, and decreased to 50% of control after the first 7 days on the
choline-deficient diet. Hepatic
methionine concentrations decreased by less than 20%, with most of this decrease occurring between days 3 and 7 of
choline deficiency. Hepatic
AdoMet concentrations decreased by 25% during the first week, and continued to decrease (in total, by over 60%) during each subsequent week during which animals consumed a
choline-deficient diet. Hepatic
S-adenosylhomocysteine (AdoHcy) concentrations increased by 50% when animals consumed a
choline-deficient diet. AdoHcy is formed when
AdoMet is utilized as a methyl donor. In summary,
choline deficiency can deplete hepatic stores of
AdoMet under dietary conditions that only minimally decrease the availability of
methionine within liver. Thus decreased availability of
methionine may not have been the only mechanism whereby
choline deficiency lowers hepatic
AdoMet concentrations. We suggest that increased utilization of
AdoMet might also have occurred.