Vitamin B-6 deficiency vs folate deficiency: Comparison of responses to methionine loading in rats

Joshua W. Miller, Marie R. Nadeau, Donald Smith, Jacob Selhub

Research output: Contribution to journalArticlepeer-review

164 Scopus citations

Abstract

The plasma homocysteine response to methionine loading was assessed in vitamin B-6- and folate-deficient rats. Rats fed vitamin B-6-or folate- deficient diets for 4 wk were administered a gastric gavage of methionine (100 mg/kg body wt). Subsequent plasma analyses revealed a peak post- methionine load increase in plasma homocysteine concentration of > 300 μmol/L in the vitamin B-6-deficient rats. Folate-deficient rats exhibited no significant changes in plasma homocysteine after the load. These disparate responses can be explained by the observed increase in hepatic S- adenosylmethionine (SAM) concentration because of the load. In vitamin B-6 deficiency, increased SAM inhibits homocysteine remethylation, which, in conjunction with the impaired homocysteine catabolism due to the deficiency and the increased synthesis of homocysteine due to the methionine load, leads to a large elevation of homocysteine in the blood. In folate deficiency, increased SAM activates homocysteine catabolism, which compensates for the increased synthesis of homocysteine due to the load and thus no change in blood homocysteine is observed. These results have significant bearing on the interpretation of both positive and negative responses to methionine loading in humans.

Original languageEnglish (US)
Pages (from-to)1033-1039
Number of pages7
JournalAmerican Journal of Clinical Nutrition
Volume59
Issue number5
StatePublished - May 1994
Externally publishedYes

ASJC Scopus subject areas

  • Food Science
  • Medicine (miscellaneous)

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