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Relationship of Urinary Methylmalonic Acid to Vitamin B-12 Concentrations and Hematologic Changes in Rats Fed Vitamin B-12-Deficient Diets¹

Department of Nutrition, Harvard School of Public Health, Boston, MA 02115

Urinary methylmalonic acid in vitamin B-12-deprived rats was examined with the objective of quantitating the relationship between vitamin B-12 status and 24-hour methylmalonate excretion. Rats fed vitamin B-12-deficient purified diets for 10 months after weaning began to excrete methylmalonic acid above control values at 6 weeks. Growth retardation relative to control animals fed vitamin B-12-supplemented diets was observed 3 weeks after deprivation and increased with time until 39 weeks when control rats averaged 29% heavier than deficient rats. Liver concentrations of vitamin B-12 in rats fed the deficient diet declined exponentially from weaning with a calculated half-life of 13.6 weeks. Urinary methylmalonate began to appear in urine when the liver vitamin B-12 concentration was approximately 84% of the initial value. Plasma vitamin B-12 concentrations also declined exponentially to undetectable levels (<0.05 ng/ml) after 27 weeks, having a half-life virtually identical to that of liver vitamin B-12. Brain vitamin B-12 levels increased threefold above the weanling value in the initial 9 weeks followed by an exponential decline with a half-life of 10.3 weeks. Nuclear hypersegmentation of neutrophils characteristic of megaloblastic granulopoiesis was observed in bone marrow and peripheral blood of deficient rats having hematocrits less than 40% after 33 weeks of dietary treatment.

KEY WORDS: • vitamin B-12 deficiency • methylmalonic acid • liver • brain and plasma vitamin B-12 • hypersegmented neutrophils

¹ This research was supported by a NSF Science Faculty Fellowship to J. J. Brink, by NIH Grant No. AM 00106 and by USDA Science and Education Administration Competitive Research Grant No. 5901-0410-8-0132-0.

² To whom reprint requests should be sent at his present address: Department of Biology, Clark University, Worcester, MA 01610.

³ Present address: Department of Food Science, Framingham State College, Framingham, MA 01701.

Manuscript received 13 December 1979.