Elevated tissue betaine contents in developing rats are due to dietary betaine, not to synthesis

The time course of betaine accumulation and activities of enzymes involved in betaine metabolism were studied in developing rats. In study 1, pups weaned oil a nonpurified diet had a transient increase in liver and kidney betaine content followed by a decline after similar to 42-56 d. In study 2, dams and, following wearing, pups were fed an AIN-93G (betaine-free or an AIN-93G betaine-supplemented diet (0.3%) to determine the source of the transient increase in betaine levels previously observed. In study 2, only rats fed betaine had an increase in plasma betaine concentration. Similarly, liver and kidney betaine contents increased postweaning; however, betaine levels returned to that found in rats fed a betaine-free diet by 49 d of age. The dietary content of betaine fed to dams did not affect pup betaine. The activities of choline dehydrogenase, an enzyme of betaine synthesis, and betaine:homocystein methyltransferase (BHMT) which is the only known betaine-consuming enzyme in mammals, were also measured in study 2. Liver BHMT activity decreased after weaning, whereas liver and kidney choline dehydrogenase activity increased with age, possibly reaching a plateau by 42 d of age. We conclude that the transient increase in betaine reflects high dietary betaine and not a change in endogenous betaine synthesis.