Regulation of hepatic betaine-homocysteine methyltransferase by dietary betaine.

The level of betaine-homocysteine methyltransferase increases in the livers of rats fed diets supplemented with betaine or choline. The increase occurs within 3 days following the change in diet. When we administered betaine by intraperitoneal injection to rats fed choline-free diets, we observed a similar increase within 24 hours. Since betaine-homocysteine methyltransferase catalyzes a reaction which is essential for the catabolism of betaine, these changes provide a means for adaptation to excessive levels of dietary choline and betaine.