Effect of oral and parenteral administration of B6 vitamers on the lymphopenia produced by feeding ammonia caramel or 2-acetyl-4(5)-(1,2,3,4-tetrahydroxy)butylimidazole to rats.

The ability of B6 vitamers to prevent the lymphopenic effects of ammonia caramel fed to rats has been evaluated. Diets containing 10 ppm pyridoxine or pyridoxal prevented the lymphopenia produced in rats consuming an 8% (w/v) solution of ammonia caramel, whereas the dietary content of pyridoxamine needed to be increased to 20 ppm to have the same effect. In contrast to the results of the enteral administration of the individual B6 vitamers, pyridoxamine was found to be the most effective vitamer in preventing the ammonia caramel-induced lymphopenia when administered parenterally. However, all the nutritionally active forms of vitamin B6 were able to prevent the depression of the peripheral blood lymphocyte count, which resulted from ingestion of ammonia caramel by rats. The proposal that oral administration of pyridoxine may prevent the intestinal absorption of the lymphopenic constituent of ammonia caramel, 2-acetyl-4(5)-(1,2,3,4-tetrahydroxy)butylimidazole (THI), is discredited, since THI was found to reduce the lymphocyte count after parenteral administration in rats fed 0.04 ppm pyridoxone in the diet and that increased amounts of dietary pyridoxine (10 ppm) could still prevent this effect. These findings further emphasise the important relationship between dietary vitamin B6 content and the lymphopenic effects of ammonia caramel/THI in the rat.