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.