Transport and metabolism of pyridoxamine and pyridoxamine phosphate in the small intestine of the rat.

The vascularly perfused small intestine of the rat was utilized to study the absorption and metabolism of pyridoxamine (PM) and pyridoxamine-5'-phosphate (PMP), independent of other tissues including erythrocytes. [3H]PM or [3H]PMP was administered intralumenally with or without the addition of unlabeled PM, or PMP or inorganic phosphate. The percentage absorption of PM was 17.1 to 19.7% in 10 minutes and was unaffected by dosages from 0.02 to 200 mumole. The isotope from [3H]PMP at a physiological level (0.02 mumole) was absorbed at the same rate as that from [3H]PM, and the distribution of the 3H remaining in the lumen and in the intestinal tissue and perfusate indicated that hydrolytic removal of the phosphate was occurring extensively in the gut. The spectrum of labeled compounds isolated from the lumen, the perfusate and the mucosa clearly indicated that PMP, unhydrolyzed, can be absorbed slowly and converted to a number of vitamin B-6 forms in the intestinal mucosa. However, the results support the view that under normal physiological conditions the majority of dietary PMP is hydrolyzed to PM which seems to be absorbed by passive diffusion and transported to other organs and tissues via the blood stream.