The biological activity of vitamin B6 analogs in the rat.

The effects of three vitamin B6 analogs were studied in young adult and weanling rats. The 2-ethyl analog was the most active. It produced higher growth rates, an average feed efficiency equal to the control and elevated liver glycogen levels. Xanthurenic acid excretion remained low with the 2-ethyl analog and pyridoxine in the diet and plasma amino acid concentration was low. Response to the 2-n-propyl analog was similar to that of a B6-deficient diet, with a large increase in xanthurenic acid excretion. Rats receiving the 2-isopropyl analog were intermediate between the ethyl group and B6-deficient animals in all parameters measured. These in vivo results parallel those reported in the in vitro yeast pyridoxine dehydrogenase enzyme system. The ethyl pyridoxine analog was the most active of all the analogs in the yeast dehydrogenase system, in supporting growth and in maintaining normal xanthurenic acid excretion in the rat.