662 THE BIOCHEMISTRY OF B VITAMINS 



two doses of desoxypyridoxine (100 y on alternate days) at approximately 

 six times the concentration of pyridoxine intake (16 y) resulted in the 

 death of all the chicks. Without simultaneous administration of pyri- 

 doxine, as little as 16 y doses of desoxypyridoxine gave similar results. 

 From the growth response of the chick to pyridoxine, the apparent 

 pyridoxine activity resulting from administration of a mixture of the 

 vitamin and analogue was determined. The difference between the amount 

 of the vitamin administered and the apparent activity of the mixture 

 was considered the amount of vitamin activity counteracted by the 

 analogue. On this basis, two molecules of the inhibitor were necessary 

 to counteract the vitamin activity of one molecule of pyridoxine at both 

 suboptimal and optimal concentrations of the vitamin for the deficient 

 chicks. 65 



Normal chicks on a diet containing adequate amounts of pyridoxine 

 were able to tolerate a total dosage of at least 600 y of the analogue, a 

 level six times the lethal concentration for more than half the pyridoxine- 

 deficient chicks on an analogous diet. 65 



Almost 100 per cent mortality of the chick embryos resulted from 

 the injection of 1 mg of desoxypyridoxine into eggs at the outset of 

 incubation. 66 The inhibitory effects were prevented by simultaneous 

 injection of one of the vitamin B G group. The ratios of analogue to the 

 vitamin at which only 50 per cent of the embryos survived were: 20 for 

 pyridoxal hydrochloride, 50 for pyridoxamine dihydrochloride, and 100 

 for pyridoxine hydrochloride. However, desoxypyridoxine was not toxic 

 to the embryo when injected after six days of incubation, except at 

 high concentrations (2.5-5 mg per egg) at which the toxicity was not 

 prevented by any of the three forms of vitamin B 6 . 66 



If desoxypyridoxine is administered to weanling rats in a purified 

 diet deficient in pyridoxine, the rate of production of acrodynia was 

 increased and the symptoms of vitamin B 6 depletion were aggravated. 67 

 Pyridoxine, as well as pyridoxal and pyridoxamine, prevents the toxicity 

 of the analogue. The ratio of desoxypyridoxine to pyridoxine at which 

 the dermatitis appears is approximately 50. With stock rations, the ratio 

 was 175. Since the other members of the vitamin B 6 group act in a manner 

 analogous to pyridoxine, the increased ratio with the stock ratios cannot 

 be accounted for on the basis of their presence in the stock diet. Adult 

 rats previously maintained on a stock diet were not affected appreciably 

 during a test period on a purified diet deficient in pyridoxine; however, 

 on the deficient diet supplemented with 0.5 mg per cent of desoxypyri- 

 doxine, rats showed deficiency symptoms, acrodynia and loss of weight, 

 at an average of 55 days. 67 



Marked reproductive upsets occur in normal female rats on a pyri- 



