Observations on pyridoxine metabolism in pregnancy

Abstract Despite the rather frequent employment of pyridoxine in obstetrics and gynecology, chiefly in the treatment of the vomiting of pregnancy, 1–4 there remains no immediate way of measuring a relative deficiency of the vitamin and no direct chemical test for B 6 is available. The evidence for the therapeutic application of pyridoxine has, of necessity, been indirect and empirical, and open to dispute. 5–6 Indirect measurements of deficiencies of this vitamin can be made, however, by observing its effect on the metabolism of tryptophan. 7–8 When tryptophan, one of the essential amino acids, is taken orally by a B 6 -deficient animal, the abnormal metabolite, xanthurenic acid, is excreted in the urine. This also occurs in the human subject, 9 and is immediately corrected by the administration of pyridoxine. Employing this test, Sprince and co-workers 10 and Wachstein and Gudaitis 8, 11 report evidences of a relative deficiency of vitamin B 6 in pregnancy. The present brief report is concerned with this test as an index of the pyridoxine status of the normal pregnant patient. Ten grams of tryptophan ∗ ∗Obtained from Merck & Co., Inc., Rahway, New Jersey, through the courtesy of Dr. R. A. Peterman. was administered orally at night, and beginning two hours later a 10 hour specimen of urine collected. From the time of taking the tryptophan to the conclusion of the test, no other food or fluids were consumed. The xanthurenic acid excreted was determined colorimetrically, using the technique of Rosen, Lowy, and Sprince, 12 as modified by Wachstein and Gudaitis, 8 and expressing the result in milligrams of xanthurenic acid excreted per total 10 hour period. Using this technique, recovery experiments of measured amounts of pure xanthurenic acid † †Obtained from Sharpe & Dohme, Inc., West Point, Pa., and from the Ortho Research Foundation, Raritan, N. J., through the courtesy of Dr. L. E. Arnow and Dr. Fred Rosen, respectively. added to urine showed statistically reliable results with an average recovery of 107.2 per cent. A total of 48 patients were studied, the individual tests being grouped to provide controls both between the pregnant and the nonpregnant, and between the pregnant patients who received pyridoxine and those who received placebos or other B fractions.