CONTRACEBTION BIOCHEMICAL BASIS FOR THE "RIBOFLAVIN DEFECT" ASSOCIATED WITH THE USE OF ORAL CONTRACEPTIVES, A STUDY IN FEMALE RATS Faizy Ahmed and Mahtab S. Bamji National Institute of Nutrition Indian Council of Medical Research Hyderabad - 500007, India ABSTRACT Administration of one-tenth tablet of the oral contra- ceptive pill, Ovulen-50 (ethinodiol diacetate 1 mg, ethinyl estradiol 50 ug) to adult female rate resulted in a significant decrease in urinary and blood riboflavin but increase in hepatic riboflavin and FAD. Of the flavin enzymes in the liver, glutathione reductase (E.C.1.6.4.2) and D-amino acid oxidase (E.C.1.4.3.3) showed a significant increase, whereas NADH dehydrogenase (E.C.1.6.99.3) tended to fall. Xanthine oxidase (E.C.1.2.3.2) and pyridoxamine phosphate oxidase (E.C.1.4.3.5) showed no change. Eryth~o- cyte glutathione reductase did not change, Accepted for publication June 23, 1976 287