Deposition of B Vitamins in Normally Developing Fetuses as Evidence for Increased Vitamin Needs of the Rat for Reproduction I. Thiamine and Riboflavin

Abstract

The transfer of thiamine and riboflavin from the mother to developing rat fetuses has been determined at several intervals during second pregnancies of healthy stock animals as a means of gaining information on the increased vitamin needs of the rat for reproduction. The occurrence of thiamine and riboflavin in placental tissue and the maintenance of maternal stores of these vitamins have also been investigated. Placental tissue contains small amounts of riboflavin and thiamine. This low concentration, plus the fact that there is only a small mass of such tissue synthesized during reproduction, means that the development of the placentae imposes a very minor need for thiamine and riboflavin during pregnancy. Fetal growth in the rat is small during the first half of pregnancy; it becomes exceedingly rapid in normal litters from the 18th day of the gestation period to parturition. This accelerated synthesis of new tissues increases the thiamine and riboflavin needs of the mother considerably. Maximum transfer of thiamine per 24 hours occurred during the 21st day of pregnancy; this deposit of the vitamin accounted for an increased need of approximately 75 µg of B₁. Maximum riboflavin demands for pregnancy occurred at the same interval of the gestation period and were equal to nearly 60 µg per day. Prior to the 16th day of pregnancy in the rat there is apparently only a minor need for thiamine and riboflavin beyond the amount recognized as being necessary for the nonpregnant adult animal.