The Passage of Vitamin A from Mother to Young in the Rat

In studying the vitamin A content of human milk Kon & Mawson (1950) noted that many of the women whose milk was examined had taken a supplement of vitamin A during pregnancy but not after the birth of the child.Although these women presumably had higher liver reserves of vitamin A than those that had taken no supplement, the difference was not reflected in the vitamin A content of their milk.Dann (1932, 1934u, b) and Baumann, Riising & Steenbock (1934) studied the effect of the liver reserves of the mother rat on the stores of the newborn young and of the young at weaning.They did not analyse the milk; at that time methods of measuring vitamin A were not sufficiently sensitive for the purpose.Nevertheless, a comparison of Dann's values for the newborn with those for the weanling indicates that large differences in maternal reserves must have been reflected in small differences in the vitamin A content of the milk.The work with rats now described was undertaken to study further the relationship between the maternal reserves of vitamin A, the vitamin A content of the milk, and the stores of vitamin A present in the young at birth and amassed during suckling.The mother rats received vitamin A either preformed or as /3-carotene. EXPERIMENTAL General procedureFemale hooded Norwegian rats from our colony were used throughout this work.Except in Exps.I and 6, the animals were weaned on to a diet low in vitamin A (diet 213) supplemented with sufficient vitamin A to maintain growth; the amount varied between 5 and 20 i.u.daily in different experiments.The percentage composition of diet 213 is given in Table I .Since the vitamin A and carotene content of this diet was equivalent to a vitamin A activity of not more than 8 i.u./Ioo g., it is unlikely that the vitamin A intake from the diet amounted to more than I i.u./rat/day.The vitamin A supplement was a concentrate prepared by Distillation Products Inc., kindly given to us by Dr T. H. Mead of British Drug Houses Ltd., and found by him to contain 170,000 i.u./g.This was suitably diluted with arachis oil for feeding by pipette.During the preparatory period vitamin A was given weekly together with 35 i.u. of vitamin D, also in arachis oil.When the animals were 34 months old and weighed about zoog., daily vaginal smears were taken and at oestrus they were mated with stock-colony males.Only eight young (four males and four females, if possible) were retained from litters con-