Marion B. Richards

The protective action of vitamin A upon various tissues in the avitaminotic rat, and the sensitivity of these tissues to vitamin A deficiency.

The experiments reported here were undertaken to compare the sensitivity of some rat tissues to relative or absolute vitamin A deficiency and to prophylactic doses of the vitamin. That there must be considerable differences in the requirements of various tissues and processes in the rat for vitamin A is suggested by the computed requirements of the entire animal found in the literature, based on such phenomena as growth, tooth colour, vaginal smears, storage, and longevity, recently summarized by Rubin & De Ritter (1954). The figures given range from 10 to 1000 i.u./kg bodyweightlday . In the present experiments the changes compared were those that occur in the incisor teeth (Wolbach & Howe, 1933), the medulla oblongata (Irving & Richards, 1938-9), the maxillary fundic alveolar bone (Irving, 1949) and the nasolacrimal duct (Irving, Pindborg, Fitzhugh, Weinmann & Schour, 1952). These were chosen as examples of two hard tissues, epithelia and nerve tissue. A preliminary account of some of these findings has already been published (Irving & Richards, 1954).

Further observations on conditioned pyridoxin deficiency in rats during lactation.

The preceding paper (Richards, 1949) described the effect of diets containing flours of different extraction rates on the conditioned pyridoxin deficiency caused by excessively high intake of vitamin B,, results being given for four generations of rats. The does of the first generation, after completing three lactations in their original groups, were used for various experiments designed to gain further information on the question of pyridoxin deficiency during lactation, and its effect on the weight of the thymus glands of the weanling rats. These experiments included: ( I ) transference of does from one group to another; (2) interchange of sucklings among different groups; (3) oral administration of pyridoxin to part of a litter during suckling. Nearly 25 yo of the does failed in the fourth mating, either when kept in their original group or when transferred to another group. A few of these had been erratic in their breeding performances in the earlier tests, but a number of the fourth-mating failures occurred in does which had had an excellent breeding record for the first three litters. Since none of the failures occurred in does of the original group which throughout received a daily supplement of 40pg. pyridoxin added to 72% extraction flour, and since some failures were recorded in each of the other groups, it seems probable that this early falling off in reproduction was partly due to the prolonged ingestion of the unbalanced diets.