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The Effect of the Vitamin A (Carotene) Intake on the Vitamin D Requirement of Rats in the Production and Cure of Rickets¹

Department of Agricultural and Biological Chemistry, Pennsylvania State College

The production of rickets in the growing rat receiving a rachitogenic diet supplemented and unsupplemented with carotene as the source of vitamin A has been studied by means of X-ray examination, line test, bone ash determinations, and by an analysis of the blood serum for calcium and phosphorus. The subsequent recalcification, when corresponding animals received such diets supplemented with vitamin D from two sources, has been investigated in a similar manner.

The manifestations of the interrelationship of vitamin A and vitamin D in the etiology of rickets depend no. doubt upon several factors, among which may be mentioned 1) past ancestral and nutritional history, 2) the age of the animals, and 3) individual variation among animals of the same age. It may be observed that the values found for the percentage of bone ash for normal animals of different ages varies with age. There is also variation in the blood calcium and blood phosphorus among normal animals of different ages. It is, therefore, highly desirable that all experimental animals used in a study of this nature be from the same genetic source and be carefully standardized according to age.

The efficient conversion of carotene to vitamin A undoubtedly varies among individual animals. Consequently, a detailed study of the problem necessitates the use of a natural vitamin A concentrate free from vitamin D in order to insure a clearer understanding of the vitamin A-vitamin D relationship. Until it is possible to procure such a supplement, this interrelationship cannot be readily demonstrated.

The following observations were made during the course of the experiment:

Rachitogenic diets containing 90 U. S. P. units of vitamin A per gram of diet seemed to produce, during the depletion period, an increase in the severity of rickets among growing rats over and above that produced by a similar diet which did not contain added vitamin A supplement.

The radiographic examination at the end of the depletion period was a more reliable index of the intensity of rickets than was the percentage of bone ash.

Evidences of satisfactory correlation between the percentage of bone ash and corresponding radiograms were not obtained.

Inconsistencies between the calcium and phosphorus content of the blood serum and bone ash values were also apparent.

When equivalent unitages of vitamin D were administered, rachitogenic diets containing 90 U. S. P. units of vitamin A per gram, with and without 5% of Wesson oil, appeared to retard recalcification (as measured by line test technic) to a greater extent than was observed when similar diets which did not contain any vitamin A supplement were fed.

Data obtained as a result of bone ash determinations and blood serum analyses did not appear to be in agreement with line test data.

From the results obtained in this investigation the line test data appeared to be the most reliable criteria of recalcification.

² Presented by Florence S. Tabor to the faculty of the Department of Agricultural and Biological Chemistry of the Pennsylvania State College in partial fulfillment of the requirements for the degree of Doctor of Philosophy.

Manuscript received 1 April 1936.