A note on the prevention of experimental low-phosphorus rickets in rats by the subcutaneous administration of potassium phosphate.

It is now well established that rachitic lesions of the bones may be readily produced in rats by a regimen deficient in available phosphate. With the standard Diet 84 in use in this laboratory, the minimal protective addition of K₂HPO₄, in the absence of effective light rays or specific antirachitic substances is in the neighborhood of 0.4 grams per cent of the diet—an amount equivalent to 75 mg. of phosphorus. The addition of 50 mg. protects in some individuals, but is on the border line. 1

It seemed of interest to ascertain whether the subcutaneous administration of inorganic phosphate also conferred protection; and if so, to make at least a rough quantitative comparison of the amount required with that necessary when administered with the food.

A solution of K₂HPO₄ was made up to contain approximately 5 mg. of phosphorus per cc. Actual analysis by the Briggs' modification of the Bell-Doisy method showed the solution to contain 4.85 mg. per cc. 2 The solution was sterilized, and kept in stoppered vaccine bottles to prevent evaporation. Graded amounts were injected 6 days a week over a period of 28 days. There was no local reaction, and the fluid was rapidly absorbed. Two litters of known stock (Gies) comprising 14 individuals, were used for the experiment. Three rats died before the termination of the experiment, and are not included. The dosage and results are shown in the accompanying table.

It is seen that complete protection was afforded by injections of 1 cc. of the solution, equivalent to an average daily dose of 3.98 mg. of phosphorus. The total amount administered during the 28 day period of the experiment was 111.55 mg. Injection of lesser amounts gave only incomplete protection.