The Influence of Roentgen Rays on the Growth and Phosphatase Activity of Bone

Abstract

SHORTLY after the discovery of the roentgen ray, it was found that exposure of growing bone to this ray is followed by a period of inhibited growth. Brooks and Hillstrom (1) have recently made a study of the amount of irradiation necessary to inhibit growth, the quantity of the effect produced, the duration of the influence, and the coincident histologic changes. In view of the significance attached by Robison (3, 4, 5) and other workers to the rôle of phosphatase in bone growth, it appeared to us that a simultaneous study of the effect of roentgen rays on growth and on phosphatase activity would be of interest. The results of such a study are given in this paper. Procedure Pups from 30 to 40 days of age, were exposed to approximately 600 roentgens over the left fore leg, the remainder of the animal's body being carefully protected with sheet lead. The factors constituting this dose were from 190 to 200 kilovolts, 20 milliamperes, target-skin distance of 55 centimeters, filter of 0.5 mm. copper and 1 mm. aluminum, and exposure of 20 minutes. The animals were sacrificed at intervals of from three to 34 days after irradiation, the bones from the right fore legs being used as controls. The bones of both fore legs were removed, and all soft tissue, including ligaments and periosteum, was carefully dissected away since accurate weight measurements were necessary. All bones were treated in as nearly uniform a manner as possible, and were then weighed in suitable weighing bottles on an analytical balance. Care was taken to avoid loss of weight by evaporation. The length, including the epiphyses, was measured with a vernier caliper; the entire bone was then cut into small bits and ground in a mortar with No. 40 carborundum. This mixture was transferred to an Erlenmeyer flask of suitable size and 25 cc. of distilled water added for each gram of bone, the water being used in small portions to thoroughly remove the traces of material adhering to mortar, pestle, and spatula. A few drops of chloroform were added, the flask stoppered, well shaken, and set aside at room temperature for a period of 72 hours, with occasional shaking. At the end of this period, the mixture was filtered through No. 40 Whatman filter paper. Determinations of phosphatase activity were made on this filtrate, using a technic similar to that described by Jenner and Kay (2) for plasma phosphatase. In these experiments, 41 animals were used. The ulnæ were used for microscopic section of the line of growth at the epiphysis. However, values for weight and length of the ulnæ were obtained and are included in the averages given in Figures I and II. The microscopic findings will be reported in a separate paper. Thus all of the data on phosphatase represent values for the radii. Figure I shows the effect of irradiation on the length of the exposed bones as compared with the controls. Appreciable differences were consistently found after from 15 to 34 days.