Serum Bilirubin Content of the Blood of Rats Consuming a Ration Deficient in Inorganic Salts. ∗

That the extreme restriction of the inorganic salts of the diet of the albino rat produces striking changes in the composition of the blood has been repeatedly demonstrated in this laboratory. 1 , 2 , 3 A marked increase in the number of erythrocytes occurs, accompanied by a progressive decrease in the concentration of hemoglobin. As yet, no satisfactory explanation for the phenomenon has been obtained. The increase in erythrocytes cannot be due to a diminution in blood volume since the plasma and total blood volume remain within normal limits. 2 Nor is there any evidence of an increased rate of erythrocyte formation, inasmuch as no apparent reticulosis occurs during the period of the rapid increase in the number of erythrocytes. 3 It seemed desirable, therefore, to seek an explanation of the polycythemia in another direction, and the possibility that a decreased rate of destruction of erythrocytes leading to a “passive accumulation” of cells might be involved seemed worthy of investigation. As an index to the rate of erythrocyte destruction, the bilirubin content of the serum is usually employed since, given a normal liver and biliary system, there appears to be a direct relation between the two. 4 , 5 If the increase in the number of erythrocytes in the blood of the “low-salt” rats is a result of a decreased rate of cell destruction there should be some detectable decrease in the concentration of bilirubin in the serum. If, however, cell destruction proceeds at a normal rate, a concentration of serum bilirubin equal to or perhaps slightly greater than normal is to be expected.

The same procedure was followed in this experiment as in a previous one. 3 Male albino rats of the Connecticut Agricultural Experiment Station strain weighing from 40 to 50 gm. at weaning (21 days of age) were placed in individual cages and fed the stock colony ration. 6 Those animals which attained a weight of 120 ± 4 gm. at 35 ± 2 days of age were divided into 2 groups: one, the control group (12 rats), received an “adequate synthetic” ration; the other (10 rats), received a diet extremely poor in inorganic salts. Both diets were fed ad libitum. The composition of these diets and of the vitamin supplements have been described in an earlier publication. 3 Quantitative analyses, recently reported, 7 of the amounts of the chief inorganic constituents present in both the “adequate” and “low-salt” diets, serve to emphasize the extreme degree of the limitation of inorganic elements in the latter ration.