Serum Calcium and Phosphorus of Guinea Pigs after Administration of Single and Repeated Doses of Parathormone

Abstract

The tendency has been to assume that hyperparathyroidism is consistently associated with hypercalcemia. We emphasize that frequently this is not the case, that hypercalcemia is not a sole criterion of hyperparathyroidism. Recorded instances of absence of hypercalcemia after parathyroid administration have sometimes been noted as merely paradoxical. The suggestion of “immunity” to parathormone is not supported by the data. On the other hand, the suggestion that an increased rate of excretion may prevent the accumulation of calcium in the blood is plausible. And a generalization (based on work with rodents) that herbivora are very resistant to parathormone injections implies an effect of diet on serum calcium response. However, the resistance of the cat would have to be explained on a different basis.

It has been established that in mice, rats and rabbits relatively small, if any, effects upon serum calcium are produced by administration of relatively huge doses of parathormone. Negative results in guinea pigs were reported by Macleod and Taylor 1 and Taylor. 2

We found that in guinea pigs consistent effects upon serum calcium and phosphorus could be produced only by very large doses; that these effects could be brought out more prominently, in young animals, after starvation; and that with doses not sufficiently great to produce effects on serum calcium and phosphorus, calcium mobilization and excretion could be demonstrated.

Controls. Normal guinea pigs, young and adult, fed and starved, showed a serum calcium of 10.4±1.0 mg. per 100 cc. The serum phosphorus varied from about 8.0 mg. in guinea pigs weighing about 300 gm. to about 4.0 mg. in adults. Starvation for about 70 hours lowered the serum phosphorus of the young animals to between 5.0 and 6.5 mg.

Effects of a Single Administration of a Large Dose: I. Calcium. With doses of 10 to 20 units per 100 gm., injected subcutaneously into adult guinea pigs, the serum calcium rose to a maximum of about 16.0 mg. about 24 hours after injection and returned within the normal range before 48 hours. Starvation did not intensify the effect.