In our experiments, chronic hypercalcaemia was produced in albino rats by prolonged administration of large doses of irradiated ergosterol. Characteristic osseous changes and metastatic calcification occurred chiefly in the blood vessels of various organs. The cartilage of the knee joints and of the intervertebral discs showed areas of degeneration with calcification,—changes not unlike those found in early degenerative arthritis of human joints. Calcification of the extra-articular collateral vessels of the knee joints was prominent, but probably of no specific significance, since the entire vascular system showed similar changes. There were no anatomical or histological changes in the parathyroid glands to support the contention of Taylor that vitamin D acts through the parathyroid glands.
The rat may recover completely from the effects of prolonged feeding of vitamin D within two to three weeks after the drug is withdrawn.