The Induction of Osteopetrotic Changes in Hypophysectomized, Thyroparathyroidectomized, and Intact Rats of Various Ages

Osteopetrotic changes were induced in hypophysectomized (Hx), thyroparathyroidectomized (TxPx), as well as intact rats of various ages by means of daily injections of parathyroid extract (PTE) for a period of three weeks. Bone and blood formation and bone remodeling were assessed by quantitative means. Serum calcium was measured and differential counts were made on the thyroid epithelium. By selectively stimulating osteoblastic activity, PTE creates an imt balance whereby bone remodeling fails to keep pace with bone formation. The younger the anik mal at the onset of the PTE regimen, the greater the augmentation of osteogenic activity and the more extensive the ensuing osteopetrotic changes. When the PTE regimen was initiated before birth, y rate of membrane bone synthesis was doubled while expansion of the medullary cavities of the long bones was arrested. The induction of osteopetrotic changes in Hx and TxPx rats, in addition to PTE, required growth hormone (GH). The osteogenic stimulating affect of PTE was distinct from that of GH. When administered together, the osteogenic promoting affect of each one was additive. When administered alone or in combination with T4 replacement therapy to TxPx rats, TCT failed to stimulate osteogenic activity or to effect any osteopetrotic changes. A chronic state of hypercalcemia was produced in intact and Hx rats by means of a calcium rich diet. Although the parafollicular cell population was vigorously stimulated by the dietary regimen osteogenic activity was not enhanced and bone remodeling was only slightly affected. (Endocrinology89: 1389, 1971)