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...