EFFECTS OF THYROXINE ON CORTICAL BONE REMODELING IN ADULT DOGS - A HISTOMORPHOMETRIC STUDY

  • 1 January 1981
    • journal article
    • research article
    • Vol. 102  (3) , 438-446
Abstract
The effects of thyroxine [T4] on cortical bone remodeling were studied under conditions of normal and accelerated remodeling, induced by surgical elevation of the periosteum. Six adult female beagle dogs were administered orally 1.0 mg of L-thyroxine per kg body wt daily for 60 day. Static and dynamic changes were evaluated using tetracycline and DCAF (2,4-bis-N,N''-dicarboxymethyl aminomethyl fluorescein) in vivo double-labeling of rib specimens, taken before treatment and after 60 days. T4 administered in moderate pharmacologic doses increased the activation frequency, number of bone-forming and -resorbing sites, and the osteoid seam circumference in unaltered bone. T4, by activating skeletal remodeling, increased bone turnover and both formation and resorption at the tissue level. In ribs with periosteal elevation and accelerated remodeling, T4 increased the activation frequency, number of bone resorption and formation sites, and ratio of bone resorptive to formative surfaces. T4 under these conditions resulted in an increase in the osteoid seam circumference, radial closure rate, and bone formation rate at the tissue level, but decreased the osteon formation time. Under conditions of accelerated remodeling, T4 increased osteoblastic and resorptive activity to a greater degree than in unaltered bone, and resulted in bone changes similar to that described in humans with thyrotoxicosis. The increased serum Ca and P levels, and urinary hydroxyproline excretion at several intervals during T4 administration, were consistent with the morphometric evidence of increased bone turnover and resorption. Thyroxine is evidently a potent activator of skeletal remodeling under conditions of both normal and accelerated remodeling.