INTERMITTENT PARATHYROID-HORMONE ADMINISTRATION STIMULATES BONE-FORMATION IN THE MANDIBLES OF AGED OVARIECTOMIZED RATS

Intermittent administration of parathyroid hormone (PTH) is known to s timulate bone formation in many skeletal sites and is being investigat ed as a possible therapeutic agent for the treatment of osteopenic con ditions, including post-menopausal osteoporosis. The purpose of this s tudy was to determine the ability of PTH to stimulate bone formation i n the mandibles of aged ovariectomized (Ovx) rats, and the results are compared with a site in the appendicular skeleton (humerus). The Ovx rat is a useful model of estrogen deficiency, replicating many aspects of post-menopausal osteoporosis. Female rats were ovariectomized or s ham-operated, and one year later a group of the ovariectomized rats wa s treated with the 1-34 fragment of human PTH daily, five days a week for 10 weeks. During the experiment, the animals were given fluorochro me bone markers for histomorphometry. More than one year after ovariec tomy or sham surgery, there were few differences in the histomorphomet ric indices of bone formation in the humerus or mandible. PTH treatmen t had no effect on dentin formation, measured in the mandibular inciso r; however, most indices of bone formation-including the double-labele d surface, mineralizing surface, mineral appositional rate, new bone a rea, and surface-referent bone formation rates-were substantially grea ter in the PTH-treated group compared with both the Ovx and the Sham c ontrols measured at the periosteal and endocortical surfaces of the hu merus and the periosteal and cancellous bone surfaces of the mandible. Ln addition, bone formation at the alveolar crest, particularly on th e buccal side, was greater in the PTH-treated group. The results from this study demonstrate that systemic intermittent PTH treatment stimul ates bone formation in the mandibles in aged, estrogen-deficient anima ls.