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Effect of Hypophysectomy and Hormonal Replacement on the Uptake of Tc-99m Methylene Diphosphonate in the Metaphysis and Shaft of the Rat Femur: Concise Communication

Veterans Administration Medical Center, and University of Colorado Health Sciences Center, Denver, Colorado

Correspondence: For reprints contact: Richard S. Trow. Nuclear Medicine Service, Veterans Administration Medical Center, 1055 Clermont St., Denver, CO 80220.

ABSTRACT

We have investigated the uptake of Tc-99m methylene diphosphonate (Tc-MDP) in the metaphysis and shaft of the rat femur as affected by hypophysectomy and hormonal replacement with growth hormone and thyroxine. Two hours following injection of Tc-MDP, the metaphysis and a speciment of shaft were obtained and the metaphysis-to-shaft radioactivity ratio was measured. By five days after hypophysectomy the metaphysis-to-shaft ratio fell from a control value of 3.8 ± 0.2 (mean ± s.e.) to 2.4 ± 0.2 (p <0.05) and remained significantly decreased throughout the 30-day study. When daily hormonal replacement with 0.5 mg of bovine growth hormone and 10 µgm of thyroxine (both administered intraperitoneally) was given, beginning on the eighth day after hypophysectomy, the metaphysis-to-shaft ratio of Tc-MDP returned to control levels in twelve days. This model demonstrates the effect of growth hormone and thyroxine on the distribution of Tc-MDP, and may be useful as a radiobioassay of net circulating skeletal growth-promoting activity.