The effects of estradiol and 1,25 (OH)₂D₃ on skeletal metabolism in female japanese quail

Two experiments were performed comparing the effects of 17β-estradiol implants or a series of intramuscular injections of either 1,25 dihydroxycholecalciferol (1,25 (OH)₂D₃) (.5 μg/injection) and 17 β-estradiol (13 μg/injection) on bone turnover, calcium content (Ca) and breaking strength. Plasma was analyzed for 1,25 (OH)₂D₃ and Ca. Bone resorption was determined by labelling the bones with tritiated tetracycline and measuring the relative decline in radioactivity over the 3 week treatment period. When 16 to 28 month old quail were given estradiol implants, significantly reduced bone turnover was observed in these ovulating quail. In experiment 2, both estradiol and 1,25-(OH)₂D₃ administration served to decrease bone turnover. Estradiol, however, had a more pronounced effect and significantly increased bone Ca and breaking strength. Both hormone treatments raised plasma Ca and 1,25 (OH)₂D₃ levels. Estradiol was more effective in increasing the bone strength and mass than 1,25-(OH)₂D₃. It appears that estradiol plays a multifaceted role in the control of bone metabolism. Part of this effect is through increased 1,25-(OH)₂D₃ levels circulating in the blood.