Inhaled glucocorticosteroids (ICS) are commonly prescribed for chronic obstructive pulmonary disease. No adverse effect on bone mineral density (BMD) has been proven. In a randomized double-blind, placebo-controlled trial at seven centers in North America, we recruited 412 current smokers or recent quitters with mild to moderate chronic obstructive pulmonary disease. They used inhaled triamcinolone acetonide, 600 mcg, or placebo, twice daily. We measured femoral neck and lumbar spine BMD at baseline and after 1 and 3 years, and serum osteocalcin at baseline, 3 months, 1 year, and 3 years. After 3 years, BMD at the femoral neck decreased 1.78% more with ICS than with placebo (p < 0.001). More participants in the ICS group experienced 6% or more loss of femoral neck BMD (p = 0.002). Lumbar spine BMD increased in the placebo group by 0.98% but decreased by 0.35% in the ICS group (a difference of 1.33%, p = 0.007). Changes in osteocalcin did not correlate with changes in BMD. Fractures, lost height, or osteoporosis diagnoses were not increased among ICS users compared with placebo users. In summary, the use of inhaled triamcinolone acetonide was associated with loss of BMD at the femoral neck and lumbar spine after 3 years of treatment.

Properties of the rat hepatic cholecalciferol 25-hydroxylase have been studied. An assay system has been developed in which 25-hydroxycholecalciferol production is linear for at least 2h in both homogenates and microsomal fraction. Furthermore, the initial reaction velocity is linearly related to the amount of liver tissue or microsomal fraction. This enzyme system also metabolizes an analogue of cholecalciferol, namely dihydrotachysterol 3, into 25-hydroxydihydrotachysterol 3. The 25-hydroxylase is in the microsomal fraction and not in mitochondria. It has a Km of 44 nM for cholecalciferol and 360 nM for dihydrotachysterol 3. Its activity is not altered by dietary concentrations of calcium and phosphorus. Vitamin D-deficient rats have higher activities of the hepatic 25-hydroxylase than those receiving 25 ng of cholecalciferol daily. The 25-hydroxylase is inhibited by metyrapone. An atmosphere of CO/O2 (9:1, v/v) inhibits the reaction by 87%. This inhibition is partially reversed by white light. Additionally, cholecalciferol and 25-hydroxycholecalciferol competitively inhibit aminopyrine demethylase. These results support the idea that the cholecalciferol 25-hydroxylase is a cytochrome P-450-dependent mono-oxygenase.

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The oxygen enzymatically inserted as a hydroxyl function by chick kidney homogenate into the 24 position of 25-hydroxyvitamin D3 to give 24,25-dihydroxyvitamin D3 is derived exclusively from 18O2. Therefore, like the 25-hydroxyvitamin D3-lalpha-hydroxylase system, the 25-hydroxyvitamin D3-24-hydroxylase system is also a monooxygenase ("mixed-function oxidase").