Long-term effects of nicotine on bone and calciotropic hormones in adult female rats

This study determined the effects of nicotine on serum concentrations of several calciotropic hormones, and bone formation and resorption end-points in 7 month old, adult female rats. Animals were administered either saline (n= 9/group), low dose nicotine at 3.0 mg/kg/day (n=10/group) or high dose nicotine at 4.5 mg/kg/day (n=11/group) by subcutaneous osmotic minipumps. At the end of a three months treatment period, serum concentrations of calcium, phosphorus, parathyroid hormone, calcitonin, 25-hydroxyvitamin D and 1,25- dihydroxyvitamin D were determined. Femora, tibiae, and lumbar vertebrae (3- 5) were collected and bone parameters evaluated included mineral density and content (femora and vertebrae), strength (femora and vertebrae) and histomorphometry (tibiae). Animals given nicotine had significantly lower levels of 25-hydroxyvitamin D than controls [20.8±1.4 ng/ml for the low dose group and 20.7±1.0 ng/ml for the high dose group versus 27.6±1.3 ng/ml for the control group (mean±S.E.M.), P<0.01]. The high dose nicotine group had smaller vertebral areas (5.4±0.2 mm² versus 6.2±0.2 mm², P<0.05) and a lower bone mineral content than the controls (0.024±0.001 g versus 0.030±0.001 g, P<0.05). Tibial endocortical mineral apposition rate was also significantly lower in the high dose nicotine group than in the control group (1.06±0.13 μm/day versus 1.42±0.08 μm/day, P<0.05). No significant treatment differences were detected in bone density, cancellous bone histomorphometry, or bone strength. Results from the present study suggest that nicotine administration may adversely affect bone formation and decrease body storage of vitamin D.