No effect of verapamil on the local bone response to in vivo mechanical loading

Verapamil, a calcium channel blocker, alters the intracellular calcium conc entration in bone cells in vitro, while mechanical loading stimulates calci um channels. The purpose of this study was to examine the effect of systemi c verapamil treatment on the bone response to in vivo external mechanical l oading. Female rats (age 5-6 months) were divided into six groups. Half wer e verapamil treated (0.75 mg/ml drinking water) for 12 weeks. After 8 weeks of treatment, the right tibia was loaded by a four-point bending device. I n one set of verapamil and control groups. the right tibia was loaded at 31 .8 +/- 0.2 N (36 cycles, 2 Hz, 3 d/wk) for four weeks. A second set was loa ded at 40.1 +/- 0.3 N and the third set remained nonloaded. Tibial cortical bone formation and femur bone mineral density (BMD) were evaluated. With l oading, bone formation was similarly elevated in loaded tibia of verapamil and control rats (P < 0.003). However, periosteal bone formation (P < 0.001 ) in the nonloaded tibia, and femoral nl diaphysis BMD (P < 0.04) were grea ter in verapamil rats than in controls. We conclude that verapamil, in the dose given, does not interfere with mech anical loading (30, 40 N) at the loaded site and that the voltage-dependent calcium channels, blocked by verapamil, are not significantly involved in the local bone response to increased strain in female rats. However, verapa mil increased bone formation and BMD at nonloaded sites of loaded rats. Pre viously unknown systemic or regional factors associated with loading may ex plain the potential mechanisms for this interaction and need further invest igation. (C) 2001 Orthopaedic Research Society. Published by Elsevier Scien ce Ltd. All rights reserved.