This experiment was performed to study the effects of colchicine and verapamil on PTH induced bone resorption in organ culture. Ulnae and radii were removed from 19day fetal rats, prelabelled by subcutaneous injection of 200,uCi 15CaC12 into their mothers on the 17th day of gestation, and then explanted on the Millipore filters in organ culture dishes. The media of normal group were exchanged with fresh media, and control group with 0.1U/ml PTHsupplemented media, while experimental group, were exchanged with 0.IU/ml PTH+10-´M colchicine, PTH+ 40,uM verapamil, or PTH+10-´M colchicine+40,uM verapamil complexed media. Radioactivity of "Ca released into media after 24, 48 and 72 hours of culture and remained in cultured bone after 72hours, were both determined.
The rates of bone resorption in each group were measured by the percentage of released 45Ca to the total radioactivity that presented in the bone at the beginning of culture. And also effects of colchicine, verapamil and colchicine + verapamil were observed by the ratios of %release of 45Ca ´between paired control and experimental group.
The following results were obtained ;
1. PTH at the concentration of 0.1U/ml, increased the fetal bone resorption by 67 and 87% after 48 and 72hours of culture, :respectively
2. Colchicine, at the concentration of 10-´M, presented significant inhibition of PTHinduced bone resorption after 48 and 72 hours of culture, and verapamil, at the concentration of 40PM, presented significant inhibition of the PTHinduced bone resorption after 72 hours of culture.
3. Colchicine plus verapamil at the concentration of 10"´M and 40PM, respectively, presented significant inhibition of PTHinduced bone resorption after 48 and 72hours of culture, but presented lack of additive or synergistic effects.
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