Calcitonin (but not calcitonin gene-related peptide) increases mouse bone cell proliferation in a dose-dependent manner, and increases mouse bone formation, alone and in combination with fluoride

Previous in vitro studies have shown that salmon calcitonin had direct effects to increase parameters associated with embryonic chicken bone formation and to increase mouse and chicken osteoblast-line cell proliferation. The current studies demonstrate increased cell proliferation (i.e., [³H]-thymidine incorporation into DNA and tetrazolium salt reduction/deposition) in the osteoblastic murine cell line MC-3T3-E1 in response to salmon calcitonin (P<0.005) and to human calcitonin (P<0.005), but not to human calcitonin gene-related peptide. The current studies also show that salmon calcitonin increased several indices of murine bone formation. We found that 72 hours of exposure to salmon calcitonin [at 5 mU/ml-about 0.37 nM; mU/ml = milliunits of calcitonin activity/ml incubation medium (at 4,000 U/mg protein)] increased net⁴⁵Ca deposition (121% of control, P<0.05), net [³H]-proline incorporation 149% of control, P<0.001), and alkaline phosphatase activity (146% of control, P<0.01), in neonatal mouse half-calvaria. The calcitonin-dependent increase in alkaline phosphatase activity was not affected by co-incubation with 1 nM parathyroid hormone. Co-incubation with fluoride (which also increased net [³H]-proline incorporation and alkaline phosphatase activity in neonatal mouse half-calvaria, P<0.05, for each) enhanced the osteogenic response to low-dose calcitonin, (i.e., co-incubation with fluoride shifted the biphasic calcitonin dose-response curve to a range of lower calcitonin concentrations). The calcitonin-fluoride combinations had proportional effects on net [³H]-proline incorporation and alkaline phosphatase in the treated mouse calvaria (r=0.78, P<0.005).