Neurogenic substance P stimulates osteogenesis in vitro

Previous studies have shown that there is colocalization of substance P (SP) and calcitonin gene-related peptide (CGRP) immunoreactive nerve fibers in bone, periosteum and bone marrow. Because SP may also possibly play a role in bone formation, we decided to test whether it has an osteogenic stimulating effect on developing bone in vitro. To this end, 0.4, 4 and 40 micrograms/ml of SP in BGJb medium was added daily to 3 million light density (LD) bone marrow white cells which were separated by Ficoll-Paque density gradient separation then seeded onto a previously prepared fibroblast feeder layer in Petri dishes. Seven days after adding SP, in the control without SP there were 2 bone colonies; with 0.4 micrograms of SP there were 3 colonies; with 4 micrograms there were 5 colonies; with 40 micrograms there were 7 colonies. In addition, there was an increase in the size of bone colonies in the SP-added group. The results indicated that SP had a dose-related osteogenic stimulating effect. The increase in the number and size of bone colonies by SP was probably caused by stimulating stem cell mitosis, osteoprogenitor cell differentiation or osteoblastic activity.