The osteogenic stimulating effect of neuroactive calcitonin gene-related peptide

Abstract

Silverman and Kruger (Somatosens. Res. 5(2): 157–175; 1987) reported that sensory nerve fibers of the dental pulp secrete calcitonin gene-related peptide (CGRP). These are localized exactly where secondary or tertiary dentin calcification occurs. Recently we found that CGRP has an osteogenic stimulating effect by increasing the number and size of bone colonies in vitro. The purpose of this study is to test whether there is a relationship between the effects of different doses of CGRP and bone colony numbers and/or size. Rat CGRP in different dosages (0.4, 4 and 40 μg/ml in BGJb medium) was added daily to 3 million light density (LD) bone marrow white cells which were harvested from adult Sprague-Dawley rats with the Ficoll-Paque density gradient separation method, then seeded onto a previously prepared feeder layer of fibroblasts in Petri dishes. Seven days after adding CGRP, in the controls without CGRP there were 2 bone colonies; with 0.4 μg of CGRP there were 4 colonies; with 4 μg of CGRP there were 6 colonies; with 40 μg there were 9 colonies, indicating there was a significant increase in number of bone colonies with an increase in dose of CGRP between individual groups, respectively ( p<0.0005 and p<0.0001). In another experiment, intravenous injection of 10 μg of rCGRP/kg body weight was performed two hours before surgery. LD bone marrow white cells were collected and seeded onto a feeder layer in Petri dishes exactly as described above. After 10 days, an average of 3 bone colonies per 3 million LD white cells were found in the rCGRP-injected group as compared to 2 colonies in the control group ( p<0.05). The first result indicates that CGRP will increase its osteogenic stimulating effect with an increase in dose. In the second experiment, it was shown that intravenous administration of CGRP will also increase bone colony formation by stimulating either stem cell mitosis or osteoprogenitor cell differentiation.