Substance P receptor expression in healthy and inflamed human pulp tissue

Aim: To use radioreceptor analysis for comparing substance P (SP) receptor expression in human pulp tissue samples collected from teeth having a clinical diagnosis of acute irreversible pulpitis, healthy pulps and teeth with induced inflammation. Methodology: Five pulp samples were obtained from teeth having a clinical diagnosis of acute irreversible pulpitis. Another 10 pulp samples were obtained from healthy premolars where extraction was indicated for orthodontic purposes. In five of these premolars inflammation was induced prior to pulp collection. All of the samples were processed and labelled with ¹²⁵I-SP. Binding sites were identified by ¹²⁵I-SP and standard SP competition assays. Kruskal-Wallis and Mann-Whitney (post-hoc) tests were used to establish statistically significant differences between the groups. Results: Substance P receptor expression was found in all human pulp tissue samples. Most receptors were found in the group of pulps from teeth having a clinical diagnosis of acute irreversible pulpitis, followed by the group of pulps having induced inflammation. The least number of receptors was expressed in the group of healthy pulps. Statistical analysis revealed significant differences between the group of healthy pulp and both inflamed pulp groups (P < 0.01). Conclusion: Substance P receptor expression in human pulp tissue is significantly increased during inflammatory phenomena such as acute irreversible pulpitis.