Tissue concentration and release of substance P-like immunoreactivity in the dental pulp

The concentration of substance P-like immunoreactivity (SPLI) was determined in dental pulps from cat, dog and man by radioimmunoassay. Pulps from mature cats showed the highest SPLI-levels (mean 32 pmol/g); these are comparable to or higher than those found in any other organ outside the central nervous system. The SPLI concentrations were lower in pulp from immature teeth. The immunological and chromatographic behaviour of the pulpal SPLI from cat and man resembled that of synthetic substance P (SP), indicating that the assayed substance is closely related to or identical with SP. Release of pulpal SPLI in canine teeth was evoked by stimulation of the inferior alveolar nerve in anaesthetized cats. In 9 of 16 experiments the amounts of SPLI found in pulp suprafusates following stimulation (4-31 fmol) were larger than those in unstimulated controls (0-7 fmol). Stimulation also reduced the pulpal tissue concentration of SPLI to 60% of that in homologous control pulps. The high concentration of SPLI found in the dental pulp and the demonstration of nerve-induced release strengthen the hypothesis that SP serves some function in the dental pulp.