ROLE OF SUBSTANCE-P (SP) IN DEVELOPMENT OF SYMPTOMS OF NEUROGENIC INFLAMMATION IN THE ORAL-MUCOSA OF THE RAT

In the present series of investigations we first studied the local eff ects of exogenous substance P (SP) on the hallmarks of neurogenic infl ammation, i.e. vascular permeability and blood flow, in the oral mucos a of the rat. Pretreatment with capsaicin was shown to attenuate the s ymptoms of neurogenic inflammation; therefore, the distribution of ner ve fibers displaying substance P-like immunoreactivity (SP-IR) in the mandibular mucosa was also assessed in control rats and in animals pre treated with capsaicin both neonatally and in adulthood using immunohi stochemical techniques. The application of SP at a dose of 7.5 nmol re sulted in an almost 70% increase of vascular permeability (NS) and the administration of a four-fold higher dose (30 nmol) produced about 15 001. increase in Evans blue extravasation compared with control values (p < 0.05). A similar increase (ca 146%) in vascular permeability was observed in response to 45 nmol SP solution (p < 0.05). While the 7.5 nmol SP-solution failed to affect blood flow, the 30 nmol SP signific antly increased it by ca. 38% (p < 0.05). The administration of the 45 nmol SP solution resulted in a similar enhancement of blood flow (43% , p < 0.05). Capsaicin pretreatment performed either neonatally or in adulthood has reduced the number of SP-immunoreactive fibers in the or al mucosa. Our functional results suggest that SP may have a role in t he experimentally-induced neurogenic inflammation of the oral mucosa i n the rat. This is also supported by our finding that capsaicin pretre atment, known to decrease the number of SP-immunoreactive fibers in th ese tissues, reduced the symptoms of neurogenic inflammation.