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 effects of exogenous substance P (SP) on the hallmarks of neurogenic inflammation, i.e. vascular permeability and blood flow, in the oral mucosa of the rat. Pretreatment with capsaicin was shown to attenuate the symptoms of neurogenic inflammation; therefore, the distribution of nerve fibers displaying substance P-like immunoreactivity (SP-IR) in the mandibular mucosa was also assessed in control rats and in animals pretreated with capsaicin both neonatally and in adulthood using immunohistochemical techniques. The application of SP at a dose of 7.5 nmol resulted in an almost 70% increase of vascular permeability (NS) and the administration of a four-fold higher dose (30 nmol) produced about 150% 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 significantly 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 oral mucosa. Our functional results suggest that SP may have a role in the experimentally-induced neurogenic inflammation of the oral mucosa in the rat. This is also supported by our finding that capsaicin pretreatment, known to decrease the number of SP-immunoreactive fibers in these tissues, reduced the symptoms of neurogenic inflammation.