[Role of substance P on neurogenic inflammation in the rat dental pulp and inferior lip].

A physiological role of substance P (SP) in inflammatory reaction was examined in the rat incisor pulp and inferior lip. SP content in pulps and lips significantly increased after antidromic stimulation of the inferior alveolar nerve. Following the same stimulation, vascular permeability also increased significantly in pulps and lips, and this permeability response was significantly inhibited by an SP-antagonist. Morphine reduced the permeability response to antidromic stimulation in pulps but had no effect in lips. N-methyl levallorphan (a peripherally selective narcotic antagonist) prevented the morphine-induced reduction, and was more potent than naloxone. Morphine caused a marked increase of SP content in pulps following antidromic stimulation of the inferior alveolar nerve but failed in lips. These suggest a possibility that a peripheral SP release-suppressive mechanism by opiates may exist in pulps but not in lips. The permeability response to antidromic stimulation was also reduced by aspirin and a bradykinin antagonist in both of the tissues, indicating that prostaglandin and bradykinin may be related to this response. Since mepyramine and methysergide inhibited the permeability response in lips but were inactive in pulps, there is a difference in participation of histamine and serotonin between the two tissues. SP injection into the dental pulp and lip induced dye leakage. This response was inhibited by compound 48/80 pretreatment in lips whereas it was resistant in pulps. Histamine content in lips decreased significantly after antidromic stimulation and compound 48/80 pretreatment, but it was not changed in pulps. The present results suggest that in lips after being released from the peripheral sensory nerve endings SP may act on vascular system through histamine release from mast cells, while in pulps SP may directly cause vascular response because mast cells may be few or not exist.