Comparative studies on the involvement of histamine and substance P in the inflammatory response of capsaicin in rat paw

Direct administration of capsaicin (isolated from Capsicum frutescens) in the rat paw caused a dose‐related inflammatory response, which reached a maximum peak within 10 min and remained steady for 180 min after injection. Pretreatment with histamine H1 receptor antagonist and substance P antagonist produced significant inhibition to this capsaicin‐induced paw oedema. Results indicate the involvement of histamine in the early phase and both histamine and substance P in the later phase of capsaicin‐induced inflammation in the rat paw.