Effects of Histidine and Dexamethasone on the Local Inflammation Induced by Histamine in Rats

In this study, the effects of separate and combined intraperitoneal (IP) injections of histidine and dexamethasone were investigated on local inflammation in rats. Local inflammation was induced by subcutaneous (SC) injection of histamine (100 μl, 0.1%) in ventral surface of right hind paw. The thickness of paw was measured at 30 min before and 30, 60, 90, 120, 150 and 180 min after injection of histamine, using a fine caliper. The number of neutrophils in paw tissue sections was counted 3 h after intraplantar (IPL) injection of histamine. The IPL injected histamine elicited an inflammatory response that was characterized by increase of paw thickness and by infiltration of neutrophils in paw tissues. IP injections of histidine at doses of 200 and 400 mg kg-1 and dexamethasone at a dose of 1 mg kg-1 significantly (P < 0.05) decreased both paw thickness and infiltration of neutrophils in paw tissues. In combined treatment, IP injection of histidine (200 mg kg-1) with dexamethasone (1 mg kg-1) produced a more documented response in comparison with histidine and dexamethasone used alone. The results suggested that histidine and dexamethasone have anti-inflammatory activities. Histidine potentiated the anti-inflammatory effect of dexamethasone in histamine-induced local inflammation.