Razi Journal of Medical Sciences

Background: Hemoglobin is a protein in red blood cells, and the role of that is to transport the oxygen and carbon dioxide in the blood. This protein has a heme group that is a prosthetic group. Hemoglobin is known as a potent inducer for heme oxygenase enzyme. Also the administration of CO releasing compounds (CORMs) can reduce the neuropathic pain. So this study is based on the assumption that intrathecal administration of hemoglobin can be lead to elevation of CO production and reduction in thermal and chemical pain and inflammation.

Methods: The male Wistar rats (200-250 g) were randomly divided into 3 groups included saline treatment, acute treatment of hemoglobin and chronic treatment of hemoglobin (1mg/ml) for 5 constitutive days. Thermal pain sensation was assessed using Tail flick test before and 5 minutes after i.t. injection and responses of chemical pain to sub plantar formalin (2.5%, 5µl) injection were recorded for one hour. Paw volume was measured before treatments and one hour after sub-plantar injection of formalin for inflammatory edema assessment using plethysmometery test.

Results: Results from this experiment showed that acute and chronic i.t. injection of hemoglobin reduced the chemical pain (p<0.01) and also inflammation (p<0.001) due to hind paw sub-plantar injection of formalin. Although the acute i.t. injection of hemoglobin had no prominent effect on thermal pain latency but chronic i.t. injection of hemoglobin reduced thermal pain latency significantly (p<0.01).

Conclusion: Hemoglobin reduces pain sensation and inflammation probably due to increasing the level of CO in spinal cord tissue. This effect was higher in chronic group that is possibly due to the effects of hemoglobin on the heme oxygenase gene expression.