Pharmacological investigations on mast cell stabilizer and histamine receptor antagonists in vincristine-induced neuropathic pain.

The present study was designed to investigate the role of mast cells and mast cell-derived histamine in vincristine-induced neuropathic pain. Neuropathic pain was induced by administration of vincristine (100 μg/kg, i.p.) over a period of 10 days, with a break of 2 days, and pain behavioural estimations including pin prick, hot plate and acetone spray tests were performed to assess mechanical and heat hyperalgesia and cold allodynia, respectively, on days 0, 14 and 28. Mast cell stabilizer, sodium cromoglycate, H1 receptor antagonist promethazine and H2 receptor antagonist ranitidine were administered over a period of 12 days. Administration of vincristine resulted in significant development of heat and mechanical hyperalgesia as well as cold allodynia. Furthermore, the pain observed was markedly elevated on the 28th day in comparison to the 14th day. Administration of sodium cromoglycate, promethazine and ranitidine significantly reduced mechanical and heat hyperalgesia and cold allodynia. However, the pain-attenuating effects of ranitidine were significantly less as compared to sodium cromoglycate and promethazine, which suggests that H1 receptors play a more important role than H2 receptors in vincristine-induced neuropathic pain. It may be concluded that vincristine may degranulate mast cells to release inflammatory mediators, particularly histamine which may act through H1 (primarily H1) and H2 receptors to induce neuropathic pain.