The effects of vasoactive intestinal peptide on dura mater nitric oxide levels and vessel-contraction responses in sympathectomized rats.

Nitric oxide (NO) and neurogenic inflammation in dura mater due to nociceptor activation has been implicated for pathophysiology of primary headache disorders. Development of migraine has also been observed in patients treated with ganglion blockage for sympathetic reflex dystrophy. Vasoactive intestinal peptide (VIP) is an antioxidant, anti-inflammatory, and neuroprotective neuropeptide. This study is intended to investigate the effects of VIP on dura mater NO levels and vessel-contraction responses in sympathectomized rats. In the experiments, 30 male rats in five groups were used. Group 1 sympathectomized: under anesthesia, superior cervical sympathetic ganglion was removed via incision at the center line in the neck area. Group 2 sympathectomized + VIP: postoperative VIP of 25 ng/kg/day (0.2 ml) intraperitoneally administered to the rats exposed to the same operations for 5 days. Group 3 sham: ganglia and nerves were exposed but not dissected. Group 4 control: no treatment was done. Group 5 VIP: only VIP was administered for 5 days. Sympathectomy induced a significant increase in dura mater NO levels and VIP decreased NO to control levels and increased the norepinephrine vessel-contraction responses of sympathectomized rats. VIP is an efficient NO modulator in superior cervical ganglionectomized rats.