Studies on the trigeminal antidromic vasodilatation and plasma extravasation in the rat

Antidromic stimulation of sensory peripheral branches of the trigeminal system (mental nerve) led to cutaneous vasodilatation and increased vascular permeability in rats anaesthetized with urethane. The antidromic vasodilatation observed in intact animals was not altered by decentralization or sympathectomy. Both antidromic vasodilatation and neurogenic plasma extravasation remained unaffected by pre-treatment with cimetidine, indomethacin, baclofen, guanethidine plus phentolamine and propranolol, but were significantly reduced by cimetidine plus mepyramine and atropine, suggesting that cholinergic and histaminergic components might be involved in the sensory neurogenic responses. Methysergide reduced only the extravasation, suggesting that probably serotonin liberated by mast cells upon sensory stimulation can contribute to the neurogenic responses. In tests using substance P (SP) antagonists (D-pro4, D- trp 7, 9, 10)-SP (4-11) and (D-pro2, D-trp 7, 9)-SP it was found that they are more active in reducing the neurogenic extravasation than the vasodilatation. In addition it was observed that (D-pro 4, D-trp 7, 9, 10)-SP (4-11) was the most potent substance P antagonist in reducing the plasma extravasation and antidromic vasodilatation resulting from sensory stimulation.