Neurogenic vasodilation in rabbit basilar isolated artery: involvement of calcitonin-gene related peptide

Neurogenic vasodilation in cranial arteries may be an important mechanism i n the pathogenesis of migraine headache. We describe a novel, in vitro assa y to characterise neurogenic vasodilator responses in endothelium-denuded s egments of rabbit isolated basilar artery, with particular focus on calcito nin-gene related peptide (CGRP). In arterial segments precontracted with pr ostaglandin F-2 alpha, relaxations evoked by exogenously applied alpha CGRP (EC50 = 2.9 nM) were inhibited by alpha CGRP-(8-37) (pA(2) = 6.49) or by d esensitisation resulting from prior exposure to aCGRP. Relaxations evoked b y exogenously applied vasoactive intestinal polypeptide (VIP) (EC50 = 2.5 n M) were inhibited by VIP-(7-28) 1 mu M. The 5-HT1 receptor agonists L-771,3 31 ((3S)-3[N-(S)-alpha-methylbenzyl]aminomethyl-(S)-1-[2-(5-(2-oxo-1,3-oxaz olidin-4-ylmethyl)-1H-indol-3-yl)ethyl]pyrrolidine) and sumatriptan exerted contractile effects (EC50 = 293 and 95 nM, respectively). In neurogenic ex periments, vasodilation evoked by electrical field stimulation was markedly attenuated by pre-treatment with capsaicin (10 mu M) Or by prior CGRP rece ptor desensitisation and to a lesser extent by pre-treatment with VIP-(7-28 ) 1 mu M. L-771,331 (100 nM) exerted a weak inhibitory effect, marked only by a short reduction in the recovery time (post-electrical stimulation) and sumatriptan (30 nM) had no effect. The neurogenic response was potentiated by alpha CGRP-(8-37) 1 mu M (reversible on wash-out). Shea application (5- 10 min) of capsaicin (10 mu M) produced vasodilation that was inhibited by alpha CGRP-(8-37) 1 mu M. These data suggest that electrically evoked neuro genic vasodilation in rabbit basilar artery has a large component resulting from the release of sensory neuropeptides in particular CGRP and a smaller component involving the release of VIP. (C) 2000 Elsevier Science B.V. All rights reserved.