Olcegepant blocks neurogenic and non-neurogenic CGRPergic vasodepressor responses and facilitates noradrenergic vasopressor responses in pithed rats.

BACKGROUND AND PURPOSE: Olcegepant (BIBN4096BS) is a selective non-peptide CGRP receptor antagonist with acute antimigraine properties. Since systemic vascular tone is modulated by perivascular (primary sensory CGRPergic and sympathetic) nerves, this randomized study investigated in pithed rats the effect of acute i.v. treatment with olcegepant on the neurogenic and non-neurogenic: (i) CGRPergic vasodepressor responses; and (ii) noradrenergic vasopressor responses. The pithed rat is an experimental model predictive of systemic (cardio) vascular side effects. EXPERIMENTAL APPROACH: Seventy-five male Wistar rats (divided into 15 groups, n = 5 each) were pithed, artificially ventilated and prepared for: (i) spinal stimulation (T9 -T12 ; 0.56-5.6 Hz) of the sensory CGRPergic vasodepressor outflow or i.v. bolus injections (0.1-1 µg·kg-1 ) of α-CGRP, substance P or acetylcholine, which induced frequency-dependent or dose-dependent vasodepressor responses; or (ii) spinal stimulation (T7 -T9 ; 0.03-3 Hz) of the sympathetic vasopressor outflow or i.v. bolus injections (0.03-3 µg·kg-1 ) of noradrenaline, which produced frequency-dependent or dose-dependent vasopressor responses. KEY RESULTS: Olcegepant (1000 and 3000 µg·kg-1 , i.v.) dose-dependently blocked the vasodepressor responses to sensory nerve stimulation or i.v. α-CGRP, without affecting those to substance P or acetylcholine. Whereas it potentiated the vasopressor responses to sympathetic nerve stimulation or i.v. noradrenaline. CONCLUSIONS AND IMPLICATIONS: Olcegepant (i.v.) selectively blocked the neurogenic and non-neurogenic CGRPergic vasodepressor responses. This blockade by olcegepant potentiated the neurogenic and non-neurogenic noradrenergic vasopressor responses in pithed rats, an effect that might result in an increased vascular resistance and, consequently, in a prohypertensive action.

Bovine isolated middle cerebral artery contractions to antimigraine drugs.

Ergot alkaloids, sumatriptan and the newer 5-HT1B/1D receptor agonists all contract cranial blood vessels and this effect seems to be primarily responsible for their efficacy in migraine. We have compared the contractile effects of a number of ergot and triptan derivatives on the bovine isolated middle cerebral artery and characterised the 5-hydroxytryptamine (5-HT) receptors involved by using 5-HT2A (ketanserin: 10, 30, 100 nM) and 5-HT1B/1D (GR127935: 30, 100, 300 nM) receptor antagonists. The rank order of agonist potency (pD2) was ergotamine (8.0+/-0.1) approximately dihydroergotamine (8.0+/-0.1) > avitriptan (7.4+/-0.3) >5-HT (7.0+/-0.1) > naratriptan (6.8+/-0.1) > methylergometrine (major metabolite of methysergide; 6.5+/-0.2) > rizatriptan (6.3+/-0.3) approximately zolmitriptan (6.2+/-0.1) approximately sumatriptan (6.0+/-0.2) approximately methysergide (5.9+/-0.3). The rank order of efficacy (Emax expressed as % of contraction to 100 mM K+) was 5-HT (127+/-11) > sumatriptan (56+/-5) > ergotamine (48+/-5) approximately dihydroergotamine (44+/-8) approximately methyl-ergometrine (44+/-7) > avitriptan (37+/-7) approximately rizatriptan (33+/-5) approximately methysergide (29+/-10) approximately zolmitriptan (28+/-3) approximately naratriptan (23+/-2). The concentration-response curve to 5-HT appeared to be biphasic in the presence of 100 nM ketanserin, which hardly affected sumatriptan-induced contractions, but clearly antagonised the second more efficacious phase of the curve to 5-HT. On the other hand, GR127935 caused a rightward shift of the concentration-response curves to 5-HT (in the presence of 10 microM ketanserin) and sumatriptan with pA2 values of 7.0 and 8.1, respectively. In conclusion, all acutely acting antimigraine drugs contract the bovine isolated middle cerebral artery. Whereas sumatriptan contracts the artery via the 5-HT1B/1D receptor, the 5-HT-induced contraction is mediated partly by the 5-HT2A receptor and partly by another, possibly novel receptor differing from the 5-HT1B/1D receptor. This receptor may be a target for the development of future antimigraine drugs.