Vascular 5-HT1-like receptors that mediate contraction of the dog isolated saphenous vein and carotid arterial vasoconstriction in anaesthetized dogs are not of the 5-HT1A or 5-HT1D subtype

Exacerbation of headache during dihydroergotamine for chronic migraine does not alter outcome

OBJECTIVE

To evaluate whether headache exacerbation associated with IV dihydroergotamine (DHE) infusion predicts medium-term headache outcome in patients with chronic migraine.

METHODS

This was a retrospective chart review study of the UCSF Headache Center's use of IV DHE for chronic migraine from 2008 to 2012. Medium-term headache outcome was assessed at 6-week follow-up. Univariate and multivariate logistic regression models were used to assess for predictors of outcome.

RESULTS

Patients with chronic migraine (n = 274) were treated with a course of IV DHE. Of 214 with 6-week follow-up, 78% had medium-term headache benefit. In a univariate logistic regression model, headache exacerbation with DHE was associated with lower odds of a positive medium-term headache outcome (odds ratio [OR] 0.43, 95% confidence interval [CI] 0.20-0.91). However, in the multivariate logistic regression model, headache exacerbation was no longer an independent predictor of treatment outcome (OR 0.65, 95% CI 0.28-1.51). Factors that independently predicted outcome were nausea (OR 0.12, 95% CI 0.02-1.00, p = 0.05), age (OR 1.68 for each decade increase in age, 95% CI 1.24-2.28), and medication overuse (OR 0.42, 95% CI 0.18-0.97).

CONCLUSIONS

After controlling for nausea and other factors, headache exacerbation with DHE infusions is not an independent predictor of poor headache outcome and clinicians should not interpret its presence as a reason to stop treatment. The focus of management should be on controlling nausea as it is the most important modifiable factor in achieving a good headache outcome with an inpatient course of IV DHE for chronic migraine.

The pharmacology of headache

Headache is a common problem which besets most of us at some time or the other. The pharmacology of headache is complex in an overall sense but can be understood in terms of the anatomy and physiology of the pain-producing structures. Migraine can be used as a template to understand the activation of nociceptive systems in the head and thus their neurotransmitter mediation and modulation. In recent years, the role of serotonin (5-HT) in headache pharmacology has been unravelled in the context of both understanding its role in the nociceptive systems related to headache and by exploiting its 5-HT1 receptor subtypes in headache therapeutics. The pharmacology of the head pain systems, as they are known and as they might evolve, are explored in the context of both, the anatomy and physiology of trigeminovascular nociception and in the context of clinical questions, such as those of efficacy, headache recurrence and adverse events.

In vivo analysis of adrenergic and serotoninergic constrictions of the rabbit saphenous vein

We aimed to develop a model to study in vivo the rabbit saphenous vein pharmacology and to investigate constrictions mediated by adrenoceptor and 5-HT receptor subtypes. We used the technique of high precision ultrasonic echo-tracking for direct measurement of saphenous vein diameters in pentobarbital anesthetized rabbits. Saphenous vein constrictions induced in rabbits by the alpha(1)-adrenoceptor agonist L-phenylephrine and the 5-HT(1B) receptor agonist sumatriptan were comparable with those induced in dogs but those induced by the 5-HT(1B) and 5-HT(7) receptor agonist 5-carboxamidotryptamine failed to appear in dogs. Dose-related constrictions of rabbit veins were obtained with L-phenylephrine and the alpha(2)-adrenoceptor agonist dexmedetomidine. Frequency-related constrictions of rabbit veins induced by nerve stimulation were partially inhibited by an alpha(1)-adrenoceptor or a postsynaptic alpha(2)-adrenoceptor antagonist (prazosin and SKF 104,078) but not affected by the pre- and post-synaptic alpha(2)-adrenoceptor antagonists BRL 44408 or rauwolscine. Constrictions of rabbit veins to sumatriptan and 5-CT were inhibited by GR 127935 and those induced by quipazine, a 5-HT(2) receptor agonist were prevented by ritanserin. The initial constrictions induced by 5-CT were followed by dilatations which were inhibited by the 5-HT(7) receptor antagonist mesulergine. These data indicate that rabbit saphenous veins, in vivo and at rest, respond to activation of 5-HT(1B) and 5-HT(2) receptors, alpha(1)- and alpha(2)-adrenoceptors and nerve stimulation; the dilator effect mediated by 5-HT(7) receptor activation was also detected. The data validate a new animal model to study superficial vein reactivity and its pharmacological sensitivity.

External carotid effects of 2-(2-aminoethyl)-quinoline (D-1997) in vagosympathectomized dogs

Serotonin (5-hydroxytryptamine; 5-HT) elicits external carotid vasoconstriction in vagosympathectomized dogs via 5-HT1B/1D receptors and a mechanism unrelated to the 5-HT1, 5-HT2, 5-HT3 and 5-HT4 types. In order to further explore the nature of this novel mechanism, the canine external carotid effects of 2-(2-aminoethyl)-quinoline (D-1997), a novel 5-HT1 receptor agonist, were analyzed and compared with those of 5-HT and sumatriptan. Intracarotid (i.c.) infusions of 5-HT, D-1997 and sumatriptan to vagosympathectomized dogs dose-dependently decreased external carotid conductance, the rank order of agonist potency being 5-HT > sumatriptan > D-1997. The effects to D-1997 were resistant to intravenous (i.v.) pretreatment with 5-HT2 and 5-HT3/5-HT4 receptor antagonists. Remarkably, the effects induced by lower (10-100 microg/min), but not higher (300-1000 microg/min), doses of D-1997 were blocked by high doses of methiothepin (1 and 3 mg/kg, i.v.), as previously shown with 5-HT. In addition, GR-127935 (1-10 microg/kg, i.v.), partially and dose-dependently antagonized D-1997-induced responses. However, the effects of D-1997 remained unaltered after blockade of alpha- and beta-adrenoceptors, muscarinic, nicotinic, histamine and dopamine receptors, or inhibition of 5-HT-uptake or cyclo-oxygenase, depletion of biogenic amines or blockade of Ca2+ channels. These results may support our previous contention that lower doses of 5-HT elicit external carotid vasoconstriction in vagosympathectomized dogs by activation of 5-HT1B/1D receptors, whilst higher doses of 5-HT stimulate a novel vasoconstrictor mechanism.

Evidence for different 5-HT1B/1D receptors mediating vasoconstriction of equine digital arteries and veins

5-hydroxytryptamine (5-HT) is a potent vasoconstrictor of equine digital arteries and veins which may play a role in the ischaemic disease, laminitis. The present investigation compared the properties of 5-HT1B/1D receptors in arteries with those in veins using isolated rings of equine digital blood vessels. The 5-HT1B/1D receptor-selective agonists, anpirtoline and sumatriptan were 17.9 and 10 times more potent and produced 4.1 and 5.6 times greater maximum contractions, respectively, in veins when compared to arteries. Other agonists tested were of equal potency and produced the same maximum responses in veins and arteries. Propranolol competitively inhibited 5-HT1B/1D receptor mediated responses in arteries, with a pKB of 6.7, but had no significant effects on responses in veins at 1 microM. Metergoline competitively inhibited 5-HT1B/1D receptor mediated responses in veins, with a pKB of 8.1, but had no significant effect in arteries at 0.1 microM. These data suggest that 5-HT1B/1D receptors mediating vasoconstriction in equine digital arteries are pharmacologically different to those found in digital veins.

Serotonin inhibits trigeminal nucleus activity evoked by craniovascular stimulation through a 5HT1B/1D receptor: a central action in migraine?

The development of serotonin (5HT1B/1D) agonists as treatments for the acute attack of migraine has resulted in considerable interest in their mechanism of action and, to some extent, renewed interest in the role of serotonin (5-hydroxytryptamine; 5HT) in the disorder. The initial synthesis of this class of compounds was predicated on the clinical observation that intravenous 5HT terminated acute attacks of migraine. In this study the superior sagittal sinus was isolated in the alpha-chloralose (60 mg/kg i.p. and 20 mg/kg i.v. injection supplementary 2 hourly) anesthetized cat. The sinus was stimulated electrically (120V, 250 microsec duration, 0.3 Hz), and neurons of the trigeminocervical complex in the dorsal C2 spinal cord were monitored using electrophysiological methods. After baseline recordings in each animal, 5HT (15 microg/kg/min) was infused for 5 minutes in the presence of either vehicle (group A) or the 5HT1B/1D antagonist GR127935 (100 microg/kg i.v. injection; group B). The baseline probability of cell firing after sagittal sinus stimulation was 0.61 +/- 0.1 at a latency to the fastest peak of 11.1 +/- 0.4 msec. In group A, 5HT infusion alone had a small effect of increasing mean blood pressure (12 +/- 3 mm Hg), which in itself did not alter cell firing. In group A, 5HT alone had an inhibitory effect on evoked trigeminal activity, which developed 15 to 20 minutes after commencement of the infusion. The inhibition of cell firing lasted for 20 minutes, after which the activity returned to baseline. In group B, the combination of 5HT and GR127935 had no effect on trigeminal cell firing, although the small hypertensive effect was still present. These data indicate that 5HT inhibits evoked trigeminal nucleus firing via the 5HT1B/1D receptor at which GR127935 is an antagonist. It is likely that some part of the effect of 5HT in migraine relates to inhibition of trigeminal nucleus activity, just as it is likely that some part of the effect of the triptans is also mediated at this central site and may be complementary to their nonneuronal actions. Moreover, the data highlight the case for describing this class of headache as neurovascular headaches rather than vascular headaches, to recognize the implicit contribution of the trigeminovascular system to their pathophysiology.

5-Hydroxytryptamine-induced contraction of the marmoset aorta is mediated by a 5-HT1-like receptor

1. 5-Hydroxytryptamine (5-HT) exerts both contractile and relaxant effects in the marmoset isolated aorta, actions that are unaffected by the 5-HT2 antagonist ketanserin. The aim of the present study was to define the receptors mediating the contractile activity of 5-HT in the marmoset aorta. 2. Contractile responses were elicited in aortic rings that were either: (i) precontracted submaximally with the thromboxane A2 agonist U44069 in order to amplify the responses; or (ii) exposed to N(omega)-nitro-L-arginine (100 micromol/L) plus LY 53857 (0.1 micromol/L; a 5-HT2 receptor antagonist shown previously to inhibit relaxation). The effect of 5-HT on adenosine 3',5'-cyclic monophosphate (cAMP) formation was also investigated. 3. The effects of agonists and antagonists comprised: (i) agonist potencies in the order 5-carboxamidotryptamine > 5-HT > sumatriptan > 8-hydroxy-2-(di-n-propylamino)tetralin; (ii) inhibition of contractile action of 5-HT by the 5-HT1D antagonist GR 127935; (iii) a contractile response to methysergide; (iv) a lack of effect of tropisetron, an antagonist of 5-HT3 and 5-HT4 receptors; and (v) inhibition of forskolin-stimulated cAMP formation by 5-HT (in the presence of LY 53857), indicative of negative coupling to adenylate cyclase. 4. The above effects fulfill the criteria for a 5-HT1-like receptor. In view of the previous finding that this contractile response is insensitive to ketanserin, it is concluded that the contractile effects of 5-HT in the marmoset aorta are mediated exclusively by a 5-HT1-like receptor.

Blockade of porcine carotid vascular response to sumatriptan by GR 127935, a selective 5-HT1D receptor antagonist

1. It has previously been shown that the antimigraine drug, sumatriptan, a putative 5-HT1D receptor agonist, decreases porcine common carotid and arteriovenous anastomotic blood flows, but slightly increases the arteriolar (capillary) blood flow to the skin and ears. Interestingly, such responses, being mediated by 5-HT1-like receptors, are resistant to blockade by metergoline, which, in addition to displaying a very high affinity for (and occasionally intrinsic efficacy at) the 5-HT1D receptor subtypes, blocks (with lower potency than methiothepin) some 5-HT1D receptor-mediated vascular responses. These findings raise doubts whether sumatriptan-sensitive 5-HT1-like receptors mediating changes in the distribution of porcine carotid blood flow are identical to cloned 5-HT1D receptors. With the recent advent of the potent and selective 5-HT1D receptor antagonist, GR127935, we have examined in the present study whether the carotid vascular effects of sumatriptan in the pig are amenable to blockade by GR127935. 2. In animals pretreated with saline, sumatriptan (30, 100 and 300 micrograms kg-1, i.v.) reduced the total carotid and arteriovenous anastomotic blood flows in a dose dependent manner. In contrast, sumatriptan increased blood flow to the skin, ears and fat, although the total capillary fraction was not significantly affected. 3. While GR127935 pretreatment (0.25 and 0.5 mg kg-1) itself slightly reduced the total carotid and arteriovenous anastomotic blood flows, carotid vasoconstrictor responses to sumatriptan were either partly (0.25 mg kg-1) or completely (0.5 mg kg-1) blocked by the compound. In GR127935 pretreated animals, the sumatriptan-induced increases in blood flow to the skin, ears and fat were also attenuated. 4. Taken together, the results suggest that arteriovenous anastomotic constriction and, possibly, arteriolar dilatation in the skin, ears and fat by sumatriptan are mediated by 5-HT1D receptors. Therefore, vascular 5-HT1-like receptors in the porcine carotid bed appear to be identical to 5-HT1D receptors.

Selective vasoconstriction by alniditan in the carotid vascular bed of anaesthetized dogs

In anaesthetized dogs, alniditan or (-)-(R)-N-[3,4-dihydro-2H-1- benzopyran-2-yl)methyl]-N'-(1,4,5,6-tetrahydro-2-pyrimidinyl)-1,3- propanediamine dihydrochloride, a new compound with 5-HT1-like receptor ligand effects, dose dependently (0.63-80 micrograms/kg i.v.) reduced common carotid arterial blood flow with comparatively little effect on other cardiovascular variables including coronary, mesenteric and renal arterial blood flow, systemic and pulmonary vascular resistance and airway resistance. The potency of alniditan was higher than that of sumatriptan and comparable to that of ergotamine (dose producing a 50% reduction: alniditan = 5.1 micrograms/kg i.v.; sumatriptan = 13.1 micrograms/kg i.v.; ergotamine = 4.6 micrograms/kg i.v.; median values). The reduction of carotid arterial blood flow by alniditan was accompanied by an increase of carotid arterial vascular resistance and correlated with the increase of the difference in oxygen saturation between arterial and jugular venous blood, suggesting a preferential reduction of extracerebral shunt flow by the compound via constriction of arteriovenous anastomoses in the carotid vascular region. The extent and duration of carotid arterial blood flow reductions after alniditan at 5 micrograms/kg i.v. were similar to those after sumatriptan 15 micrograms/kg i.v. but larger/longer after alniditan at 15 micrograms/kg i.v. than after sumatriptan at 15 micrograms/kg i.v. The dose-dependent increase of carotid arterial vascular resistance by alniditan was similar in dogs premedicated daily for 4 days with solvent or active compound (20 micrograms/kg i.v.), indicating absence of tolerance or resetting of sensitivity to the compound.

The vasomotor effects of 5-hydroxytryptamine on equine basilar arteries in vitro

The vasomotor effects of 5-hydroxytryptamine (5-HT) on isolated equine basilar arteries were studied. 5-HT induced contractions of equine basilar arteries in a concentration-dependent manner, with a pEC50 value (with 95% confidence limits) of 7.35 (7.08-7.62). Similar results were obtained with endothelium-denuded basilar arteries. Contractions were not competitively inhibited by the 5-HT2 receptor antagonist ketanserin at low concentrations of 5-HT. Conversely, at high concentrations of 5-HT, contractions were inhibited by ketanserin in a concentration-dependent manner, with a pA2 value of 8.91 (8.62-9.20). The 5-HT1 and 5-HT2 receptor antagonist methiothepin shifted the concentration-response curve of 5-HT downwards and to the right in a concentration-dependent manner. In the presence of 10(-6) mol/L ketanserin, however, methiothepin antagonized 5-HT-induced contractions competitively with a pA2 value of 7.95 (7.59-8.31). The 5-HT3 receptor antagonist MDL 72222 had no effect on 5-HT-induced contractions. The findings of this study indicate that 5-HT1 and 5-HT2 receptors are located in equine basilar arterial smooth muscle cells, and that stimulation of these receptors results in contraction.

Pharmacological profile of the receptors that mediate external carotid vasoconstriction by 5-HT in vagosympathectomized dogs

1. 5-Hydroxytryptamine (5-HT) can produce vasodilatation or vasoconstriction of the canine external carotid bed depending upon the degree of carotid sympathetic tone. Hence, external carotid vasodilatation to 5-HT in dogs with intact sympathetic tone is primarily mediated by prejunctional 5-HT1-like receptors similar to the 5-HT1D subtype, which inhibit the carotid sympathetic outflow. The present investigation is devoted to the pharmacological analysis of the receptors mediating external carotid vasoconstriction by 5-HT in vagosympathectomized dogs. 2. Intracarotid (i.c.) infusions for 1 min of 5-HT (0.3, 1, 3, 10, 30 and 100 micrograms) resulted in dose-dependent decreases in both external carotid blood flow and the corresponding conductance; both mean arterial blood pressure and heart rate remained unchanged during the infusions of 5-HT. These responses to 5-HT were resistant to blockade by antagonists at 5-HT2 (ritanserin) and 5-HT3/5-HT4 (tropisetron) receptors, but were partly blocked by the 5-HT1-like and 5-HT2 receptor antagonist, methiothepin (0.3 mg kg-1); higher doses of methiothepin (1 and 3 mg kg-1) caused little, if any, further blockade. These methiothepin (3 mg kg-1)-resistant responses to 5-HT were not significantly antagonized by MDL 72222 (0.3 mg kg-1) or tropisetron (3 mg kg-1). 3. The external carotid vasoconstrictor effects of 5-HT were mimicked by the selective 5-HT1-like receptor agonist, sumatriptan (3, 10, 30 and 100 micrograms during 1 min, i.c.), which produced dose-dependent decreases in external carotid blood flow and the corresponding conductance; these effects of sumatriptan were dose-dependently antagonized by methiothepin (0.3, 1 and 3 mg kg-1), but not by 5-HT1D-like receptor blocking doses of metergoline (0.1 mg kg-1). 4. The above vasoconstrictor effects of 5-HT remained unaltered after administration of phentolamine, propranolol, atropine, hexamethonium, brompheniramine, cimetidine and haloperidol, thus excluding the involvement of alpha- and beta-adrenoceptors, muscarinic, nicotinic, histamine and dopamine receptors. Likewise, inhibition of either 5-HT-uptake (with fluoxetine) or cyclo-oxygenase (with indomethacin), depletion of biogenic amines (with reserpine) or blockade of calcium channels (with verapamil) did not modify the effects of 5-HT. 5. Taken together, the above results support our contention that the external carotid vasoconstrictor responses to 5-HT in vagosympathectomized dogs are mainly mediated by activation of sumatriptan-sensitive 5-HT1-like receptors. It must be emphasized, notwithstanding, that other mechanisms of 5-HT, including an interaction with a novel 5-HT receptor (sub)type and/or an indirect action that may lead to the release of a known (or even unknown) neurotransmitter substance cannot be categorically excluded.

Vascular 5-HT1-like receptors mediating vasoconstriction and vasodilatation: their characterization and distribution in the intact canine cardiovascular system

1. In anaesthetized dogs, intra-left atrial administration of 5-hydroxytryptamine (5-HT) and selected tryptamine analogues (5-carboxamidotryptamine, 5-CT; 5-methyl tryptamine, 5-MT; alpha-methyl 5-hydroxytryptamine, alpha-HT; sumatriptan, Sum) in the presence of ketanserin and MDL72222 (5-HT2 and 5-HT3 receptor antagonists, respectively), produced dose-related changes in carotid, coronary and renal vascular conductance mediated by vascular 5-HT1-like receptors. 2. In the carotid vascular bed, 5-HT, 5-MT, alpha-HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5-HT = Sum > 5-MT > alpha-HT. By contrast in this vascular bed, 5-CT was a potent vasodilator. 3. In the coronary vascular bed, 5-HT, 5-CT, 5-MT and alpha-HT were vasodilators with a rank order of potency (comparing ED50 values) of 5-CT > 5-HT > 5-MT > alpha-HT. In this vascular bed, Sum was without effect. 4. In the renal vascular bed, 5-HT, 5-CT, 5-MT, alpha-HT and Sum were vasoconstrictors with a rank order of potency (comparing ED50 values) of 5-CT > 5-HT > Sum > 5-MT > alpha-HT. 5. The coronary (and carotid) vasodilator responses to 5-CT were antagonized by the 5-HT1-like receptor antagonists, spiperone (1 mg kg-1) and methiothepin (0.1 mg kg-1), whereas the renal vasoconstrictor responses to this tryptamine analogue were antagonized only by methiothepin. 6. It is concluded from these studies that agonist finger-printing in vivo, using tryptamine analogues,identifies and confirms the functional presence of at least two pharmacologically distinct subtypes of the 5-HT1-like receptor in the intact canine cardiovascular system. These two subtypes are located on the vascular smooth muscle and mediate direct vasoconstriction and vasodilatation responses in vivo.7. In addition, these studies confirm that the distribution of these subtypes within the major vascular beds, shows a marked heterogeneity. The carotid vascular responses to the tryptamine analogue sindicate the presence of both the vasodilator and the vasoconstrictor subtypes. The coronary vascular responses to these analogues are, however, consistent with presence of the vasodilator subtype, only. By contrast, the renal vascular responses to these analogues indicates only the presence of the vasoconstrictor subtype.

The 5-HT1-like receptor mediating the increase in canine external carotid blood flow: close resemblance to the 5-HT1D subtype

1. It has recently been shown that the increase in external carotid blood flow induced by 5-hydroxy-tryptamine (5-HT) in the anaesthetized dog, being mimicked by 5-carboxamidotryptamine (5-CT), inhibited by methiothepin, vagosympathectomy and sympatho-inhibitory drugs, and resistant to blockade by ritanserin and MDL 72222, is mediated by stimulation of prejunctional 5-HT1-like receptors leading to an inhibitory action on carotid sympathetic nerves; these 5-HT1-like receptors are unrelated to either the 5-HT1A, 5-HT1B or 5-HT1C (now 5-HT2C) receptor subtypes. Inasmuch as 5-CT, 5-methoxytryptamine, sumatriptan and metergoline display high affinity, amongst other 5-HT binding sites, for the 5-HT1D subtype, in the present study we have used these drugs in an attempt to determine whether the above inhibitory prejunctional 5-HT1-like receptors correlate with the 5-HT1D subtype. 2. One-minute intracarotid (i.c.) infusions of 5-HT (0.3, 1, 3 and 10 micrograms), 5-CT (0.01, 0.03, 0.1 and 0.3 micrograms), 5-methoxytryptamine (1, 3, 10 and 30 micrograms) and sumatriptan (1, 3, 10, 30 and 100 micrograms) resulted in dose-dependent increases in external carotid blood flow (without changes in mean arterial blood pressure or heart rate) with the following rank order of agonist potency: 5-CT >> 5-HT > 5-methoxytryptamine > or = sumatriptan. Interestingly, sumatriptan-induced vasodilatation was followed by a more pronounced vasoconstriction. 3. The external carotid vasodilator effects of 5-HT, 5-CT, 5-methoxytryptamine and sumatriptan were dose-dependently and specifically antagonized by metergoline (10, 30 and/or 100 micrograms kg-1, i.v.). In addition, 5-methoxytryptamine- and sumatriptan-induced vasodilator effects were, respectively, markedly inhibited or abolished after vagosympathectomy, as previously shown for 5-CT and 5-HT.4. Sumatriptan showed tachyphylaxis in its vasodilator component and antagonized 5-HT-induced external carotid vasodilatation in a specific manner, suggesting that a common site of action may be involved.5. Taken together, the above results support our contention that 5-HT, 5-CT, 5-methoxytryptamine and sumatriptan produce external carotid vasodilatation in the dog by an action that might primarily involve a prejunctional inhibition on carotid sympathetic nerves; a secondary component of this vasodilator response may be postsynaptic (endothelium-dependent and/or even directly on the vasculature).Based on the rank order of agonist potency, inhibition by vagosympathectomy and blockade by metergoline, we suggest that the inhibitory prejunctional 5-HT1-like receptors mediating external carotid vasodilatation in the dog closely resemble the 5-HTID receptor subtype. The pharmacological profile of these receptors is similar (sympathetic nerves of the rat kidney and human saphenous vein, as well as porcine coronary endothelium) to other putative 5-HTID receptors mediating vascular responses.

Sumatriptan. A reappraisal of its pharmacology and therapeutic efficacy in the acute treatment of migraine and cluster headache

Sumatriptan is a potent and selective agonist at a vascular serotonin1 (5-hydroxytryptamine1; 5-HT1) receptor subtype (similar to 5-HT1D) and is used in acute treatment of migraine and cluster headache. Following administration of sumatriptan 100mg orally, relief of migraine headache (at 2 hours) was achieved in 50 to 67% of patients compared with 10 to 31% with placebo in controlled clinical trials. In a comparative study, oral administration of sumatriptan 100mg consistently achieved significantly greater response rates than a fixed combination of ergotamine 2mg plus caffeine 200mg during 3 consecutive migraine attacks (66 vs 48% for first attack). Oral sumatriptan 100mg was also more effective than aspirin 900mg plus metoclopramide 10mg orally in a similar study. In the majority of controlled clinical trials, headache relief (at 1 hour after administration) was achieved in 70 to 80% of patients with migraine receiving sumatriptan 6mg subcutaneously compared with 18 to 26% of placebo recipients. Approximately 40% of patients who initially responded to oral or subcutaneous sumatriptan experienced recurrence of their headache, usually within 24 hours, but the majority of these patients responded well to a further dose of sumatriptan. Patients with cluster headache were treated for acute attacks with sumatriptan 6mg subcutaneously or placebo in 2 crossover trials. Headache relief was achieved within 15 minutes in 74 and 75% of patients receiving sumatriptan in these studies compared with 26 and 35%, respectively, with placebo. Patients receiving sumatriptan 12mg had a similar response rate as those receiving 6mg, but the higher dose was associated with an increased incidence of adverse events. Based on extensive safety data pooled from controlled clinical trials, sumatriptan is generally well tolerated and most adverse events are transient. The most frequently reported adverse events following oral administration include nausea, vomiting, malaise, fatigue and dizziness. Injection site reactions (minor pain and redness of brief duration) occur in approximately 40% of patients receiving subcutaneous sumatriptan, although the incidence appears to be markedly reduced when patients self-administer the drug with an auto-injector. Chest symptoms (mainly tightness and pressure) occur in 3 to 5% of sumatriptan recipients, but have not been associated with myocardial ischaemia except in a few isolated cases. Sumatriptan is contraindicated in patients with ischaemic heart disease, angina pectoris including Prinzmetal (variant) angina, previous myocardial infarction and uncontrolled hypertension, but is not contraindicated in patients with migraine and asthma. Data from long term studies in acute treatment of migraine and cluster headache suggest that sumatriptan remains effective and well tolerated over several months.(ABSTRACT TRUNCATED AT 400 WORDS)

Receptors for 5-hydroxytryptamine: current perspectives on classification and nomenclature

With the increasing number of 5-HT receptors recently identified, using molecular biology techniques, the classification of 5-HT receptors is under review. An integrated approach is proposed to include operational and transductional as well as structural criteria for definitive receptor characterization. On this basis the existence of as many as seven classes of 5-HT receptor are recognized although only the 5-HT1, 5-HT2 and 5-HT3 receptor classes are well defined.

Serotonin-induced contraction in canine coronary artery and saphenous vein: role of a 5-HT1D-like receptor

The identity of the serotonin (5-HT) receptor(s) that mediate(s) contraction in canine coronary artery and saphenous vein remains controversial. Ring segments of endothelium-denuded coronary artery and helical strips of saphenous vein were suspended in organ chambers for measurement of isometric force. 5-HT, alpha Me-5-HT and sumatriptan contracted both coronary artery and saphenous vein and the non-selective 5-HT receptor antagonist 1-naphthylpiperazine (100nM) blocked 5-HT- and sumatriptan-induced contraction in both tissues. The agonist rank order potency for contraction (5-HT > sumatriptan > alpha Me5-HT > 5-MeOT > 5-MeT) was similar in both tissues and was consistent with that for a 5-HT1D receptor. Oligonucleotide primers specific for the 5-HT1D receptor sequence were designed for use in a polymerase chain reaction (PCR). cDNA derived from total RNA or mRNA from canine tissues was used in the PCR. PCR resulted in the amplification of a 632 base pair sequence in both canine coronary artery and saphenous vein; consistent with that expected for the 5-HT1D receptor. Southern blot analysis, with an oligonucleotide probe internal to the sequence amplified by the PCR primers, confirmed that the sequence amplified by PCR was the 5-HT1D receptor. Thus, the 5-HT1D receptor is expressed in canine coronary artery and saphenous vein and taken together with the pharmacological data, supports the possibility that a 5-HT1D-like receptor mediates contraction in these two tissues.

Inhibition by 5-HT of forskolin-induced cAMP formation in the renal opossum epithelial cell line OK: mediation by a 5-HT1B like receptor and antagonism by methiothepin

The functional activity of various 5-HT receptor agonists, including 5-CT, sumatriptan, CP 93, 129 and 1-naphtylpiperazine, and of drugs known to bind with high affinity to 5-HT1B (pindolol, propranolol, cyanopindolol, SDZ 21,009 and isamoltane) or 5-HT1D binding sites (yohimbine and rauwolscine) was measured at 5-HT receptors that are negatively coupled to adenylate cyclase in cultures of the renal epithelial cell line OK. 5-HT receptor-mediated inhibition of adenylate cyclase was studied by measuring inhibition of cAMP formation, induced by 100 microM forskolin. Besides 5-HT, various other compounds with affinity for 5-HT receptors behaved as agonists with the following rank order of potency: RU 24,969 > 5-CT > dihydroergotamine = 5-HT > CP 93,129 > d-LSD > 1-naphtylpiperazine > sumatriptan > TFMPP = mCPP > CGS 12066B = metergoline > methysergide. The beta-adrenergic receptor blockers cyanopindolol, SDZ 21,009, (-)-pindolol and (-)-propranolol, and the alpha 2-adrenergic blockers yohimbine and rauwolscine yielded agonist activity at nanomolar and micromolar concentrations, respectively. Isamoltane acted as a partial agonist. Methiothepin was the only compound that antagonised the OK cell 5-HT receptor-mediated inhibition of forskolin-induced cAMP formation. We conclude that the OK cell 5-HT receptor has properties consistent with a 5-HT1B receptor, although differences are apparent with regard to potencies of some compounds. Methiothepin is probably the only effective antagonist at 5-HT1B receptor sites, whereas the described putative 5-HT1B receptor antagonists have to be considered as partial agonists, yielding agonist or antagonist activity depending on the system that is studied.

What intracranial tissues in humans contain sumatriptan-sensitive serotonin 5-HT1-type receptors?

We investigated the presence of sumatriptan-sensitive serotonin (5-HT)1 receptors in different human tissues by using a radioligand-binding technique with [3H]5-HT. Sumatriptan displaced [3H]5-HT from frontal cortical and striatal membranes in a biphasic manner, with a high-affinity site corresponding to binding to the 5-HT1D receptor. In blood platelet membranes, sumatriptan displaced [3H]5-HT with a 100-fold lower affinity. Sumatriptan failed to displace [3H]5-HT in membranes from large cerebral arteries, pial vessels, coronary arteries and dura mater. These findings suggest that either there are no sumatriptan-sensitive 5-HT1 receptors on intracranial blood vessels or they are so small in number that they cannot be detected by the radioligand-binding technique. Other mechanisms, possibly centrally mediated, may be responsible for the antimigraine action of sumatriptan.

5-Hydroxytryptamine (5-HT) contracts the guinea-pig isolated iliac artery via 5-HT1-like and 5-HT2 receptors

The characterization of 5-hydroxytryptamine (5-HT) receptors mediating contractions of the guinea-pig isolated iliac artery was studied when the basal tone was slightly increased by prostaglandin F2 alpha (PGF2 alpha). In the presence of ketanserin (1 mumol/l), 5-HT and several 5-HT receptor agonists induced contractile responses with the rank order of agonist potency: 5-HT = 5-carboxyamidotryptamine (5-CT) = lysergol > ergometrine = methylergometrine > RU 24969 approximately 5-methoxytryptamine (5-MeOT) > methysergide > sumatriptan > tryptamine. Concentration-effect curves to the ergot alkaloids, lysergol, ergometrine, methylergometrine and methylsergide, were biphasic. In the presence of ketanserin (1 mumol/l), contractile responses to 5-HT, 5-CT, RU 24969, 5-MeOT, sumatriptan and tryptamine were antagonized by methiothepin (30 nmol/l) and flesinoxan (3 mumol/l) with approximate pKB values of 8.5-9.0 and 6.0-6.3, respectively. The first phase of contraction produced by the ergot alkaloids, lysergol, ergometrine, methylergometrine and methysergide, were blocked by methiothepin (30 nmol/l) and flesinoxan (3 mumol/l), respectively, with approximate pKB values about 8.4-8.7 and 6.2-6.4, respectively. The mechanism underlying the second phase of contraction remains to be established. Maximum responses of the concentration-effect curves to 5-HT (1 nmol/l-1 mumol/l) were concentration-dependently depressed by ketanserin (1 nmol/l-1 mumol) and spiperone (30 nmol/l-0.3 mumol/l) and reached approximately 60% of the 5-HT maximum response in the presence of ketanserin (1 mumol/l) and spiperone (0.1 mumol/l), respectively. Agonist potency of 5-HT was not affected by the antagonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Sumatriptan relaxes isolated porcine ophthalmic artery, but inhibits VIP-induced relaxation

Sumatriptan, a 5-hydroxytryptamine (5HT)1-like receptor agonist, is a new antimigraine drug which is also effective in cluster headache (CH), a disorder with marked ocular circulatory abnormalities. Sumatriptan could putatively exert a therapeutic effect in this vascular bed. The present study is an attempt to assess sumatriptan's vasoactivity in isolated porcine ophthalmic artery (POA) and to verify whether it has similar activity to 5HT, and whether it interferes with the vasodilation induced by calcitonin gene-related peptide (CGRP) and vasoactive intestinal peptide (VIP). In contrast to 5HT, sumatriptan induced only slight contraction in POA at high concentrations. However, in some artery segments pre-contracted with PGF2 alpha, sumatriptan induced a slight and short-lasting but marked relaxation. In addition, relaxations induced by VIP were inhibited significantly by sumatriptan, whereas CGRP effects were not influenced by the drug. Such reactions suggest that sumatriptan's effect in CH is probably unrelated to direct ocular arterial vasoconstriction.

Role of 5-HT1-like receptors in the increase in external carotid blood flow induced by 5-hydroxytryptamine in the dog

This study investigated the receptor involved in the 5-hydroxytryptamine (5-HT)-induced increase in external carotid blood flow in pentobarbital-anaesthetized dogs. One-minute intracarotid (i.c.) infusions of 5-HT (0.3, 1, 3 and 10 micrograms) and 5-carboxamidotryptamine (5-CT; 0.01, 0.03, 0.1 and 0.3 micrograms) produced dose-dependent increases in external carotid blood flow without changes in mean arterial blood pressure or heart rate. After vagosympathectomy, the above vasodilator responses to 5-HT and 5-CT were abolished and remained so even after restoration of carotid vascular tone with noradrenaline. Furthermore, the 5-HT- and 5-CT-induced increases in external carotid blood flow were not modified by the 5-HT2 receptor antagonist, ritanserin (100 micrograms/kg i.v.), nor the 5-HT3 receptor antagonist, 1 alpha H,3 alpha, 5 alpha H-tropan-3yl-3,5-dichlorobenzoate (MDL 72222; 140 micrograms/kg i.v.), but were potently and dose dependently antagonized by the mixed 5-HT1-like and 5-HT2 receptor blocker, methiothepin (3, 10 and 30 micrograms/kg i.v.). Interestingly, the 5-HT1A and 5-HT1B receptor antagonist, cyanopindolol (100, 300 and 1000 micrograms/kg i.v.), blocked the effects of 5-HT, but the block was not elicited in a dose-dependent manner, with only the response induced by 0.3 microgram/min 5-CT being significantly antagonized by the highest dose of cyanopindolol; however, this blockade was not selective. Unlike 5-HT and 5-CT, 1 min i.c. infusions of either the 5-HT1C/5-HT2 receptor agonist, 1-(2,5-dimethoxy-4-iodophenyl)-aminopropane (DOI; 30-300 micrograms), or the 5-HT3 receptor agonist, 2-methyl-5-HT (10-300 micrograms), were devoid of effects on the canine external carotid blood flow. It is concluded that the 5-HT-induced increase in external carotid blood flow is mediated by 5-HT1-like receptors probably located on carotid sympathetic nerves. These receptors, however, do not seem to correspond to either the 5-HT1A, 5-HT1B or 5-HT1C receptor subtypes.

5-HT1B receptors mediate potent contractile responses to 5-HT in rat caudal artery

5-Hydroxytryptamine (5-HT) evoked potent contractile responses in phenoxybenzamine-treated ring segments of rat caudal artery, partially contracted with U46619. Responses were mimicked by 5-HT1-selective agonists with the potency order: RU24969 > 5-carboxamidotryptamine > 5-HT = CP-93,129 >> sumatriptan. 8-Hydroxy-N,N-dipropylaminotetralin was virtually inactive. Responses were unaffected by spiperone (0.1 microM) and mesulergine (1.0 microM), but were antagonized competitively by (+/-)-cyanopindolol affording agonist-independent pKB estimates of 8.4 to 8.9. The pharmacological profile of this receptor is consistent with that of the 5-HT1B subtype. Since the 5-HT1B receptor is the rodent homologue of the 5-HT1D beta subtype, it might be anticipated that 5-HT1D beta receptors will be found to mediate vasoconstrictor responses in non-rodent species.

On serotonin and migraine: a clinical and pharmacological review

Migraine patients have chronically low systemic 5-HT, predisposing them to develop migrainous headache once an attack has been initiated. Changes in platelet 5-HT content are not causally related, but reflect similar changes at a neuronal level. Stimulation of vascular 5-HT1 receptors, probably located in the vessel wall within the dural vascular bed, may alleviate the headache and associated symptoms, but does not interact with earlier mechanisms within the pathophysiological cascade. These receptors are of an as yet unidentified 5-HT1 subtype, closely resembling, but not identical to 5-HT1D receptors. Activation of these receptors results in vasoconstriction, inhibiting depolarization of sensory perivascular afferents within the trigemino-vascular system and thus stopping the headache. Additional inhibition of the release of vasoactive neuropeptides may be involved, but seems to be of only secondary clinical importance.

Serotonin receptor cDNA cloned from Lymnaea stagnalis

Serotonin (5-HT) is a major neurotransmitter that influences various behaviors, neuronal plasticity, learning, and memory in molluscs. Although the physiology of 5-HT transmission in molluscs is well studied, little is known about the pharmacology and diversity of the 5-HT receptor system. Based on the high homology of genes coding for guanine nucleotide-binding protein (G protein)-coupled receptors, we have cloned a gene for the Lymnaea stagnalis 5-HT (5HTlym) receptor. The putative receptor protein, 509 amino acids long, has highest homology with the Drosophila 5-HT receptors and mammalian 5HT1 receptors. As revealed by RNA blot-hybridization analysis, two mRNA species of 2.3 and 3.2 kb are detected in the central nervous system of Lymnaea. Transient expression of 5HTlym in COS-7 cells showed saturable [3H]lysergic acid diethylamide binding with an estimated dissociation constant of 0.9 nM. The 5HTlym receptor exhibited a mixed 5HT-like pharmacology that cannot be precisely categorized with existing mammalian classification nomenclature. However, the 5HTlym receptor does display some characteristics that have been attributed to the putative mammalian vascular 5HT1-like receptor.

Effect of the thromboxane A2-mimetic U46619 on 5-HT1-like and 5-HT2 receptor-mediated contraction of the rabbit isolated femoral artery

1. The influence of the thromboxane A2-mimetic U46619 (11 alpha, 9 alpha-epoxymethano PGH2) on 5-hydroxy-tryptamine (5-HT)-induced contractions of the rabbit isolated femoral artery has been examined. 2. In the absence of U46619, 5-HT responses were mediated predominantly by 5-HT2-receptors as judged by potent, surmountable antagonism by the selective 5-HT2 receptor antagonists, spiperone and ketanserin. Both antagonists unmasked a population of 5-HT1-like receptors which accounted for approximately 10-15% of the 5-HT maximum response. 3. In the presence of U46619 (3-10 nM), 5-HT-induced contractions were largely resistant to blockade by 5-HT2 receptor antagonists since 5-HT1-like receptor-mediated contraction now accounted for approximately 60% of the 5-HT maximum response. 4. These results show that activation of thromboxane A2 receptors in a tissue possessing both 5-HT2 and 5-HT1-like receptors can convert 5-HT-induced contraction from one mediated predominantly by 5-HT2 receptors to one which is mediated predominantly by 5-HT1-like receptors.

Agonist activity of sumatriptan and metergoline at the human 5-HT1D beta receptor: further evidence for a role of the 5-HT1D receptor in the action of sumatriptan

We have recently cloned a novel human 5-HT1D receptor subtype termed 5-HT1D beta. CHO K1 cells expressing the human serotonin 5-HT1D beta receptor were assayed to determine the second messenger system of this receptor. Cyclic AMP radioimmunoassays revealed that the 5-HT1D beta receptor is negatively coupled to adenylate cyclase in this cell system. A maximum of 50% inhibition of forskolin stimulated cAMP production was obtained with 5-HT1 receptor agonists which was blocked by the non-selective 5-HT receptor antagonist methiothepin (pKB = 100 nM). The novel anti-migraine drug sumatriptan, a putative 5-HT1D selective compound, acted as an agonist at the 5-HT1D beta receptor. Most notably metergoline, a putative 5-HT1 receptor antagonist, did not block the effects of 5-HT and was found to be acting as a full agonist at the 5-HT1D beta receptor. The ability of metergoline to act as an agonist at the 5-HT1D beta receptor may explain why it does not inhibit 5-HT and sumatriptan induced contraction of dog saphenous vein and other large conducting arteries. These results suggest that the 5-HT1D beta receptor may be the site of action of sumatriptan in preventing migraine, and that metergoline's actions on the dog saphenous vein are not contradictory to that hypothesis, as previously reported.

Further characterization of the 5-hydroxytryptamine 5-HT1-like receptor mediating contraction of guinea-pig iliac artery

We recently described a 5-hydroxytryptamine 5-HT1-like receptor mediating contraction in guinea-pig isolated iliac artery. The present study was aimed at characterizing this receptor with respect to the currently recognized 5-HT1 receptor subtypes (5-HT1A, 5-HT1B, 5-HT1C and 5-HT1D). The potencies of 13 drugs tested as agonists correlated with their affinities for 5-HT1D binding sites only. The concentration-response curve for 5-carboxamidotryptamine (5-CT, a 5-HT1-like receptor agonist) was unaffected by propranolol (10 microM), which is reported to have affinity for 5-HT1A, 5-HT1B and 5-HT1C recognition sites. Yohimbine (3 microM) and metergoline (1 microM) antagonized 5-CT with pKB values of 6.15 and 6.96, respectively. These values are close to those found in a functional correlate of 5-HT1D sites in the same species, namely the presynaptic 5-HT autoreceptor in guinea-pig brain cortex. The overall results support the view that the receptor studied is of the 5-HT1D subtype. The receptor shares close similarities with other vascular 5-HT1-like receptors mediating contraction, for example the receptor present in dog saphenous vein.

An endothelial 5-HT receptor that mediates relaxation in guinea-pig isolated jugular vein resembles the 5-HT1D subtype

1. Endothelium-dependent and -independent, concentration-related, relaxations to 5-hydroxytryptamine (5-HT) are described in a preparation of guinea-pig isolated jugular vein. 2. An endothelial 5-HT receptor was studied in the presence of mesulergine (at 10.0 microM, a concentration sufficient to antagonize 5-HT2 receptor-mediated contractions and endothelium-independent relaxations to 5-HT). Relaxations mediated by the endothelial 5-HT receptor were resistant to antagonism by mesulergine. 3. Several 5-HT receptor agonists activated the endothelial receptor with the following rank order of potency: 5-carboxamidotryptamine (5-CT) greater than 5-HT greater than methysergide greater than or equal to alpha-methyl-5-HT greater than sumatriptan greater than 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) greater than 2-methyl-5-HT. 4. Relaxations to 5-HT were not blocked by (+/-)-pindolol (1.0 microM), (-)-propranolol (1.0 microM), spiperone (1.0 microM), ondansetron (1.0 microM) or ICS 205-930 (10.0 microM). 5. Both 5-HT and sumatriptan evoked endothelium-dependent relaxations which were sensitive to antagonism (pA2 and apparent pA2 values respectively) by methiothepin (8.1 and 8.6), metergoline (7.4 and 7.5), PAPP (8.2 and 8.2), yohimbine (7.1 and 6.8), rauwolscine (6.8 and 6.7), but not by corynanthine (10.0 microM). 6. These observations are consistent with a 5-HT1D receptor-mediated effect, and provide further support for the concept that differences exist between endothelial 5-HT receptors in different tissues and species.

5-HT1-like receptor mediated changes in porcine carotid haemodynamics: are 5-HT1D receptors involved?

5-Hydroxytryptamine (5-HT) reduces porcine arteriovenous shunting in the carotid vascular bed by stimulation of both 5-HT1-like and 5-HT2 receptors and increases capillary flow to some tissues, like the skin and ears, by different 5-HT1-like receptors. In view of the heterogeneous nature of the 5-HT1-like receptors and the relative selectivity for the 5-HT1D binding sites of sumatriptan, which also reduces porcine arteriovenous shunting and slightly increases capillary blood flow towards skin and ears by 5-HT1-like receptors, we have attempted to determine whether one or both of these carotid 5-HT1-like receptors belong to the 5-HT1D subtype. Pentobarbitone anaesthetized pigs, subjected to bilateral cervical vagosympathectomy, received either 5-HT (2 micrograms.kg-1.min-1) in the carotid artery or cumulative i.v. doses of sumatriptan (10, 30, 100 and 300 micrograms.kg-1). Their effect on the total carotid blood flow and its distribution into capillary and arteriovenous anastomotic parts was determined with radioactive microspheres. The effect of metergoline (1 mg.kg-1), a substance with a very high affinity for the 5-HT1D receptor as well as for the 5-HT1A, 5-HT1B, 5-HT1C and 5-HT2 receptors, was studied on the responses to 5-HT and sumatriptan. Both 5-HT and sumatriptan reduced carotid arteriovenous anastomotic blood flow. 5-HT and, to a lesser extent, sumatriptan also increased capillary blood flow towards some tissues. Metergoline by itself did not affect the distribution of porcine carotid blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

Sumatriptan. A review of its pharmacodynamic and pharmacokinetic properties, and therapeutic efficacy in the acute treatment of migraine and cluster headache

Sumatriptan is a serotonin1 (5-HT1) receptor agonist, which is effective in the acute treatment of migraine headache. Its antimigraine activity is believed to derive from selective vasoconstriction of cranial blood vessels which are dilated and distended during migraine headache and/or from inhibition of neurogenically mediated inflammation in the dura mater. In placebo-controlled comparative studies, sumatriptan reduced migraine headache from 'moderate or severe' to 'mild or none' within 2 hours in 50 to 73% of patients following oral administration of 100 or 200 mg, and within 1 hour in 70 to 80% of patients following subcutaneous doses of 6 to 8 mg or intranasal doses 20 mg into each nostril. In addition, sumatriptan alleviated the accompanying symptoms of nausea, vomiting, and photophobia/phonophobia more effectively than placebo, and permitted higher percentages of patients to resume normal daily activities. Sumatriptan 100 mg orally was more effective in the acute treatment of migraine than oral combination therapy consisting of ergotamine 2 mg plus caffeine 200 mg or aspirin 900 mg plus metoclopramide 10 mg. Pooled data from nearly 5000 patients treated with either oral or subcutaneous sumatriptan in clinical trials indicate that it is well tolerated. However, migraine recurrence within 24 or 48 hours of initial symptom resolution developed in approximately 40% of patients treated with sumatriptan, irrespective of route of administration. It is likely that migraine recurrence is related to the short half-life of the drug (approximately 2 hours). Future studies should attempt to ascertain whether additional doses of sumatriptan will help prevent migraine recurrence in patients with attacks of long duration and if so, should determine the optimum interval between dosages. In conclusion, sumatriptan is an important addition to the range of drugs currently available for acute treatment of migraine. It provides rapid relief from debilitating symptoms in a high percentage of patients, particularly after subcutaneous administration. At this stage in its development a number of questions remain to be answered - most notably whether repeat doses will help prevent recurrent attacks and which patients are most likely to respond to therapy. Nevertheless, sumatriptan presently offers a combination of efficacy and tolerability that is unique in this particular clinical setting.

Studies on the mechanism of 5-HT1 receptor-induced smooth muscle contraction in dog saphenous vein

1. We have investigated the mechanism of smooth muscle contraction evoked by activation of 5-HT1-like receptors in dog isolated saphenous vein. 2. In the presence of the 5-HT2 receptor antagonist, ritanserin (0.1 microM), concentration-effect curves (10 nM-300 microM) for 5-hydroxytryptamine (5-HT)-induced smooth muscle contraction were biphasic. This could be attributed to a direct action on 5-HT1-like receptors at low concentrations of 5-HT (10 nM-10 microM) and an indirect (through the release of noradrenaline from sympathetic neurones) activation of postjunctional alpha-adrenoceptors at higher 5-HT concentrations. In contrast, concentration-effect curves (100 nM-100 microM) for sumatriptan-induced contractions were not biphasic, and were due solely to activation of 5-HT1-like receptors. 3. Smooth muscle contractions evoked either by low concentrations of 5-HT or by sumatriptan were abolished by removal of extracellular calcium and were markedly inhibited, but not abolished, by the calcium channel blocker, verapamil (1-30 microM). In contrast, contractions evoked by high concentrations of 5-HT were markedly less sensitive to removal of extracellular calcium or to verapamil. 4. 5-HT and sumatriptan also inhibited (to a maximum of about 50%) prostaglandin E2 (PGE2, 5 microM)-stimulated adenosine 3':5'-cyclic monophosphate (cyclic AMP) formation. This effect was mimicked by the alpha 2-adrenoceptor agonist, azepexole (B-HT933) but not by the alpha 1-adrenoceptor agonist, methoxamine.5. In contrast to mediation of smooth muscle contraction, the 5-HT1-like receptor-mediated inhibition of PGE2-stimulated cyclic AMP formation evoked by 5-HT or sumatriptan was not attenuated by removal of extracellular calcium or by verapamil (1 microM).6. A directly-acting inhibitor of adenylyl cyclase, 2',3'-dideoxyadenosine (1 mM) inhibited PGE2-stimulated cyclic AMP formation but did not produce smooth muscle contraction.7. These results suggest that contractile responses of dog isolated saphenous vein arising through activation of 5-HT1-like receptors are associated with both an influx of extracellular calcium ions (to a large extent via voltage-dependent channels) and an inhibition of adenylyl cyclase. However, although these two responses are coupled to the same receptor, they appear to be independent.

Rationale for the use of 5-HT1-like agonists in the treatment of migraine

Migraine headache is thought to be associated with a dilatation of cranial blood vessels, particularly those in the dura mater, and an accompanying localized sterile inflammatory response. Sumatriptan is a highly selective 5-HT1-like receptor agonist which selectively constricts cranial blood vessels (including those in the dura mater). It also inhibits neurogenically-mediated plasma protein extravasation in the dura mater. Haemodynamic studies in anaesthetized animals have shown that sumatriptan selectively constricts the carotid arterial circulation and this effect appears to be restricted to an effect on carotid arteriovenous anastomoses. Sumatriptan has a much more selective pharmacological profile than ergot preparations which are also used in the acute treatment of migraine. The development of sumatriptan has been based on a vascular theory of migraine and its high degree of efficacy in the treatment of migraine strengthens the argument that dilatation of cranial blood vessels is the cause of vascular headache.

Role of 5-HT1-like receptors in the reduction of porcine cranial arteriovenous anastomotic shunting by sumatriptan

1. The new tryptamine derivative sumatriptan (GR43175) is effective in the treatment of migraine. Since several antimigraine agents reduce cranial arteriovenous anastomotic blood flow in the anaesthetized pig, we have investigated the carotid haemodynamic effects of sumatriptan. 2. Sumatriptan (10, 30, 100 and 300 micrograms kg-1, i.v.) reduced total common carotid blood flow, exclusively by affecting its arteriovenous anastomotic fraction; the capillary fraction even increased with the highest doses. 3. These reductions in the carotid arteriovenous anastomotic ('shunt') blood flow were mediated by a 5-HT1-like receptor, as methiothepin, but not ketanserin, antagonized the responses to sumatriptan. 4. Sumatriptan increased the difference in oxygen saturation between arterial and jugular venous blood, which is likely to be a consequence of the reduction of the carotid shunt blood flow. 5. The selective reduction in arteriovenous anastomotic blood flow produced by sumatriptan may reflect its antimigraine action, thought to involve vasoconstriction of those cranial vessels, be they 'shunt' vessels or not, which are distended and inflamed during a migraine attack.