5-HT(1)-like receptor agonists and the pathophysiology of migraine

Oral sumatriptan: effect of a second dose, and incidence and treatment of headache recurrences

Oral sumatriptan in a dose of 100 mg aborts about 60% of migraine attacks within 2 h, but the headache may recur within 24 h. We investigated: (i) the incidence of headache recurrence after oral sumatriptan (ii) whether a second tablet of sumatriptan at 2 h increases initial efficacy and/or (iii) prevents headache recurrence and (iv) whether a further tablet of sumatriptan treats headache recurrence. In a randomized parallel-group clinical trial, 1246 patients treated one to three migraine attacks (with or without aura), with 100 mg oral sumatriptan. Two hours later they all took a double-blind randomized second table of sumatriptan (group I) or placebo (group II). Patients who initially improved, but then experienced headache recurrence took a further double-blind randomized tablet of sumatriptan or placebo. Proportions of patients who improved from moderate/severe headache to mild/none were similar in groups I and III at 2 h (55 vs 56%) and 4 h (80 vs 77%). Incidences of headache recurrence (moderate/severe-any grade of headache) and median times to headache recurrence were also similar: 22-32% at 16 h in group I and 25-33% at 16.5 h in group II. Sumatriptan was superior to placebo in treating headache recurrence: 74 vs 49% (p = 0.017) in group I and 70 vs 30% (p = 0.0001) in group II. Thus, one-fourth of patients experience headache recurrence at about 16 h after successful treatment of a migraine attack with 100 mg oral sumatriptan. A second tablet of sumatriptan at 2 h does not increase initial efficacy and neither prevents nor delays headache recurrence.(ABSTRACT TRUNCATED AT 250 WORDS)

Functional 5-HT receptor subtypes in the isolated canine common carotid artery

The vascular responses to 5-hydroxytrypamine (5-HT), 5-carboxamidotryptamine (5-CT, a selective 5-HT1-like receptor agonist), alpha-methyl-5-HT (alpha-M-5-HT, a relatively selective 5-HT2 receptor agonist), noradrenaline (NA), and KCl were examined in isolated, cannulated, and perfused canine common carotid arterial preparations. They caused strong vasoconstrictions. The rank order of vasoconstrictive potency was 5-HT > alpha-M-5-HT > or = NA > 5-CT >> KCl. The 5-HT-induced vasoconstriction was significantly depressed by methysergide (a 5-HT1 and 5-HT2 receptor antagonist), ketanserin (a selective 5-HT2 receptor antagonist), and spiperone (a selective 5-HT2 receptor antagonist). The 5-CT- and alpha-M-5-HT-induced vasoconstrictions were also significantly inhibited by methysergide, spiperone, and ketanserin. The NA-induced vasoconstriction was readily inhibited by bunazosin (an alpha-adrenoceptor antagonist) and ketanserin but not significantly inhibited by spiperone and methysergide. KCl has a weak potency for producing a vasoconstriction of the canine common carotid artery. A relatively large dose of diltiazem (a calcium channel-blocker) did not modify 5-HT-induced vasoconstrictions.(ABSTRACT TRUNCATED AT 250 WORDS)

Sumatriptan for the treatment of migraine attacks--a review of controlled clinical trials

Sumatriptan, a 5HT1-like receptor agonist, is a completely new treatment principle for migraine. In an extensive international programme of controlled clinical trials, sumatriptan, 6 mg subcutaneously and 100 mg orally, was superior to placebo in reducing headache and associated symptoms. The response rate for subcutaneous sumatriptan (70-84% after 1 h and 81-87% after 2 h) was higher than for oral sumatriptan (50-67% after 2 h). Additional doses did not increase efficacy. Oral sumatriptan was superior to Cafergot (2 mg ergotamine plus 200 mg caffeine) and somewhat better than aspirin (900 mg) plus metoclopramide (10 mg). Recurrence of migraine occurred in approximately 40% of attacks. Side effects were generally mild and short-lived in the controlled clinical trials. However, in clinical practice sumatriptan has subsequently caused rare cases of heart ischemia and sumatriptan is contraindicated in patients with a history of ischemic heart disease.

A chloroform extract of the herb feverfew blocks voltage-dependent potassium currents recorded from single smooth muscle cells

We have studied the effects of a chloroform extract of fresh leaves from the herb feverfew (Tanacetum parthenium) on potassium currents in smooth muscle. The currents were recorded from single cells dissociated from the rat anococcygeus and the rabbit ear artery using the whole-cell patch-clamp technique. When applied to cells isolated from the rat anococcygeus, the extract reduced the inactivating voltage-dependent potassium current in a concentration-related manner, with an IC50 value (the concentration that reduced the current by 50%) of 56 micrograms mL-1. Complete block of the current occurred at 1 mg mL-1. In addition to reducing the peak current, feverfew decreased the time to peak of the current and increased the rate of decay of the current. These effects can be explained by the feverfew extract blocking open potassium channels. In single cells isolated from rabbit ear artery the feverfew extract again reduced the voltage-dependent potassium current, whilst at the same time having no effect on the spontaneous transient outward currents which arise as a consequence of activation of calcium-dependent potassium channels. These results suggest that chloroform extracts of feverfew leaf contain an as yet unidentified substance capable of producing a selective, open-channel block of voltage-dependent potassium channels.

A novel rat serotonin receptor: primary structure, pharmacology, and expression pattern in distinct brain regions

Serotonin mediates various central and peripheral functions by its ability to bind to and activate a variety of receptors that belong to four pharmacologically defined classes termed 5-HT1 to 5-HT4. Using a polymerase chain reaction-derived probe, a clone, GPRFO, was isolated from a rat brain cDNA library. This cDNA encodes a putative G protein-coupled receptor that exhibits highest similarity to receptors for biogenic amines. RNA blot analysis indicated that the corresponding gene is expressed in the diencephalon. Consistent with the RNA blot data, GPRFO mRNA has been detected by in situ hybridization in the centrolateral, central medial, and intermediodorsal thalamic nuclei. Highest amounts of GPRFO mRNA, however, have been observed in a small area, i.e., the hippocampal rudiments and the stria longitudinalis. COS-7 cells transiently transfected with the GPRFO cDNA acquire saturable high-affinity binding sites for [3H]serotonin (KD = 41 nM). The pharmacological properties of the receptor differ from those of the known serotonin receptor subtypes, suggesting that the GPRFO cDNA encodes a novel serotonin receptor that is expressed in distinct rat brain regions.

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.

Characterization of 5-HT receptors in simian isolated gastroepiploic artery

The vascular responses of simian gastroepiploic arteries to 5-hydroxytryptamine (5-HT), 5-carboxamidotryptamine (5-CT, a selective 5-HT1-like receptor agonist), 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT, a selective 5-HT1A receptor agonist), m-trifluoromethylphenylpiperazine (TFMPP, a selective 5-HT1B receptor agonist), noradrenaline and KCl were examined in isolated, cannulated and perfused preparations. 5-HT induced dose-dependent vasoconstrictions more potently than noradrenaline did. The rank order of potency was 5-HT > noradrenaline > 5-CT >> 8-OH-DPAT = TFMPP. 5-HT- and 5-CT-induced vasoconstrictions were not significantly changed by endothelial denudation, although acetylcholine-induced vasodilatations were abolished. 5-HT-induced vasoconstrictions were depressed by phentolamine (an alpha-adrenoceptor antagonist), diltiazem (a calcium ion channel inhibitor), methysergide (a 5HT1- and 5HT2-receptor antagonist) and ketanserin (a selective 5-HT2 receptor antagonist). Noradrenaline-induced vasoconstrictions were readily inhibited by phentolamine and ketanserin. 5-CT-, 8-OH-DPAT- and TFMPP-induced vasoconstrictions were inhibited by both methysergide and ketanserin. KCl-induced vasoconstrictions were blocked by diltiazem. From these results, we conclude that (1) the simian gastroepiploic artery contains 5-HT receptors, (2) 5-HT1-like and 5-HT2 receptors are involved in the vasoconstriction of the simian gastroepiploic artery, and (3) the vasoconstriction is at least partially related to the activation of calcium ion channels.

5-Hydroxytryptamine receptor characterization of human cerebral, middle meningeal and temporal arteries: regional differences

We have studied the regional distribution of 5-hydroxytryptamine (5-HT) receptor subtypes in fresh circular segments of human cerebral, middle meningeal, and temporal arteries. Vasomotor responses induced by a series of 5-HT agonists and antagonists with some degree of selectivity were studied by using a sensitive in vitro system. Nine 5-HT agonists were examined for contractile effects on the arteries. In cerebral and meningeal arteries 5-carboxamidotryptamine (5-CT) was more potent than 5-HT. The opposite order of potency (5-HT-5-CT) was found in temporal arteries. In the cerebral arteries 5-methoxytryptamine (5-MeOHT) was more potent than sumatriptan while sumatriptan was more potent than 5-MeOHT in meningeal and temporal arteries. The 5-HT1 receptor antagonist, methiothepin, competitively antagonized 5-CT-induced contractions in cerebral arteries, with a pA2 value of 9.05. 5-HT-induced contractions were competitively antagonized by ketanserin (5-HT2) in the temporal arteries pA2 value of 9.06). Methiothepin and ketanserin had non-competitive antagonistic effects in the middle meningeal arteries. The 5-HT3 selective antagonist ondansetron did not cause any shift of the contractions induced by 2-methyl-5-HT in the temporal, cerebral and middle meningeal arteries. These results suggest that the cerebral arteries mainly contain 5-HT1D or 5-HT1-like receptors, and the temporal artery 5-HT2 receptors; the data further indicate the presence of both receptor subtypes in the middle meningeal artery.

Immunohistochemical evidence for the absence of central neuron projection to pial blood vessels and dura mater

The present work shows that, in rat pial vessels and dura mater, all the nerve fibres observable by confocal fluorescence microscopy belong to the peripheral nervous system. It has been postulated that central nervous structures such as the raphe nuclei and the locus coeruleus could send direct projections to meningeal blood vessels. Mature neurons, whose perikaryons and axons are entirely located within the central nervous system, express the low molecular mass neurofilament protein and not the 57,000 mol. wt intermediate filament protein called "peripherin". This is the case for both raphe nuclei and locus coeruleus neurons [Leonard et al. (1988) J. Cell Biol. 106, 181-193]. Neurons which send axons outside the central nervous system or ganglionic neurons of the peripheral nervous system systematically express both proteins [Portier et al. (1984) Devl Neurosci. 6, 335-344]. Double labelling of pial vessels and meningeal tissue with antibodies directed against low molecular mass neurofilament and peripherin revealed nerve fibres immunoreactive to both antibodies and no nerve fibres reactive only to the low molecular mass neurofilament antibody. Conversely, cortical nerve fibres were immunoreactive only to the low molecular mass neurofilament antibody. It is thus concluded that the raphe nuclei and the locus coeruleus do not directly innervate meningeal tissues and, therefore, that these nuclei cannot directly intervene in cerebrovascular pathologies such as migraine headache or vasospasm. Secondarily, the present work also allowed for the first time the accurate observation of the spatial organization of the complete cerebrovascular innervation. Three main types of nerves can be defined on a morphological basis. A high proportion of these nerve fibres, either isolated or grouped in bundles, are varicose nerve fibres. Contacts between adjacent varicosities of the same type, which have been occasionally observed by electron microscopy, appear to be a very frequent feature.

Effects of tertatolol, a beta-adrenoceptor antagonist with agonist affinity at 5-HT1A receptors, in an animal model of migraine: comparison with propranolol and pindolol

Constriction of carotid arteriovenous anastomoses is a common property of several antimigraine drugs. The present study concerns the effects of tertatolol (0.1, 0.3, 1 and 3 mg/kg i.v.), a novel beta-adrenoceptor antagonist with an agonist action on 5-HT1A receptors, on systemic haemodynamics and carotid blood flow distribution in the anaesthetized pig. Two other beta-adrenoceptor antagonists, one (propranolol) with and one (pindolol) without antimigraine actions, were compared (doses: 0.03, 0.1, 0.3 and 1 mg/kg i.v.) with tertatolol in this animal experimental model of migraine. While the beta-adrenoceptor antagonist with partial agonist action, pindolol, increased heart rate and cardiac output, propranolol and tertatolol decreased these variables moderately. Mean arterial blood pressure also decreased with the two highest doses of propranolol and with the highest dose of tertatolol. The calculated total peripheral conductance decreased with the first three doses of tertatolol. Carotid haemodynamic variables were not affected by pindolol, except for some increase in the nutrient fraction after the highest dose. Propranolol and especially tertatolol decreased both total carotid blood flow and arteriovenous anastomotic blood flow without affecting the nutrient fraction. In the case of tertatolol, blood flow decreases were accompanied by similar decreases in vascular conductance, indicating active arteriovenous anastomotic constriction. It is therefore suggested that tertatolol may prove effective in the treatment of migraine.

Treatment of migraine attacks with subcutaneous sumatriptan: first placebo-controlled study. The Subcutaneous Sumatriptan International Study Group

The results of the very first large-scale placebo-controlled dose-response trial with the novel selective 5-hydroxytryptamine1-like (5HT1-like) receptor agonist sumatriptan are presented. We studied the efficacy and tolerability of subcutaneous injections of 1 mg, 2 mg and 3 mg of sumatriptan in alleviating migraine attacks in a double-blind, placebo-controlled, parallel-group, multicentre clinical trial. Six-hundred and ninety patients were randomized and 685 received study medication. At 30 min, reduction of headache severity to mild or none (primary efficacy endpoint) was achieved in 22% (95% CI: 15-28%) of placebo-treated patients and in 39% (CI: 31-46%) of patients treated with 1 mg sumatriptan, 44% (CI: 36-51%) treated with 2 mg sumatriptan and 55% (CI: 48-63%) treated with 3 mg sumatriptan. Differences from placebo were 17% (CI: 8-27%) for 1 mg sumatriptan, 22% (CI: 13-32%) for 2 mg sumatriptan and 34% (CI: 24-44%) for 3 mg sumatriptan (p < 0.001 for all three comparisons). Other migraine symptoms were also more effectively treated by sumatriptan than by placebo. Subsequently, an open-label 3 mg dose subcutaneous sumatriptan was given to partial or non-responders. Thirty minutes after this open dose the response rate to sumatriptan had improved to between 70 and 80%. Adverse events after sumatriptan were minor and short-lived. We conclude that subcutaneous sumatriptan is well tolerated in doses up to 3 + 3 mg and may rapidly abort migraine attacks.

From serotonin receptor classification to the antimigraine drug sumatriptan

After the synthetic serotonin 5-hydroxytryptamine (5-HT) became available in the early 1950s, attempts were soon under way to study the nature of 5-HT receptors. Using the guinea-pig isolated ileum, Gaddum and Picarelli (1957) suggested that 5-HT-induced contractions were mediated by a morphine-sensitive "M" receptor located on the parasympathetic ganglion and a dibenzyline-sensitive "D" receptor located on the smooth muscle. Though this classification ws used during the next three decades, it was realized that some effects of serotonin, for example vasoconstriction within the carotid vascular bed, were not mediated by either "M" or "D" receptors. When radioligand binding studies led to the identification of 5-HT1 and 5-HT2 "receptors" in the rat brain membranes, it became increasingly apparent that the two receptor classifications were not identical. Thus, a new framework for serotonin receptor nomenclature and classification was proposed: 5-HT1-like (5-HT1), 5-HT2 (formerly "D") and 5-HT3 (formerly "M") receptors. At the present time, several subtypes of 5-HT1 receptors as well as a 5-HT4 receptor are also recognized. As the serotonin receptor classification was emerging to indicate that carotid vasoconstriction by serotonin is mediated by a subtype of 5-HT1 receptors, on the migraine front it was being suggested that the disease is associated with vasodilation within the cranial extracerebral circulation and deranged serotonin metabolism and that certain antimigraine drugs caused a selective carotid vasoconstriction, probably via serotonin receptors. Therefore, Humphrey and colleagues conceived that synthesis of serotonin derivatives may lead to a compound that would elicit highly selective carotid vasoconstriction and abort migraine attacks. Indeed, via the synthesis of 5-carboxamidotryptamine and AH25086, sumatriptan was designed. The drug acts as an agonist at the vasoconstrictor 5-HT1 receptor subtype and has proved highly effective in the therapy of migraine attacks.

Clinical effects and mechanism of action of sumatriptan in migraine

Sumatriptan is a novel, highly effective drug against migraine and cluster headache attacks. It shows a remarkably selective pharmacological profile in animals. Determination of its mechanism of action in human should further the understanding of the pathophysiology of migraine and cluster headache. We, therefore, review current knowledge on the clinical and pharmacological effects of sumatriptan. Important pharmacological actions of sumatriptan are (i) poor penetration of the blood-brain barrier suggesting a peripheral point of action; (ii) 5-HT1-like/5-HT1d receptor-mediated vasoconstriction of large cerebral arteries and dural vessels; and (iii) blockade of neurogenic dural inflammation via 5-HT1d autoreceptor-mediated inhibition of vasoactive neuropeptides within the trigeminovascular system. Future research will tell which mechanism is involved in the pathophysiology of migraine and cluster headache.

Receptor mediation of 5-HT-induced inflammation and nociception in rats

In light of evidence suggesting the proinflammatory and nociceptive action of peripheral serotonin (5-HT), the present study examined dose-dependent parameters of edema and algesia produced by intraplantar injections of 5-HT and the role of heterogeneous 5-HT receptors in these 5-HT-induced responses. Intraplantar 5-HT (0.05, 0.25, 0.5, or 1.0 mumols) produced paw edema at each 5-HT concentration and produced concentration-dependent increases in the nociceptive response as indexed by lifts of, and licks to the affected paw. Intraplantar pretreatment with the 5-HT1 receptor antagonist methysergide at concentrations greater than or equal to 3 nmol attenuated the 5-HT-induced (25 mumols) inflammatory and nociceptive responses. At concentrations greater than or equal to 300 nmol, both 5-HT2 receptor antagonist ketanserin and 5-HT3 receptor antagonist odansetron pretreatment blocked 5-HT-induced inflammatory and nociceptive responses. These results more completely define peripheral 5-HT-receptor-dependent systems of 5-HT-induced inflammation and nociception in rats.

Contractile effects of 8-hydroxy-2-(di-n-propylamino)tetralin and flesinoxan in human isolated basilar artery

The aim of the present study was to assess the effects of the 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and flesinoxan in ring preparations of human basilar artery. 5-Hydroxytryptamine-(5-HT), 8-OH-DPAT and flesinoxan induced concentration-dependent contractions of human basilar artery, the rank order of agonist potency being 5-HT greater than 8-OH-DPAT approximately flesinoxan. The rank order of maximum response, relative to 5-HT was 5-HT (100%) much greater than 8-OH-DPAT (40.4 +/- 4.4%) much greater than flesinoxan (7.0 +/- 2.3%). The contractile effects of 8-OH-DPAT were blocked by phentolamine (10 microM) but not by labetalol (10 microM). Spiperone (1 microM) had no significant effect on either 5-HT or 8-OH-DPAT-induced contraction, however methiothepin (100 nM) produced inhibition of both 5-HT- and 8-OH-DPAT-induced contraction of human basilar artery. In addition, flesinoxan (100 microM) produced blockade of 5-HT-, 8-OH-DPAT- and sumatriptan (a 5-HT1-like receptor agonist)-induced contraction of human basilar artery, although full concentration-effect curves were not obtained. In some preparations 8-OH-DPAT produced a concentration-dependent relaxation of tone. This effect was particularly apparent in the presence of phentolamine. We conclude from the relative rank order of antagonist potency that 8-OH-DPAT and 5-HT produce contraction of the human basilar artery by activation of the same receptor, a 5-HT1-like receptor distinct from the 5-HT1A receptor subtype.(ABSTRACT TRUNCATED AT 250 WORDS)

Carotid vascular effects of ergotamine and dihydroergotamine in the pig: no exclusive mediation via 5-HT1-like receptors

1. Though it is well known that the antimigraine drugs ergotamine and dihydroergotamine reduce carotid arteriovenous anastomotic shunting, it is uncertain whether a 5-HT1-like receptor is responsible for this effect. Using a high dose of methiothepin (3 mg kg-1), which completely blocks the carotid vascular effects of sumatriptan, we have attempted to study the role of 5-HT1-like receptors in the carotid vascular effects of ergotamine as well as dihydroergotamine in anaesthetized pigs. 2. Both ergotamine and dihydroergotamine increased arterial blood pressure and decreased heart rate. 3. The ergot alkaloids reduced dose-dependently total carotid blood flow and conductance as a result of a selective decrease in the arteriovenous anastomotic fraction. The nutrient fraction increased, particularly to bones, tongue and salivary glands with ergotamine and to ears, head skin, bones and salivary glands with dihydroergotamine. In contrast, dural vascular conductance tended to decrease. 4. Methiothepin (3 mg kg-1) partially antagonized the decrease in total carotid and arteriovenous anastomotic blood flow and conductance by the ergot alkaloids; the ED30 for ergotamine and dihydroergotamine (agonist dose eliciting a 30% decrease in arteriovenous anastomotic conductance) was raised by 3.1 and 5.2 fold respectively. 5. These results indicate that the effects of ergotamine and dihydroergotamine are partly mediated by methiothepin-sensitive receptors, which may probably belong to either 5-HT1-like or alpha 2-adrenoceptor category. However, an important part of the effect of ergot alkaloids is left after methiothepin and this could be mediated by other, perhaps novel, receptors.

Treatment of migraine attacks with sumatriptan

BACKGROUND

The headache in migraine attacks may be caused by dilatation of certain cranial arteries or arteriovenous anastomoses, by neurogenic dural plasma extravasation, or by both of these mechanisms. Sumatriptan, a novel selective agonist of 5-hydroxytryptamine-like receptors, blocks these phenomena. We investigated its efficacy in migraine.

METHODS

We studied 639 patients with migraine attacks in a randomized, double-blind, placebo-controlled, parallel-group clinical trial. We assessed the effect of subcutaneous injections of 6 or 8 mg of sumatriptan or placebo on the severity of headache and associated migrane symptoms 30, 60, and 120 minutes after treatment. Patients who were not free of pain after 60 minutes subsequently received placebo if they had initially received placebo or 8 mg of sumatriptan, and 6 mg of sumatriptan or placebo if they had initially received 6 mg of sumatriptan.

RESULTS

After 60 minutes, the severity of headache was decreased in 72 percent (95 percent confidence interval, 68 to 76 percent) of the 422 patients given 6 mg of sumatriptan, 79 percent (95 percent confidence interval, 71 to 87 percent) of the 109 patients given 8 mg of sumatriptan, and 25 percent (95 percent confidence interval, 17 to 33 percent) of the 105 patients given placebo (data on 3 patients could not be evaluated). As compared with the placebo group, 47 percent (95 percent confidence interval, 38 to 57 percent) more patients who had received 6 mg of sumatriptan and 54 percent (95 percent confidence interval, 43 to 65 percent) more patients who had received 8 mg of sumatriptan had a decrease in the severity of headache (P less than 0.001 for both comparisons). After 120 minutes, 86 to 92 percent of the 511 patients treated with sumatriptan (202 assigned to 6 mg plus placebo, 203 to 6 mg plus 6 mg, and 106 to 8 mg plus placebo) had improvement in the severity of headache, as compared with only 37 percent of the 104 patients who received placebo once or twice (P less than 0.001 for all comparisons). Twenty-one patients were excluded from the analysis because of missing data (19) or protocol violations (2). The response rates did not differ significantly among the sumatriptan regimens. Adverse events were minor and transient in all groups.

CONCLUSIONS

We conclude that a single 6-mg dose of sumatriptan given subcutaneously is a highly effective, rapid-acting, and well-tolerated treatment for migrane attacks. The administration of a second dose 60 minutes later to patients not responding well to an initial dose affords little additional benefit.

5-Hydroxytryptamine: a chameleon in the heart

5-HT has profound effects on cardiac rate and force in a variety of animal species, including humans. The main initial response to 5-HT is a short-lasting bradycardia, mediated via a Bezold-Jarisch-like reflex, and initiated by stimulation of 5-HT3 receptors present on cardiac vagal afferents. Once this bradycardia is suppressed, 5-HT induces cardiac stimulation which, true to its chameleonic nature described here by Pramod Saxena and Carlos Villalón, is mediated by different mechanisms and receptors in different species. In several species, including humans, coronary vasodilatation is mediated by 5-HT1-like receptors, while both 5-HT1-like and 5-HT2 receptors mediate vasoconstriction. This knowledge may lead to a better assessment of the possible role of 5-HT in cardiovascular pathologies and to the development of selective 5-HT receptor agonists and antagonists for therapeutic usefulness in heart failure, coronary vasospasm and to avoid potential cardiac side-effects.

Efficacy of ICS 205-930, a novel 5-hydroxytryptamine3 (5-HT3) receptor antagonist, in the prevention of migraine attacks. A complex answer to a simple question. ICS 205-930 Migraine Study Group

To investigate whether the novel, potent and highly selective 5-hydroxytryptamine3 (5-HT3) receptor antagonist ICS 205-930 can prevent migraine attacks, we conducted simultaneously two randomized, double-blind, placebo-controlled, multicentre, international trials, involving a total of 204 patients, suffering from classic or common migraine. Both trials had the same parallel-group design (1 month baseline observation, followed by 3 months treatment) and both produced remarkably similar results. The primary efficacy parameter was the proportional reduction in attack frequency recorded after 3 months of treatment. Twenty-two patients withdrew prematurely from the trials and could not be assessed for efficacy. Mild to severe constipation was reported by about 50% of the patients on active treatment. None of the doses of ICS 205-930 tested (50 mg, 25 mg and 15 mg daily) produced a statistically significantly better result to reduce attack frequency than did placebo. However, confidence intervals for the difference in effect with placebo were wide, indicating that 15 mg ICS 205-930 may produce a 57% reduction in attack frequency as compared to placebo. The most unusual finding was that, for all efficacy parameters, the best results were obtained with the lowest dose (15 mg), the worst results with the highest dose (50 mg) and an intermediate effect with 25 mg. Such an inverse relation between dose and efficacy suggests a bell-shaped dose-response curve, implying that doses lower than 15 mg might well prove to be more effective. Thus, the present study has produced inconclusive, but intriguing results. Lower doses should be further investigated before drawing any definite conclusion on the efficacy of ICS 205-930 in the prophylactic treatment of migraine.

Comparison of endothelium-dependent responses of monkey cerebral and temporal arteries

1. Endothelium-dependency of vasodilator responses was compared in helical strips of monkey cerebral and superficial temporal arteries contracted with prostaglandin F2 alpha. Acetylcholine produced an endothelium-dependent relaxation in the temporal arteries, but did not consistently alter the tone of cerebral arteries. 2. Adenosine 5'-triphosphate (ATP) produced a transient contraction followed by a relaxation in the temporal and cerebral arteries; removal of the endothelium partially attenuated the relaxation of the cerebral arteries and markedly suppressed the relaxation in the temporal arteries. The dependency of adenosine 5'-diphosphate (ADP)-induced relaxations on the endothelium was also greater in temporal arteries than in cerebral arteries. 3. Histamine-induced relaxations in the temporal arteries were independent of the endothelium and were reversed to contractions by cimetidine. Cerebral arterial relaxations induced by histamine were partly dependent on the endothelium. Relaxations caused by substance P were reversed to contractions by removal of the endothelium in the temporal arteries, whereas the peptide did not consistently alter the tone of cerebral arteries. 4. The Ca2+ ionophore, A23187, relaxed the temporal and cerebral arteries to a similar extent; removal of the endothelium abolished these relaxations. Glyceryl trinitrate elicited similar relaxation of cerebral and temporal arteries, and these were independent of the endothelium. 5. These findings clearly indicate heterogeneity in the endothelium-dependency of several vasodilator responses in monkey intra- and extracranial arteries, although the ability of these arteries to respond to A23187 and glyceryl trinitrate does not appear to differ. The heterogeneous responses observed so far could therefore be due to different distributions of receptors or to variation in receptor-effector coupling in endothelial cells.

A peripheral 5-HT1D-like receptor involved in serotonergic induced hindlimb scratching in rats

The pharmacological characteristics of hindlimb scratching induced by serotonergic compounds were studied. We conclude that hindlimb scratching induced by serotonergic compounds is mediated by a serotonin1D (5-HT1D) or 5-HT1D-like receptor outside the blood-brain barrier because hindlimb scratching could be induced by s.c. injection of 5-methoxytryptamine (5-MeOT), 5-carboxamidotryptamine (5-CT), bufotenine, 5-hydroxytryptamine (5-HT) and tryptamine. These compounds have high affinity for 5-HT1A and 5-HT1D receptors. The 5-HT1A receptor agonist 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), the 5-HT1C receptor agonist MK 212, and the mixed 5-HT1C/5-HT2 receptor agonists (dl)-1-(2,5 dimethoxy-4-iodophenyl)-2-aminopropane (DOI) and quipazine did not induce hindlimb scratching. Rather, the latter compounds attenuated 5-MeOT-induced hindlimb scratching. The 5-HT releasing compounds fenfluramine and p-chloroamphetamine (PCA) inhibited whereas the 5-HT re-uptake inhibitors fluvoxamine and indalpine potentiated 5-MeOT-induced hindlimb scratching. 5-MeOT-induced hindlimb scratching could be inhibited dose dependently by the alpha 2-adrenoceptor blockers yohimbine and rauwolsince, which also have high affinity for 5-HT1D receptors, whereas the alpha 2-adrenoceptor blocker piperoxan only weakly counteracted hindlimb scratching. Haloperidol, apomorphine, morphine, clonidine and methiothepin strongly attenuated hindlimb scratching, atropine, naloxone and ICS 205930 attenuated it weakly whereas domperidone, methylatropine and mepyramine were inactive in doses up to 10 mg/kg. Hindlimb scratching induced by 5-MeOT was potentiated by the 5-HT receptor antagonists metergoline, methysergide, mesulergine, mianserin, ritanserin and xylamidine. Hindlimb scratching was not induced by i.c.v. injection of 5-MeOT.(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Pharmacology of antimigraine drugs

The drugs used in migraine therapy can be divided into two groups: agents that abort an established migraine attack and agents used prophylactically to reduce the number of migraine attacks. Both groups have drugs that are specific for migrainous headaches and that are non-specific, and are used to treat the accompanying headache (analgesics), vomiting (anti-emetics), anxiety (sedatives and anxiolytics), or depression (antidepressants). The main drugs with specific action on migraine include ergot alkaloids (ergotamine, dihydroergotamine), agonists (sumatriptan) or partial agonists (methysergide) at a specific subtype of 5-HT1-like receptors, beta-adrenoceptor antagonists (propranolol, metoprolol), calcium antagonists (flunarizine) and anti-inflammatory agents (indomethacin). The pharmacological basis of therapeutic action of several of these drugs is not well understood. In the case of the ergot alkaloids and 5-HT1-like receptor agonists, however, it is likely that the antimigraine effect is related to the potent and rather selective constriction of the large arteries and arteriovenous anastomoses in the scalp and dural regions. In addition, these drugs inhibit plasma extravasation into the dura in response to trigeminal ganglion stimulation, but it is possible that this effect is related to the selective vasoconstriction in the extracerebral vascular bed. The selectivity of the pharmacological effects of these antimigraine drugs (constriction of the extracerebral arteries and arteriovenous anastomoses, poor penetration into the central nervous system and the absence of an antinociceptive effect even after intrathecal administration) strongly suggests that excessive dilatation in the extracerebral cranial vasculature, probably initiated by a neuronal event, is an integral part of the pathophysiology of migraine.

5-HT3 receptor antagonists and migraine therapy

Neuronal 5-hydroxytryptamine3 (5-HT3) receptors mediate the excitatory effects of 5-HT. They are located in pain- and nausea-modulating areas in the central nervous system and on C-fibre primary afferents in the peripheral nervous system. Consequently, these receptors mediate the painful and emetic effects of 5-HT. Selective and potent 5-HT3 receptor antagonists have been shown to block inflammatory and 5-HT induced and potentiated "vascular pain". Based on the hypothesis that 5-HT3 receptor antagonists may block neurogenic dural inflammation in the distribution area of the trigeminal nerve and, thus, could potentially prevent migraine (pain), four highly selective and potent 5-HT3 receptor antagonists have been tested in both the acute and prophylactic treatment of migraine. Unfortunately, except for a clear anti-emetic effect, none of these drugs has shown unequivocal efficacy in the treatment of migraine. This may be partly due to the complex (bell-shaped) dose-response relationship of these compounds, making exact titration of the correct dose difficult. Moreover, most 5-HT3 receptor antagonists have proved to be toxic in man on chronic administration thereby preventing further trials in migraine with adjusted doses. Short-term treatment for cytotoxic drug-induced emesis so far appears to be the only proven indication for 5-HT3 receptor antagonists.

Supraspinal and spinal monoamine-modified function and the expression of opioid antinociception

Opioids are highly valuable clinical agents for the treatment of pain which are thought to act both at the spinal and supraspinal level. During the course of their actions, they have complex interactions with monoamine systems. These include 5-hydroxytryptamine (5-HT) and noradrenaline (NA), so this topic is discussed using these two transmitter systems, their locations and receptor sub-types, as prime candidates for modulating nociceptive and antinociceptive processes. Several classes of 5-HT receptors, as well as α(2)-adrenoceptors, appear to be clearly involved in antinociception and the functions of systems carrying these receptors may be modified using psychotropic agents. In particular, some antidepressants may acutely augment opioid antinociception and this property may be exploited to delay the onset of opioid tolerance in the sub-acute situation.

5-HT1-like receptors mediate contractions of the rabbit saphenous vein

5-Hydroxytryptamine (5-HT) elicited concentration-dependent contractions of the rabbit isolated saphenous vein. The effects of 5-HT were mimicked by 5-carboxamidotryptamine (5-CT), 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT), 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole succinate (RU 24969) and sumatriptan; the rank order of potency (pD2 values) was 5-CT (7.6) greater than 5-HT (6.9) greater than 8-OH-DPAT (6.2) greater than RU 24969 (6.1) greater than sumatriptan (5.7). The maximal response to RU 24969 was less than that to the other compounds, implying that RU 24969 may behave as a partial agonist. Methiothepin (10(-8), 3 x 10(-8) and 3 x 10(-7) M), ketanserin (10(-7), 3 x 10(-7) and 10(-6) M) and spiperone (10(-7), 10(-6) and 10(-5) M), but not 1 alpha H,3 alpha,5 alpha H- tropan-3-yl-3,5-dichlorobenzoate (MDL 72222; 10(-7), 10(-6) or 10(-6) M), cyanopindolol (10(-7) and 10(-6) M) or propranolol (10(-7) and 10(-6) M), shifted the concentration-effect curve of 5-HT to the right in a concentration-dependent manner with pA2 values of 8.25, 7.51 and 6.12, respectively. The high activity of 5-CT and methiothepin compared to, respectively, 5-HT and ketanserin (and spiperone) suggests that the contraction of the rabbit saphenous vein is not mediated by 5-HT2 receptors. The receptor involved seems to be mainly 5-HT1-like, similar to the one mediating contraction of the dog saphenous vein, human basilar artery and porcine cranial arteriovenous anastomoses.

Constriction of porcine arteriovenous anastomoses by indorenate is unrelated to 5-HT1A, 5-HT1B, 5-HT1C or 5-HT1D receptor subtypes

The study concerns the effects of indorenate, a tryptamine derivative with antihypertensive properties as well as high affinity for the 5-HT1A binding site, on carotid haemodynamics in anaesthetized pigs. Intracarotid infusions of indorenate (0.3, 1.0, 3.0 and 10.0 micrograms.kg-1.min-1 for 10 min each) caused dose-related decreases in total common carotid artery blood flow due almost exclusively to a reduction in arteriovenous anastomotic flow. These effects of indorenate were not appreciably modified after treatment with the 5-HT2 receptor antagonist ketanserin (0.5 mg.kg-1 i.a.), but were markedly reduced after treatment with methiothepin (1.0 mg.kg-1 i.a.), which antagonizes not only 5-HT2 receptors, but also the putative 5-HT1A, 5-HT1B 5-HT1C and 5-HT1D subtypes of 5-HT1-like receptors. Nonetheless, metergoline (1 mg.kg-1 i.a.), a drug with higher affinity than methiothepin for the above 5-HT1 receptor subtypes, failed to significantly modify the responses to indorenate. It is therefore concluded that, like 8-hydroxy-2-(di-n-propylamino)tetralin (8-OH-DPAT) and 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969), indorenate reduces both total common carotid and cephalic arteriovenous anastomotic blood flow in the pig by stimulating 5-HT1-like receptors; these receptors, however, do not seem to correspond to either 5-HT1A, 5-HT1B, 5-HT1C or 5-HT1D binding sites.

Evidence that the reversible MAO-A inhibitor moclobemide increases prolactin secretion by a serotonergic mechanism in healthy male volunteers

The serotonin receptor antagonist methysergide was used to investigate the mechanism mediating stimulation of prolactin release after single doses of the reversible MAO-A inhibitor moclobemide. Eight healthy male volunteers participated in a placebo-controlled cross-over study, where pretreatment with methysergide almost totally prevented the moclobemide-induced increase in plasma prolactin levels. MAO-A inhibition, as evidenced by up to 80% decreases in the plasma concentration of 3,4-dihydroxyphenylglycol, a deaminated metabolite of norepinephrine, was similar after both pretreatments. This result suggests that moclobemide stimulates prolactin release through activation of serotonergic receptors, and provides evidence that the drug is capable of augmenting central serotonergic neurotransmission in humans.

The 5-HT1-like receptor mediating reduction of porcine carotid arteriovenous shunting by RU 24969 is not related to either the 5-HT1A or the 5-HT1B subtype

Using the radioactive microsphere technique in anaesthetized pigs, we studied the systemic and carotid haemodynamic effects of intracarotid infusions (0.3, 1, 3 and 10 micrograms/kg.min) of 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole succinate (RU 24969), a drug with high affinity for 5-HT1A and 5-HT1B recognition sites. Unlike in the rat, RU 24969 did not elicit hypotension in the pig. Instead, the two highest doses of the drug caused a slight increase in blood pressure. RU 24969 reduced common carotid artery blood flow by decreasing the non-nutrient, arteriovenous anastomotic blood flow; the nutrient, arteriolar blood flow was mildly increased. The decrease in common carotid and arteriovenous anastomotic blood flow was only slightly attenuated in animals pretreated with the 5-HT2 receptor antagonist, ketanserin (0.5 mg/kg i.a.), but was markedly reduced in animals pretreated with the 5-HT1-like and 5-HT2 receptor antagonist, methiothepin (1.0 mg/kg i.a.). However, these responses were not modified after pretreatment with the putative 5-HT1A and 5-HT1B receptor antagonist, (+/-)-pindolol (4.0 mg/kg i.v.). The slight increase in arteriolar blood flow was attenuated in the animals pretreated with either ketanserin, methiothepin or (+/-)-pindolol. It is concluded that the RU 24969-induced reduction in common carotid and arteriovenous anastomotic blood flow is mediated mainly by 5-HT1-like receptors, which do not seem to correspond to either the 5-HT1A or 5-HT1B receptor subtypes.