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

Migraine drugs

According to recent studies, migraine affects more than 1 billion people worldwide, making it one of the world’s most prevalent diseases. Although this highly debilitating illness has been known since ancient times, the first therapeutic drugs to treat migraine, ergotamine (Gynergen) and dihydroergotamine (Dihydergot), did not appear on the market until 1921 and 1946, respectively. Both drugs originated from Sandoz, the world’s leading pharmaceutical company in ergot alkaloid research at the time. Historically, ergot alkaloids had been primarily used in obstetrics, but with methysergide (1-methyl-lysergic acid 1′-hydroxy-butyl-(2S)-amide), it became apparent that they also held some potential in migraine treatment. Methysergide was the first effective prophylactic drug developed specifically to prevent migraine attacks in 1959. On the basis of significantly improved knowledge of migraine pathophysiology and the discovery of serotonin and its receptors, Glaxo was able to launch sumatriptan in 1992. It was the first member from the class of triptans, which are selective 5-HT1B/1D receptor agonists. Recent innovations in acute and preventive migraine therapy include lasmiditan, a selective 5-HT1F receptor agonist from Eli Lilly, the gepants, which are calcitonin gene-related peptide (CGRP) receptor antagonists discovered at Merck & Co and BMS, and anti-CGRP/receptor monoclonal antibodies from Amgen, Pfizer, Eli Lilly, and others.

Graphical abstract

Revisiting Migraine: The Evolving Pathophysiology and the Expanding Management Armamentarium

Migraine affects about one billion people worldwide yearly and is one of the most common neurologic illnesses, with a high prevalence and morbidity, particularly among young adults and females. Migraine is associated with many comorbidities, including stress, sleep difficulties, and suicidal ideation. Migraine, despite its widespread occurrence, is underdiagnosed and undertreated. Because of the complicated and primarily unknown mechanisms of migraine formation, several social and biological risk factors, such as hormone imbalances, genetic and epigenetic impacts, and cardiovascular, neurological, and autoimmune illnesses, have been proposed. Through the mid-20th century diversion of the now-defunct vascular theory, the pathophysiology of migraine has developed from a historical study of the "humours" to a distinct entity as a neurological disorder. The range of therapeutic targets has broadened significantly, increasing the number of specialized clinical trials. Understanding the biology of migraine through careful research has resulted in the identification of major therapeutic classes: (i) triptans, serotonin 5-HT1B/1D receptor agonists, (ii) gepants, calcitonin gene-related peptide (CGRP) receptor antagonists, (iii) ditans, 5-HT1F receptor agonists, (iv) CGRP monoclonal antibodies, and (v) glurants, mGlu5 modulators, with further targets being explored. This review provides a comprehensive overview of the most recent literature on epidemiology and risk factors and exposes knowledge gaps.

Lasmiditan and 5-Hydroxytryptamine in the rat trigeminal system; expression, release and interactions with 5-HT1 receptors

Background

5-Hydroxytryptamine (5-HT) receptors 1B, 1D and 1F have key roles in migraine pharmacotherapy. Selective agonists targeting these receptors, such as triptans and ditans, are effective in aborting acute migraine attacks and inhibit the in vivo release of calcitonin gene-related peptide (CGRP) in human and animal models. The study aimed to examine the localization, genetic expression and functional aspects of 5- HT_1B/1D/1F receptors in the trigeminal system in order to further understand the molecular sites of action of triptans (5-HT_1B/1D) and ditans (5-HT_1F).

Methods

Utilizing immunohistochemistry, the localization of 5-HT and of 5-HT_1B/1D/1F receptors was examined in rat trigeminal ganglion (TG) and combined with quantitative polymerase chain reaction to quantify the level of expression for 5-HT_1B/1D/1F receptors in the TG. The functional role of these receptors was examined ex vivo with a capsaicin/potassium induced 5-HT and CGRP release.

Results

5-HT immunoreactivity (ir) was observed in a minority of CGRP negative C-fibres, most neuron somas and faintly in A-fibres and Schwann cell neurolemma. 5-HT_1B/1D receptors were expressed in the TG, while the 5-HT_1F receptor displayed a weak ir. The 5-HT_1D receptor co-localized with receptor activity-modifying protein 1 (RAMP1) in Aδ-fibres in the TG, while 5-HT_1B-ir was weakly expressed and 5-HT_1F-ir was not detected in these fibres. None of the 5-HT₁ receptors co-localized with CGRP-ir in C-fibres.

5-HT_1D receptor mRNA was the most prominently expressed, followed by the 5-HT_1B receptor and lastly the 5-HT_1F receptor. The 5-HT_1B and 5-HT_1D receptor antagonist, GR127935, could reverse the inhibitory effect of Lasmiditan (a selective 5-HT_1F receptor agonist) on CGRP release in the soma-rich TG but not in soma-poor TG or dura mater. 5-HT release in the soma-rich TG, and 5-HT content in the baseline samples, negatively correlated with CGRP levels, showing for the first time a physiological role for 5-HT induced inhibition.

Conclusion

This study reveals the presence of a subgroup of C-fibres that store 5-HT. The data shows high expression of 5-HT_1B/1D receptors and suggests that the 5-HT_1F receptor is a relatively unlikely target in the rat TG. Furthermore, Lasmiditan works as a partial agonist on 5-HT_1B/1D receptors in clinically relevant dose regiments.

Supplementary Information

The online version contains supplementary material available at 10.1186/s10194-022-01394-z.

Metabolic activation of zolmitriptan mediated by CYP2D6

Zolmitriptan (ZOL), a member of triptans, has been used for the treatment of migraine with definite therapeutic effects. However, several cases of liver injury associated with ZOL have been reported and the underlying mechanisms remain unclear.The present study aimed to investigate the metabolic activation of ZOL in vitro and in vivo. ZOL-derived glutathione (GSH) and N-acetyl cysteine (NAC) conjugates were detected in rat liver microsomal incubations. In addition, the GSH and NAC conjugates were also found in bile and urine of rats given ZOL, respectively.ZOL-derived GSH conjugate M1 was also observed in ZOL-treated rat primary hepatocytes, and the formation of M1 was inhibited by pre-cultured with quinidine (a selective inhibitor of CYP2D6). Combining with recombinant P450 enzymes incubations, we found that CYP2D6 was the predominant enzyme responsible for the metabolic activation of ZOL.ZOL can be metabolized to an α,β-unsaturated imine intermediate by CYP2D6. Pre-treatment of primary hepatocytes with quinidine was able to reverse ZOL-induced cytotoxicity. The finding facilitates the understanding of the mechanisms involved in ZOL-associated liver adverse reactions.

Utilization of B12 for the treatment of chronic migraine

Chronic migraine is a particular classification of a headache that is typically unilateral and pulsatile and lasts for at least 3 months. Owing to its high prevalence and detrimental impact on personal, social, and economic aspects of patient lives, much desire has gone into fully understanding the pathogenesis of migraine, and to search for therapeutic agents. In addition to current therapeutics such as triptans, ergotamine, and monoclonal antibodies targeting calcitonin gene-related peptide receptors, vitamin B12 has been investigated for its possible use as a prophylactic agent for migraines. Specifically, the observed effects of vitamin B12 on nitric oxide and homocysteine prompt further investigation of its underlying mechanisms in migraine pathophysiology. In this comprehensive review, we provide a brief overview of migraines and current therapies while focusing on the promising role of vitamin B12 as a possible treatment option for chronic migraine management.

The need for new acutely acting antimigraine drugs: moving safely outside acute medication overuse

Background

The treatment of migraine is impeded by several difficulties, among which insufficient headache relief, side effects, and risk for developing medication overuse headache (MOH). Thus, new acutely acting antimigraine drugs are currently being developed, among which the small molecule CGRP receptor antagonists, gepants, and the 5-HT_1F receptor agonist lasmiditan. Whether treatment with these drugs carries the same risk for developing MOH is currently unknown.

Main body

Pathophysiological studies on MOH in animal models have suggested that decreased 5-hydroxytryptamine (5-HT, serotonin) levels, increased calcitonin-gene related peptide (CGRP) expression and changes in 5-HT receptor expression (lower 5-HT_1B/D and higher 5-HT_2A expression) may be involved in MOH. The decreased 5-HT may increase cortical spreading depression frequency and induce central sensitization in the cerebral cortex and caudal nucleus of the trigeminal tract. Additionally, low concentrations of 5-HT, a feature often observed in MOH patients, could increase CGRP expression. This provides a possible link between the pathways of 5-HT and CGRP, targets of lasmiditan and gepants, respectively. Since lasmiditan is a 5-HT_1F receptor agonist and gepants are CGRP receptor antagonists, they could have different risks for developing MOH because of the different (over) compensation mechanisms following prolonged agonist versus antagonist treatment.

Conclusion

The acute treatment of migraine will certainly improve with the advent of two novel classes of drugs, i.e., the 5-HT_1F receptor agonists (lasmiditan) and the small molecule CGRP receptor antagonists (gepants). Data on the effects of 5-HT_1F receptor agonism in relation to MOH, as well as the effects of chronic CGRP receptor blockade, are awaited with interest.

Migraine Treatment: Current Acute Medications and Their Potential Mechanisms of Action

Migraine is a common and disabling primary headache disorder with a significant socioeconomic burden. The management of migraine is multifaceted and is generally dichotomized into acute and preventive strategies, with several treatment modalities. The aims of acute pharmacological treatment are to rapidly restore function with minimal recurrence, with the avoidance of side effects. The choice of pharmacological treatment is individualized, and is based on the consideration of the characteristics of the migraine attack, the patient's concomitant medical problems, and treatment preferences. Notwithstanding, a good understanding of the pharmacodynamic and pharmacokinetic properties of the various drug options is essential to guide therapy. The current approach and concepts relevant to the acute pharmacological treatment of migraine will be explored in this review.

Acute treatment of migraines

Migraine is a prevalent and disabling brain disorder that costs billions of dollars annually in direct healthcare costs, and school and work absenteeism and presenteeism. The objective of acute treatment is a cost-effective, rapid restoration of functional ability, with minimal recurrence and adverse effects. The acute treatment of migraine includes specific drugs, which currently all have vasoconstrictive effects (dihydroergotamine and triptans), and nonspecific drugs that include paracetamol (acetaminophen), combination analgesics, non-steroidal anti-inflammatory drugs (NSAIDs), dopamine antagonists, narcotics and corticosteroids. NSAIDs have both peripheral and central effects on reversing migraine, and so may represent the best alternative for patients who cannot use triptans and ergots due to vascular contraindications. Narcotics and habituating medications should be avoided in the acute treatment of migraine, as the risk for transformation to chronic daily headache is excessively high at a relatively infrequent rate of exposure.

Therapeutic applications for subcutaneous triptans in the acute treatment of migraine

BACKGROUND

The features of migraine attacks and the contexts in which migraine attacks occur vary from attack to attack and from patient to patient. Current treatment strategies, which are dominated by the use of oral forms of migraine medication, do not address this patient-to-patient and attack-to-attack heterogeneity. While current therapies, and, in particular, oral triptan tablets can be effective for many types of migraine attacks that a patient can experience, they may not be the optimum treatment for every migraine in every patient.

SCOPE

This clinical review of subcutaneous sumatriptan discusses its characteristics, efficacy, and tolerability and considers its place in clinical practice. The review focuses particularly on several specific clinical settings in which subcutaneous sumatriptan might be a more appropriate therapeutic choice than the oral triptan tablet.

FINDINGS

Of the triptan formulations, subcutaneous sumatriptan is the most rapidly absorbed and demonstrates a favorable pharmacokinetic profile. Data from randomized, double-blind, clinical trials and studies of patients' perceptions and preferences suggest that subcutaneous sumatriptan can be particularly useful to help restore normal work functioning, for migraine attacks that cannot be treated early in their course, for migraine attacks associated with gastrointestinal symptoms, such as nausea or vomiting, and for difficult-to-treat migraines, including early-morning migraine and menstrual migraine. The majority of patients (9 in 10) trying subcutaneous sumatriptan indicated that they will use it again. Patients not fully satisfied with previous triptan therapy reported enhanced satisfaction with, and confidence in, treatment after trying subcutaneous sumatriptan.

CONCLUSIONS

By virtue of their availability as multiple compounds and in multiple formulations including oral, intranasal, and injectable forms, triptans can be used to customize migraine therapy to the individual patient and the individual migraine attack. Due to its route of delivery and favorable pharmacokinetic profile, subcutaneous triptans may represent an attractive alternative for specific clinical settings. Subcutaneous sumatriptan can play a key role in maximizing likelihood of pain-free response and rapid return to normal daily activities and, as such, should be considered an important part of the treatment armamentarium for migraine.

Chronic migraine classification: current knowledge and future perspectives

In the field of so-called chronic daily headache, it is not easy for migraine that worsens progressively until it becomes daily or almost daily to find a precise and universally recognized place within the current international headache classification systems. In line with the 2006 revision of the second edition of the International Classification of Headache Disorders (ICHD-2R), the current prevailing opinion is that this headache type should be named chronic migraine (CM) and be characterized by the presence of at least 15 days of headache per month for at least 3 consecutive months, with headache having the same clinical features of migraine without aura for at least 8 of those 15 days. Based on much evidence, though, a CM with the above characteristics appears to be a heterogeneous entity and the obvious risk is that its definition may be extended to include a variety of different clinical entities. A proposal is advanced to consider CM a subtype of migraine without aura that is characterized by a high frequency of attacks (10-20 days of headache per month for at least 3 months) and is distinct from transformed migraine (TM), which in turn should be included in the classification as a complication of migraine. Therefore, CM should be removed from its current coding position in the ICHD-2 and be replaced by TM, which has more restrictive diagnostic criteria (at least 20 days of headache per month for at least 1 year, with no more than 5 consecutive days free of symptoms; same clinical features of migraine without aura for at least 10 of those 20 days).

Feverfew Extracts and Parthenolide Irreversibly Inhibit Vascular Responses of the Rabbit Aorta

Samples prepared from chloroform extracts of fresh leaves of feverfew (Tanacetum parthenium) strongly inhibited responses of rabbit aortic rings to phenylephrine, 5-hydroxytryptamine, thromboxane mimetic U46619 (9,11-dideoxy-11α,9α-epoxy-methano-PGF2α), and angiotensin II, but the inhibition to contractions induced by potassium depolarization was much less. The inhibition was concentration- and time-dependent, non-competitive, and irreversible, and also occurred in endothelium-denuded preparations. The feverfew extracts also caused a progressive loss of tone of pre-contracted aortic rings and appeared to impair the ability of acetylcholine to induce endothelium-dependent relaxations of the tissue. These effects were mimicked by a purified preparation of an α-methylenebutyrolactone, parthenolide, obtained from the extract. Our results demonstrate a nonspecific and potentially toxic response to feverfew on the vasculature.

Serotonin 5-HT7 receptor agents: Structure-activity relationships and potential therapeutic applications in central nervous system disorders

Since its discovery in the 1940s in serum, the mammalian intestinal mucosa, and in the central nervous system, serotonin (5-HT) has been shown to be involved in virtually all cognitive and behavioral human functions, and alterations in its neurochemistry have been implicated in the etiology of a plethora of neuropsychiatric disorders. The cloning of 5-HT receptor subtypes has been of importance in enabling them to be classified as specific protein molecules encoded by specific genes. The 5-HT(7) receptor is the most recently classified member of the serotonin receptor family. Since its identification, it has been the subject of intense research efforts driven by its presence in functionally relevant regions of the brain. The availability of some selective antagonists and agonists, in combination with genetically modified mice lacking the 5-HT(7) receptor, has allowed for a better understanding of the pathophysiological role of this receptor. This paper reviews data on localization and pharmacological properties of the 5-HT(7) receptor, and summarizes the results of structure-activity relationship studies aimed at the discovery of selective 5-HT(7) receptor ligands. Additionally, an overview of the potential therapeutic applications of 5-HT(7) receptor agonists and antagonists in central nervous system disorders is presented.

Why pharmacokinetic differences among oral triptans have little clinical importance: a comment

Triptans, selective 5-HT1B/1D receptor agonists, are specific drugs for the acute treatment of migraine that have the same mechanism of action. Here, it is discussed why the differences among kinetic parameters of oral triptans have proved not to be very important in clinical practice. There are three main reasons: (1) the differences among the kinetic parameters of oral triptans are smaller than what appears from their average values; (2) there is a large inter-subject, gender-dependent, and intra-subject (outside/during the attack) variability of kinetic parameters related to the rate and extent of absorption, i.e., those which are considered as critical for the response; (3) no dose-concentration–response curves have been defined and it is, therefore, impossible both to compare the kinetics of triptans, and to verify the objective importance of kinetic differences; (4) the importance of kinetic differences is outweighed by non-kinetic factors of variability of response to triptans. If no oral formulations are found that can allow more predictable pharmacokinetics, the same problems will probably also arise with new classes of drugs for the acute treatment of migraine.

The 5-HT7 receptor and disorders of the nervous system: an overview

RATIONALE

The 5-HT(7) receptor is a more recently discovered G-protein-coupled receptor for serotonin. The functions and possible clinical relevance of this receptor are not yet fully understood.

OBJECTIVE

The present paper reviews to what extent the use of animal models of human psychiatric and neurological disorders have implicated the 5-HT(7) receptor in such disorders. The studies have used a combination of pharmacological and genetic tools targeting the receptor to evaluate effects on behavior.

RESULTS

Models of anxiety and schizophrenia have yielded mixed results with no clear role for the 5-HT(7) receptor described in these disorders. Some data are available for epilepsy, migraine, and pain but it is still very early to draw any definitive conclusions. There is a considerable amount of evidence supporting a role for the 5-HT(7) receptor in depression. Both blockade and inactivation of the receptor have resulted in an antidepressant-like profile in models of depression. Supporting evidence has also been obtained in sleep studies. Especially interesting are the augmented effects achieved by combining antidepressants and 5-HT(7) receptor antagonists. The antidepressant effect of amisulpride has been shown to most likely be mediated by the 5-HT(7) receptor.

CONCLUSIONS

The use of pharmacological and genetic tools in preclinical animal models strongly supports a role for the 5-HT(7) receptor in depression. Indirect evidence exists showing that 5-HT(7) receptor antagonism is clinically useful in the treatment of depression. Available data also indicate a possible involvement of the 5-HT(7) receptor in anxiety, epilepsy, pain, and schizophrenia.

5-HT7 receptor-mediated dilatation in the middle meningeal artery of anesthetized rats

Topical administration of 5-carboxamidotryptamine (5-CT; 0.01-1000 microM) to the exposed dura mater encephali of anesthetized rats produced decreases in blood pressure and dilatation in the middle meningeal artery. Pretreatment with the 5-HT(1B/1D) receptor antagonist, N-[4-methoxy-3-(4-methyl-1-piperazinyl) phenyl]-2'-methyl-4'-(5-methyl-1,2,4-oxadiazol-3-yl) [1,1-biphenyl]-4-carboxamide hydrochloride monohydrate (GR-127935; 1 mg/kg, i.v.), unmasked meningeal dilator responses to lower concentrations of 5-CT, and attenuated those to higher concentrations; GR-127935 also inhibited 5-CT-induced hypotension. The 5-HT7 receptor antagonist, (R)-1-{(3-hydroxyphenyl)sulfonyl}-2-{2-(2-(4-methyl-1-piperidinyl) ethyl} pyrrolidine (SB-269970; 1 mg/kg, i.v.), strongly inhibited dilator and hypotensive responses to 5-CT; the combination of GR-127935+SB-269970 (1 mg/kg, i.v., each) further inhibited meningeal and hypotensive responses. Thus, 5-CT may produce dilatation in the middle meningeal artery via 5-HT7 receptors; complex effects appear to involve 5-HT(1B/1D) receptors.

Development and application of hybrid structure based method for efficient screening of ligands binding to G-protein coupled receptors

G-protein coupled receptors (GPCRs) comprise a large superfamily of proteins that are targets for nearly 50% of drugs in clinical use today. In the past, the use of structure-based drug design strategies to develop better drug candidates has been severely hampered due to the absence of the receptor's three-dimensional structure. However, with recent advances in molecular modeling techniques and better computing power, atomic level details of these receptors can be derived from computationally derived molecular models. Using information from these models coupled with experimental evidence, it has become feasible to build receptor pharmacophores. In this study, we demonstrate the use of the Hybrid Structure Based (HSB) method that can be used effectively to screen and identify prospective ligands that bind to GPCRs. Essentially; this multi-step method combines ligand-based methods for building enriched libraries of small molecules and structure-based methods for screening molecules against the GPCR target. The HSB method was validated to identify retinal and its analogues from a random dataset of approximately 300,000 molecules. The results from this study showed that the 9 top-ranking molecules are indeed analogues of retinal. The method was also tested to identify analogues of dopamine binding to the dopamine D2 receptor. Six of the ten top-ranking molecules are known analogues of dopamine including a prodrug, while the other thirty-four molecules are currently being tested for their activity against all dopamine receptors. The results from both these test cases have proved that the HSB method provides a realistic solution to bridge the gap between the ever-increasing demand for new drugs to treat psychiatric disorders and the lack of efficient screening methods for GPCRs.

Prevalence of migraine and response to sumatriptan in patients self-reporting tension/stress headache

OBJECTIVE

This study was conducted to evaluate the prevalence of migraine and its responsiveness to migraine-specific therapy in patients with self-reported tension-type headache.

METHODS

Patients were adults (n = 423) consulting one of 54 North American study sites including primary care clinics, neurology clinics, and headache clinics. The study comprised an initial diagnosis phase to determine the headache diagnosis of patients entering the study with self-reported tension/stress headache, including that previously diagnosed by a health care provider. Patients reporting tension/stress headache were evaluated and diagnosed as having migraine with or without aura, probable migraine, tension-type headache, or another headache type. Exclusion criteria included prior diagnosis of migraine or probable migraine and the presence of headache for at least 15 days monthly during either of the 2 months before screening. The initial phase was followed by a randomized, double-blind treatment phase to evaluate the efficacy of sumatriptan 100 mg tablets for the treatment of a single migraine attack in those meeting International Headache Society (IHS) criteria for migraine during the diagnosis phase.

RESULTS

Of 423 patients reporting tension/stress headache at study entry, 84% (n = 357) were diagnosed at the clinic visit as fulfilling IHS criteria for migraine without aura or migraine with aura, and 65% (n = 276) were diagnosed with migraine only (i.e., with no other concurrent headache diagnosis). Three hundred thirty-two (332) patients entered the double-blind treatment phase. Headache relief rates 2h post-dose, the primary efficacy endpoint, did not significantly differ between sumatriptan and placebo (p = 0.099). However, improvements were significantly (p < 0.05) greater with sumatriptan than placebo on several other headache-related efficacy measures.

CONCLUSIONS

Migraine headache may go unrecognized in patients with self-reported tension headache. Among patients having self-reported tension headache and diagnosed with migraine during the study, response to acute treatment with sumatriptan was inconclusive. Improvement with sumatriptan versus placebo was observed for some measures and not for others. The results should be interpreted in the context of study limitations including use of patient self-reports to assess headache diagnosis and possible lack of representativeness arising from the predominantly white sample.

Kynurenine aminotransferase in the supratentorial dura mater of the rat: effect of stimulation of the trigeminal ganglion

Electrical stimulation of the trigeminal ganglion has been widely used as a model of nociception, characterizing migraine. This treatment is known to evoke release of neuropeptides and neurotransmitters from nerve fibers of the dura mater. On the basis of immunocytochemical investigations, we found that under normal conditions, surface membranes of Schwann cells surrounding nerve fibers in the supratentorial dura mater display kynurenine aminotransferase-immunoreaction (KAT-IR); also KAT-IR are the granules of mast cells and the cytoplasms of macrophages (histiocytes). In consequence of stimulation of the trigeminal ganglion, Schwann cells in the dura mater became conspicuously swollen while their KAT-IR decreased considerably; also KAT-IR of mast cells and macrophages decreased significantly. At the same time, nitric oxide synthase (NOS)-IR of nerve fibers in the dura mater increased, suggesting release of nitric oxide (NO), this is known to be involved in NMDA receptor activation leading to vasodilation followed by neurogenic inflammation. Because kynurenic acid (KYNA) is an antagonist of NMDA receptors, we hypothesize that KYNA and its synthesizing enzyme, KAT, may play a role in the prevention of migraine attacks.

Novel potent 5-HT(1F) receptor agonists: structure-activity studies of a series of substituted N-[3-(1-methyl-4-piperidinyl)-1H-pyrrolo[3,2-b]pyridin-5-yl]amides

Compound 1a (LY334370), a selective 5-HT(1F) receptor agonist (SSOFRA), inhibited dural inflammation in the neurogenic plasma protein extravasation model of migraine and demonstrated clinical efficacy for the acute treatment of migraine. Although 1a was greater than 100-fold selective over both the 5-HT(1B) and 5-HT(1D) receptors, it exhibited appreciable 5-HT(1A) receptor affinity. Described here is the synthesis and evaluation of a series of pyrrolo[2,3-c]pyridine and pyrrolo[3,2-b]pyridine (2a and 3a) as well as pyrrolo[3,2-d]pyrimidine (4a) analogues of 1a, compounds prepared in an effort to identify SSOFRAs with improved selectivity over other 5-HT(1) receptor subtypes. The pyrrolo[3,2-b]pyridine analogue 3a showed high 5-HT(1F) receptor affinity but offered no improvement in selectivity compared to 1a. However, the C-5 acetamide derivative, 3b, was greater than 100-fold selective over the 5-HT(1A), 5-HT(1B), and 5-HT(1D) receptors. SAR studies of this series determined that alkylamides in particular exhibited high selectivity for the 5-HT(1F) receptor. Replacement at C-5 with other substituents decreased affinity or selectivity. These SAR studies identified SSOFRAs that demonstrated oral activity in the neurogenic plasma protein extravasation model, a model indicative of antimigraine activity.

Effects of sumatriptan on cerebral blood flow under normo- and hypercapnia in rats

To investigate further the pharmacological mechanism of an anti-migraine drug, sumatriptan, a 5-HT1B/1D receptor agonist, we studied its effect on the cerebral circulation in seven anaesthetized rats, particularly during hypercapnia. After injection of 0.6 or 6.0 microg/kg sumatriptan succinate, no significant change in cerebral blood flow (CBF) was observed either in the striatum or in the parietal cortex. The increase in CBF both in the parietal cortex and the striatum during 5% CO2 inhalation was significantly less when sumatriptan succinate 6.0 microg/kg was injected. Sumatriptan appeared to have a vasoconstrictor effect on the relaxed vessels by CO2 inhalation. This mechanism might be attributable to vasoconstriction through activation of 5-HT1B receptors located in the vascular smooth muscle rather than 5-HT1B receptors in the vascular adventitia.

Triptans: do they differ?

Headache care specialists agree that the introduction of sumatriptan constitutes a major advance in headache therapy, but they differ about whether other triptans offer clinically significant advantages over sumatriptan. This article examines this issue by considering the similarities and differences among triptans.

Is the 5-HT(7) receptor involved in the pathogenesis and prophylactic treatment of migraine?

The mechanisms underlying the pathogenesis of migraine and their possible association with serotonin (5-hydroxytryptamine; 5-HT) have not yet been elucidated. One of the major obstacles in achieving this goal is the lack of information on the mechanisms by which the monoamine could possibly trigger and/or modulate the basic pathophysiological features of the condition, that is, cranial vasodilatation and neurogenic inflammation. This information should provide a useful theoretical framework to insight the nature of the postulated fundamental triggering mechanism in the brain that ultimately results in head pain. Novel avenues for research and drug development may be envisaged upon the recent observations showing that 5-HT is actually able to produce vasodilatation of intra- and extra-cranial blood vessels through a mechanism pharmacologically resembling the 5-HT(7) receptor type, and that the messenger RNA (mRNA) encoding for this receptor is highly expressed in cranial vessels. Other lines of evidence have suggested that the 5-HT(7) receptor may play an excitatory role in neuronal systems and that it may be involved in hyperalgesic pain and neurogenic inflammation. On the basis of these observations, it is proposed that the 5-HT(7) receptor may well represent a link between the abnormal phenomena of 5-HT processing and neurotransmission that are observed in migraine patients, and the vascular and neurogenic alterations that account for migraine headache. This view is supported by the fact that most of the migraine prophylactic 5-HT receptor antagonists display relatively high affinity for the 5-HT(7) receptor, which significantly correlates with their pharmaceutically active oral doses.

Almotriptan increases sustained pain-free outcomes in acute migraine: results from three controlled clinical trials

OBJECTIVE

Evaluate the effect of almotriptan on sustained pain-free outcome in patients with acute migraine.

METHODS

Three randomized, double-blind, placebo-controlled trials of almotriptan for the treatment of acute migraine were examined. Two trials evaluated almotriptan 6.25 mg and 12.5 mg, and the third evaluated almotriptan 12.5 mg and sumatriptan 100 mg. Patients aged 18 to 65 years were instructed to take 1 dose of study medication at the onset of a moderate-to-severe migraine headache. A second dose was allowed for relapse. Sustained pain-free was defined as a decrease in pain severity from moderate or severe at baseline to no pain at 2 hours postdose and without relapse or the use of escape medication between 2 and 24 hours.

RESULTS

A total of 1791 adult migraine sufferers were studied. The proportion of patients achieving a sustained pain-free state was significantly (P<.05) higher in the almotriptan 6.25-mg (21.7% to 22.5%) and 12.5-mg (24.6% to 27.6%) groups than in the placebo group (7.5% to 12.1%). The proportion of patients achieving a sustained pain-free state was comparable between almotriptan 12.5 mg (24.6%) and sumatriptan 100 mg (28.5%) and significantly (P<.05) greater than with placebo (12.1%). Among patients with severe baseline pain, a sustained pain-free state was achieved in significantly more patients (P<.05) with almotriptan 12.5 mg (17.3% to 20.9%) than with placebo (3.1% to 3.2%). Among those with moderate baseline pain, a sustained pain-free state was achieved in significantly more patients (P<.01) with almotriptan 12.5 mg (31.3% to 32.0%) than with placebo (10.2% to 16.1%).

CONCLUSIONS

Almotriptan 12.5 mg is significantly better than placebo and comparable to sumatriptan 100 mg for achieving a sustained pain-free state.

Acute treatment of migraine and the role of triptans

The use of triptans has improved the ability to treat migraine successfully compared with older treatments. Speed of relief, consistency of effect, and good tolerability have been the hallmarks of these agents. All of the currently available triptans have comparable efficacy and tolerability. Variables between the agents may lead to one agent or dose form being preferred over another in various clinical scenarios. The triptans that are forthcoming may improve on these options through enhanced efficacy rates, tolerability, and headache recurrence rates. There exist increasing options for migraine treatment that may further improve the clinical effects of the older and newer triptans through early treatment of migraine at the stages of mild migraine pain, or even during the prodromal phase of the attack. Additionally, recent work suggests that mini-prophylaxis of migraine at the menses is a highly successful treatment option with the triptans. In this age of managed care, providing cost-effective treatment of headache will take on increasing importance. Techniques such as stratification of acute treatments may enhance cost-effective care, whereas ready availability of the triptans may lead to significant improvements in utilization of parameters such as office visits, emergency room treatment, and even hospitalization.

Triptans in migraine: a comparative review of pharmacology, pharmacokinetics and efficacy

Triptans are a new class of compounds developed for the treatment of migraine attacks. The first of the class, sumatriptan, and the newer triptans (zolmitriptan, naratriptan, rizatriptan, eletriptan, almotriptan and frovatriptan) display high agonist activity at mainly the serotonin 5-HT1B and 5-HT1D receptor subtypes. As expected for a class of compounds developed for affinity at a specific receptor, there are minor pharmacodynamic differences between the triptans. Sumatriptan has a low oral bioavailability (14%) and all the newer triptans have an improved oral bioavailability and for one, risatriptan, the rate of absorption is faster. The half-lives of naratriptan, eletriptan and, in particular, frovatriptan (26 to 30h) are longer than that of sumatriptan (2h). These pharmacokinetic improvements of the newer triptans so far seem to have only resulted in minor differences in their efficacy in migraine. Double-blind, randomised clinical trials (RCTs) comparing the different triptans and triptans with other medication should ideally be the basis for judging their place in migraine therapy. In only 15 of the 83 reported RCTs were 2 triptans compared, and in 11 trials triptans were compared with other drugs. Therefore, in all placebo-controlled randomised clinical trials, the relative efficacy of the triptans was also judged by calculating the therapeutic gain (i.e. percentage response for active minus percentage response for placebo). The mean therapeutic gain with subcutaneous sumatriptan 6mg (51%) was more than that for all other dosage forms of triptans (oral sumatriptan 100mg 32%; oral sumatriptan 50mg 29%: intranasal sumatriptan 20mg 30%; rectal sumatriptan 25mg 31%; oral zolmitriptan 2.5mg 32%; oral rizatriptan 10mg 37%; oral eletriptan 40mg 37%; oral almotriptan 12.5mg 26%). Compared with oral sumatriptan 100mg (32%), the mean therapeutic gain was higher with oral eletriptan 80mg (42%) but lower with oral naratriptan 2.5mg (22%) or oral frovatriptan 2.5mg (16%). The few direct comparative randomised clinical trials with oral triptans reveal the same picture. Recurrence of headache within 24 hours after an initial successful response occurs in 30 to 40% of sumatriptan-treated patients. Apart from naratriptan, which has a tendency towards less recurrence, there appears to be no consistent difference in recurrence rates between the newer triptans and sumatriptan. Rizatriptan with its shorter time to maximum concentration (tmax) tended to produce a quicker onset of headache relief than sumatriptan and zolmitriptan. The place of triptans compared with non-triptan drugs in migraine therapy remains to be established and further RCTs are required.

Effect of naratriptan on myocardial blood flow and coronary vasodilator reserve in migraineurs

BACKGROUND

Migraine drugs can produce adverse cardiac effects. The authors have demonstrated previously that ergotamine can lead to a significant reduction of hyperemic myocardial blood flow, but little is known about the effect of the newer serotonin analogues. Coronary artery constriction caused by serotonin or its analogues is mediated mainly by 5HT2 receptors. The selective 5HT1B/1D agonist naratriptan has no significant activity at 5HT2 receptors; however, like all 5HT1B/1D agonists developed for the acute treatment of migraine, naratriptan could potentially constrict coronary arteries by activation of 5HT1B receptors.

METHODS

The effects on myocardial blood flow of subcutaneous naratriptan 1.5 mg compared with placebo were assessed under resting and hyperemic conditions with PET using oxygen-15 labeled water during two separate visits. This study was a randomized, double-blind, placebo-controlled crossover trial in 34 migraine subjects with no evidence of ischemic heart disease, studied outside a migraine attack.

RESULTS

Naratriptan did not differ significantly from placebo in its effects on resting myocardial blood flow, but did evoke a small, significant fall in hyperemic myocardial blood flow (-13% versus placebo) and an increase in hyperemic coronary resistance (+19% versus placebo) without any signs or symptoms suggestive of myocardial ischemia. Naratriptan did not significantly affect the coronary vasodilator reserve (hyperemic/resting blood flow) compared with placebo.

CONCLUSIONS

These results show that at therapeutic doses, naratriptan exerts only a minor effect on myocardial blood flow, coronary vasodilator reserve, or coronary resistance among subjects with no evidence of ischemic heart disease. These results should not be extrapolated to patients with coronary artery disease, in whom all 5HT1 agonists for migraine are contraindicated.

Pharmacological aspects of experimental headache models in relation to acute antimigraine therapy

The last decade has witnessed a tremendous progress in the acute therapy of migraine, with sumatriptan, belonging to a new class of drugs, now known as 5-HT(1B/1D/1F) receptor agonists, leading the way. The undoubted success of sumatriptan stimulated the development of new triptans as well as other suitable pharmacological tools and experimental models to probe into complex migraine mechanisms. In this review, we discuss the main experimental models for migraine, against the background of the disease pathophysiology and 5-HT receptors considered most important for migraine therapy. We believe that the use of these migraine models will provide even better treatment for migraine patients in the next millennium.

Pharmacological evidence for the 5-HT7 receptor mediating smooth muscle relaxation in canine cerebral arteries

1. We investigated in the present study whether 5-HT is able to exert direct relaxant responses in canine basilar and middle cerebral arteries via the 5-HT7 receptor. 2. In arterial rings deprived of endothelium and pre-contracted with prostaglandin F2 alpha (2 microM), 5-HT, 5-carboxamidotryptamine (5-CT), 5-methoxytryptamine, sumatriptan or alpha-methyl-5-HT produced further increase in tone and/or slight relaxation. Blockade of 5-HT1B 1D and 5-HT2A receptors with GR127935 (1 microM) and ketanserin (0.1 microM), respectively, antagonized the vasoconstrictor component of the response and unmasked a concentration-dependent relaxation to 5-HT, 5-CT and 5-methoxytryptamine; sumatriptan and alpha-methyl-5-HT remained inactive as relaxant agonists. The rank order of agonist potency in both arteries was 5-CT > 5-HT > 5-methoxytryptamine >> sumatriptan > or = alpha-methyl-5-HT. 3. In dog basilar artery, pre-incubated with GR127935 (1 microM) and ketanserin (0.1 microM) and precontracted with prostaglandin F2 alpha (2 microM), the 5-HT7 ligands, clozapine (1 microM), mesulergine (0.3 microM), methiothepin (3 nM), risperidone (3 nM), spiperone (1 microM) and LY215840 (10-100 nM), produced significant rightward shifts of the concentration-response curves for 5-HT and 5-CT. Only methiothepin and risperidone reduced significantly the maximum relaxant response (Emax), whilst the other drugs behaved as competitive antagonists with affinity values (pKB) that significantly correlated with their binding affinity (pKi) at recombinant 5-HT7 receptors. 4. These data disclosing the involvement of the 5-HT7 receptor in cerebrovascular relaxation may be strongly relevant in the light of: (1) the involvement of 5-HT in migraine; (2) the putative linkage between cephalovascular vasodilatation and migraine headache; and (3) the relatively high 5-HT7 receptor affinity of migraine prophylactic 5-HT antagonists.

The induction of pain: an integrative review

The highly disagreeable sensation of pain results from an extraordinarily complex and interactive series of mechanisms integrated at all levels of the neuroaxis, from the periphery, via the dorsal horn to higher cerebral structures. Pain is usually elicited by the activation of specific nociceptors ('nociceptive pain'). However, it may also result from injury to sensory fibres, or from damage to the CNS itself ('neuropathic pain'). Although acute and subchronic, nociceptive pain fulfils a warning role, chronic and/or severe nociceptive and neuropathic pain is maladaptive. Recent years have seen a progressive unravelling of the neuroanatomical circuits and cellular mechanisms underlying the induction of pain. In addition to familiar inflammatory mediators, such as prostaglandins and bradykinin, potentially-important, pronociceptive roles have been proposed for a variety of 'exotic' species, including protons, ATP, cytokines, neurotrophins (growth factors) and nitric oxide. Further, both in the periphery and in the CNS, non-neuronal glial and immunecompetent cells have been shown to play a modulatory role in the response to inflammation and injury, and in processes modifying nociception. In the dorsal horn of the spinal cord, wherein the primary processing of nociceptive information occurs, N-methyl-D-aspartate receptors are activated by glutamate released from nocisponsive afferent fibres. Their activation plays a key role in the induction of neuronal sensitization, a process underlying prolonged painful states. In addition, upon peripheral nerve injury, a reduction of inhibitory interneurone tone in the dorsal horn exacerbates sensitized states and further enhance nociception. As concerns the transfer of nociceptive information to the brain, several pathways other than the classical spinothalamic tract are of importance: for example, the postsynaptic dorsal column pathway. In discussing the roles of supraspinal structures in pain sensation, differences between its 'discriminative-sensory' and 'affective-cognitive' dimensions should be emphasized. The purpose of the present article is to provide a global account of mechanisms involved in the induction of pain. Particular attention is focused on cellular aspects and on the consequences of peripheral nerve injury. In the first part of the review, neuronal pathways for the transmission of nociceptive information from peripheral nerve terminals to the dorsal horn, and therefrom to higher centres, are outlined. This neuronal framework is then exploited for a consideration of peripheral, spinal and supraspinal mechanisms involved in the induction of pain by stimulation of peripheral nociceptors, by peripheral nerve injury and by damage to the CNS itself. Finally, a hypothesis is forwarded that neurotrophins may play an important role in central, adaptive mechanisms modulating nociception. An improved understanding of the origins of pain should facilitate the development of novel strategies for its more effective treatment.

5-HT1-like receptors: a time to bid goodbye

It is exactly half a century ago that 5-hydroxytryptamine was discovered and over four decades ago two types of 5-HT receptors were described. In this article, Pramod Saxena, Peter De Vries and Carlos Villalón trace the development of the modern classification and nomenclature of 5-HT receptors, which now include more than a dozen subtypes. In doing so, they advocate that the so-called '5-HT1-like' receptors, having been shown to be a heterogeneous population of 5-HT1B, 5-HT1D and 5-HT7 receptors, are now redundant.

BMS-181885, a 5-HT1B/1D receptor ligand, in experimental models predictive of antimigraine activity and coronary side-effect potential

Many acutely acting antimigraine drugs have the ability to constrict porcine arteriovenous anastomoses as well as the human isolated coronary artery. These two experimental models seem to serve as indicators, respectively, for the therapeutic and coronary side-effect potential of the compounds. Using these two models, we have investigated the effects of BMS-181885 (3-[3-[4-(5-methoxy-4-pyrimidyl)-1-piperazinyl]propyl]-5-(1,2-dioxo-4-me thyl-3-cyclobuten-3-yl)amino-1H-indole), a 5-HT1B/1D receptor ligand. In anaesthetised pigs, BMS-181885 (10, 30, 100 and 300 microg kg(-1)) decreased the total carotid blood flow and conduction, exclusively at the expense of the arteriovenous anastomotic fraction as the capillary fraction did in fact increase. The highest dose (300 microg kg(-1)) produced a reduction of 52+/-6% from the baseline arteriovenous anastomotic flow. When carotid haemodynamic changes after a single 100 microg kg(-1)dose of BMS-181885 or sumatriptan were studied at different time-points, BMS-188185 had a longer duration of action. Both BMS-181885 (pD2:7.9+/-0.1; Emax:9+/-3% of the contraction to 100 mM K+) and sumatriptan (pD2:6.3+/-0.1; Emax:28+/-8% of the contraction to 100 mM K+) contracted the human isolated coronary artery. The above results suggest that (i) the longer-lasting vasoconstrictor action of BMS-181885 on porcine carotid arteriovenous anastomoses may be related to its reported slow dissociation from 5-HT1B/1D receptor, and (ii) BMS-181885 should be able to abort migraine headaches in patients. It will be interesting to find out whether these properties are clinically important so that the drug exhibits less headache recurrence and coronary side-effects than sumatriptan.

Cardiovascular activity of A-74283, a 5-hydroxytryptamine 1A agent, in the spontaneously hypertensive rat

A-74283, (+,-)trans-2-(4-(3a,4,4a,6a,7,7a-hexahydro-4,7-etheno-1 H cyclobut [f] isoindol-1,3-dionyl)-butyl)-9-methoxy-2,2,2a,4,5,9b-hexahydr o-1 H-benz[e]isoindol HC1, was studied in receptor binding assays and in the spontaneously hypertensive rat (SHR). In radioligand binding to rat cortex, A-74283 had high affinity (equipotent to 8-OH-DPAT) and high selectivity for 5HT1A receptors compared to 5HT1B sites. In conscious SHR, A-74283 lowered mean arterial pressure (MAP) in a dose-related fashion with a prolonged effect after oral administration of higher doses, but heart rate (HR) was not changed. In anesthetized SHR, i.v. administration of A-74283 decreased MAP and total peripheral resistance, but not cardiac output. Pretreatment of conscious SHR with the selective 5TH1A receptor antagonists spiroxatrine or BMY 7378 reduced the hypotensive effect of A-74283 significantly, but pretreatment with adrenergic antagonists phenoxybenzamine or idazoxan or the 5HT2 receptor blocker ketanserin did not alter the effect of A-74283. Intracisternal administration of A-74283 also decreased MAP; however, A-74283 had no effect on blood pressure in pithed SHR in which blood pressure was supported with vasopressin, in contrast to nitroprusside. These data demonstrate that A-74283 exerts a potent hypotensive effect in SHR via systemic vasodilation originating from a central 5HT1A receptor mechanism. A-74283 may be useful for studying 5HT1A receptors and cardiovascular function.

Detailed mapping of serotonin 5-HT1B and 5-HT1D receptor messenger RNA and ligand binding sites in guinea-pig brain and trigeminal ganglion: clues for function

The similar pharmacology of the 5-HT1B and 5-HT1D receptors, and the lack of selective compounds sufficiently distinguishing between the two receptor subtypes, have hampered functional studies on these receptors. In order to provide clues for differential functional roles of the two subtypes, we performed a parallel localization study throughout the guinea-pig brain and the trigeminal ganglia by means of quantitative in situ hybridization histochemistry (using [35S]-labelled riboprobes probes for receptor messenger RNA) and receptor autoradiography (using a new radioligand [3H]alniditan). The anatomical patterns of 5-HT1B and 5-HT1D receptor messenger RNA were quite different. While 5-HT1B receptor messenger RNA was abundant throughout the brain (with highest levels in the striatum, nucleus accumbens, olfactory tubercle, cortex, hypothalamus, hippocampal formation, amygdala, thalamus, dorsal raphe and cerebellum), 5-HT1D receptor messenger RNA exhibited a more restricted pattern; it was found mainly in the olfactory tubercle, entorhinal cortex, dorsal raphe, cerebellum, mesencephalic trigeminal nucleus and in the trigeminal ganglion. The density of 5-HT(1B/1D) binding sites (combined) obtained with [3H]alniditan autoradiography was high in the substantia nigra, superior colliculus and globus pallidus, whereas lower levels were detected in the caudate-putamen, hypothalamus, hippocampal formation, amygdala, thalamus and central gray. This distribution pattern was indistinguishable from specific 5-HT1B receptor labelling in the presence of ketanserin under conditions to occlude 5-HT1D receptor labelling; hence the latter were below detection level. Relationships between the regional distributions of the receptor messenger RNAs and binding sites and particular neuroanatomical pathways are discussed with respect to possible functional roles of the 5-HT1B and 5-HT1D receptors.

Binding profile of the novel 5-HT1B/1D receptor antagonist, [3H]GR 125,743, in guinea-pig brain: a comparison with [3H]5-carboxamidotryptamine

Native brain 5-HT1B/1D) receptors were studied using the novel antagonist, [3H]GR 125,743 (N-[4-methoxy-3-(4-methylpiperazin-1-yl)phenyl]-3-methyl-4-(4-pyri dyl)benzamide). In guinea-pig striatal membranes, [3H]GR 125,743 displayed rapid association (t1/2 = 4.5 min), high (90%) specific binding and high affinity (K(d) = 0.29 nM), although B(max) values (fmol/mg protein) varied according to brain region-striatum: 199; frontal cortex: 89; hippocampus: 79; cerebellum: 26. In frontal cortex, the B(max) determined with [3H]5-CT ([3H]carboxamidotryptamine) was significantly higher (178; P < 0.05), suggesting that it also labels other binding sites. In striatal membranes, guanylylimidodiphosphate (GppNHp) inhibited [3H]5-CT but not [3H]GR 125,743 binding, suggesting that the latter has antagonist properties. Nevertheless, in competition binding experiments, the pK(i) values obtained with [3H]GR 125,743 and [3H]5-CT for 20 serotonergic ligands, including L 694,247 (2-[5-[3-(4-methylsulphonylamino)benzyl-1,2,4-oxadiazol-5-yl ]-1H-indole-3-yl]ethylamine), GR46,611 (3-[3-(2-dimethylamino-ethyl)-1H-indol-6-yl]-N-(4-methoxybenzyl)acrylami de), sumatriptan and alniditan, were highly correlated (r = 0.99). Ketanserin and ritanserin showed low affinity for [3H]GR 125,743 binding to guinea-pig striatal sites (K(i) = 12600 and 369 nM), suggesting that 5-HT1B (rather than 5-HT1D) receptors are predominantly labelled in this tissue. The present data indicate that [3H]GR 125,743 is a useful tool for studying native 5-HT1B/1D receptors.

New benzocycloalkylpiperazines, potent and selective 5-HT1A receptor ligands

A series of 1-(benzocycloalkyl)-4-(benzamidolkyl)piperazine derivatives was prepared in order to obtain compounds with a high affinity and selectivity for 5-HT1A receptors. The modifications of aromatic substituents, the length of the alkyl chain, and the size of the ring were explored. Most of N-(1,2,3,4-tetrahydronaphthyl)-N'-(benzamidoethyl)piperazines (32-37) were bound to 5-HT1A receptors in a nanomolar range and presented a high degree of selectivity. After resolution, levorotatory enantiomers showed affinity and selectivity higher than those of dextrorotory ones for 5-HT1A sites. The agonist type activity of selected derivatives was also confirmed in vitro on the inhibition of the activation of adenylate cyclase induced by forskolin and, in vivo, on the induction of the lower lip retraction in rats.

5-HT1-like receptor-mediated contraction in the human internal mammary artery

We wished to characterize the 5-hydroxytryptamine (5-HT) receptors mediating vasoconstriction in the human internal mammary artery (IMA). Segments of the IMA obtained from patients undergoing coronary by-pass surgery were suspended in an organ bath and exposed to 5-HT and sumatriptan (SUM), a 5-HT1-like receptor agonist, in the presence and absence of potassium chloride (KCl) and angiotensin II. 5-HT induced concentration-dependent contractions in all quiescent and pre-contracted preparations. SUM induced small contractions in 70% of quiescent IMA rings, whereas it elicited marked and concentration-dependent contractions in all of the preparations given a moderate tone by a threshold concentration of KCl and angiotensin II. The efficacy of SUM was higher in precontracted arteries. Concentration-effect curves (CEC) of 5-HT and SUM were not affected by the 5-HT3-receptor antagonist tropisetron (1 microM). The nonselective antagonist, methiothepin (30 nM), shifted the CEC of SUM to the right. 5-HT2A-receptor antagonist, ketanserin (1 microM) inhibited responses to 5-HT, whereas it affected only the responses to the smaller concentrations of SUM. When methiothepin (30 nM) was applied in the presence of ketanserin (1 microM), a further inhibition in the responses to 5-HT was observed. These results suggest that 5-HT1-like receptors mediate the contractile action of SUM and contribute to that of 5-HT in IMA.

Migraine and cluster headache--their management with sumatriptan: a critical review of the current clinical experience

Sumatriptan is a potent and selective agonist at the vascular 5HT1 receptor which mediates constriction of certain large cranial blood vessels and/or inhibits the release of vasoactive neuropeptides from perivascular trigeminal axons in the dura mater following activation of the trigeminovascular system. The mode of action of this drug in migraine and cluster headache is discussed. On the basis of a detailed review of all published trials and available data from post-marketing studies, the efficacy, safety, tolerability and the place of oral and subcutaneous sumatriptan in the treatment of both conditions are assessed. A number of double-blind clinical trials have demonstrated that sumatriptan 100 mg administered orally is clearly superior to placebo in the acute treatment of migraine headache and achieves significantly greater response rates than ergotamine or aspirin. In other studies, 70 to 80% of patients receiving sumatriptan 6 mg sc experienced relief of migraine headaches by 1 or 2 h after administration, and patients consistently required less rescue medication for unresolved symptoms. Sumatriptan was also effective in relieving associated migraine symptoms like nausea and vomiting. Sumatriptan was equally effective regardless of migraine type or duration of migraine symptoms. Overall, approximately 40% of patients who initially responded to oral or subcutaneous sumatriptan experienced recurrence of their headache usually within 24 h, effectively treated by a further dose of this drug. In 75% of patients with cluster headache treated with sumatriptan 6 mg sc, relief was achieved within 15 min. Based on pooled study data, sumatriptan is generally well tolerated and most adverse events are transient. Adverse events following oral administration include nausea, vomiting, malaise, fatigue and dizziness. With the subcutaneous injection, injection site reactions occur in approximately 30%. Chest syumptoms are reported in 3 to 5% but have been associated with myocardial ischaemia only in rare isolated cases. The recommended dosage of sumatriptan at the onset of migraine symptoms is 100 mg orally or 6 mg subcutaneously. The recommended dosage for cluster headache is 6 mg sumatriptan sc. Sumatriptan must not be given together with vasoconstrictive substances, e.g., ergotamines, or with migraine prophylactics with similar properties, e.g., methysergide. Sumatriptan should not be given during the migraine aura. It is contraindicated in patients with ischaemic heart disease, previous myocardial infarction, Prinzmetal (variant) angina and uncontrolled hypertension.

A comparison of the contractile effects of 5-hydroxytryptamine, sumatriptan and MK-462 on human coronary artery in vitro

1. MK-462 (N,N-dimethyl-2-[5-(1,2,4-triazol-1-ylmethyl)-1H- indol-3-yl]ethylamine) is a novel selective 5-HT1D-receptor agonist which in clinical trials has been shown to be an effective antimigraine agent. As angiographic studies have shown that sumatriptan (an established 5-HT1D-receptor agonist) can cause coronary artery vasoconstriction in patients, we compared the effects of MK-462 with those of 5-HT and those of sumatriptan, on isolated segments of human coronary artery in vitro. 2. Coronary arteries were obtained from explanted hearts from patients (n = 22, 2 females, 20 males, aged 21-60 years) undergoing cardiac transplantation. Endothelium-denuded ring segments of coronary artery, 2mm long were mounted in organbaths for isometric tension recording. For each arterial ring segment, a cumulative concentration-effect curve to either 5-HT, sumatriptan or MK-462 was determined. After maximal response to each agonist had been obtained, ketanserin (a 5-HT2 receptor antagonist) 0.6 microM was added to the tissue bath, followed by methiotepin (0.6 microM) and the reduction in tension produced by the addition of each antagonist was determined. 3. Out of 22 coronary arteries studied, only 10 showed any response (contraction) to 5-HT. Not all arteries which responded to 5-HT contracted in response to both sumatriptan and MK-462 (one ring from each artery being exposed to a single agonist in each case).(ABSTRACT TRUNCATED AT 250 WORDS)

Interrelationships of neurochemicals, estrogen, and recurring headache

Recurring headache syndromes, such as migraine, are common problems for women throughout their adult lives. Headache symptoms often fluctuate over the years that they are present and, for most headache sufferers, these changes seem to occur randomly. For many women, however, chronic headache changes in predictable patterns in relation to alterations in hormonal states. Clinically, headache is often modified during menses, pregnancy, and menopause. Although sex hormones are changing with these clinical events, this paper will present the more important link between altered sex hormones and changes in neurochemicals believed to be responsible for recurring headache syndromes according to the neurobiological theory of migraine.

Serotonin receptors: subtypes, functional responses and therapeutic relevance

Recent, rapid progress in the molecular biology of serotonin (5-HT) receptors requires conceptual re-thinking with respect to receptor classification. Thus, based on operational criteria (agonist and antagonist rank order), as well as transduction mechanisms involved and the structure of the receptor protein, the Nomenclature Committee of the Serotonin Club has proposed the following classification and nomenclature: the main receptor types 5-HT1 to 5-HT4, recombinant receptors (e.g. 5-ht5 to 5-ht7) and 'orphan' receptors. The aim of the present review is to discuss the events leading to this classification, the criteria for and functional responses mediated by various 5-HT receptors, as well as the therapeutic possibilities with 5-HT ligands.

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)