Comparative trial of serotonin antagonists in the management of migraine

Exploring the Tryptophan Metabolic Pathways in Migraine-Related Mechanisms

Migraine is a complex neurovascular disorder, which causes intense socioeconomic problems worldwide. The pathophysiology of disease is enigmatic; accordingly, therapy is not sufficient. In recent years, migraine research focused on tryptophan, which is metabolized via two main pathways, the serotonin and kynurenine pathways, both of which produce neuroactive molecules that influence pain processing and stress response by disturbing neural and brain hypersensitivity and by interacting with molecules that control vascular and inflammatory actions. Serotonin has a role in trigeminal pain processing, and melatonin, which is another product of this pathway, also has a role in these processes. One of the end products of the kynurenine pathway is kynurenic acid (KYNA), which can decrease the overexpression of migraine-related neuropeptides in experimental conditions. However, the ability of KYNA to cross the blood-brain barrier is minimal, necessitating the development of synthetic analogs with potentially better pharmacokinetic properties to exploit its therapeutic potential. This review summarizes the main translational and clinical findings on tryptophan metabolism and certain neuropeptides, as well as therapeutic options that may be useful in the prevention and treatment of migraine.

Pizotifen for the treatment of migraine. A systematic review and meta-analysis

Introduction Pizotifen is an oral drug developed many years ago for the prophylaxis of migraine. Trials on pizotifen are decades old, and there has never been a systematic review and meta-analyses of data from these clinical studies. Methods This is a systematic review and meta-analyses on pizotifen's efficacy and safety for prophylactic migraine treatment. We considered for inclusion only randomized clinical trials (RCTs). A comprehensive electronic search was performed without language, date or publication status restrictions in the formal electronic databases, clinical trial registration platforms and grey literature. Results There were eight RCTs of pizotifen compared either to placebo or to other drugs. Very low certainty of evidence showed that pizotifen seems to be superior to placebo regarding clinical symptoms improvement (Relative risk [RR] 6.00; 95% Confidence interval [CI] 1.63 to 22.03; p = 0.007), but not inferior to naproxen, flunarizine, valproate or clonidine. Weight gain was the most frequent adverse event of pizotifen but there was no difference with placebo (RR 1.92; 95% CI 0.30 to 12.38; 2 RCTs; 142 participants; I2 = 67%; p = 0.49). Conclusion The RCTs of pizotifen were decades old. It is a safe and potentially efficacious inexpensive drug that deserves a better designed, modern clinical trial before being dismissed as an option for migraine therapy. PROSPERO Register: CRD42020194347.

Histamine and migraine revisited: mechanisms and possible drug targets

OBJECTIVE

To review the existing literature on histamine and migraine with a focus on the molecule, its receptors, its use in inducing migraine, and antihistamines in the treatment of migraine.

BACKGROUND

Histamine has been known to cause a vascular type headache for almost a hundred years. Research has focused on antihistamines as a possible treatment and histamine as a migraine provoking agent but there has been little interest in this field for the last 25 years. In recent years two additional histamine (H3 and H4) receptors have been discovered and a series of non-sedating antihistamines have been developed. It is therefore timely to review the field again.

METHODS

For this review the PubMed/MEDLINE database was searched for eligible studies. We searched carefully for all articles on histamine, antihistamines and histamine receptors in relation to migraine and the nervous system. The following search terms were used: histamine, migraine disorders, migraine, headache, antihistamines, histamine antagonists, clinical trials, induced headache, histamine H3 receptor, histamine H4 receptor and pharmacology. Four hundred thirty-six titles were read, 135 abstracts were read, 112 articles were read in full and 53 articles were used in this review. Review process resulted in 12 articles added to a total of 65.

FINDINGS

Early studies of H1 and H2 antihistamines lack scientific strength and show conflicting results. Most of the antihistaminic drugs used in these trials bind also to other receptors which makes it difficult to conclude on the antihistaminic effect. Histamine is an efficient inducer of migraine attacks in migraine patients by an H1 mechanism most likely extracerebrally. These findings merit further investigation of antihistamines in clinical drug trials. The H3 and H4 receptors are found in primarily in CNS and immune tissues, respectively. H3 is likely to be involved in antinociception and has been linked with cognitive, neurodegenerative and sleep disorders. The only marketed H3 agent, pitolisant, is a brain penetrant H3 antagonist/inverse agonist which increases central histamine and causes headache. The experimental H3 agonist Nα-methylhistamine has shown promising results as a migraine preventative in studies of uncertain quality. With the current limited knowledge of the H4 receptor it is questionable whether or not the receptor is involved in migraine.

CONCLUSION

There is insufficient support for first generation antihistamines (both H1 and H2) as preventive migraine medications and sedation and weight gain are unacceptable side effects. Non-sedating H1 antihistamines need to be appropriately tested. Central H3 receptors seem to have a role in migraine that merit further investigation. The histaminergic system may be a goal for novel migraine drugs.

Putative role of 5-HT2B receptors in migraine pathophysiology

Objective

In this review we attempt to characterize the acute and chronic role of 5-HT2B receptors with regard to meningeal nociception in animal experiments and clinical data targeting migraine therapy.

Background

Migraine is a common disabling neurovascular primary headache disease, the pathomechanism of which is still unclear. Serotonin (5-HT) and its receptors might play an important role in some aspects of migraine pathogenesis. The ability of the unselective 5-HT2B receptor agonist m-chlorophenylpiperazine to induce migraine attacks in migraine sufferers, the high affinity of prophylactic antimigraine drugs to this receptor and its expression in migraine-relevant structures like the dura mater argue for a role of 5-HT2B receptors in the pathogenesis of migraine attacks.

Methods

For this review, the relevant databases such as PubMed, MEDLINE®, Cochrane Library and EMBASE, respectively, were searched to December 2015 using the keywords “migraine, 5-HT2, trigeminal, neurogenic inflammation, nitric oxide, nitroxyl, vasodilatation, plasma protein extravasation” and combinations thereof.

Conclusion

Our literature review suggests an important role of 5-HT2B receptor activation in meningeal nociception and the generation of migraine pain.

Triptan use in pediatric migraine: focus on rizatriptan

Migraines are a common complaint in children and can cause a significant burden to both the child and their families, with a substantial loss in both school and work days, as well as having negative effects on the child’s self-esteem and peer relations. It has become clear that migraine-specific medications are needed in this population of patients and their use may result in a significant improvement of the child’s headaches and quality of life. Rizatriptan benzoate (Maxalt®) is a selective 5-hydroxytryptamine/serotonin1B/1D (5-HT1B/1D ) agonist that was approved by the US FDA in 1998 for the acute treatment of migraine attacks in adults. Despite having been widely used in the pediatric population, rizatriptan was most recently approved in December 2011 for pediatric use in children aged 6–17 years. The advantage of rizatriptan over some other triptans is its rapid onset of action, which is thought to be beneficial in the generally shorter migraine attacks of children when compared with adults. It may also be an appealing choice for young children because it comes in an orally disintegrating form for those who may have difficulty in swallowing tablets or who have significant gastrointestinal complaints accompanying their headaches, including nausea, vomiting and abdominal pain.

Optimizing prophylactic treatment of migraine: Subtypes and patient matching

Advances in our understanding of the pathophysiology of migraine have resulted in important breakthroughs in treatment. For example, understanding of the role of serotonin in the cerebrovascular circulation has led to the development of triptans for the acute relief of migraine headaches, and the identification of cortical spreading depression as an early central event associated wih migraine has brought renewed interest in antiepileptic drugs for migraine prophylaxis. However, migraine still remains inadequately treated. Indeed, it is apparent that migraine is not a single disease but rather a syndrome that can manifest itself in a variety of pathological conditions. The consequences of this may be that treatment needs to be matched to particular patients. Clinical research needs to be devoted to identifying which sort of patients benefit best from which treatments, particularly in the field of prophylaxis. We propose four patterns of precipitating factors (adrenergic, serotoninergic, menstrual, and muscular) which may be used to structure migraine prophylaxis. Finally, little is known about long-term outcome in treated migraine. It is possible that appropriate early prophylaxis may modify the long-term course of the disease and avoid late complications.

The Discovery of a New Drug Class for the Acute Treatment of Migraine

The history of the scientific ideas and events that led to the discovery of sumatriptan is outlined with personal reminiscences about individuals who influenced the approach. The development of sumatriptan revolutionized the acute treatment of migraine and led to the availability of a number of other triptans. The anti-migraine effects of all the triptans are mediated via 5-HT(1B), and possibly 5-HT(1D) receptors, which transduce their effects via G; proteins. This suggests that agonists at other G(i) protein-coupled receptor types appropriately located (eg, somatostatin sst(2), adenosine A(1)) should be examined for their effects on the trigeminovascular system, Studies on such receptor targets may provide insight into a novel approach towards the design of new anti-migraine drugs.

In vitro pharmacological investigations of Sapindus trifoliatus in various migraine targets

Phytotherapies have offered alternative sources of therapy for migraine and gained much importance in prophylactic treatment. The aqueous extract of pericarp of fruits of Sapindus trifoliatus Linn (ST), family Sapindaceae was evaluated for its affinity for 5-HT(1B/1D) receptors in rabbit saphenous vein, alpha-adrenoceptors in rabbit aorta, GABA receptors in guinea pig ileum, 5-HT(2B) receptors in rat fundus and vanilloid receptors in guinea pig trachea. The calcium blocking effect was studied in rabbit aorta while the modulatory role of ST on platelet serotonin release was evaluated in human platelets. The aqueous extract of Sapindus trifoliatus exhibited significant 5-HT(2B) receptor inhibition and moderate platelet serotonin release inhibition.

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.

Activation of meningeal 5-HT2B receptors: an early step in the generation of migraine headache?

Several pharmaceuticals are frequently dispensed to prevent or reduce the occurrence of migraine attacks. The prophylactic effect of these drugs has been suggested to be caused through blockade of serotonin (5-HT) receptors of type 5-HT2B or 5-HT2C. To elucidate which of these receptors is involved, we first used radioligand binding assays to determine the pharmacological profile of the human and rat-5-HT2B receptor. Furthermore, the potency of drugs used in migraine prophylaxis to stimulate or inhibit 5-HT2B or 5-HT2C receptor-mediated potency of drugs used in migraine prophylaxis to stimulate or inhibit 5-HT2B or 5-HT2C receptor-mediated phosphatidyl inositol hydrolysis was measured. All these drugs were found to block both human receptors. Correlation of the receptor affinities with the potencies used in migraine prophylaxis showed significant correlations, which were better for the 5-HT2B (P = 0.001) than for the 5-HT2C receptor (P = 0.005). Migraine headache is thought to be transmitted by the trigeminal nerve from the meninges and their blood vessels. Using the reverse transcription-polymerase chain reaction, the expression patterns of all cloned G-protein-coupled serotonin receptors were analysed in various human meningeal tissues. All tissues expressed 5-HT1Dbeta, 5-HT2A, 5-HT2B, 5-HT4 and 5-HT7 mRNAs. Only trace amounts of 5-HT2C receptor mRNA were found. With organ bath experiments we showed that the 5-HT2B receptor stimulated the relaxation of the pig cerebral artery via the release of nitric oxide. Our data support the hypothesis that 5-HT2B receptors located on endothelial cells of meningeal blood vessels trigger migraine headache through the formation of nitric oxide.

Is migraine prophylactic activity caused by 5-HT2B or 5-HT2C receptor blockade?

It has been suggested that activation of 5-HT2C receptors is involved in the initiation of a migraine attack. The 5-HT2C receptor and the newly cloned rat fundus 5-HT2B receptor show close pharmacological and structural resemblance. Antagonist pA2 values from the rat stomach and pKD values from a 5-HT2C receptor binding assay correlated both highly significantly (p < 0.005) with the daily dose of eight migraine prophylactic compounds. Although the small difference in antimigraine potency between the enantiomers of propranolol agrees with the lack of stereo-selectivity found on the rat fundus 5-HT2B receptor but not with the 5-HT2C receptor, the evidence available does not allow one to distinguish between 5-HT2C and 5-HT2B receptor blockade as possible mechanisms for prophylactic activity.

5-HT2 receptor antagonists and migraine therapy

5-Hydroxytryptamine (5-HT; serotonin) has been implicated in the pathophysiology of migraine, and several drugs with potent 5-HT2 receptor blocking activity (methysergide, pizotifen, cyproheptadine and mianserin) have been recognized as being clinically effective in migraine prophylaxis, although the selective 5-HT2 receptor antagonist ketanserin (the principal agent used to identify 5-HT2 receptor-mediated actions) seems to be ineffective in migraine. Pizotifen is the most widely used 5-HT2 receptor antagonist in migraine prophylaxis, because of its superior efficacy compared with cyproheptadine, and because the incidence and severity of adverse effects with pizotifen is lower compared with methysergide and mianserin. These agents have additional antagonistic effects at histamine H1, muscarinic cholinergic, alpha 1-adrenergic, alpha 2-adrenergic and dopamine receptors, but drugs which are selective for these non-5-HT receptors appear to be of no benefit in migraine. Actions mediated by 5-HT2 receptors which could be of relevance to migraine comprise cranial vasoconstriction, increased cranial capillary permeability and platelet aggregation, and some central nervous system effects and neuroendocrine functions. Although pizotifen, cyproheptadine and mianserin are considered to be relatively specific for 5-HT2 receptors, these agents and methysergide all share a high affinity for 5-HT1C binding sites; ketanserin, however, has little affinity for these sites, thus activation of 5-HT1C receptors may be an important step in the pathogenesis of migraine. It is not yet known which 5-HT1C receptor-mediated actions of 5-HT are relevant to migraine, but some behavioural actions and cranial vasodilatation via release of endothelium-derived relaxing factor may be involved.(ABSTRACT TRUNCATED AT 250 WORDS)

Neurotologic findings in basilar migraine

Treatment of a patient with otologic symptoms and associated migraine-like headache presents the otolaryngologist with formidable problems. Although clinical practice and scientific publications recognize their frequent association, relationships have yet to be well defined. This study seeks to add order to disarray by delineating symptoms and signs of a clearly identified group of migraine patients. Fifty patients with well-defined basilar migraine underwent a thorough neurotologic examination, as well as comprehensive auditory and vestibular testing. Patients were selected from 5880 patients seen over a 2-year period and were prospectively entered into the study after detailed questionnaires and testing were completed for each patient. The most common symptoms found were dysequilibrium, phonophobia, and head pressure. The most common signs were positional nystagmus, low-frequency hearing loss, abnormal loudness discomfort level, and an abnormality on caloric examination. Advanced vestibular testing showed abnormal amplitude scaling, abnormal toes-down pertubation, and an abnormal sway (condition 6) on dynamic posturography. There was frequently an asymmetry on computerized rotation. The author concludes that the majority of patients have subtle findings on testing, but a few have severe peripheral injury due to the basilar migraine. Findings are consistent with the theory that basilar migraine is a central nervous system maladaptation syndrome which creates otoneurologic symptoms and, in a small percentage of cases, may injure the peripheral end-organ.

Visual disturbances of migraine

Migraine, a clinical syndrome of unknown etiology, is a common cause of a variety of visual disturbances. This review describes the visual alterations associated with migraine syndromes of particular interest to the ophthalmologist; acephalgic, ocular, and ophthalmoplegic. Several current theories of migraine pathophysiology are discussed. Migrainous episodes are common and must be differentiated from neurologic dysfunction due to ischemia, inflammation, seizure, and compression. The differentiating characteristics of these conditions as well as a diagnostic algorithm are presented.

Antimigraine drug interactions with serotonin receptor subtypes in human brain

The interactions of antimigraine agents with serotonin (5-hydroxytryptamine, 5-HT) receptor subtypes were analyzed in human frontal cortex membranes. The drugs studied included 5-HT antagonists, beta-adrenergic antagonists, and calcium channel blockers. At 5-HT1A sites labeled by 3H-8-hydroxy-2-(N,N-dipropylamino)-tetralin, (-)pindolol, alprenolol, (-)propranolol, methysergide, cyproheptadine, and pizotifen are similar in that they display affinities of approximately 100 nM for this receptor. By contrast, only methysergide displays relatively high affinity (120 +/- 60 nM), whereas all other drugs have affinities greater than 1,000 nM for non-5-HT1A sites labeled by 3H-5-HT in human cortex. Finally, at 5-HT2 receptors labeled by 3H-spiperone, cyproheptadine, methysergide, and pizotifen are extremely potent agents (affinity constants of 1 to 10 nM), whereas amitriptyline (23 +/- 4 nM), verapamil (140 +/- 50 nM), and nifedipine (320 +/- 80 nM) are moderately potent. All other drugs are inactive at concentrations below 1,000 nM. These data demonstrate that most antimigraine drugs display high affinity for the 5-HT1A and/or 5-HT2 receptor subtypes in human brain. However, antimigraine efficacy cannot be explained by drug interactions with a single 5-HT receptor subtype.

Serotonin antagonists

The realisation that serotonin plays a role not only in the carcinoid syndrome but also in migraine, nociception, dumping syndrome, vascular disease and hypertension, has led to an enormous amount of activity in search of serotonin antagonists. Numerous such pharmacological agents have been identified but only few have found their way into clinical use. All of them are competitive serotonin inhibitors, in that they vie for the same receptor as the amine itself and are thus able to block its action as well as imitate its effects. By far the widest use of such inhibitors is in the prevention of migraine, where they have effectively eliminated the dread of an attack from the life of the majority of patients. Whilst useful in the control of diarrhea in patients with carcinoid and dumping syndromes, their role in these diseases is limited. However, the possible role of serotonin in hypertension and nociception opens new avenues in the use of existing serotonin antagonists and calls for the discovery of a new generation of such pharmacological agents for the control of these conditions.

Influence of pizotifen and ergotamine on the venoconstrictor effect of 5-hydroxytryptamine and noradrenaline in man

The influence of locally infused pizotifen (80 ng) and ergotamine (16 ng and 4 ng) on the compliance of superficial hand veins in man, and their interactions with the venoconstrictor effects of noradrenaline and 5-hydroxytryptamine (5-HT), were investigated in a placebo-controlled study in healthy volunteers. Pizotifen alone reduced venous compliance and produced a parallel displacement to the right of the 5-HT dose-response curve suggestive of competitive antagonism. The venoconstrictor effect of noradrenaline was not influenced by pizotifen. This confirms the selective antagonism of 5-HT by pizotifen and supports the existence of specific 5-HT receptors on human veins. After infusion of 16 ng ergotamine, which by itself reduced venous compliance, the venoconstrictor effects of the lower doses of 5-HT and of all doses of noradrenaline were larger but still never exceeded the arithmetic sum of the separate effects of noradrenaline or 5-HT and ergotamine. A lower dose of ergotamine (4 ng) induced only a small venoconstriction and did not influence the constrictor effect of noradrenaline. Therefore, in contrast to previous observations, no potentiation of the venoconstrictor effect of noradrenaline by ergotamine was observed under the present experimental conditions. The additive effect of noradrenaline and ergotamine may well explain its therapeutic action in the treatment of migraine.

Dopaminergic and serotonergic mediation of the discriminable effects of ergot alkaloids

The involvement of dopamine (DA) and serotonin (5-HT) neuronal systems in the discriminative stimulus effects of various ergot derivatives was assessed by administering four ergots to 36 rats which had been trained to discriminate either apomorphine (APO) or d-lysergic acid diethylamide (LSD) from saline. Lergotrile, lisuride and LSD substituted for APO (0.25 mg/kg) while bromocriptine and ergonovine (ergometrine) did not; only lisuride mimicked LSD (0.08 mg/kg). Antagonism tests showed that the DA antagonist haloperidol but not the 5-HT antagonist BC-105 (pizotifen) blocked the APO cue; both the LSD cue and the substitution of LSD for APO were blocked by BC-105 but not by haloperidol. It was concluded that DA receptor activation plays a prominent role in the discriminative stimulus effects of lergotrile and lisuride as well as APO and a secondary role in the LSD cue; 5-HT seems to be of major importance in the mediation of the effects of LSD and, to a lesser extent, lisuride. The functions of the two monoamines in the discriminable effects of bromocriptine and, particularly, ergonovine are less clear.

Psychophysiological aspects of migraine headaches

So complex are migraine headaches that the interplay of both psychological and physiological components is needed to explain and relieve symptoms. The difficulties of defining and delimiting migraine attacks, etiological theories and treatment approaches were reviewed with emphasis on the psychosomatic aspects.

Interaction of a potential antimigraine drug (Org GC 94) with the vasomotor action of serotonin

The interaction of a potential anti-migraine drug (Org GC 94) with the vasomotor action of 5-HT in vitro in feline, canine and human intra- and extracranial arteries, as well as in vivo in the canine nasal vascular bed as been investigated. In the two in vitro preparations, i.e. using superfusion or bath techniques, the intracranial vessels were more sensitive to 5-HT vasoconstriction than the extracranial ones. As both the maximum contraction and the slope of the dose-response curves were reduced by increasing concentrations of Org GC 94, the antagonism of 5-HT did not involve competitive blockade of 5-HT receptors. The dilator response was tested in arteries brought to a higher tone with prostaglandin F2 alpha. 5-HT produced a dose-dependent dilatation which, like the vasoconstriction, was antagonized in a non-competitive manner by Org GC 94. Intra-arterial injections of 5-HT provoked nasal vasoconstriction and this response was clearly potentiated by Org GC 94 in low doses while higher doses inhibited the vascular response to 5-HT. The specific effect of Org GC 94 in vivo may be the potentiation of 5-HT-induced vasoconstriction. The hypothesis is discussed that the so-called anti-5-HT agents act in migraine patients as partial agonists of 5-HT, mimicking rather than antagonizing 5-HT.

Inhibition of insulin secretion from the perfused pancreas of the rat by pizotifen

1 In the perfused rat pancreas the effects of pizotifen on insulin release induced by 20 mM glucose were studied. 2 Pizotifen (10 and 100 muM) significantly reduced the insulin release during a 25 min perfusion period to 49% and 7% of the controls. 3 The same concentrations of the structurally related agents cyproheptadine, doxepin, and chlorpromazine produced a comparable inhibition.

Aspirin prophylaxis in migraine

A prospective double-blind trial of aspirin prophylaxis demonstrated a reduction of more than 50% in headache frequency in 9 of 12 migraine patients. Response to aspirin did not correlate with age, duration of headache history, family history, or platelet ultrastructure. There is some evidence that response to aspirin is associated with raised platelet aggregation. This pilot study indicates that aspirin is effective in migraine prophylaxis.

A comparison between placebo, pizotifen and 1-isopropyl-3-hydroxy-5-semicarbazono-6-oxo-2.3.5.6-tetrahydroindol (Divascan) in migraine prophylaxis

The effects and side-effects in migraine prophylaxis of placebo, Divascan (1-isopropylnoradrenochrome--5--monosemicarbazone) and pizotifen were compared in a double-blind cross-over study. The dosage was for Divascan 15 mg a day and for pizotifen 3 mg a day. Data from the last 6 weeks of each test period of 8 weeks were used to assess the effect of the treatment. Thirty patients entered the trial. Data from 28 patients treated with placebo and Divascan and 27 patients treated with pizotifen were used for final evaluation. Pizotifen significantly reduced the number of migraine attacks, headache index and the consumption of ergotamine. Divascan also seemed to have effect. The consumption of ergotamine was reduced compared with placebo and there was a reduction, although not significant, of headache frequency and headache index. Pizotifen gave significantly larger reduction in headache frequency and headache index than Divascan and signficantly more patients stated a preference for pizotifen compared with Divascan. A good or very good effect was reported by 11 per cent of the patients on placebo, 39 per cent on Divascan and 70 per cent on pizotifen. Pizotifen had frequent side-effects, mainly drowsiness and weight gain, whereas Divascan in this respect did not differ from placebo. Physical examinations and laboratory investigations did not show any significant changes, apart from weight gain.

Receptors for 5-hydroxytryptamine and noradrenaline in rabbit isolated ear artery and aorta

5-Hydroxytryptamine (5-HT) is thought to be implicated in the vascular disturbances of the external carotid artery bed associated with migraine. As part of a study of the pharmacology of some 5-HT antagonists used in the treatment of migraine we have examined the interactions of these drugs with 5-HT and noradrenaline in rabbit isolated ear artery and aortic strip. The results provide new information on the distribution of 5-HT-receptors in these preparations. In the aorta, 5-HT and noradrenaline were of similar potency in producing contractions. Methysergide produced very small contractions and was about 1000 times less potent than the other two agonists. In the ear artery noradrenaline produced monophasic vasoconstrictor responses, whereas 5-HT and methysergide produced prolonged biphasic responses. 5-HT was about 700 times less potent and methysergide about 4500 times less potent than noradrenaline. Methysergide was a better agonist in the ear artery than in the aorta. Biphasic responses to 5-HT and methysergide were also obtained in ear arteries from reserpine-treated rabbits indicating that neither agonist was acting by releasing endogenous noradrenaline. Pizotifen, cyproheptadine and phentolamine had no agonistic actions in either the aorta or ear artery. In the aorta methysergide, pizotifen and cyproheptadine were potent antagonists of 5-HT and much weaker antagonists of noradrenaline. Phentolamine possessed the opposite profile of selectivity. These results show that there are distinct receptors for 5-HT and noradrenaline in rabbit aorta. In the ear artery the pA2 values for each of the four antagonists were virtually identical against 5-HT and noradrenaline and similar to those obtained on alpha-adrenoceptors in the aorta. We conclude that 5-HT and noradrenaline act directly at alpha-receptors to produce vasoconstriction in the ear artery and that this preparation does not contain specific 5-HT receptors. This insight into the distribution of 5-HT receptors and alpha-receptors allows interpretation of the various actions of methysergide. In the aorta, methysergide was a potent antagonist at 5-HT-receptors and a weak partial agonist at alpha-receptors. In the ear artery, methysergide was a partial agonist at alpha-receptors; it was only a weak antagonist of 5-HT because this preparation does not contain specific 5-HT-receptors. The cross-reactivity demonstrated throughout these experiments indicates that 5-HT-receptors and alpha-receptors, although distinct entities, have features in common. These results are discussed in relation to the mode of action of methysergide, pizotifen and cyproheptadine in the treatment of migraine.

Comparative effects of four migraine prophylactic drugs on an isolated extracranial artery

Clonidine and methysergide constrict the rabbit auricular artery by activating smooth muscle alpha-adrenoceptors. Clonidine inhibits and methysergide enhances responses to stimulation of the sympathetic nerves. Both drugs sensitise the artery to a variety of vasoconstrictor stimuli, although not to potassium chloride. This weak generalised sensitisation may depend on clonidine and methysergide themselves being vasoconstrictor since sensitisation after clonidine did not occur when vasoconstriction was abolished with phentolamine. The marked potentiation of 5-HT and tryptamine observed during clonidine perfusion may reflect a property of the tryptamines since it was observed during perfusion with histamine but not when histamine vasoconstriction was abolished with mepyramine. Cyproheptadine and pizotifen neither constrict the artery nor sensitise it to vasoconstrictor agents. They inhibit responses to nerve stimulation, alpha-adrenoceptor agonists, potassium chloride and particularly histamine. Sensitisation of blood vessels reinforced by direct vasoconstriction may contribute to the mechanism of action of clonidine and methysergide in migraine. Conversely, alterations in vascular function may be less important to the antimigraine actions of either cyproheptadine or pizotifen.

Pizotifen (BC 105) in migraine prophylaxis

Pizotifen, an antaminic, was investigated in a double-blind placebo controlled trial to evaluate its efficacy in migraine prophylaxis. It was found to be and effective prophylactic in a proportion of migraine patients, reducing the frequency as well as the severity of headaches. Some patients showed weight gain. Several patients have continued treatment for up to 2 years with good control of their migraine and a reduction in the amount of medicament required for the acute attack.

Effects of ergotamine and methysergide on blood platelet aggregation responses of migrainous subjects

Platelet aggregation responses to 5-hydroxytryptamine (5-HT) were measured in plasma from migrainous subjects taking either methysergide maleate or ergotamine tartrate and were found to be reduced. Blood 5-HT levels of subjects free of headache were not affected by these drugs. The results support the hypothesis that methysergide and ergotamine act by occupying 5-HT uptake sites in vessel walls, leaving 5-HT molecules available to occupy receptors concerned with vasoconstriction.

Amitriptyline in migraine prophylaxis. Changes in pattern of attacks during a controlled clinical trial

A double-blind controlled clinical trial of crossover design was conducted in 26 volunteers suffering from migraine. Of 20 subjects who completed the trial, 16 had fewer attacks on amitriptyline than on placebo. Amitriptyline was found to have the greatest effect in reducing attacks with a short warning and in which no specific cause could be recognized. It had least effect in attacks with a long warning and recognized as due to fatigue. The drug was effective only in reducing those attacks with shorter duration and its effect was irrespective of severity. A dosage of between 10 and 60 mg, usually taken at night, was found to be adequate.