Cerebral and ocular hemodynamic effects of sumatriptan in the nitroglycerin headache model

Duality in response of intracranial vessels to nitroglycerin revealed in rats by imaging photoplethysmography

Among numerous approaches to the study of migraine, the nitroglycerin (NTG) model occupies a prominent place, but there is relatively insufficient information about how NTG affects intracranial vessels. In this study we aim to assess the effects of NTG on blood-flow parameters in meningeal vessels measured by imaging photoplethysmography (iPPG) in animal experiments. An amplitude of the pulsatile component (APC) of iPPG waveform was assessed before and within 2.5 h after the NTG administration in saline (n = 13) or sumatriptan (n = 12) pretreatment anesthetized rats in conditions of a closed cranial window. In animals of both groups, NTG caused a steady decrease in blood pressure. In 7 rats of the saline group, NTG resulted in progressive increase in APC, whereas decrease in APC was observed in other 6 rats. In all animals in the sumatriptan group, NTG administration was accompanied exclusively by an increase in APC. Diametrically opposite changes in APC due to NTG indicate a dual effect of this drug on meningeal vasomotor activity. Sumatriptan acts as a synergist of the NTG vasodilating action. The results we obtained contribute to understanding the interaction of vasoactive drugs in the study of the headache pathophysiology and methods of its therapy.

The human NTG model of migraine in drug discovery and development

INTRODUCTION

Various triggers can originate a migraine attack. In healthy volunteers and patients with migraine, the nitroglycerin (NTG) provocation model induces a headache that resembles migraine in pain characteristics and vascular manifestations. This headache is reversible and treatable in monitored conditions, providing an opportunity to test novel antimigraine medications in early clinical development.

AREAS COVERED

This perspective covers the main characteristics and applications of the human NTG model of migraine with effective and ineffective antimigraine therapies.

EXPERT OPINION

The NTG model represents a potential de-risking strategy to test novel hypotheses for antimigraine mechanisms in humans. Considering previous studies conducted with effective and ineffective antimigraine therapies, the sensitivity of the model was 71% while the specificity was 100%. The probability that following an analgesic effect, that compound would truly be efficacious in individuals with migraine was 100%. Following a negative result, the probability that such compound would truly be ineffective in patients with individuals was 33%. A clinical trial testing the analgesic properties of novel compounds after a sublingual and/or intravenous NTG challenge in migraine patients may support a subsequent phase 2 trial for the treatment of migraine.

PARACENTRAL ACUTE MIDDLE MACULOPATHY FOLLOWING ORAL INTAKE OF SUMATRIPTAN

PURPOSE

The purpose of this report was to describe a case with paracentral acute middle maculopathy after oral intake of sumatriptan.

METHODS

Case presentation.

RESULTS

One patient showed typical findings on fundoscopic examination and optical coherence tomography consistent with paracentral acute middle maculopathy following oral intake of sumatriptan.

CONCLUSION

Sumatriptan may be a trigger for paracentral acute middle maculopathy.

Retinal nerve fiber layer changes in migraine: a systematic review and meta-analysis

BACKGROUND

Migraine is one of the most common disabling diseases in the world. Its recurrent attacks may lead to abnormalities in the structure of the brain and retina. An increasing number of studies have investigated retinal nerve fiber layer (RNFL) thickness alterations in migraine by the optical coherence tomography (OCT); however, no consensus has yet reached.

METHOD

We searched Pubmed, Embase, and Web of Science databases to identify studies that investigated RNFL thickness in migraine by OCT measurement and performed a meta-analysis of eligible studies.

RESULTS

Twenty-six studies were included in the meta-analysis, comprising 1530 migraine patients and 1105 healthy controls. The mean RNFL thickness was thinner in the migraine group compared to the control group (SMD =- 0.53). In the subgroup analyses, RNFL thickness were decreased most significantly in the superior (SMD = - 0.71) and inferior (SMD = - 0.63) quadrants among all quadrants. Migraine with aura (SMD = - 0.91) showed a greater effect size of RNFL thickness reduction than migraine without aura (SMD =- 0.47). Spectral-domain OCT (SMD = - 0.55) seems more sensitive to detect RNFL thickness reduction than time-domain OCT (SMD = - 0.44). In addition, age, sex, disease duration, attack frequency, and intraocular pressure were not significantly associated with RNFL thickness.

CONCLUSIONS

The findings from our comprehensive meta-analysis with large datasets strengthen the clinical evidence of the RNFL thickness reduction in migraine. RNFL thickness via spectral-domain OCT measurement demonstrates the potential role in differentiating patients with migraine, especially migraine with aura, from healthy controls.

Human models of migraine - short-term pain for long-term gain

Migraine is a complex disorder characterized by recurrent episodes of headache, and is one of the most prevalent and disabling neurological disorders. A key feature of migraine is that various factors can trigger an attack, and this phenomenon provides a unique opportunity to investigate disease mechanisms by experimentally inducing migraine attacks. In this Review, we summarize the existing experimental models of migraine in humans, including those that exploit nitric oxide, histamine, neuropeptide and prostaglandin signalling. We describe the development and use of these models in the discovery of molecular pathways that are responsible for initiation of migraine attacks. Combining experimental human models with advanced imaging techniques might help to identify biomarkers of migraine, and in the ongoing search for new and better migraine treatments, human models will have a key role in the discovery of future targets for more-specific and more-effective mechanism-based antimigraine drugs.

An Emergency Department Approach to Drug Treatment of Hypertensive Urgency and Emergency

Patients who present with hypertensive urgency or emergency require immediate attention to assess the severity of illness. Guidelines from the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure are available but do little to address the management of acute elevations in blood pressure. Various treatment options, both old and new, exist to manage these patients in the emergency department. Decisions on therapy are patient specific and depend on the underlying cause of elevated blood pressure. This article sets out to describe specific patient presentations and reviews current available options in the management of hypertensive urgencies and emergencies.

Foveal Thickness Alterations in Patients with Migraine

AIM

To investigate the alterations in foveal retinal thickness (FT) values in patients with migraine and to reveal the correlations between FT and clinical characteristics of migraine disease.

METHODS

This study included sixty-eight eyes of 34 migraine patients [twenty-eight eyes of 14 patients with aura (group 1), and forty eyes of 20 patients without aura (group 2)] and forty eyes of 20 healthy volunteer who served as the control group (group 3). FT values were measured by optical coherence tomography (OCT) in each group.

RESULTS

Mean age of patients in group 1, 2, and 3 was 34.0± 6.82, 35.2±10.12, and 35.1± 6.85 years, respectively (p=0.84). Mean FT was 211.07±7.36, 220.0±12.01, and 221.85±12.27 in groups 1, 2, and 3, respectively. There was statistically significance among the group 1-2 and 1-3 (p=0.002 and p< 0.001). There was no statistically significance between group 2-3 (p=0.88).

CONCLUSION

This study suggests that in particular migraine with aura may lead to a reduction in FT values. This finding can be explained by the blood flow decrease theory in migraine; however larger studies seem mandatory.

The impact of migraine on posterior ocular structures

Purpose. To investigate the thickness of the retinal nerve fiber layer (RNFL) and choroid in patients who have migraines in comparison to healthy controls. Methods. This study included 76 eyes and patients in the migraine group, 36 with aura (MWA group) and 40 without (MWoA group), and 38 eyes as control subjects. The RNFL and macular thicknesses were analysed with standard OCT protocol while choroidal thickness was analysed with EDI protocol in all subjects. Choroidal thickness was measured at the fovea, 1500 µm nasal and 1500 µm temporal to the fovea in a horizontal section. Results. The mean RNFL thickness for nasal and nasal inferior sectors was significantly thinner (P ≤ 0.018) in the migraineurs' eyes than in those of the controls, as was the mean choroid thickness at the fovea and measured points (P < 0.0001). However, the mean macular thickness was not significantly different between the groups. Conclusions. This study suggests that migraine leads to a reduction in the peripapillary RNFL thickness and to thinning in choroidal structures. These findings can be explained by a chronic ischemic insult related to migraine pathogenic mechanisms and these findings are considered supportive of the relationship between glaucoma and migraine.

Pearls and pitfalls in human pharmacological models of migraine: 30 years' experience

In vitro studies have contributed to the characterization of receptors in cranial blood vessels and the identification of new possible anti-migraine agents. In vivo animal models enable the study of vascular responses, neurogenic inflammation, peptide release and genetic predisposition and thus have provided leads in the search for migraine mechanisms. All animal-based results must, however, be validated in human studies because so far no animal models can predict the efficacy of new therapies for migraine.

Given the nature of migraine attacks, fully reversible and treatable, the headache- or migraine-provoking property of naturally occurring signaling molecules can be tested in a human model. If such an endogenous substance can provoke migraine in human patients, then it is likely, although not certain, that blocking its effect will be effective in the treatment of acute migraine attacks.

To this end, a human in vivo model of experimental headache and migraine in humans has been developed. Human models of migraine offer unique possibilities to study mechanisms responsible for migraine and to explore the mechanisms of action of existing and future anti-migraine drugs. The human model has played an important role in translational migraine research leading to the identification of three new principally different targets in the treatment of acute migraine attacks and has been used to examine other endogenous signaling molecules as well as genetic susceptibility factors. New additions to the model, such as advanced neuroimaging, may lead to a better understanding of the complex events that constitute a migraine attack, and better and more targeted ways of intervention.

What have we learnt from triggering migraine?

PURPOSE OF REVIEW

This review presents what we have learnt from triggering migraine.

RECENT FINDINGS

Experimental studies have shown that glyceryl trinitrate (GTN), calcitonin gene-related peptide (CGRP), pituitary adenylate cyclase activating polypeptide-38 (PACAP38) and prostaglandin I2 (PGI2) induce migraine-like attacks in migraine suffers indistinguishable from their spontaneous attacks. These studies point to two key pathways to play an important role in migraine pathophysiology: cyclic guanosine monophosphate (cGMP) and cyclic adenosine monophosphate (cAMP). At present, no valid experimental model exists to reproduce aura episodes in migraine with aura patients. Familiar hemiplegic migraine patients seem to be less sensitive to GTN and CGRP provocation compared with common types of migraine. Advances in recent imaging studies suggest neuronal mechanisms to be behind migraine attacks. The experimental headache models have resulted in development and an ongoing search of new migraine targets.

SUMMARY

Human models of migraine offer unique possibilities to study mechanisms responsible for different migraine subtypes and to explore the mechanisms of action of existing and future antimigraine drugs. Adding advanced imaging techniques to the models may lead to a better understanding of the complex events that constitutes a migraine attack and thereby more targeted ways of intervention.

Pharmacological migraine provocation: a human model of migraine

In vitro studies have contributed to the characterization of receptors in cranial blood vessels and the identification of possible new antimigraine agents. Animal models enable the study of vascular responses, neurogenic inflammation, and peptide release, and thus have provided leads in the search for migraine mechanisms. So far, however, animal models cannot predict the efficacy of new therapies for migraine. Because migraine attacks are fully reversible and can be aborted by therapy, the headache- or migraine-provoking property of naturally occurring signaling molecules can be tested in a human model. If a naturally occurring substance can provoke migraine in human patients, then it is likely, although not certain, that blocking its effect will be effective in the treatment of acute migraine attacks. To this end, a human in vivo model of experimental headache and migraine in humans has been developed. This model has predicted the efficacy of nitric oxide synthase inhibition and calcitonin gene-related peptide receptor blockade, and has been used to examine other endogenous signaling molecules as well as genetic susceptibility factors.

Origin of pain in migraine: evidence for peripheral sensitisation

Migraine is the most common neurological disorder, and much has been learned about its mechanisms in recent years. However, the origin of painful impulses in the trigeminal nerve is still uncertain. Despite the attention paid recently to the role of central sensitisation in migraine pathophysiology, in our view, neuronal hyperexcitability depends on activation of peripheral nociceptors. Although the onset of a migraine attack might take place in deep-brain structures, some evidence indicates that the headache phase depends on nociceptive input from perivascular sensory nerve terminals. The input from arteries is probably more important than the input from veins. Several studies provide evidence for input from extracranial, dural, and pial arteries but, likewise, there is also evidence against all three of these locations. On balance, afferents are most probably excited in all three territories or the importance of individual territories varies from patient to patient. We suggest that migraine can be explained to patients as a disorder of the brain, and that the headache originates in the sensory fibres that convey pain signals from intracranial and extracranial blood vessels.

Nitroglycerin headache and nitroglycerin-induced primary headaches from 1846 and onwards: a historical overview and an update

Nitroglycerin (NTG) (glyceryl trinitrate) was synthesized by the Italian chemist Ascanio Sobrero in Paris in 1846. A very unstable explosive, Alfred Nobel while working on explosives, combined it with Kiselguhr and patented it as dynamite in 1867. NTG was introduced in 1879 in medicine in the treatment of angina pectoris by the English doctor William Murrell. NTG-induced headache was quickly recognized as an important adverse event both in the industrial use of NTG, where it was used to produce dynamite, as well as in the use of NTG as drug. This review traces the evolution of our understanding of NTG headache.

Nitric oxide-induced headache may arise from extracerebral arteries as judged from tolerance to isosorbide-5-mononitrate

Long-term exposure to organic nitrates influences different sections of the vascular bed heterogeneously. Continuous dosage of nitrates leads to the development of tolerance both to the vascular effects and to the unwanted adverse effect, headache. Human data on the development of tolerance in different cranial arteries over more than 24 h are lacking. We compared the vascular changes of the middle cerebral, superficial temporal and radial arteries during oral administration of isosorbide-5-mononitrate (5-ISMN) 30 mg three times daily for 7 days in 11 healthy subjects in a double-blind, randomised, placebo controlled cross-over design. Blood velocity in the middle cerebral artery was measured with transcranial Doppler and the diameters of the temporal and radial arteries were measured with high frequency ultrasound. Headache recordings were compared to the observed vascular changes over time. Tolerance was complete within 24 h in the middle cerebral artery whilst in the superficial temporal and the radial arteries, tolerance was only partial and developed much more slowly, i.e. after 7 days correlating with the disappearance of NO-induced headache. The present study thus demonstrated the important differences in the time profiles of appearance of nitrate tolerance in arteries of different vascular beds in man. If vasodilatation is the cause of NO-induced headache the results point to extracerebral arteries as the locus of nociception. Due to a variety of other possible pain-inducing effects of nitric oxide our results do not exclude cerebral arteries.

Intracranial hemodynamics during intravenous infusion of glyceryl trinitrate

The mechanisms of glyceryl trinitrate (GTN)-induced headache are not fully elucidated. In this study we administered GTN 0.5 μg/kg/min i.v. for 20 min in six healthy volunteers. Before, during and 60 min after the infusion, we investigated regional cerebral blood flow (rCBF), cerebral blood volume (CBV), both estimated with SPECT, and blood flow velocity (BFV) in the middle cerebral artery (MCA), measured with transcranial Doppler. Headache was scored on a numerical verbal rating (0–10) scale. rCBF was unchanged, CBV was slightly increased (13%) during GTN infusion, whereas BFV decreased both during (20%) and 60 min (15%) after GTN. Headache was short-lived and maximal during infusion. This discrepancy of time-effect curves for the effect of GTN on headache and dilatation of MCA indicates that MCA is most likely not the primary source of pain in GTN-induced headache. The time-effect curves for the effect of GTN on headache and on dilation of MCA differed markedly. This indicates that MCA is most likely not the primary source of pain in GTN-induced headache.

Transcranial Doppler in migraine attacks before and after treatment with oral zolmitriptan or sumatriptan

BACKGROUND

Intracranial blood flow velocity (BFV) changes in migraine have been studied fairly extensively. Although a number of investigations have been performed in migraineurs with nitroglycerin-induced attacks, there has been no reported transcranial study involving such attack treated with zolmitriptan or sumatriptan.

METHODS

With ultrasound, we studied the BFV and pulsatility index (PI) changes in the middle cerebral artery in 45 symptom free, otherwise healthy, unmedicated patients with migraine without aura, and in 15 age- and sex-matched controls before nitroglycerin, at the time of maximum head pain induced by nitroglycerin and every 30 minutes for 2 hours after zolmitriptan (15 subjects) or sumatriptan (15 subjects) administration. Headache was rated on a 4-point scale.

RESULTS

During headache attacks, BFV decreased significantly (36.7+/-3.3, 38.4+/-3.4, and 37.4+/-4 cm/sec, respectively, in the zolmitriptan, sumatriptan, and nontreated migraine groups, but not in the controls who were migraine free (P <.01). These abnormalities disappeared 1 hour after zolmitriptan or sumatriptan administration (49.7+/-3.7 and 48.9+/-3.9 cm/sec, respectively). There were no significant changes in PI.

CONCLUSION

Our data indicate that nitroglycerin-induced headache in individuals with migraine without aura is associated with BFV changes that are reversed by administration of an oral triptan.

Brain blood flow in the nitroglycerin (GTN) model of migraine: measurement using positron emission tomography and transcranial Doppler

Nitroglycerin has been widely used as a model of experimental migraine. Studies combining measurement of flow velocity using transcranial Doppler (TCD) concurrently with measures of cerebral blood flow (CBF) are uncommon. We report the results of a study combining TCD and positron emission tomography (PET). Healthy volunteers with no personal or family history of migraine underwent measurement of CBF using H215O PET, and velocity using TCD. Measurements were done at baseline, and following i.v. nitroglycerin at 0.125, 0.25 and 0.5 micro g/kg per min. Subcutaneous sumatriptan (6 mg) was injected, with CBF and velocity measured 15, 30, and 60 min later. Nitroglycerin was terminated and measurements obtained 30 min later. Six male and six female subjects were studied. Nitroglycerin increased global CBF while flow velocities decreased. Sumatriptan did not have a significant effect on these values. Regions of increased flow included the anterior cingulate, while regions of decreased flow included the occipital cortex. Our data suggest that nitroglycerin induces regional changes in CBF that are similar to changes reported in spontaneous migraine, but produces distinctly different effects on global CBF and velocity.

Nitric oxide potentiates response of trigeminal neurones to dural or facial stimulation in the rat

Infusing glyceryl trinitrate as a donor molecule, we have used electrophysiological and c-fos immunostaining techniques to study the effects of nitric oxide on neurones in the nucleus trigeminalis caudalis. Following infusion of glyceryl trinitrate, responses of neurones to electrical stimulation of periorbital cutaneous afferents were potentiated and threshold for activation of neurones by stimulation of dural afferents was reduced. Expression of c-fos was unchanged by glyceryl trinitrate compared to saline controls. Intradermal injection of capsaicin in the periorbital area increased c-fos expression in nucleus trigeminalis caudalis; this was significantly potentiated by glyceryl trinitrate. These results suggest that, in the anaesthetized rat, glyceryl trinitrate alone may not acutely activate the trigeminovascular system to a significant degree at doses that cause headache and later trigger migraine headache in migraineurs. Nevertheless, it is susceptible to exogenous nitric oxide in that activation of trigeminal neurones through cutaneous or dural pathways is potentiated. This may in some measure underlie the pathogenesis of migraine headache.

A comparison between laser interferometric measurement of fundus pulsation and pneumotonometric measurement of pulsatile ocular blood flow. 1. Baseline considerations

PURPOSE

Several methods have been proposed for the investigation of the human choroidal circulation. The aim of the present study was to compare laser interferometric measurements of cardiac synchronous fundus pulsations with pneumotonometric measurements of intraocular pressure pulse and pulsatile ocular blood flow in humans.

METHODS

The association between fundus pulsation amplitude as assessed with laser interferometry and pulse amplitude (PA) and pulsatile ocular blood flow (POBF) as assessed with pneumotonometry was investigated in 28 healthy subjects. Additionally, we investigated the distribution of fundus pulsation amplitude (FPA) in a region of -15 degrees to +15 degrees around the macula (n = 18) and the influence of accommodation paralysis with cyclopentolate on FPA (n = 10).

RESULTS

There was a high association between FPA and PA (r = 0.86, p < 0.001) and FPA and POBF (r = 0.70, p < 0.001). Fundus pulsations in the macula were significantly smaller than in the optic disc, but significantly larger than those in peripheral regions of the retina. Administration of cyclopentolate did not influence FPA.

CONCLUSIONS

On the basis of the strong correlation between laser interferometric measurements of FPA and pneumotonometric measurements of PA and POBF, we conclude that the FPA is a valid index of pulsatile choroidal perfusion in humans.

Vasoneuronal coupling in migraineurs after subcutaneous sumatriptan: a TCD study

According to the trigeminovascular model of pain in migraine, sterile neurogenic inflammation of dural vessels stimulates nociceptive fibres of the trigeminal nerve. Sumatriptan, a 5-HT1 receptor agonist, blocks this reaction and mediates vasoconstriction of meningeal arteries. However, it is uncertain, whether sumatriptan also has a vasoconstrictive effect on cerebral arteries, which may influence vasoneuronal coupling and induce secondary cerebral blood flow changes. We studied changes of cerebral blood flow velocity (CBFV) and the pulsatility index (PI) in the posterior cerebral artery (PCA) after stimulus activation before, 10 min and 30 min after subcutaneous application of 6 mg sumatriptan, in order to assess potential vasoactive effects on cerebral circulation. CBFV was recorded from both PCAs simultaneously in 27 migraineurs (twenty women, seven men, mean age 29 years), and arterial blood pressure (BP), heart rate (HR) and respiration rate (RR) were monitored. Although the mean diastolic blood pressure rose significantly from 75 mm Hg to 81 mm Hg (P<0.05) and systolic blood pressure and respiration rates remained constant, average CBFV values remained constant. Similarly, the relative increase of CBFV by visual stimulation, which is clearly higher compared to controls in other studies (55.0% before, 52.6% after 10 min, and 52.4% after 30 min), and absolute mean values for CBFV and PI did not change after visual stimulation. These results provide evidence against the hypothesis that sumatriptan produces vasoconstriction in the intracranial human arterial circulation as a potential risk of cerebral ischemia.

Differential pharmacology between the guinea-pig and the gorilla 5-HT1D receptor as probed with isochromans (5-HT1D-selective ligands)

1. Both the 5-HT1D and 5-HT1B receptors are implicated in migraine pathophysiology. Recently isochromans have been discovered to bind primate 5-HT1D receptors with much higher affinity than 5-HT1B receptors. In the guinea-pig, a primary animal model for anti-migraine drug testing, however, isochromans bound the 5-HT1D receptor with lower affinity than the gorilla receptor. 2. This species-specific pharmacology was investigated, using site-directed mutagenesis on cloned guinea-pig receptors heterologously expressed in human embryonic kidney 293 cells. Mutations of threonine 100 and arginine 102 at the extracellular side of transmembrane II of the guinea-pig 5-HT1D receptor to the corresponding primate residues, isoleucine and histidine, respectively, enhanced its affinity for isochromans to that of the gorilla receptor, with little effects on its affinities for serotonin, sumatriptan and metergoline. Free energy change from the R102H mutation was about twice as much as that from the T100I mutation. 3. For G protein-coupling, serotonin marginally enhanced GTPgamma35S binding in membranes expressing the guinea-pig 5-HT1D receptor and its mutants, but robustly in membranes expressing the gorilla receptor. Sumatriptan enhanced GTPgamma35S binding in the latter nearly as much as serotonin, and several isochromans by 30-60% of serotonin. 4. We discovered key differences in the function and binding properties of guinea-pig and gorilla 5-HT1D receptors, and identified contributions of I100 and H102 of primate 5-HT1D receptors to isochroman binding. Among common experimental animals, only the rabbit shares I100 and H102 with primates, and could be useful for studying isochroman actions in vivo.

The pharmacodynamics of sumatriptan in nitroglycerin-induced headache

Migraine is a common disorder that causes significant morbidity in those afflicted. Many novel antimigraine compounds are in clinical development, yet full characterization of each one's pharmacodynamic behavior is a formidable task due to the difficulty in studying a migraineur during an attack. Nitroglycerin (NTG) administration commonly causes a headache with some features similar to those of a migraine. As such, NTG has been used as a model of vascular headaches, including migraine. The pharmacodynamic effects of nitroglycerin and sumatriptan on middle cerebral artery blood flow velocity (MCAv) and headache scores were studied in 10 healthy male volunteers. An intravenous infusion of NTG titrated to 0.5 mcg/kg/min over 30 minutes resulted in a median reduction from baseline in MCAv of 27% (range: 16.4%-37.3%). Nine of the subjects developed a headache with a median verbal score of 3.5 of 10 (range: 0-5). Subjects received sumatriptan either 2 mg intravenously or 6 mg subcutaneously, which abated clinical headache in 9 of the 10 subjects (p = 0.030). A median sumatriptan-induced increase in MCAv of 21% (p = 0.054) suggested a constricting effect on the NTG-induced dilated MCA. A two-compartment pharmacokinetic/indirect-effects pharmacodynamic model was fit to the sumatriptan concentration and MCAv data using iterative two-stage analysis. This model was unbiased and fit the concentration (r2 = 0.98) and the MCAv (r2 = 0.79) data well. These results suggest that NTG-induced headache and the development of pharmacokinetic/pharmacodynamic models could serve as a useful method for exploring the mechanisms of abortive migraine drugs.

Characterization of ligand binding properties of the 5-HT1D receptors cloned from chimpanzee, gorilla and rhesus monkey in comparison with those from the human and guinea pig receptors

The 5-HT1D receptor is a potential target of anti-migraine drugs, and here its genes were cloned from chimpanzee, gorilla and rhesus monkey, via polymerase chain reactions with their genomic DNAs and the primers designed from the 5' and 3' untranslated regions of the human receptor. Direct sequencing of the polymerase chain reaction (PCR) products revealed high degrees of identity between their deduced amino acid sequences (the chimpanzee, gorilla and rhesus monkey) and that of human, differing by two, four and 11 residues, respectively. The binding properties of the receptors, as expressed in human embryonic kidney 293 cells, were compared to those obtained with the human and guinea pig receptors, the latter differing by 33 residues from the human receptor. Standard serotonergic ligands including several indoles, ergots and methiothepin bound all the cloned primate and guinea pig receptors with comparable, low nanomolar affinities, leading to high correlation coefficients among their Ki values. R(+)-8-Hydroxydipropylaminotetralin, on the other hand, bound the human receptor with the affinity higher than those for the primates and guinea pig receptors. This indicates that certain chemical templates may differentiate the molecular divergences among the 5-HT1D receptors of various animal species, and the use of the non-human primates will be beneficial for pharmacological characterizations, more relevant to the human receptor, of future novel ligands for the 5-HT1D receptor, which are potential anti-migraine drugs.

Nitric oxide synthase inhibition in the histamine headache model

Histamine has been widely used experimentally to induce headache in healthy subjects and migraine in migraineurs. There is evidence that the vascular effects of histamine are at least partially mediated by nitric oxide (NO). Hence we hypothesized that subjective symptoms and hemodynamic effects of histamine could be reduced by systemic NO-synthase inhibition. We therefore studied the effect of pretreatment with N-monomethyl-L-arginine (L-NMMA), a competitive inhibitor of NO-synthase, or placebo on headache, flush and discomfort scores during histamine infusion. Additionally, blood flow velocities in the middle cerebral and the ophthalmic artery and ocular fundus pulsations were measured. Whereas L-NMMA blunted the effect of histamine in the ophthalmic artery and the ocular circulation, NO-synthase inhibition did not mitigate subjective symptoms. Histamine did not affect mean blood flow velocities in the middle cerebral artery. Hence, we conclude that NO-synthase inhibition reduces the histamine-induced vascular effects in the ocular circulation, but is not sufficient to attenuate or abort the subjective symptoms provoked by histamine infusion.

Effects of antiglaucoma drugs on ocular hemodynamics in healthy volunteers

BACKGROUND AND PURPOSE

There is evidence that ocular blood flow plays a critical role in the clinical course of glaucoma. Hence a reduction in ocular blood flow due to topical antiglaucoma treatment should be avoided. The purpose of this study was to characterize the effect of antiglaucoma drugs on ocular hemodynamics.

METHODS

In a double-blind, placebo-controlled, randomized crossover study, we investigated the effects of single topical doses of five beta-blocking agents (befunolol, betaxolol, levobunolol, metipranolol, and timolol), two adrenergic agents (clonidine and dipivefrin [INN, dipivefrine]), and a parasympathomimetic agent (pilocarpine) on ocular and systemic hemodynamics in healthy subjects (n = 10). Fundus pulsation amplitudes in the macula and the optic disc were measured to characterize pulsatile choroidal and optic disc blood flow, respectively. Moreover, central retinal and ophthalmic artery blood flow velocities were measured by Doppler ultrasound.

RESULTS

Befunolol, metipranolol, timolol, clonidine, and dipivefrin reduced fundus pulsations in the macula and the optic disc (-9% to -14% versus baseline). In contrast, betaxolol, levobunolol, and pilocarpine had no effect on fundus pulsations. Antiglaucoma drugs had no effect on either blood flow velocities in the central retinal or the ophthalmic artery or systemic hemodynamics.

CONCLUSIONS

Our results indicate that befunolol, metipranolol, timolol, clonidine, and dipivefrin reduce choroidal and optic disc blood flow. This could be caused by drug diffusion to the choroid, which may cause vasoconstriction. Ocular blood flow reduction was not observed with betaxolol, levobunolol, or pilocarpine. The lack of effect of all drugs under study on central retinal blood flow velocity might partially be the result of autoregulative mechanisms. Because optic nerve head blood flow likely plays a critical role in the clinical course of glaucoma, the use of antiglaucoma drugs, which reduce blood flow, should be reconsidered.