EVALUATION OF VASOMOTOR RESPONSE IN OPHTHALMIC MIGRAINE PATIENTS

Introduction. Hemodynamic changes of the cerebral arteries in ophthalmic migraine may be an important pathophysiological mechanism of the disease. The nitric oxide (NO) synthesis plays a signifi cant role in hemodynamic changes due to vasodilatation effect. The purpose of this study is to evaluate the possible hemodynamic changes by Doppler measurements and their correlation with NO synthesis in ophthalmic migraine. Method. 37 ophthalmic migraine patients were compared with 35 healthy volunteers. Other cerebral and ophthalmic diseases were excluded by ophthalmological, neurological, and cranial MRI examinations. The migraine assessment scale (MIDAS) was used for clinical evaluation. Transcranial Doppler ultrasonography (TCD) was performed using 2 and 4 MHz frequencies transducers. The fl ow velocities of the internal carotid artery, middle cerebral artery, posterior cerebral artery, and NO plasma concentration were assessed 2 hours after migraine attacks. Results. The NO synthesis was signifi cantly increased compared to the control group. The fl ow velocities decreased in internal carotid artery, middle cerebral artery, and posterior cerebral artery. The correlation between decreased fl ow velocities and NO plasma concentration was signifi cant. Conclusions. Autonomic nervous system dysfunction in ophthalmic migraine is an important pathophysiological mechanism. The fl ow velocity status may refl ect the vasomotor response and endothelial reactivity induced by NO synthesis. Further studies on the vasomotor response are necessary for the evaluation of this pathophysiological mechanism implication in ophthalmic migraine.


INTRODUCTION
Hemodynamic changes of the cerebral arteries in ophthalmic migraine may be an important pathophysiological mechanism of the disease. Depending on the signal perceived by endothelial cells, it can result in a vasoconstrictor or vasodilator effect. The nitric oxide (NO) synthesis plays a signifi cant role in hemodynamic changes due to vasodilatation effect (1). NO is well known for its ability to relax blood vessels in addition to other biological effects. One of the most important harmful effects is its contribution to nitro-oxidative stress (2). Therefore, the increased synthesis of NO may lead to cells damage due to nitro-oxidative stress, despite of its vasodilatation benefi c effect that contributes to adequate blood fl ow into the tissues. The synthesis of NO from L-arginine is controlled by nitricoxide synthase (NOS) which requires NADPH and molecular oxygen (3). Constitutional forms of NOS are endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) (4). In pathological conditions such is infl ammation, an inducible form of NOS (iNOS) is produced during the infl ammatory process being able to modulate biosynthesis of prostaglandins through non-COX-related pathways (5). In these instances the increasing synthesis of NO can exceed the physiological quantities that serve for vasodilatation and adequate blood fl ow, contributing to the onset of nitro-oxidative stress and stimulating the pain transmission (6). NO may cause activity alterations on different levels of the trigeminal system including enhancement of calcitonin gene related protein (CGRP) release. Both mediators (NO and CGRP) facilitate nociceptive transmission, possibly via presynaptic mechanisms (7). NO itself is a short-lived, highly reactive species, but its major products nitrate and nitrite (collectively termed NOx) can readily measured retrospectively in biological samples as markers of NO production (8). The decreasing production of NO is a biomarker for endothelial dysfunction, and increasing productions is associated with nitro-oxidative stress (9,10).
Trascranial Doppler ultrasonography (TDU) represents a noninvasive modern method of determining the fl ow velocities in cerebral arteries. The fl ow velocities in cerebral arteries can be a good indicator for cerebral circulation in various pathological circumstances associated with occlusive or vasospastic mechanisms or with pathological vasodilatation mechanism (11). This method is of particular value for the detection of pathological variation of blood fl ow due to permanent lesions as are atherosclerosis plaques or anevrisma, or due to episodic variation of vessel wall diameter due to vasospasm (12). The functional parameters that characterize the blood circulation in cerebral arteries can be correlated with biological marker in order to a better characterization of pathophysiological mechanism associated with various vascular cerebral pathologies. Vascular changes associated with migraine are considered to involve selectively cranial blood vessels and is found to share the same risk factors as cardiovascular disease (13). The mechanisms underlying the relation between migraine and cardiovascular risk factors remain unclear but include the impairment of large vessels compliance (14).
The purpose of this study is to evaluate the possible hemodynamic changes by Doppler measurements and their correlation with NO synthesis in ophthalmic migraine.

METHOD Study groups and protocol
The study had the local Ethics Committee approval (Clinical Rehabilitation Hospital, Cluj-Napoca, Romania) and the Informed Consent for each patient. 37 ophthalmic migraine patients were compared with 35 healthy volunteers. Ophthalmic migraine (or retinal migraine) was suspected when the patient suffered of repeated episodes of short-lasting, diminished vision or blindness that preceded or accompanied a headache (15). The attacks of ophthalmic migraine (unlike a migraine aura that affect the vision) affected only one eye, not both (16). Pathological other ophthalmological conditions were excluded by ophthalmologic examination.
Other cerebral diseases were excluded by neurologic, carotid Doppler ultrasound, and cranial MRI examinations. The migraine assessment scale (MIDAS) was used for clinical evaluation. Transcranial Doppler ultrasonography (TCD) was performed using 2 and 4 MHz frequencies transducers. The fl ow velocities of the internal carotid artery (ICA), middle cerebral artery (MCA), posterior cerebral artery (PCA), ophthalmic artery (OA) and NO plasma concentration were assessed 2 hours after migraine attacks. The patients with cardiovascular risk factors were excluded. Exclusion criteria were age above 40, hypertension, diabetes mellitus, obesity, dyslipidemia, chronis alcoholism, current smoking, and any previous cardio-vascular or cerebro-vascular events. Total nitrate and nitrite (NOx) were measured in plasma by Griess reaction using commercial kits (17).

Statistical analysis
The comparison between groups was made with Student test for normal distributed data, with Man-Whitney test for non-normal distributed data, and Chi-square test for non-parametric data. Spearman test were applied for correlation calculation for non-normal distributed data, and Pearson test for correlation of normal distributed data. p < 0.05 were considered signifi cant. The correlations were made between fl ow velocities values in cerebral vessels assessed by TDU and NOx level.

RESULTS
The NO synthesis was signifi cantly increased compared to the control group (Table1). The fl ow velocities signifi cantly decreased in internal carotid artery, middle cerebral artery, and posterior cerebral artery, and ophthalmic artery fl ow velocities were found to be increased (Table2). The correlations between pathological fl ow velocities and NOx plasma concentration were signifi cant for MCA-PSFV and OA-PSFV (Table 3).
Signifi cant monotonic positive relationship was identifi ed for NOx with MCA-PSFV and, a negative monotonic relationship between NOx and OA-PSFV. No signifi cant relationship was identifi ed between NOx and other arteries PSFV in study group patients.

DISCUSSIONS
Our study group presented a signifi cant increased NOx synthesis that proved that endothelial function is normal. Our previous study also demonstrated signifi cant changes of NOx plasma level associated with ophthalmic migraine (18). Due to aging process the endothelial dysfunction is leading to decrease of NOx synthesis (19,20) and a low bioavailability of nitric oxide to maintain the physiological cerebral vasodilatation (21). Increased NOx synthesis produce vasodilatation in large arteries demonstrated by systolic fl ow velocities in our study group. Decreasing fl ow velocities in ophthalmic artery showed a hemodynamic perturbation with possible vasospasm in ophthalmic artery. There are other factors that may contribute to he-modynamic perturbation in ophthalmic artery as are the presence of infl ammatory processes (demonstrated by signifi cant CRP increasing in study group). Our results demonstrated that the decreasing ophthalmic artery diameter due to vasospasm may lead to visual symptoms associated migraine. The correlation on NOx synthesis with increased diameter of large arteries demonstrated that the vasodilatation of these vessels can lead to decrease of blood fl ow in ophthalmic artery possible due to "vascular steal syndrome". A genetic predisposition to this vasomotor response, to increased glutamate neurotransmission and proper synaptic plasticity may play an important role (22).
Our results that demonstrated the increases proinfl ammatory plasma markers as is C reactive protein, brings the connection between the existence of infl ammatory status in ophthalmic migraine patients and increased synthesis of nitric oxide, due to infl ammation. The presence of an infl ammatory   mechanism may lead to central sensitization and under repetition even that is low-intensity stimulation induces a cephalic allodynia (23). Clinically, central sensitization is manifested as decreased pain threshold and exaggerated pain response that is referred outside the original pain site (24). The application of infl ammatory substances on the exposed rat dura, which activates the trigeminovascular pathway induces long-lasting sensitization in dorsal horn neurons that receive intracranial input from the dura and extracranial input from the periorbital area (25). Increased nitric oxide level may contribute to this mechanism. The associated vascular and neural contribution may explain some pathophysiological aspects in migraine mechanism (26). The effi ciency of non-steroidal anti-infl ammatory drug in treatment of migraine attack may demonstrate de correlation between nitric oxide synthesis augmentation (due to activation on iNOS) and increasing the prostaglandin synthesis (27,28). Administration of parenteral COX1/COX2 inhibitors may block sensitization in meningeal nociceptors and suppressed ongoing sensitization in spinal trigeminovascular neurons (29). Furthermore, the vasodilatation induced by increased NO synthesis, may lead to increased blood-brain barrier permeability and infl ammation associated hyperalgesia (30). These two opposite diameters changes may underlie to pain associated with vasodilatation and visual symptoms associated with ophthalmic artery constriction. That evidence may lead to possibility for new strategies of migraine treatment directed to the inhibition or decreasing of NO synthesis.

CONCLUSIONS
Hemodynamic perturbation in ophthalmic artery is an important pathophysiologic mechanism associated with ophthalmic migraine. The patients' age in our study group can contribute to higher synthesis of NO. The fl ow velocity status may refl ect the vasomotor response and endothelial reactivity induced by NO synthesis. Further studies on the vasomotor response are necessary for evaluation of this pathophysiological mechanism implication in ophthalmic migraine.