External Ophthalmic Artery Research Articles

A novel swine model of selective middle meningeal artery catheterization and embolization

BackgroundMiddle meningeal artery (MMA) embolization is a promising intervention as a stand-alone or adjunct treatment to surgery in patients with chronic subdural hematomas. There are currently no large animal models...

Blood supply to the cranial cavity in the patagonian mara (Dolichotis patagonum)

Rodents are the most numerous order of mammals. The literature presents information on the arterial circle of the brain in capybara, the guinea pig of the family Caviidae and many other not so closely related rodent species. Information on the blood supply to the brain is often incomplete and focuses on one pathway in a broader comparative aspect. The supply of oxygen and nutrients to the brain is very important for its proper functioning. The aim of this study is to describe the pathways supplying blood to the cranial cavity and to describe the arterial circle of the brain in the Patagonian mara. The study was conducted on 46 specimens using two methods. The first of them used a stained solution of the chemo-setting acrylic material. The second one, the colored liquid LBS 3060 latex. The arterial circle of the brain is a heart-shaped structure. It is formed by rostral cerebral arteries, caudal communicating arteries and the basilar artery. Blood supplies the arterial circle of the brain in three ways. First one is the basilar artery, which originates from the vertebral arteries. The second one is the internal carotid artery which joins a branch from the external ophthalmic artery. The third is the internal ophthalmic artery, which branches from the external ophthalmic artery.

Anatomical study of the eye arterial blood supply in adult river buffalo (Bubalus bubalis).

Obtaining information about the eye arterial supply in the buffalo can be a criterion for ocular diseases diagnosis and give a morphological basis for even more researches on the related clinical surgery of this animal. The aim of the present study was to describe the course and branches of the arteries supplying the eye in the adult river buffalo (Bubalus bubalis). In this study, the heads of eight buffaloes were prepared from the public slaughterhouse and dissected to study the eye arterial supply. This research results showed that the eye blood supply in the buffalo originates from the external ophthalmic, internal ophthalmic, superficial temporal and malar arteries. The external ophthalmic artery was given rise to branches to take part in the ophthalmic rete mirabile formation and also given off lacrimal, external ethmoidal, supraorbital and ciliary arteries as well as muscular branches to supply the eye ball and extra-ocular muscles. The internal ophthalmic artery was one of the sources of lateral posterior long ciliary artery. The superficial temporal artery was detached off some branches to supply the lateral angle of inferior and superior eyelids as well as lacrimal branch to supply lacrimal gland. The malar artery was originated from the infra-orbital artery and its branches were supplied the medial angle of inferior, superior and third eyelids. There were no obvious differences between buffalo and yak regarding arteries supplying the eyes. However, there were minor differences between buffalo and oxen, sheep and goat and there were obvious differences between buffalo and camel and giraffe.

Ocular Echobiometry and Resistivity Index of External Ophthalmic Artery in Agoutis (Dasyprocta prymnolopha)

Background: Veterinary Ophthalmology provides complementary information for the diagnosis of ocular pathologies. Studies in wild species are essential. Among the diagnostic techniques in ophthalmology, two-dimensional ultrasonography stands out. The agouti is a rodent belonging to the Dasyproctidae family that has been widely used as an experimental model. For these animals, sight is one of the crucial senses for their survival. The aim of this study was to evaluate the effectiveness of the two-dimensional ocular ultrasound technique to obtain anatomical measurements and the external ophthalmic artery resistivity index, presumably normal in the species Dasyprocta prymnolopha.Materials, Methods & Results: Forty eye bulbs of 20 adult rodents of the species were evaluated by ultrasonography. In these animals, B-mode echobiometry was performed using the transpalpebral approach and the hemodynamic study of the external ophthalmic artery using the color Doppler technique. All examinations were initiated by the left eye bulb and all measurements were performed by only one examiner. The collected data related to echobiometry were analyzed using Bioest 5.0 for Windows. Initially, normality was tested using the Shapiro-Wilk test for each parameter, then the paired t-test was performed, comparing right and left eyes, and a significance level of 5% (P < 0.05) was adopted. Based on the methodology used, the following values were obtained for the right and left eyeballs, respectively: anterior chamber thickness - mean of 1.28 ± 0.3 mm and 1.22 ± 0.1 mm; lens thickness - 8.27 ± 0.9 mm and 8.11 ± 0.9 mm; vitreous chamber thickness - 5.35 ± 0.48 mm and 5.30 ± 0.47 mm and axial length - 12.7 ± 0.9 mm and 13 ± 0.68 mm. The mean external ophthalmic artery resistivity values were 0.4305 ± 0.0390 and 0.4258 ± 0.0387 (right and left eye, respectively), characterizing a low resistance. There was no statistical difference between the right and left eyeballs in any of the studied parameters.Discussion: The use of the convex transducer was feasible, promoting adequate contact with the ocular surface and images of satisfactory quality for obtaining measurements, similar to what was observed in studies evaluating the ocular biometry of primates and dogs. The anterior chamber thickness values in this experiment did not differ statistically between the antimers, as well as observed for dogs. The data obtained for lens thickness did not differ statistically for antimers, like those obtained for other rodent species evaluated with the same methodology. The mean values of vitreous chamber thickness were like those observed in chinchillas but correspond to about half of that obtained for capybaras. In this study, the external ophthalmic artery was characterized in all animals, but obtaining the spectral tracing was difficult due to its fine caliber. In wild animals, and especially in wild rodents, there are few data reporting the resistivity of the ophthalmic artery, and there is a lack of studies, which can be explained by the behavioral characteristics of defense and by the high susceptibility to stress in capture, since the performing the technique requires, as in other procedures, the use of chemical containment.Keywords: Doppler flow, ultrasound, eye, agouti.

Lamina Cribrosa Capillaries Straighten as Intraocular Pressure Increases

PurposeThe purpose of this study was to visualize the lamina cribrosa (LC) capillaries and collagenous beams, measure capillary tortuosity (path length over straight end-to-end length), and determine if capillary tortuosity changes when intraocular pressure (IOP) increases.MethodsWithin 8 hours of sacrifice, 3 pig heads were cannulated via the external ophthalmic artery, perfused with PBS to remove blood, and then perfused with a fluorescent dye to label the capillaries. The posterior pole of each eye was mounted in a custom-made inflation chamber for control of IOP with simultaneous imaging. Capillaries and collagen beams were visualized with structured light illumination enhanced imaging at IOPs from 5 to 50 mm Hg at each 5 mm Hg increment. Capillary tortuosity was measured from the images and paired two-sample t-tests were used to assess for significant changes in relation to changes in IOP.ResultsCapillaries were highly tortuous at 15 mm Hg (up to 1.45). In all but one eye, tortuosity decreased significantly as IOP increased from 15 to 25 mm Hg (P < 0.01), and tortuosity decreased significantly in every eye as IOP increased from 15 to 40 mm Hg (P < 0.01). In only 16% of capillaries, tortuosity increased with elevated IOP. Capillaries had a surprisingly different topology from the collagen beams.ConclusionsAlthough high capillary tortuosity is sometimes regarded as potentially problematic because it can reduce blood flow, LC capillary tortuosity may provide slack that mitigates against reduced flow and structural damage caused by excessive stretch under elevated IOP. We speculate that low capillary tortuosity could be a risk factor for damage under high IOP.

Angiographic investigation of orbital vascular variations in the rabbit and implications for endovascular intra-arterial chemotherapy models

BackgroundThe New Zealand White rabbit (NZWR) is the first small-animal experimental model of intra-arterial chemotherapy (IAC) for retinoblastoma treatment. The NZWR has dual ophthalmic arteries (OA): the external OA (EOA)...

B-Mode and Doppler Ocular Ultrasound Evaluation in Healthy and Positive Dogs for Visceral Canine Leishmaniasis

Background: The use of ultrasound examination in the evaluation of ophthalmopathies has been gaining more and more space within the ophthalmologic clinical routine. The hemodynamic study of ocular vascularization may anticipate future changes, aiding in the adequate establishment of therapeutic conduits. The objective of this study was to evaluate the structures of the ocular bulb and to perform the hemodynamic evaluation of the flow of the external ophthalmic artery of dogs with canine visceral leishmaniasis (CVL) correlating with healthy animals.Materials, Methods &amp; Results: For this purpose, 100 animals were used, of these 70 positive for CVL and 30 healthy animals, submitted to B-mode and Doppler ultrasound examination. Two-dimensional evaluation included identification of ocular changes and biometry of the following segments: axial length (M1), anterior chamber depth (M2), lens thickness (M3), lens length (M4), glass chamber depth (M5), optical disc length (M6) and optic nerve length (M7). The Doppler velocimetric evaluation included the identification and hemodynamic evaluation of the external ophthalmic artery, being measured: systolic peak velocity (SPV), final diastolic velocity (FDV), resistivity index (RI) and pulsatility index (PI). Ophthalmopathies were frequent in animals with leishmaniasis in both right (91.42%) and left (29.14%) eyes, with identification of capsular cataract, lens dislocation, retinal detachment and lens rupture. No significant statistical difference (P &gt; 0.05) was observed when comparing the biometric values between the right and left eyes of the animals with CVL, as well as for the measurements between healthy and CVL animals. Hemodynamic indexes of the flow of the external ophthalmic artery presented narrow limits for the right and left eyes of the positive animals, not statistically different from each other. However, a significant difference was observed when compared to hemodynamic evaluations of the flow of the ophthalmic artery between the right eyes of the group of normal animals and that of the carriers of leishmaniasis, with the latter presenting values superior to the first one. The B-mode and Doppler ultrasonographic evaluation enabled the morphological characterization of the ocular bulb, the identification of ophthalmopathies and the hemodynamic evaluation of the external ophthalmic artery of dogs with canine visceral leishmaniasis, establishing values that could be used in clinical ophthalmologic routine.Discussion: The presence of ocular changes diagnosed by B-mode ultrasonography were common in dogs with canine visceral leishmaniasis. Ocular lesions were observed in 80.5% of dogs with leishmaniasis, presenting a high frequency, corroborating with the results in the present research. In 22% of the animals, B-mode ultrasonographic lesions were identified in both eyes, 64 of these presented changes only in the right eye and 16 in the left eye. Ophthalmopathies can be uni or bilateral and cause more than one alteration in the same eye, resulting from both the immune-mediated mechanisms caused by the agent and direct parasitism. Although the literature reports that the highest frequency of lesions is bilateral, only 16 animals had alterations in both eyes. The origin of ophthalmopathies may be related to the species and tropism of the parasite, type and duration of the immune response developed by the host. The greater frequency of bilateral ophthalmopathies can have correlation with the systemic disease, in which in the initial stages of the disease only one eye is affected and the occurrence of bilateral manifestations is related to the chronic cases.

Macroanatomic structure and morphometric analysis of middle ear in ostrich (Struthio camelus)

Ostrich (Struthio camelus) is a species belonging to the Struthionidae family of Struthioniformes order that does not have the flying ability among birds. The aim of this study was to make a subgross investigation on anatomical structures of middle ear in ostrich and to determine the morphometry of the columella. In the present study, 4 adult ostrich heads were used in the study. Tympanic cavity and the formations inside are removed from the skull by protecting the cranial roof. Subgross examinations of tympanic cavity, columella and other anatomic structures were then performed, and morphometric measurements of columella and some anatomical structures were performed using a digital calliper.It was determined that tympanic cavity, surrounded by ear capsule (os oticum), had a conical shape and was covered with mucosa that was tightly adjacent to the periosteum. Tympanic membrane, columella and osteochondral structures, ligaments, a branch of external ophthalmic artery and the presence of chorda tympani were detected in tympanic cavity. It was observed that columella was placed diagonally in tympanic cavity. The vestibular (proximal) end having a circular shape was found to have a large basis and annular ligament which ended up with thickened, small columns. Finally, we demonstrated anatomy and morphometric values of middle ear in ostrich. The anatomy and formations of the middle ear are clearly shown. It can be asserted that anatomical formations in the middle ear of an ostrich are similar to other birds.

Biometric, B-mode and color Doppler ultrasound assessment of eyes in healthy dogs

ABSTRACT: B-scan ultrasonography is an important diagnostic tool that allows characterization of internal organ anatomy and, when complemented by Doppler ultrasound, allows vascular hemodynamic assessment, increasing the diagnostic accuracy. Thus, the aim of the present study was the B-scan ultrasound characterization and measurement of the eyeball segments and assessment of the external ophthalmic artery by color and pulsed Doppler. Sixty eyeballs were assessed from 30 dogs of different breeds using an 8.5MHz microconvex transductor. First, biometry was performed by B-scan of the following segments: axial length (M1), anterior chamber depth (M2), lens thickness (M3), lens length (M4), vitreous chamber depth (M5), optical disc length (M6) and optic nerve diameter (M7). Colored Doppler identified the external ophthalmic article and pulsed Doppler assessed its flow, and the following were measured: systolic peak velocity (VPS), final diastolic velocity (VDF), resistivity index (IR) and pulse index (IP). No statistical difference was observed for the biometric values of the eye segments between the right and left eyes (p&gt;0.05). The vitreous chamber depth (M5) was shown to be the biometric variable with greatest bilateral symmetry, varying from 0.79 to 0.87cm and 0.78 to 0.86cm for the right and left eye, respectively. The ophthalmic artery was visualized over the optic nerve towards the eyeball, with flow stained red. There was no significant statistical difference between the Doppler velocimetric values for the ophthalmic artery between the right and left eye of the animals assessed (p&gt;0.05). The mean resistivity index (RI) showed average values equal to 0.63±0.03, bilaterally. The mean base velocity was 17.50cm/s and 18.18cm/s at the systolic peak and 6.21cm/s and 6.68cm/s at the end of the diastole, for the right and left eyes respectively. The anatomic, biometric and hemodynamic characterization using the ultrasound B-scan and the Doppler modalities permitted the ultrasonographic and Doppler velocimetric assessment of the eyeball components in dogs of different breeds, and it can be used in ophthalmic clinical routine to identify eye pathologies.

Ocular perfusion pressure and color Doppler imaging of the external ophthalmic artery of rabbits treated with sildenafil citrate.

BackgroundIt has been proposed that sildenafil citrate can increase ocular blood flow, and that this property can be used to treat ocular disorders that involve reflex vasoconstriction. This study therefore proposes to ascertain the vasodilator effect of the drug on retrobulbar circulation in healthy rabbits. For this matter rabbits treated with sildenafil citrate or saline solution had their intraocular pressure (IOP), mean arterial pressure (MAP), ocular perfusion pressure (OPP) and color Doppler imaging of the external ophthalmic artery measured prior to treatment and on days one (moment M1), seven (when M2), fourteen (moment M3), twenty-one (moment M4), and thirty (moment M5) of treatment.ResultsThe MAP and OPP values of treated group were lower than those of control group at all times, and the mean values differed statistically at moments M1 (S = 71.52 mmHg, C = 84.76 mmHg, p = 0.0356) and M5 (S = 71.38 mmHg, C = 85.52 mmHg, p = 0.0252). The IOP and color Doppler values of the external ophthalmic artery did not differ between tested groups.ConclusionsThe dose of 10 mg of sildenafil citrate administered to healthy rabbits causes systemic vasodilation and consequently lower values of MAP and OPP. However, it does not induce changes in IOP and retrobulbar hemodynamics identifiable by color Doppler assessment of the external ophthalmic artery.

Analysis of morphological variation of the internal ophthalmic artery in the chinchilla (Chinchilla laniger, Molina)

The aim of this investigation was the analysis of the variability within the internal and external ophthalmic artery in the chinchilla (Chinchilla laniger, Molina). The head vasculature of 65 individuals was analysed, with particular emphasis on the internal ophthalmic artery originating from the central and rostral part of the cerebral arterial circle. Head blood vessels were filled with acrylic latex for vascular corrosion casting. The results showed ten variants of blood supply for the orbit, with a predominance of the first variant (66.1%) = bilateral presence of the external ophthalmic artery originating from the maxillary artery. Other variants differed in symmetry and asymmetry, sites of origination and the coexistence of both internal and external arteries. Vascularisation of the brain in chinchillas originates mainly from the vertebra-basilar system. The observed variability seems to confirm the role of the basilar artery in the arterial blood supply of the brain in this species.

Ophtalmic Artery Microcatheterization for Research Purposes in Pigs. A Technical Note

ABSTRACTPurpose: To describe a technique for micro catheterization of the external ophthalmic artery (EO) in pigs for investigational and training purposes. Methods: Carotid angiography was performed in seven male domestic pigs. The external ophthalmic artery was reached with a microcatheter in order to administer a neoplastic drug in the eye. Results: The external ophthalmic artery could be found arising from the infraorbital (IO) artery in the bend of the internal maxillary (IM) artery. It could be reached in every animal. Conclusion: Following anatomic landmarks of the external carotid (EC) artery the ophthalmic artery can be easily reached and catheterized for training and investigational purposes.

Myogenic Oscillations in Rabbit Ocular Vasculature Are Very Low Frequency

Background/Aims: In a previously described model of isolated rabbit eye, we detected myogenic intrinsic vascular tone of unknown origin in the ophthalmic artery. In order to better understand the origin of these low frequency oscillations, we analyzed their spectral characteristics using fast Fourier. Methods: Hybrid New Zealand rabbits of either sex (n = 24) were used; they were divided into 2 groups according to age. The spectral characteristics of the myogenic behaviour of the rabbit external ophthalmic artery were analyzed using the fast Fourier algorithm. Results: The frequency of the oscillations of the myogenic activity seen in the rabbit external ophthalmic artery varied between 0.033 and 0.066 Hz (mean 0.045 ± 0.012 Hz), all in the region of very low frequency (VLF) oscillations (VLF <0.07 Hz for the rabbit). The frequency of spontaneous oscillations was higher in younger animals. Conclusion: Fast Fourier analysis proved to be an adequate mathematical tool to analyze the myogenic tone oscillations, which were all in the range of VLF in the model we used. These results indicate that myogenic vascular function of ocular blood flow is composed of VLF oscillations, and they provide a new explanation for the origin of VLF in arterial spectra. They also suggest that the ocular local myogenic vascular function observed is more efficient in younger animals.

Modulation of vasomotive activity in rabbit external ophthalmic artery by neuropeptides.

Purpose. To investigate the vasomotive activity upon the external ophthalmic artery of vasointestinal peptide (VIP) and neuropeptide Y (NPY) using a previously developed model. Methods. Isolated rabbit eyes (n = 12) were perfused in situ with tyrode through the external ophthalmic artery. Effects of intra-arterial injections of NPY 200 μg/ml (Group A; n = 6) and VIP 200 μg/ml (Group B; n = 6) on the recorded pressure were obtained. For statistical analysis, Student's paired t-test and Fast Fourier Transform were used. Results. Spontaneous oscillations were observed before any drug administration in the 12 rabbit models. NPY produced an increase in total vascular resistance and a higher frequency and amplitude of oscillations, while VIP evoked the opposite effects. Conclusions. This study provides evidence of vasomotion in basal conditions in rabbit external ophthalmic artery. Concerning drug effects, NPY increased arterial resistance and enhanced vasomotion while VIP produced opposite effects which demonstrates their profound influence in arterial vasomotion.

A Porcine Model of Selective Retinal Capillary Closure Induced by Embolization with Fluorescent Microspheres

To investigate the feasibility of creating an animal model of selective retinal capillary closure to mimic the capillary closure that occurs in diabetic retinopathy. Fluorescent microspheres of 10- or 15-μm diameter were delivered to one eye of anesthetized pigs via a customized cannula advanced through the carotid arterial system to the origin of the external ophthalmic artery that supplies blood to the eye in this species. After preliminary trials in 10 pigs, embolization was performed in one eye of 34 animals that were allowed to survive for 7, 14, or 28 days. Embolized eyes were assessed by fluorescein angiography, electroretinography (ERG), and, after enucleation, light (LM) and electron (EM) microscopy. The microspheres were detectable in the retina immediately after embolization, were restricted to the nerve fiber layer of the retina, and remained thereafter within the retina for periods up to 28 days. They effectively occluded embolized capillaries and some precapillary arterioles. No systemic or cerebral adverse effects were noted, thus allowing survival and subsequent follow-up. Embolization caused a reduction in the b-wave amplitude and the oscillatory potentials of the rod-cone bright-flash ERG but did not affect the amplitude of the a-wave. Embolization induced extracellular and intracellular edema confined to the inner and mid retina, and as a result the retinas of embolized eyes were thicker than those of fellow, nonembolized eyes. The outer retina and RPE were unaffected. This survival model of retinal embolization with microspheres should be useful in the study of the retinal effects of the capillary closure that may occur in diabetic eyes.

Amlodipine effects on vasomotion in rabbit external ophthalmic artery

In order to understand the role of ocular blood flow in normal and pathological conditions, knowledge of the pharmacological control mechanisms involved in the ocular vascular bed is essential. The present study was designed to investigate the reactivity of the rabbit external ophthalmic artery and its collaterals to amlodipine, in order to answer two questions: (1) What are amlodipine effects upon perfusion pressure and spontaneous oscillations in the in situ perfused rabbit eyes? (2) Can intraarterial amlodipine counteract ET-1 induced vasoconstriction? Rabbit external ophthalmic arteries (n = 12) in a head-mounted preparation were cannulated and perfused with warmed tyrode. Vasomotor response curves to intraarterial injections of amlodipine 3 mg/ml followed by phenylephrine 250 microg (group A, n = 6) and to amlodipine 3 mg/ml after an intraarterial injection of endothelin-1 (ET-1) 27 microg/ml (group B, n = 6) were obtained. For statistical analysis, the paired t-test and Fourier analysis of frequency spectrums of spontaneous oscillations were used. Before any drug administration, spontaneous oscillations were observed in the 12 rabbit models. In group A, amlodipine elicited vasodilation and a decrease in frequency and amplitude of the oscillations. In group B, ET-1 induced an increase in vasoconstrictor tone and vasomotion became more evident. With amlodipine after ET-1, we obtained vasodilation and abolition of the vasospasm. Our study has two main conclusions: (1) amlodipine, an L-type calcium channel blocker, caused intense vasodilation and decreased both frequency and amplitude of the spontaneous oscillations observed in the rabbit external ophthalmic artery and its collaterals, and (2) when we applied amlodipine in arteries previously contracted by the administration of ET-1, vascular resistance greatly decreased and spontaneous oscillations were abolished. Since ET-1 levels are increased in several ischemic ocular diseases, amlodipine might be beneficial in these patients, allowing a protective action against vasospasm.

L-Arginine and L-Nitroarginine Methylester Effects on Vasomotion in Isolated Rabbit Eyes

Background/Aims: Although nitric oxide (NO) has been shown to be essential for maintaining the basal blood flow in the retina and optic nerve head, its exact role in vasomotion is still controversial. This study investigated L-arginine (L-Arg) and N-nitro-L-arginine methylester (L-NAME) effects on vascular reactivity in a model of isolated rabbit eye. Methods: Rabbit external ophthalmic arteries (n = 12) in a head-mounted preparation were cannulated and perfused with warmed Tyrode solution. The effect of intraluminal pressure as a measure of total vascular resistance was assessed. Response curves to intra-arterial injections of 3 growing concentrations of L-Arg (n = 6) and L-NAME (n = 6) were obtained. Results: Without any drug administration, spontaneous oscillations were observed in all the models. L-Arg (NO precursor) induced vasodilation and decreased both frequency and amplitude of the periodic oscillations. L-NAME (NO synthase inhibitor) produced a strong vasoconstrictor tone and stimulated vasomotion, causing a faster rate of pulsatility. Conclusion:L-Arg and L-NAME acted as modulators of ocular vascular tone. L-Arg elicited vasodilation and decreased vasomotion while L-NAME produced a strong vasoconstrictor tone and caused a faster rate of pulsatility. These findings justify the need to investigate NO precursors and antagonists as possible alternative therapeutics in vascular eye diseases.

Endothelin-1 effects on spontaneous oscillations in choroidal arterioles

This study characterizes the effects of endothelin-1 (ET-1) on the perfusion pressure of the choroidal vasculature using in situ perfused isolated rabbit eyes. Rabbit external ophthalmic arteries (n = 12) in a head-mounted preparation were cannulated and perfused with warmed tyrode. The three-way polypropylene catheter was further connected to a pressure transducer and the effect of intraluminal pressure as a measure of total vascular resistance was assessed. Response curves to intra-arterial injections of ET-1 (group A; n = 6) and to an intravitreal injection followed by an intra-arterial injection of ET-1 (group B; n = 6) were obtained. Data were studied using paired t-test and fast Fourier transform. Before any drugs were administered, spontaneous oscillations were observed in the 12 rabbit models. In group A, ET-1 induced a short and weak vasodilating effect followed by a strong and long-lasting vasoconstrictor tone. Vasomotion became more evident, showing a higher frequency and shorter amplitude of oscillations. In group, B the intravitreal injection produced no significant changes in registered pressure or vasomotion characteristics. The intra-arterial injection produced effects similar to those observed in group A. Our study has three main findings: (i) the choroidal vasculature demonstrated spontaneous oscillations in perfusion pressure in basal conditions in all rabbit eye models; (ii) ET-1 applied intra-arterially induced a short drop in perfusion pressure followed by a long withstanding contraction; and (iii) intra-arterial ET-1 modulated the frequency and amplitude of the spontaneous oscillations, causing a faster rate of pulsatility.

Intrinsic vasomotricity and adrenergic effects in a model of isolated rabbit eye

We aimed to investigate the responsiveness of the ocular arteries to adrenergic drugs in a model of perfused isolated rabbit eye. Rabbit external ophthalmic arteries (n = 15) in a head-mounted preparation were cannulated and the retinal and uveal vasculature perfused at a constant flow with warmed tyrode. The three-way polypropylene catheter was further connected to a pressure transducer and intraluminal pressure was taken as a measure of vascular resistance. Effects of intra-arterial injections of phenylephrine (group A, n = 5), prazosin (group B, n = 5) and phentolamine (group C, n = 5) on the recorded pressure were obtained. Student's paired-t test and one-way analysis of variance were used for statistical analysis (p < 0.05). Intrinsic vasomotricity was observed in all preparations prior to any drug administration. Phenylephrine produced an increase in total vascular resistance. Intrinsic vasomotricity became more evident, showing a lower frequency but higher amplitude of oscillations. Evoked vasomotor responses with phenylephrine (250 microg/ml) were inhibited by intra-arterial administration of the selective alpha(1)-adrenergic antagonist, prazosin (0.5 mg/ml), as well as the non-selective alpha-adrenergic antagonist phentolamine (6 mg/ml). Rabbit external ophthalmic arteries showed spontaneous contractions under constant perfusion. Phenylephrine elicited a vasoconstrictor response that was inhibited by adrenergic antagonists. In addition, the intrinsic vasomotricity was enhanced by phenylephrine and blocked by adrenergic antagonists. These results show that under in vitro perfusion the territory presents similar responses to adrenergic drugs to those observed in in vivo models and also provides evidence of myogenic autoregulatory properties in the rabbit ophthalmic artery and/or choroid.

Correlação entre a pressão arterial média e o fluxo sangüíneo na artéria oftalmica externa em gatos (felis catus linnaeus, 1758)

Foram utilizados 20 gatos sem raça definida, com massa corpórea entre 2 e 4 quilogramas, hígidos, anestesiados com tiletamina e zolazepam (6,0 mg/kg). A artéria femoral foi canulada de forma asséptica e um manômetro acoplado a uma coluna de ar foi conectada ao cateter, a PAM foi aferida antes e a cada 15 minutos até o término do exame ultra-sonográfico. A fluxometria da artéria oftálmica externa foi obtida através do equipamento de ultra-sonografia dotado de eco-doppler, com transdutor setorial de 6,0 MHz, aplicado diretamente sobre a córnea. Cada olho teve o fluxo de sua artéria aferido pelo programa do próprio aparelho, sendo tomadas três amostras. O índice de resistência vascular foi calculado com base nos valores do fluxo sistólico e diastólico médio de cada vaso. Obteve-se um valor médio para a PAM de 144,9 ± 26,68 mmHg e uma velocidade de fluxo de 41,3 ± 14,28 cm/s para a artéria oftálmica externa no olho direito em sístole, 23,95 ± 11,46 cm/s em diástole e 42,75 ± 12,64 cm/s no olho esquerdo em sístole, 25,45 ± 9,61 cm/s em diástole, não existindo diferença significativa entre os olhos. O índice de resistência vascular calculado foi de 0,4175 para a artéria oftálmica externa no olho direito e 0,4015 para a do olho esquerdo, sem diferença significativa entre os olhos. Os resultados apontam para um mecanismo intrínseco de controle do fluxo, controlado por fatores locais na artéria oftálmica externa. Os valores do índice de resistência denotam uma artéria de baixo fluxo. Como conclusão, têm-se os valores de referência acima citados para a PAM e para o fluxo sangüíneo na artéria oftálmica externa em gatos sem raça definida anestesiados com tiletamina e zolazepam, e a informação de que não existe correlação entre esses valores.