Characterization of postjunctional alpha-adrenoceptors in the isolated aorta of the snake Bothrops jararaca

1. To characterize the alpha-adrenoceptors present in Bothrops jararaca aorta, selective alpha-adrenoceptor agonists and antagonists were used.2. The relative order of potency of the tested agonists was noradrenaline > phenylephrine > clonicline.3. Prazosin was more potent than phentolamine and yohimbine in antagonizing noradrenaline response, since the PA₂ values were 9.91, 7.59 and 7.33, respectively.4. Yohimbine was also able to block the contraction produced by phenylephrine, an alpha-1 agonist.5. These results suggest the existence of an alpha-1 subtype of adrenoceptor in this preparation which, however, presents some different characteristics from those described for mammals.     

Surgical anatomy of the internal carotid artery

Starting from the carotid trigone, a surgical approach to the parapharyngeal part of the internal carotid artery is described. The retrostyloidal part of the lateropharyngeal space is opened up from laterocaudal after resecting the posterior belly of the digastric muscle and the styloidal muscles. Vulneration of the cranial nerves (VII, IX, X) has to be prevented.     

On the atrophy of the internal carotid artery in capybara

Capybara might be a useful model for studying changes in cerebral circulation as the natural atrophy of the internal carotid artery (ICA) occurs in this animal at maturation. In this study, confocal and electron microscopy combined with immunohistochemical techniques were applied in order to reveal the changes in morphology and innervation to the proximal part of ICA in young (6-month-old) and mature (12-month-old) capybaras. Some features of the basilar artery (BA) were also revealed. The ICA of young animals degenerated to a ligamentous cord in mature animals. Immunolabelling positive for pan-neuronal marker protein gene product 9.5 but negative for tyrosine hydroxylase was observed in the proximal part of ICA at both ages examined. Axon varicosities positive for synaptophysin were present in the adventitia of ICA of young animals but were absent in the ligamentous cord of mature animals. In the ICA of young animals, adventitial connective tissue invaded the media suggesting that the process of regression of this artery began within the first 6 months of life. An increase in size of the BA was found in mature animals indicating increased blood flow in the vertebro-basilar system, possibly making capybara susceptible to cerebrovascular pathology (e.g. stroke). Capybara may therefore provide a natural model for studying adaptive responses to ICA regression/occlusion.The financial support of the Graduate Fund, UCL, London, UK (C. Steele) and the Brazilian Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPQ) Brazil (200516/01-9; A.A.C.M. Ribeiro) is gratefully acknowledged.     

Effect of various types of sports on the anatomy of the common carotid artery and the internal jugular vein

By means of ultrasonography the common carotid artery and the internal jugular vein at certain sports have been investigated. In swimmers the internal jugular vein is essentially dilated as compared to the common carotid artery. In high jumpers there is not any noticeable differences between the width of the artery and the vein. These data should be taken into account at training sportsmen. They are also important for development of investigations in the ultrasound anatomy.     

Biomechanical properties of canine vertebral and internal carotid arteries

In order to understand the participation of the geometrical and elastic properties of the large cerebral arteries in the maintenance of brain circulatory homeostasis, biomechanical properties of isolated internal carotid artery (extracranial part) and vertebral artery (intrathoracic part) were investigated both in a relaxed and in an activated (3x 10(-6) mol.l-1 norepinephrine) state of the smooth muscle. Quasi-static large deformation mechanical test was carried out by means of changing the intraluminal pressure slowly (2.5 mmHg.sec-1) and cyclicly in a range of 0-250 mmHg at in vivo length while external diameter was recorded continuously as a function of the intraluminal pressure. Maximum active tangential strain was found to be -2.7 +/- 1.6% at 70 mmHg for the internal carotid artery, and -5.9 +/- 1.1% at 100 mmHg for the vertebral artery. Incremental elastic modulus decreased and distensibility increased in both arteries following smooth muscle activation, these alterations, however, were larger in the case of the vertebral artery. A U-shaped characteristic impedance of vertebral artery was found both in relaxed and in constricted states of this vessel. Minimum values for the relaxed and the activated segments were found at 90 mmHg and 120 mmHg, respectively. These results support the hypothesis that certain biomechanical properties of the large arteries, like impedance, can be regarded as controlled variables that may contribute to the optimization of circulatory functions.     

The homologies of the lorisoid internal carotid artery system

The development of the “internal carotid” arterial system of the lesser galago (Galago senegalensis senegalensis)is described. The first artery to be formed is a typical promontory artery which runs through the middle-ear cavity and gives off the stapedial artery. It terminates in the cranial cavity by dividing into the middle cerebral, anterior cerebral, and two ophthalmic arteries. It is accompanied by the internal carotid nerve. A medially directed artery to the external carotid rete arises from the commencement of the promontory artery and joins the caudal end of the rete, whose cranial end lies in the foramen lacerum. As the promontory artery enters the cranial cavity, it communicates with the cranial end of the rete. The promontory artery, between the origin of the artery to the rete and its connection with the rete, becomes narrowed and eventually disappears. Thus the internal carotid artery is formed from the commencement of the promontory artery, the artery to the rete, the external carotid rete, and the terminal intracranial part of the promontory artery. The relationships of the artery to the rete indicate that it is the homologue of the human ascending pharyngeal artery.     

Energy dissipation and pulse wave attenuation in the canine carotid artery

This paper presents methods for calculating, for a segment of artery in vivo, (1) viscous and viscoelastic energy dissipation as a function of time, and (2) the viscous and viscoelastic components of the frequency-dependent attenuation coefficient. The calculations require measurement of arterial diameter and of intra-arterial pressure and flow-rate at two sites along the vessel. Viscous energy dissipation is calculated from the radius-dependent velocity shear in the lumen given by linear theory from the pressure measurements. The attenuation coefficient for a given harmonic of heart rate is calculated as half the sum of the viscous and viscoelastic components at that frequency of the energy dissipated per unit length by forwardtravelling waves, divided by the forward-wave flow work input to the segment at that frequency. Measurements in canine carotid arteries indicate that wall viscoelasticity contributes relatively little to energy dissipation per cardiac cycle and pulse wave attenuation.     

The primitive course of the internal carotid artery in mammals.

In all recent mammals the internal carotid artery at the level of the auditory capsule is derived from the embryonic dorsal aorta. In adults of various groups, the artery lies in positions which are classified as medial or promontory. It is shown that these character states arise by a process of differential growth affecting the relative positions of the dorsal aorta and the cochlear promontory. There is no evidence for separate vessels in the embryo which could give rise to non-homologous internal carotid arteries in the two positions. It follows that the concept of a primitive mammalian morphotype with both a medial and a promontory internal carotid artery in the same individual presents a formidable embryological problem. It is recommended that, in the absence of supporting evidence, the widespread current taxonomic and palaeontological use of this hypothetical morphotype should be regarded with suspicion.     

Effects of prostacyclin on the canine isolated basilar artery

Prostacyclin (PGI₂) produced a biphasic response in canine isolated basilar arteries. In low doses (1 × 10^?8M?1 × 10^?7M) PGI₂ caused a slight but consistent relaxation of resting muscle tone. In low concentrations (1 × 10^?8M?1 × 10^?6M) PGI₂ antagonized muscle contractions caused by serotonin or prostaglandin (PG) F_2α. This relaxant effect with low doses of PGI₂ on the isolated cerebral artery contrasts with findings obtained with other PGs and supports the hypothesis that PGI₂ is a mediator of vasodilatation. However, in 1 × 10^?5M concentrations PGI₂ contracted the arterial muscle and did not antagonize contractions induced by serotonin or PGF_2α.     

A morphometric study of age-related changes in the elastic systems of the common carotid artery and internal carotid artery in humans

The present study aims to quantify the distribution of the elastic fiber system in the walls of the common carotid artery and the internal carotid artery in humans. In order to identify specific fibers, segments of carotid arteries were stained using the Verhoeff (for elastic fibers), Weigert (for elastic and elauninic fibers) and Weigert-oxone (for elauninic and oxytalanic fibers) methods. A histomorphometric study was undertaken in order to estimate the linear density (LV) of the fibrous components present in the elastic system and determine the total length of these components in each segment. Microscopic fields were sampled using a test system in which the colors and bands defined in the current study were superimposed on the histological preparations. Data were analyzed through linear regression using first-order rate equations and computer software. The internal carotid artery can be loosely defined as muscular in nature. In order to classify common carotid arteries, it is necessary to consider subject age. From 0 to 30 years of age, the LV of mature elastic fibers does not change significantly in either (left or right) common carotid artery, although a significant reduction in the LV of this type of fiber occurs in the right internal carotid artery. The most marked reduction in oxytalanic and elauninic fibers occurs between 0 and 10 years of age, becoming less intense between the ages of 10 and 30.     

Stenotic occlusive lesions of internal carotid artery in diabetic patients

Diabetes deteriorates atherosclerotic changes in the arteries. The aim of the study was to assess the prevalence and localization of stenotic atherosclerotic lesions of the internal carotid artery (ICA) in patients with diabetes. A prospective analysis of angiography findings was carried out in 150 diabetic and 150 non-diabetic patients with symptoms of cerebral ischemia using double-blind angiogram readings by two independent investigators. The degree of stenosis was determined using the North American Symptomatic Carotid Endarterectomy Trial (NASCET) criteria. Stenoses of the proximal arterial segment accounted for the majority of extracranial ICA stenoses, being more frequent in diabetic (left ICA 50.7%, right ICA 58.0%) than in the non-diabetic patients (left ICA 29.3%, right ICA 32.7%). Diabetic patients revealed a more significant rate of unilateral tandem ICA stenoses (14.0-21.3%), as well as a statistically significantly higher prevalence of intracranial ICA stenoses (left ICA 24.0% and right ICA 17.3%) than did non-diabetic patients (left and right ICA 3.3% each). Our results confirm that there is a morphological basis in ICA for increased incidence of ICA lesions in patients with diabetes as compared to those without it. Data on the incidence of stenotic ICA lesions in diabetes suggest the importance of assessing overall ICA status using digital subtraction angiography. Such an assessment is a precondition for an optimal therapeutic approach, especially in diabetic patients who are at an increased risk of cerebrovascular disease.