Decrease In Vessel Diameter Research Articles

Iloprost dilates rat small arteries: role of K(ATP)- and K(Ca)-channel activation by cAMP-dependent protein kinase.

The effect of the stable prostacyclin analog iloprost and its mechanism of action were investigated with the use of pressurized rat tail small arteries with a spontaneous myogenic tone. Iloprost concentration dependently dilated these vessels with a half-maximal effective dose of 5.0 +/- 0.5 x 10(-8) M. Application of 10(-7)-10(-6) M glibenclamide, a blocker of ATP-sensitive potassium (K(ATP)) channels, inhibited the iloprost-induced dilation. Glibenclamide did not affect the basal vessel diameter. The application of 5 x 10(-5)-10(-3) M tetraethylammonium (TEA) and 5 x 10(-9)-10(-7) M iberiotoxin, blockers of calcium-activated potassium (K(Ca)) channels, decreased vessel diameter in the presence of iloprost. Both TEA and iberiotoxin reduced the basal vessel diameter. Glibenclamide at 10(-6) M inhibited the dilation produced by 5 x 10(-5) M Sp-5,6-DCl-cBIMPS, an activator of adenosine 3',5'-cyclic monophosphate (cAMP)-dependent protein kinase. Iberiotoxin at 10(-7) M decreased vessel diameter in the presence of Sp-5,6-DCl-cBIMPS. H-89 and Rp-8-CPT-cAMPS, blockers of cAMP-dependent protein kinase A (PKA), inhibited the iloprost-induced dilation of these vessels. With use of the whole cell configuration of the patch-clamp technique, it was observed that 5 x 10(-7) M iloprost enhanced an outward current, determined largely by K(Ca) channels, 1.79 +/- 0.17-fold in freshly isolated smooth muscle cells from rat tail small artery. These data show that iloprost dilates rat tail small arteries with a spontaneous myogenic tone and suggest that K(ATP) as well as K(Ca) channels are involved in this effect, which is mediated, at least partly, by PKA.

Change in intramural strain distribution in rat aorta due to smooth muscle contraction and relaxation.

Effect of smooth muscle contraction on intramural strain distribution in rat thoracic aorta was investigated with residual strain considered. Short segments sliced from the aortas were cut radially to release residual strain in an aerated Krebs-Ringer solution (37 degrees C). Each segment opened up immediately to form an arc. Opening angle was measured at this point and after smooth muscle contraction and relaxation. The angle increased from 97 +/- 11 degrees (means +/- SE, n = 14) to 153 +/- 14 degrees with the contraction and decreased to 68 +/- 9 degrees with the relaxation, indicating increase in residual strain with smooth muscle contraction. Intramural strain distribution at various pressures was calculated from the opening angle and pressure-diameter relations of the aortas. Strain distribution was almost uniform at 55 mmHg under smooth muscle relaxation, whereas this pressure exceeded 200 mmHg because of the increase in residual strain and decrease in vessel diameter under smooth muscle contraction. These results suggest aortic smooth muscle may change its contractile state through myogenic response to keep intramural strain distribution uniform against temporary change in blood pressure and thus maintain mechanical homeostasis in the aortic wall.

Fundamental Concepts Regarding Sizing and Discrimination of Air Bubbles and Red Cell Aggregates Using Pulsed-Doppler Ultrasound.

The embolus to blood power ratio (EBR) model is briefly described, which predicts that emboli become more detectable as Doppler carrier frequency decreases and vessel diameter decreases. The EBR model indicates that the use of the backscattered power from the blood in the Doppler sample volume and the use of more than one carrier frequency will be useful in discriminating size and composition of an embolic signal. The EBR model is shown to provide both sizing and discrimination of red cell aggregates from air bubbles, using dual frequency interrogation of an embolus (1.6 and 2.4 MHz). (ECHOCARDIOGRAPHY, Volume 13, September 1996)

Influence of glycemic control on viscosity and density of plasma and whole blood in Type-1 diabetic patients

The hemorheological properties of blood play an important role in determining blood flow. Blood inertia, as characterized by blood density, controls blood flow in the large arteries, whereas blood viscosity becomes increasingly important with decreasing vessel diameter. In order to evaluate the impact of glycemic control on the rheological properties of blood, we examined viscosity (shear range: 600-0.2 s −1) and density of plasma and whole blood in 26 Type-1 diabetic patients and in 24 healthy controls, matched for age and sex. The diabetic subjects were subdivided into two groups according to their degree of glycemic control: 14 patients with good (HbA 1c = 7.1 ± 0.6%), and 12 patients with poor control (HbA 1c = 8.7 ± 0.7%). Diabetic patients as a whole did not differ from healthy controls in any of the rheological parameters. Subdivision of the patients due to their degree of glycemic control led to a marked rheological separation of Type-1 diabetic subjects with significantly lower plasma ( P < 0.008) and whole blood viscosity ( P < 0.03 at 10 and 25 s −1), and plasma density ( P < 0.05) in well controlled patients. Compared with healthy controls, well controlled diabetic patients had significantly lower values of viscosity ( P < 0.005) and density ( P < 0.05) of plasma. Poorly controlled patients, on the other hand, did not differ from healthy controls in the examined rheological parameters. There seems to be a positive influence of good glycemic control on hemorheology in Type-1 diabetic patients.

Prevention of cerebral vasospasm after experimental subarachnoid hemorrhage by RO 47-0203, a newly developed orally active endothelin receptor antagonist.

Since their discovery in 1988, endothelins have attracted scientific interest because of their extremely potent and long-lasting vasoconstrictive effects, similar to cerebral vasospasm in humans. In this study, the efficacy of the orally active endothelin receptor antagonist RO 47-0203 for prevention of cerebral vasospasm after experimental subarachnoid hemorrhage, using the two-hemorrhage dog model, was investigated. Twenty-eight beagle dogs were used in this laboratory experiment. Fourteen animals each were assigned to the treatment and control groups. In the treatment group, each dog received two single doses of 30 mg/kg RO 47-0203 orally per day. The diameter of the basilar artery decreased from 1.36 +/- 0.17 mm on Day 1 to 1.19 +/- 0.23 mm on Day 8 in the treatment group, whereas in the control group, the vessel diameter decreased from 1.48 +/- 0.19 mm on Day 1 to 1.02 +/- 0.22 mm on Day 8. These results corresponded to a decrease of vessel diameter of 13.1% +/- 11.2% in the treatment group and a decrease of vessel diameter of 30.7% +/- 12.4% in the control group (P < 0.001). Concentrations of endothelin-1 in cerebrospinal fluid significantly increased with time after subarachnoid hemorrhage. These results emphasize the important role of endothelin in the development of cerebral vasospasm and present first-time evidence that prevention of cerebral vasospasm can be achieved by the endothelin receptor antagonist RO 47-0203.

Effect of standing on non-pregnant uterine blood flow.

Uterine artery blood flow measurements made solely in the recumbent position may miss physiological changes that occur while patients are upright. We evaluated the effect of standing on the minute blood flow volume of the ascending uterine artery, the pulsatility index (PI), resistance index (RI) and waveforms and on the PI and RI of the myometrial spiral arteries and waveforms at 3-8 and at 9-14 min standing in 74 non-pregnant women. At 9-14 min, the uterine artery blood flow volume had decreased by an average of 34% and the RI had significantly increased in 70% of subjects. Decreased uterine artery blood flow volume was associated with increased distal resistance and with decreased vessel diameter, possibly due to stretching or kinking of the uterine arteries. Changes in the spiral artery PI paralleled changes in the uterine artery PI at 9-14 min, but were less pronounced. Spiral artery PI and RI were not related to the uterine artery blood flow volume while women were recumbent, although they were significantly related while women were standing. The effects of age, uterine mobility and uterine position on uterine artery or spiral artery blood flow were apparent only while women were standing. We conclude that standing as well as recumbent studies are necessary when uterine and myometrial blood flow are evaluated, and that uterine flow volume per minute should be measured whenever possible.

Pulmonary parenchymal abnormalities of vascular origin: high-resolution CT findings.

High-resolution computed tomography (HRCT) is a proved imaging modality for use in assessment of infiltrative lung disease. Findings suggestive of infiltrative lung disease on HRCT scans include ground-glass attenuation, consolidation, nodules, and interlobular septal thickening. Similar patterns, however, may be caused by various vascular abnormalities including regional or diffuse increase in blood flow, pulmonary edema, pulmonary hypertension, and thromboembolism. A correct diagnosis can usually be made by careful analysis of the pulmonary vasculature. Parenchymal abnormalities of vascular origin are associated with increased or decreased vessel diameter, vascular compression, or intraluminal filling defect.

Flow pulsation and network structure in mesenteric microvasculature of rats.

Red cell velocity was measured by a fiber-optic laser-Doppler anemometer microscope in microvessels of the mesentery of spontaneously hypertensive rats (SHR) and normotensive Wistar-Kyoto control rats (WKY) with high temporal resolution. Based on the velocity data, the propagation velocity of flow pulse along single microvessels as well as the arteriovenous distributions of the mean volumetric flow, the amplitude of flow pulsation, and the phase lag of the flow relative to the systemic pressure were analyzed in relationship to the vessel wall rheology and the network topology. The propagation velocity was 3.5-134 cm/s in arterioles of 12-43 microns in diameter, and it increased with increasing diameter. The mean volumetric flow exhibited a power law relationship to the vessel diameter, in which the exponents were 3.16 and 3.30 for arterioles and 3.03 and 2.85 for venules in SHR and WKY, respectively. The exponents for arterioles were > 3 (P < 0.1) and different between SHR and WKY (P < 0.12). The amplitude of the flow pulsation also varied in a power law with the vessel diameter, whose exponents for arterioles were 3.41 and 3.52 for SHR and WKY, respectively. The flow phase lag increased gradually with decreasing vessel diameter in arterioles and increased comparatively rapidly with increasing vessel diameter in venules, which suggests more compliant vessel walls for venules than arterioles. The slope of the increase in the flow phase lag with the vessel diameter in arterioles of SHR was larger than that for WKY (P < 0.05). This difference in the flow phase lag distribution and the difference in the exponent of the mean flow rate vs. diameter relationship may reflect that the number of small arterioles relative to large ones is reduced in SHR microvasculature compared with that in WKY.

Xylem vascular anatomy and water transport of Salicornia europaea

The xylem anatomy, changes in vessel member diameter at stem nodes and branch junctions, and effects of these changes on water flow rates and water potential in greenhouse and field grown Salicornia europaea L. (Chenopodiaceae) have been investigated. There was a two-fold decrease in vessel diameter at branch junctions and stem nodes. In greenhouse grown plants, this decrease resulted in a 1000-fold decrease in water flow rates, and a four-to eight-fold increase in resistance to water flow across branch junctions and stem nodes relative to within-internode flow rates. However, in field grown plants, there were no differences in water flow across branch junctions and stem nodes compared with water flow within internodes. Water potentials in field plants were 3–15 times lower than in greenhouse plants. Under field conditions, hypersalinity is probably the key determinant of Salicornia water relations. Localized reductions in vessel member diameter in Salicornia appear to result from developmental changes in vasculature attending axillary bud growth. Reductions in Salicornia vessel diameter, therefore, may not be hydraulically functional adaptations per se. Rather, they may reflect a consequence of developmental branching.

"Caged" phenylephrine: development and application to probe the mechanism of alpha-receptor-mediated vasoconstriction.

A "caged" analogue of the alpha-adrenergic receptor agonist phenylephrine (PE) was prepared by exploiting the 2-nitrobenzyl protecting group and using a synthetic procedure developed to permit preferential derivatization at the amino group. On isolated adult rat mesenteric arterioles, caged-PE had no measurable effects at concentrations up to 100 microM; 0.5-ms light flashes in the presence of caged-PE, however, produced marked and dose-dependent vasoconstriction. Flash-induced vasoconstrictions were blocked by the alpha-receptor antagonist phentolamine and were unaffected by the beta-receptor antagonist propranolol, indicating that the light-induced responses reflect the selective activation of alpha-adrenergic receptors. After a single flash, a large transient decrease in vessel diameter was recorded, and in most vessels, this was followed by a smaller, sustained constriction. The sustained component of the contraction was selectively eliminated when Ca2+ was removed from the bath, which suggests that different mechanisms underlie the transient and the sustained responses to PE. The responses to single flashes of varying intensities occurred with a mean latency of 460 ms, which is consistent with the intermediacy of several steps between alpha-receptor activation and contraction. We anticipate that it will be possible to extend this approach to develop caged analogues of other neurotransmitters for mechanistic and kinetic studies.

Interaction between adenosine and angiotensin II in renal microcirculation

In order to examine the possibility of an interaction between adenosine and angiotensin II (A II) in the control of the renal microcirculation, we studied the effects of agonists and antagonists of both substances by means of in vivo microscopy in the split hydronephrotic rat kidney. In a first series of experiments ( n = 6), local application of the A II receptor antagonist saralasin (10 −6 mol · liter −1 abolished the vasoconstriction and the reduction of glomerular blood flow induced by the A 1-adenosine receptor agonist N 6-cyclohexyladenosine (CHA, local concentration 10 −7 mol · liter −1). Without saralasin (second series, n = 6), CHA reduced glomerular blood flow and decreased vessel diameters as previously reported from our laboratory. In a third series of experiments ( n = 6), A II significantly reduced vessel diameters and glomerular blood flow both alone and during blockage of the A 1-adenosine receptor by the selective antagonist 1,3-dipropyl-8-cyclopentylxanthine (DPCPX, 10 −5 mol · liter −1). In additional experiments, we excluded nonspecific receptor effects of saralasin and confirmed the inhibitory action of DPCPX on the adenosine-induced vasoconstriction. We suppose that adenosine needs a functioning A II receptor system for its vasoconstrictor action, whereas A II can induce a nonadenosine-dependent vasoconstriction.

Endothelin-1 Is a Potent Constrictor in Conductive and Resistive Coronary Arteries

The action of endothelin-1 (ET-1) in canine and porcine coronary artery ring preparations and perfused canine and porcine myocardium was examined in vitro to determine the site of action of ET-1 in the coronary vasculature. ET-1 had a vasoconstrictor effect that was more potent in smaller diameter ring preparations. The EC50s for both canine and porcine ring preparations decreased with a decrease in vessel diameter and the EC50 of ET-1 in the perfused myocardium was three to four times lower than in the smallest ring preparation. The results suggest that ET-1 may cause cardiac ischemia by constriction of resistive vessels rather than by epicardial coronary artery spasm.

Studies In Vitro and in Canine Mesenteric Vessels

The accuracy and reliability of a noninvasive pressure-sensitive capsule for the endoscopic measurement of esophageal varix pressure was evaluated. Capsule pressure was correlated with direct intraluminal pressure measurements. The influence of vessel wall tension on capsule pressure was also assessed. In vitro studies demonstrated an excellent correlation (r greater than or equal to 0.94; p less than 0.001) between the pressure obtained with the capsule and intraluminal pressure over a range of vessel diameters and wall thicknesses. In vivo correlation of pressures obtained with the capsule with direct venous pressure measurements was excellent (r = 0.85). However, this correlation decreased with a decrease in vessel diameter (group 1 diameter greater than or equal to 10 mm, r = 0.95; group 2 diameter greater than or equal to 5 mm but less than 10 mm, r = 0.75; group 3 diameter greater than or equal to 3 mm but less than 5 mm, r = 0.81). This decrease in accuracy was significant (p less than 0.001) between group 1 and groups 2 and 3. In vitro and in vivo, capsule pressure variability was significantly greater (p less than 0.001) in vessels of smaller diameter. Wall tension significantly influenced capsule pressure (p less than 0.05), although this effect was only seen in large "vessels" with a diameter beyond a clinically relevant range. Therefore, despite obtaining technically acceptable capsule pressure measurements in ideal experimental conditions, the accuracy and variability of these measurements are limited by vessel size.

Vasoconstriction and neural excitation in response to transient hypoxia in the rat hippocampal slice

The vascular and neural responses to transient hypoxia in the rat hippocampal slice were studied. Neural hyperexcitability produced by tissue hypoxia was associated with localized decreases in the diameter of precapillary arterioles. Vasoconstriction occurred periodically along the length of vessels observed. The mean percent decrease in vessel diameter in these narrowed regions was 10.25%. Population spikes recorded in the cell body layer of the dentate gyrus showed a mean increase in amplitude of 71.3%. The mean latency to peak response was similar for both the vessels and neurons. The results suggest mechanisms by which autoregulatory influences on microvessel caliber may be counteracted in conditions of hypoxia and hypotension in the whole animal.

Fossil Root- and Stemwood of Chionanthus Retusus Lindl. Et Paxt. from the Late Pleistocene of Akashi, Japan

Fossil root- and stemwood of Chionanthus retusus has been found from the Late Pleistocene stratum at Akashi, Hyogo Prefecture, central Japan. The woods of fossil and extant C. retusus are described and compared. The fossil rootwood closely resembles that of the extant individuals in being ring-porous with large pores arranged in one layer in the earlywood, and small pores that gradually decrease in diameter from the earlywood, and are arranged in a flame-like pattern in the latewood. It differs from the wood of the extant species in the larger diameter of wide pores, the quite gradual decrease in vessel diameter from the earlywood to the latewood, and the narrower and lower rays. The fossil stemwood is quite similar to the stemwood of extant C. retusus in being ring-porous with large pores arranged in one or two layers in the earlywood, and small pores .that abruptly decrease in diameter from the earlywood, and are arranged in a flame-like pattern. It differs from the wood of the extant species in the larger diameter of wide pores, and the lower rays. Based on their similarity, these fossil woods are identified as the rootand stemwood of C. retusus.

Rheological Properties of Blood and their Possible Role in the Circulation and Development of Intracranial Hemorrhage in Preterm Infants

Blood viscosity and other rheological properties of blood have important effects on blood circulation. In preterm infants, blood viscosity (at given hematocrit), plasma viscosity and red cell aggregation are decreased compared to term neonates and adults. In addition, the Fahraeus-Lindqvist effect (i.e., decrease in blood viscosity with decreasing vessel diameter) is more pronounced in preterm infants. This suggests that blood flow through arteries, arterioles and veins is facilitated in preterm infants. The large neonatal red cells are less filterable and less able to enter small capillaries than adult red cells. This suggests that the passage of neonatal red cells through narrow capillaries and splenic pores is impaired. The high risk of intracranial hemorrhage in small preterm infants may in part result from poor red cell aggregation, impeded passage of their large red cells through narrow cerebral capillaries and raised blood viscosity due to rapid transfusion of adult blood.

Mechanisms of endothelium-dependent vascular smooth muscle relaxation

In recent years, it has become apparent that several agents which relax blood vessels do so by endothelium-dependent mechanisms. Among the first group of agents shown to modulate vascular tone via an interaction with the endothelium were angiotensin II and bradykinin. Subsequent studies indicated that the endothelium responded to these polypeptides by producing and releasing prostacyclin (PGI,) which, in turn, could modulate the change in vascular tone. In 1980, Furchgott and Zawadzki [l] reported that the endothelium was requisite for acetylcholine (Ach)-induced vasodilation. The relaxing factor, however, was not PG12 since relaxation was not blocked by cyclooxygenase inhibitors (i.e. indomethacin or aspirin; Fig. 1). Since this initial report, numerous laboratories have confirmed the endothelium-dependence of Ach and a variety of other vasodilators (for review, see Refs. 2-4). Dr. Furchgott and his colleagues coined the term “endothelium-delved relaxing factor” (EDRF) for the substance(s) which mediates the decrease in smooth muscle contraction. Numerous techniques have been used to remove the endothelium from the intima of arteries: (1) mechanical (i.e. rubbing, blotting with filter paper, balloon catheter, frayed nylon cord, adhesion to glass coverslip), (2) physical (blowing air on the intima, hypotonic perfusion, perfusion for up to 10min with distilled H20, exposure to hype~onic medium with added IV), (3) chemical (removal of Ca2+ and addition of chelators-EGTA/EDTA), and (4) enzymatic (perfusion or incubation with trypsin or collagenase). In all cases, coincident with endothelium disruption as verified by microscopy, is the loss of a relaxation response observed in conduit and muscular arteries to the agents summarized in Table 1. In arteries, the endothelium becomes increasingiy difficult to remove as the vessel diameter decreases. Some laboratories using the techniques above have been unsuccessful in removing the endothelium from isolated mesenteric arterioles (75-100 pm in diameter). In the perfused mesenteric arcade of the rat, exposure to distilled water for 5-10 min was required to destroy the endothelium. Obviously, when harsh measures are required to remove the endothelium, the medial layer of smooth muscle may also be

Wood Anatomy of Begoniaceae, with Comments on Raylessness, Paedomorphosis, Relationships, Vessel Diameter, and Ecology

CARLQUIST, S. (Rancho Santa Ana Botanic Garden and Department of Biology, Pomona College, Claremont, CA 9171 1). Wood anatomy of Begoniaceae, with comments on raylessness, paedomorphosis, relationships, vessel diameter, and ecology. Bull. Torrey Bot. Club 112: 59-69. 1985.-Six collections of four species of Begonia ranging from moderately to markedly woody (for the genus) are analyzed for qualitative and quantitative wood features. Begonia wood has vessels mostly solitary and oval or circular in outline, scalariform lateral wall pitting on vessels, tyloses in vessels, libriform fibers which are sometimes septate, vasicentric scanty axial parenchyma, tall and wide multiseriate rays (uniseriates absent) composed of erect cells (near-rayless in one collection), and storied structure. These features match those of Datiscaceae closely; features which do not may be related to the distinctive habit of woody Begoniaceae: semisucculent canelike stems of finite duration produced by a rhizome. As with similar stems of Piperaceae (which is not closely related to Begoniaceae), rays have erect cells predominantly or exclusively, rays alter little during ontogeny, and vessels have scalariform lateral wall pitting almost exclusively. These three features seem related to paedomorphosis, as does the presence of occasional scalariform perforation plates in early secondary xylem of Begonia. Quantitative features of Begonia wood mark all species as mesomorphic. Wood mesomorphy of B. parviflora increases with age of stem, suggesting greater transpiration from taller stems. Increase in vessel diameter with age is common in many dicotyledon trees and shrubs, and may relate to ability of progressively larger root systems to tap greater water supplies, as well as to the tendency for a larger and more exposed crown to transpire more. Some annual and short-lived perennial dicotyledons tend to have a progressive decrease in vessel diameter with age, which can be correlated with progressive drying of soil in the habitats of these species.

Incidence of recurrent stenosis after carotid endarterectomy determined by digital subtraction angiography

The results of recent reports of nonselected patients studied by noninvasive techniques suggest there is a 10 to 36 percent rate of restenosis within the first 1 to 2 years after carotid endarterectomy. In the present study of nonselected patients examined by intravenous digital subtraction angiography, only 6.7 percent of operated vessels had recurrent stenosis with a 50 percent or greater decrease in vessel diameter at a mean of 28.5 months postoperatively. These data, when compared with the results of most noninvasive studies, suggest that many of the early lesions regress after 1 to 2 years, as suggested by Zierler et al [ 8] or that there is a true difference in the rates of restenosis between centers, possibly due to subtle differences in surgical technique or patient risk factors, or both. A symptomatic recurrence rate of only 2.7 percen and a 6.7 percent overall rate of hemodynamically significant recurrent stenosis support the conclusions from earlier and larger series that carotid endarterectomy is a highly effective and durable operation. Although it is important that research centers continue to study the natural history of carotid artherosclerosis and serial changes after carotid endarterectomy, these results suggest that for routine clinical follow-up, frequent and expensive periodic tests to detect recurrent stenosis may not be warranted.

The ultrastructure of the middle cerebral artery and its associated nerve fibers in the squirrel monkey and baboon

This study describes the ultrastructural characteristics of the middle cerebral artery and its related neural elements in the squirrel monkey and baboon. The cytoarchitecture of the M-1 segment as well as that of the smaller extracerebral and intracerebral vessels is comparable in both animals. Smooth muscle elements are occasionally found within the intimai lining. The nerve bundles associated with vessels contain fewer myelinated fibers as the vessel diameter decreases. The cytological relationship between the neural structures and the smooth muscle cells are discussed.