Decrease In Vessel Diameter Research Articles

A novel method for subarachnoid hemorrhage to induce vasospasm in mice

Mouse models take advantage of genetic manipulations that can be achieved in this species. There are currently two accepted mouse models of subarachnoid hemorrhage (SAH) and cerebral vasospasm (CVs). Both are technically demanding and labor intensive. In this study, we report a reproducible and technically feasible method to induce SAH, and subsequently CVs, in mice. We tested this model in multiple strains of mice that are commonly used for genetic manipulation. MethodsSAH was induced in C57BL/6NCr, FVB, 129S1, BalbC and SJL mice, weighing 28–32g, by an intracisternal vessel transection technique. Animals were perfused with India ink at 24h postprocedure and vessel diameters were quantified. Brain slices were obtained for hematoxylin–eosin staining (H&E) to look for vascular changes consistent with CVs. ResultsThere was no mortality during or after the procedure. Four of the five mouse strains showed significant CVs at 24h postprocedure characterized by decreased vessel diameter of the middle cerebral artery close to the Circle of Willis. Histologically, the vessel wall displayed significant corrugation and thickening, consistent with CVs. ConclusionA novel mouse model to induce SAH is described and tested in several mouse strains. Four of the five strains used in this study developed CVs after the induction of SAH. The procedure is brief, straightforward, reproducible with low mortality, and applicable to commonly used background strains for genetically engineered mice.

Cardiovascular effects of fentanyl and propofol on hemodynamic function in rabbits

To evaluate short-term cardiovascular effects after IV administration of boluses of fentanyl in rabbits. 6 healthy New Zealand White rabbits. Each rabbit was anesthetized with propofol (4.0 to 8.0 mg/kg, IV); anesthesia was maintained by administration of propofol (1.2 to 1.3 mg/kg/min, IV). Subsequently, 3 injections of fentanyl (0.0053 mg/kg) were administered. Before and for 10 minutes after injections, the following variables were measured: vessel diameter, peak systolic blood flow velocity, minimum diastolic blood flow velocity, end-diastolic blood flow velocity, time-average blood flow velocity, mean volumetric flow (VFmean), resistance index (RI), and pulsatility index for the left common carotid artery after the first injection and abdominal aorta after the third injection; mean arterial pressure (MAP); heart rate (HR); arterial oxygen saturation; end-tidal partial pressure of carbon dioxide; and body temperature. Echocardiography was performed after the second injection. Fentanyl injections caused a transient and significant decrease in diameter and VFmean of the abdominal aorta and end-diastolic blood flow velocity of the left common carotid artery and an increase in peak systolic blood flow velocity and RI of the left common carotid artery. Also, MAP, HR, and body temperature decreased significantly after injections. Fentanyl injections induced a short-term decrease of vessel diameter in the abdominal aorta and increased resistance in the distal distribution area of the left common carotid artery. Results revealed decreases in MAP, HR, and body temperature, with an increasing effect after the third bolus injection, which indicated a cumulative drug effect.

Selective Inhibition of Angiogenesis in Small Blood Vessels and Decrease in Vessel Diameter throughout the Vascular Tree by Triamcinolone Acetonide

To quantify the effects of the steroid triamcinolone acetonide (TA) on branching morphology within the angiogenic microvascular tree of the chorioallantoic membrane (CAM) of quail embryos. Increasing concentrations of TA (0-16 ng/mL) were applied topically on embryonic day (E) 7 to the chorioallantoic membrane (CAM) of quail embryos cultured in petri dishes and incubated for an additional 24 or 48 hours until fixation. Binary (black/white) microscopic images of arterial end points were quantified by generational analysis of vessel branching (VESGEN) software to obtain major vascular parameters that include vessel diameter (D(v)), fractal dimension (D(f)), tortuosity (T(v)), and densities of vessel area, length, number, and branch point (A(v), L(v), N(v), and Br(v)). For assessment of specific changes in vascular morphology induced by TA, the VESGEN software automatically segmented the vascular tree into branching generations (G(1)... G(10)) according to changes in vessel diameter and branching. Vessel density decreased significantly up to 34% as the function of increasing concentration of TA according to A(v), L(v), Br(v), N(v), and D(f). TA selectively inhibited the growth of new, small vessels because L(v) decreased from 13.14 +/- 0.61 cm/cm(2) for controls to 8.012 +/- 0.82 cm/cm(2) at 16 ng TA/mL in smaller branching generations (G(7)-G(10)) and for N(v) from 473.83 +/- 29.85 cm(-2) to 302.32 +/- 33.09 cm(-2). In contrast, vessel diameter (D(v)) decreased throughout the vascular tree (G(1)-G(10)). By VESGEN analysis, TA selectively inhibited the angiogenesis of smaller blood vessels, but decreased the vessel diameter of all vessels within the vascular tree.

Effects of propofol on ultrasonic indicators of haemodynamic function in rabbits

ObjectiveTo evaluate the cardiovascular effects of intravenous propofol in rabbits. Study designRandomized, prospective, experimental study. AnimalsThirty-one female New Zealand White rabbits. MethodsRabbits were allocated to one of two groups [propofol (P) or conscious (C)]. In C (n = 16) vascular dimensions were measured using ultrasound of the left common carotid artery (ACC) and the abdominal aorta (AA). Group P (n = 15) received propofol 4.0–8.0 mg kg−1 intravenously (IV). Anaesthesia was maintained with propofol at 1.2–1.3 mg kg−1 minute−1. Subsequently, three propofol injections (8 mg kg−1) were given. Before and for 10 minutes after each injection the following vascular and haemodynamic variables were recorded (a) at the ACC after the first injection; and (b) at the AA after the second injection: vessel diameter [D, (mm)], peak systolic, minimum diastolic, end-diastolic and average blood flow velocities [psBFV, mdBFV, edBFV, Vave (cm second−1)], average volumetric flow [VFave (mL s−1)], resistance index (RI) and pulsatility index (PI) mean arterial pressure (MAP), heart rate (HR), arterial oxygen saturation (SpO2) and end-tidal CO2 (Pe′CO2). Echocardiography was performed after the third propofol bolus injection to investigate changes in cardiac parameters [fractional shortening, FS (%)]. ResultsIntravenous propofol injections caused a significant decrease in vessel diameter, volumetric flow and edBFV, and significant increases in psBFV, RI and PI. Baseline levels for vessel diameter and psBFV were restored 6–8 minutes after injection. Propofol injection decreased FS significantly by 7 minutes after injection while MAP and HR were significantly reduced for 4 minutes.Conclusion and clinical relevance Injections of propofol (8 mg kg−1) produced an immediate, transient decrease in vascular diameters, a significant decrease in ventricular performance and an increase in peripheral vascular resistance (ACC and AA). Propofol should probably not be or only carefully used in rabbits with ventricular dysfunction.

Inhibition of Nitric Oxide Synthase Enhances Cocaine's Developmental Toxicity: Vascular and CNS Effects

Ischemia and/or reperfusion injury from free radicals may cause cocaine's toxicity, including its effect upon neurobehavioral development. We previously used salicylate to measure hydroxyl free radicals in chick embryos exposed to cocaine. The combination was more toxic than cocaine alone. We postulated that salicylate enhanced the vasoconstriction and toxicity via inhibition of compensatory processes (eg by inhibition of the synthesis of vasodilatory prostanoids and/or nitric oxide). A nontoxic dose of N(G)-nitro-L-arginine methyl ester (L-NAME) was used to inhibit nitric oxide synthase to test this hypothesis. In one experiment, cocaine was injected every 1.5 h (total dose =67.5 mg/kg egg) on day 15 of development, 1 h after injection of L-NAME (200 mg/kg egg) to determine viability and hatchability, which are measures of toxicity. Another experiment measured diameters of blood vessels after L-NAME injection, followed by NaCl or cocaine infusion (0.23 mg/egg/min; total dose=67.5 mg/kg egg) at 15 and 5 min afterwards. Lastly, brains of embryos pretreated with L-NAME before cocaine injections were analyzed for nitric oxide synthase activity. Cocaine decreased viability and hatchability. L-NAME enhanced cocaine's effect upon both parameters. Blood vessel diameters were decreased by cocaine after 15 min of infusion. L-NAME+cocaine caused a decrease in vessel diameter as soon as 5 min into the infusion and was greater with time, compared with other groups. Enzyme activity in brains was decreased only in the L-NAME+cocaine group. Thus, inhibition of nitric oxide synthesis interferes with the embryos' capacity to mount a compensatory vasodilatory response.

SU‐FF‐I‐51: New Combined High‐Resolution Region‐Of‐Interest Microangiographic Detector and Large Field of View Image Intensifier System: A Contrast‐To‐Noise Comparison

Purpose: To demonstrate the advantage of combining a new high‐resolution region‐of‐interest (ROI) microangiographic detector (MA) and a standard x‐ray image intensifier (II), using contrast‐to‐noise ratios (CNR) of vessel phantoms within a scattering medium. Methods and Materials: The MA was mounted onto a Toshiba Infinix 3000 C‐arm angiographic unit so that the user can switch between the MA and II during an intervention at any viewing angle. Projection images can be acquired at nearly identical geometry with either detector, allowing for accurate inter‐comparisons. CNRs were measured for vessel phantoms (50–1000μm inner‐diameter polyethylene tubing) filled with iodine‐contrast agent and placed on a uniform head‐equivalent phantom used to simulate the scatter and beam hardening effects of the head. Both detectors were operated with optimal exposure techniques (allowing the II system to choose the ‘best’ kVp and mAs settings and selecting an exposure (mAs) that provides a sufficiently high signal for the MA). The CNR provides a quantitative measure of object visibility in the image, and hence system performance. Results: Compared to the II, the MA provides consistently higher CNR for all vessel sizes, with an average improvement factor (CNRMA/CNRII) of 1.6. A clear trend is observed, with CNR improvement factors increasing with decreasing vessel diameter. Conclusion: A new MA‐II system has been developed allowing use of the high resolution MA as an alternative to a standard II and easy switching between the two during a procedure, when the imaging task demands. The MA is shown to provide increased CNR for all vessel phantoms in a uniform head‐equivalent scattering material. This combined system should lead to improved neurovascular image‐guided interventions. (Partial support from NIH Grants R01EB002873, R01NS43924, Toshiba Medical Systems Corp., and the Frank B. Silvestro Endowment Scholarship).

Selective Photothermolysis of Blood Vessels Following Flashlamp-Pumped Pulsed Dye Laser Irradiation: In Vivo Results and Mathematical Modelling Are in Agreement

Laser therapy using the pulsed dye laser is the standard treatment for port-wine stains (PWS). But the mechanism of action has not been elucidated completely, yet. The dorsal skin-fold chamber model in hamsters was used to investigate the effects of laser treatment (lambda(em)=585 nm; pulse duration: 0.45 ms; fluence: 6 J per cm2) on blood vessels. Vessels (n=3394) were marked with FITC dextran (MW 150 kDa) and diameters (2-186 microm) were measured using intravital fluorescence microscopy up to 24 h following irradiation. Histology (H&E, TUNEL, CD31) was taken 1 or 24 h after irradiation. The experimental results were compared with the predictions of a mathematical model based on the finite-element method. Following irradiation treatment the number of unperfused vessels decreases with decreasing vessel diameter in vivo. Histology indicated a restriction of tissue injury to the irradiated area after 1 h. Blood vessels contained aggregated red blood cells. After 24 h tissue damage occurred also outside the irradiated area and thrombus formation was visible. These results were in agreement with the mathematical calculations. In addition to initial physical effects after pulsed dye laser treatment delayed biological processes contribute significantly to the reduction of perfused blood vessels. Because of incomplete photocoagulation of smaller blood vessels (diameter 2-16 microm) a complete bleaching of PWS seems to be unlikely.

Pharmacology and Pharmacodynamics of Bevacizumab as Monotherapy or in Combination with Cytotoxic Therapy in Preclinical Studies

Preclinical models have examined the pharmacologic and pharmacodynamic activities of an anti-vascular endothelial growth factor (VEGF) humanized, monoclonal antibody, bevacizumab, and/or its murine equivalent A4.6.1. These studies found that single-agent therapy with bevacizumab/A4.6.1 resulted in tumor growth inhibition of 20 different human tumor cell lines (13 tumor types) implanted into nude mice irrespective of the route of administration or tumor location. Several of these studies also observed significant inhibition of tumor metastases. Various studies have examined the feasibility of combining anti-VEGF therapy with cytotoxic or biological agents. Combining bevacizumab/A4.6.1 with doxorubicin, topotecan, paclitaxel, docetaxel, or radiotherapy resulted in additive or synergistic tumor growth inhibition. Changes in vascular functions were frequently reported, including decreased vessel diameter, density, and permeability in response to treatment. A reduction in interstitial fluid pressure was also observed. In some studies, these improvements resulted in an increase in intratumoral uptake of chemotherapy, implying that the most effective use of anti-VEGF therapy is in combination with chemotherapy. Alternatively, combination treatment with radiation increased tumor oxygenation and tumor growth inhibition. Interestingly, anti-VEGF therapy has also been reported to reduce the development of ascites in ovarian mouse models. Finally, safety pharmacology studies with bevacizumab in cynomolgus monkeys showed that this agent is generally well tolerated with no unexpected adverse events.

Influence of Gravity on Radiographic Contrast Material–Based Measurements of Regional Blood Flow Distribution

Rationale and Objectives Radiographic measurement of regional blood flow distribution in the lungs is potentially biased because the contrast material used to track flow is denser than blood. The authors performed this study to evaluate the effect of gravity on flow estimates by using an experimental test phantom and numeric simulations. Materials and Methods Cross-sectionally uniform boluses of radiopaque contrast material were delivered at the upstream end of a horizontal inlet tube connected to a downstream axisymmetric bifurcation attached to collecting tubing spirals. The phantom was imaged by using both planar angiography and dynamic multi–detector row computed tomography (CT) during the passage of the bolus through the phantom. The images were analyzed to determine the relative amounts of contrast material traveling through the top and bottom branches of the bifurcation by using varying Reynolds numbers and ratios of inlet tube volume to bolus volume. Numeric simulations of flow within a straight channel, with use of a dispersion operator intended to simulate settling of the bolus due to gravity, were performed under conditions representative of those in the experiments. Results When the plane of the bifurcation was vertical and actual flow through the two branches was equal, the fraction of contrast material passing through the downward-directed branch increased with decreasing Reynolds number and increasing inlet tube–bolus volume ratio. This occurred in both the experiments and the simulations. Conclusion Because in the circulation Reynolds number decreases and pathway length increases with decreasing vessel diameter, the accuracy of regional flow measurements obtained with angiography or CT within the lungs may be limited by density differences between contrast material and blood.

Inhibition of Endothelin-converting Enzyme Activity in the Rabbit Basilar Artery

OBJECTIVE Endothelin (ET)-1 may be involved in the regulation of cerebrovascular resistance under pathological conditions, most notably during the development of vasospasm after subarachnoid hemorrhage. Blocking ET-converting enzyme activity may be a promising approach to the prevention of cerebral vasospasm after subarachnoid hemorrhage. METHODS In this study, the effects of several putative ET-converting enzyme inhibitors were investigated after intracisternal application in rabbits, to inhibit basilar artery contractions induced by big ET-1 (2 × 10−6 mol/L). RESULTS In the group pretreated with [d-Val22]big ET-1[16–38] (2 × 10−5 mol/L) (n = 8), the angiographically measured diameter of the basilar artery changed from 0.63 ± 0.12 mm to 0.66 ± 0.12 mm. In the control group (n = 8), the diameter of the basilar artery decreased from 0.71 ± 0.13 mm to 0.57 ± 0.15 mm. These results corresponded to an increase in vessel diameter of 5 ± 10% in the treatment group and a decrease in vessel diameter of 20 ± 16% in the control group (P = 0.014). In the group pretreated with captopril (2 × 10−4 mol/L) (n = 8), the angiographically measured diameter of the basilar artery changed from 0.64 ± 0.11 mm to 0.71 ± 0.10 mm. These results corresponded to an increase in vessel diameter of 14 ± 19% in the treatment group, compared with a decrease in vessel diameter of 20 ± 16% in the control group (P = 0.014). CONCLUSION These results demonstrate that [d -Val22]big ET-1[16–38] and captopril act as highly potent ET-converting enzyme inhibitors, affecting big ET-1-induced contraction of the rabbit basilar artery.

Branching exponent heterogeneity and wall shear stress distribution in vascular trees.

A bifurcating arterial system with Poiseuille flow can function at minimum cost and with uniform wall shear stress if the branching exponent (z) = 3 [where z is defined by (D(1))(z) = (D(2))(z) + (D(3))(z); D(1) is the parent vessel diameter and D(2) and D(3) are the two daughter vessel diameters at a bifurcation]. Because wall shear stress is a physiologically transducible force, shear stress-dependent control over vessel diameter would appear to provide a means for preserving this optimal structure through maintenance of uniform shear stress. A mean z of 3 has been considered confirmation of such a control mechanism. The objective of the present study was to evaluate the consequences of a heterogeneous distribution of z values about the mean with regard to this uniform shear stress hypothesis. Simulations were carried out on model structures otherwise conforming to the criteria consistent with uniform shear stress when z = 3 but with varying distributions of z. The result was that when there was significant heterogeneity in z approaching that found in a real arterial tree, the coefficient of variation in shear stress was comparable to the coefficient of variation in z and nearly independent of the mean value of z. A systematic increase in mean shear stress with decreasing vessel diameter was one component of the variation in shear stress even when the mean z = 3. The conclusion is that the influence of shear stress in determining vessel diameters is not, per se, manifested in a mean value of z. In a vascular tree having a heterogeneous distribution in z values, a particular mean value of z (e.g., z = 3) apparently has little bearing on the uniform shear stress hypothesis.

Nitric oxide-mediated arteriolar dilation after endothelial deformation.

Previously, we frequently observed dilation of arterioles after agonist-induced constrictions. We hypothesized that deformation of the endothelium during decreases in diameter of isolated arterioles elicits the release of nitric oxide (NO). In isolated arterioles of rat mesentery, phenylephrine (PE, 10(-7) M)-, U-46619 (10(-7) M)-, and KCl (50 mM)-induced constrictions were followed by potent dilations. Inhibition of NO synthase with N(omega)-nitro-L-arginine (L-NNA, 2 x 10(-4) M) or removal of the endothelium significantly enhanced constriction and reduced the postconstriction dilation. In the presence of 80 mmHg of intraluminal pressure, an increase in extraluminal pressure (P(e)) to 75 mmHg for 20 s and 1 and 2 min decreased vessel diameter. After release of P(e), arterioles dilated as a function of the duration of diameter reduction by P(e). Removal of the endothelium or administration of L-NNA significantly diminished the post-P(e) dilations. In cultured mesenteric arteriolar endothelial cells (EC), PE, U-46619, or KCl did not increase, whereas ACh did increase, the production of NO, as measured by a fluorometric assay for nitrite. Furthermore, when EC, cultured on a stretched silicone membrane, were subjected to deformation by shortening the membrane to 50% of its original length, NO release increased significantly. Based on all of the above, we propose that deformation of EC per se elicits release of NO, a mechanism that modulates arteriolar constriction.

Decreased compliance on arterial anastomoses.

The present study was undertaken to examine the cross-sectional vascular compliance at the anastomotic site. We performed end-to-end anastomosis on the carotid artery of six pigs using continuous 6/0 polypropylene. Four carotid arteries were excised and mounted in a perfusion chamber while the remaining two were left in living animals. We used pulsed ultrasound (NIUS 02) to generate detailed longitudinal profiles of diameter and compliance in the proximity and on the anastomosis. On the anastomosis, the vessel diameter decreases (-1 to -2.6% of diastolic diameter) when blood pressure increases with an exponential correlation (R2 = 0.75). The arterial compliance at the anastomosis was negative: the vessel cross-section reduction for a pulse pressure of 1 up to 32 mmHg was 0.9 to 2% of diastolic vessel cross-section. Vessel movement generated a dynamic stenosis whose magnitude seems to depend on blood pressure level. Increasing blood pressure causes the retraction of vessel ends which causes vessel lumen reduction. These results suggest that continuous suture does not provide the continuity of mechanical properties of the artery.

Vascular smooth muscle mechanics in isolated perfused segments of carotid arteries

Background: We hypothesized that smooth muscle contraction and relaxation responses in a muscle bath (isometric tension) would be different than responses of intact vessels (isotonic tension). Methods: Bovine carotid artery contractile responses to the catecholamine, norepinephrine, and smooth muscle relaxant, 3-isobutyl-1-methylxanthine, were examined in strips of vessels in a muscle bath and in intact whole vessels in an isolated perfused whole-vessel perfusion apparatus. Results: The maximal tension in the muscle bath depended on the length of the strip. The responses of whole vessels to increasing pressure was curvilinear. The maximal decrease in vessel diameter in intact vessels in response to the catecholamine and norepinephrine occurred at low intraluminal pressures. The dose-response curve to norepinephrine was shifted to the left in intact vessels compared with strips of vessels in the muscle bath, which suggests that whole vessels were more sensitive to norepinephrine. The maximal increase in diameter to increasing intraluminal pressure occurred in the presence of the phosphodiesterase inhibitor, 3-isobutyl-1-methylxanthine, which suggests that there was significant intrinsic tone in the vascular smooth muscle. Conclusions: These results suggest that there are differences in the contractile properties of the vascular smooth muscle that are related to the ex vivo system used to examine smooth muscle responses. Responses obtained in isolated perfused whole vessels may more closely approximate in vivo responses. (Surgery 2000;127:148-54.)

Voxel sensitivity function description of flow‐induced signal loss in MR imaging: Implications for black‐blood MR angiography with turbo spin‐echo sequences

The conditions in which the image intensity of vessels transporting laminar flow is attenuated in black-blood MR angiography (BB-MRA) with turbo spin-echo (TSE) and conventional spin-echo (CSE) pulse sequences are investigated experimentally with a flow phantom, studied theoretically by means of a Bloch equation-voxel sensitivity function (VSF) formalism, and computer modeled. The experiments studied the effects of: a) flow velocity, b) imaging axes orientation relative to the flow direction, and c) phase encoding order of the TSE train. The formulated Bloch equation-VSF theory describes flow effects in two-dimensional (2D)- and 3D-Fourier transform magnetic resonance imaging. In this theoretical framework, the main attenuation mechanism instrumental to BB-MRA, i.e., transverse magnetization dephasing caused by flow in the presence of the imaging gradients, is described in terms of flow-induced distortions of the individual voxel sensitivity functions. The computer simulations predict that the intraluminal homogeneity and extent of flow-induced image intensity attenuation increase as a function of decreasing vessel diameter, in support of the superior image quality achieved with TSE-based BB-MRA in the brain. Magn Reson Med 41:575–590, 1999. © 1999 Wiley-Liss, Inc.

Interpretation of Nonpulsatile Arterial Pressure-Flow Relations During Cardiopulmonary Bypass

To the Editor: We read with great interest the recent article by Urzua et al. [1]. The authors state that linear regression of in vivo steady-state, nonpulsatile pressure-flow relationships reveals a non-zero pressure intercept that is much higher than central venous pressure. The authors interpret this "waterfall" pressure as possibly resulting from high "yield pressure" in smaller vessels. The authors also suggest that a more accurate index of systemic vascular resistance (SVR) may be obtained by using this waterfall pressure intercept, rather than central venous pressure. We believe that there is a more reasonable interpretation of the data of Urzua et al. [1] that involves direct application of Poiseuille's law. In the case of nonpulsatile flow, hydraulic resistance is inversely proportional to peripheral vessel diameter raised to the power of 4. When steady-state, nonpulsatile flow is decreased, there is a corresponding change in distending pressure and, hence, vessel diameter. According to Poiseuille's law, incremental decreases in vessel diameter lead to disproportionately larger increases in hydraulic resistance. Indeed, Figure 3in the authors' manuscript demonstrates nonlinear increases in SVR as blood flow decreases. It is expected that further increases in SVR would occur at lower blood flows. The authors offer two potential explanations for the proposed "linear" pressure-flow relation, a constant resistor and a diode, but ignore the third, and by far most likely, explanation: a variable resistor. Because the author's data did not quantify blood flow at very low blood pressures, it is very likely that their data could be equally well fit to the nonlinear Poiseuillean relation that would intersect the y-axis very close to central venous pressure. Thus, the slope of the curvilinear Poiseuillean pressure-flow curve would increase greatly at low flows as vessel diameter decreases. This is a fundamental concept in biofluid mechanics that the authors seem to have overlooked. Douglas A. Hettrick, PhD* Judy R. Kersten, MD* Paul S. Pagel, MD, PhD* David C. Warltier, MD, PhD*[dagger][double dagger] Departments of * Anesthesiology, [dagger] Pharmacology and Toxicology, and [double dagger] Medicine Medical College of Wisconsin Zablocki Veterans Affairs Medical Center; Milwaukee, WI 53226

The never ripe mutant provides evidence that tumor-induced ethylene controls the morphogenesis of agrobacterium tumefaciens-induced crown galls on tomato stems

We confirm the hypothesis that Agrobacterium tumefaciens-induced galls produce ethylene that controls vessel differentiation in the host stem of tomato (Lycopersicon esculentum Mill.). Using an ethylene-insensitive mutant, Never ripe (Nr), and its isogenic wild-type parent we show that infection by A. tumefaciens results in high rates of ethylene evolution from the developing crown galls. Ethylene evolution from isolated internodes carrying galls was up to 50-fold greater than from isolated internodes of control plants when measured 21 and 28 d after infection. Tumor-induced ethylene substantially decreased vessel diameter in the host tissues beside the tumor in wild-type stems but had a very limited effect in the Nr stems. Ethylene promoted the typical unorganized callus shape of the gall, which maximized the tumor surface in wild-type stems, whereas the galls on the Nr stems had a smooth surface. The combination of decreased vessel diameter in the host and increased tumor surface ensured water-supply priority to the growing gall over the host shoot. These results indicate that in addition to the well-defined roles of auxin and cytokinin, there is a critical role for ethylene in determining crown-gall morphogenesis.

Remodeling with neointima formation in the mouse carotid artery after cessation of blood flow.

The ability of gene targeting in the mouse species presents a powerful tool to determine the role of specific molecules in vascular biology. Using a denuding-injury procedure, we recently reported that intimal lesions can be induced in the carotid artery of outbred mice. The technical challenge associated with achieving complete denudation and the relatively small size of the developing lesions prompted us to design the present model of neointima formation and vascular remodeling in the carotid artery of the inbred FVB mouse strain. Complete ligation of the vessel near the carotid bifurcation induced rapid proliferation of medial smooth muscle cells, leading to extensive neointima formation in the presence of an endothelial lining. Thrombus formation was not observed except in the most distal part of the vessel adjacent to the ligature. At 4 weeks after ligation, luminal area was reduced by approximately 80% through a combination of decreased vessel diameter and neointima formation. Ultrastructural analysis provided evidence for cell death in the developing neointima as well as the remodeling media. The present model might be useful in identifying those genes important for neointima formation and vascular remodeling.

Vasoconstriction Increases Pulmonary Nitric Oxide Synthesis and Circulating Cyclic GMP

Vascular shear stress increases when blood flow or blood viscosity increases or when vessel diameter decreases. In the systemic circulation, shear stress is a potent stimulus for endothelial nitric oxide synthesis. We studied isolated rat lungs to determine whether increasing shear stress increases nitric oxide synthesis in the pulmonary circulation. Lungs were given the vasoconstrictor, U46619 (a thromboxane analogue), and perfused at constant flow rates or at constant pressure, since constant pressure perfusion minimizes changes in shear stress with vasoconstriction. The subsequent effect of the NOS inhibitor,Nω-methyl-l-arginine (LMA), or the soluble guanylyl cyclase inhibitor, 6-anilino-5,8-quinolinodione (LY83583) was assessed. Changes in pulmonary vascular resistance (PVR), pulmonary vascular compliance, and perfusate cyclic GMP concentration were measured as indicators of nitric oxide synthesis. The effect of the cyclic GMP-specific (type V) phosphodiesterase inhibitor, zaprinast, on perfusate cyclic GMP concentrations was also examined. An infusion of U46619 consistently increased PVR and decreased compliance. LMA and LY83583 also increased PVR in U46619-treated lungs perfused at constant flow rates, primarily by increasing precapillary resistance. LMA had no effect in U46619-treated lungs perfused at constant pressure. Perfusate cyclic GMP concentrations increased significantly after U46619 in lungs perfused at constant flow rates, but cyclic GMP levels did not change after U46619 in lungs perfused at constant pressure. Zaprinast also increased perfusate cyclic GMP, demonstrating that increases in intracellular cyclic GMP are reflected in circulating cyclic GMP concentrations. We conclude that vasoconstriction with U46619 increases nitric oxide synthesis in isolated rat lungs. Lungs perfused at constant pressure respond differently to NOS inhibitors compared to those perfused at constant flow, suggesting that shear stress may increase nitric oxide synthesis in the lung. Perfusate concentrations of cyclic GMP reflect activation of soluble guanylyl cyclase in this model.

Effect of Dexamethasone on a1-adrenergic Tone During Nitric Oxide Synthase Inhibition in Neonatal Rat Carotid Artery. • 1103

Although dexamethasone has been used to treat the severe hypotension in extremely low birth weight infants, the mechanism of action of dexamethasone is unknown. Previously we observed an increase in carotid artery contractile response to al-adrenergic agonists over the first two weeks of life in rats. We also observed that dexamethasone enhances maturation of α1-adrenergic mediated vessel contraction in 3-5 day old rats. In this study we tested the hypothesis that dexamethasone enhances α1-adrenergic receptor response by suppression of nitric oxide synthase production. Pups were treated with SC dexamethasone 0.4μg/gm body weight or saline from DOL 2 until sacrifice. Carotid arteries were isolated and vessel responses were studied in a myograph. The results in the table below represent maximum percent decrease in vessel diameter in reponse to phenylephrine (PE) in the presence or absence of L-NAME. Data were analyzed by Student's t test. In separate experiments, carotid arteries from dexamethasone and control rats were isolated for nitric oxide synthase mRNA expression. There was no difference in inducible or endothelial nitric oxide synthase expression in control vs. dexamethasone treated rats. These results indicate there is nitric oxide production in these vessels, which when inhibited by L-NAME allows greater contraction to the α1-adrenergic agonist phenylephrine. Although dexamethasone enhances α1-adrenergic contractile response in vessels from first week of life animals, the action of dexamethasone in these vessels does not appear to be related to downregulation of nitric oxide synthase mRNA expression.