The effect of celiac and renal artery outflows on near-wall velocities in the porcine iliac arteries

The effects of the outflow of aortic blood through the celiac and renal arteries on the flow field in the external iliac arteries were studied under steady and physiologically realistic pulsatile flow conditions. Laser Doppler velocimetry (LDV) measurements were made close to the medial, lateral, ventral, and dorsal walls of the external iliac branches of a clear, flow-through replica of a porcine aorta and its daughter vessels. The outflow from each branch of the replica was controlled so that the infrarenal aortic flow rate and the flow partition at the aortic trifurcation were the same for all experiments. LDV measurements were made with flow exiting through both the renal and celiac artery ostia, only the celiac ostium, and neither ostium. The steady flow results indicate that while the outflow through the renal arteries did not have a significant effect on near wall shear rate in the external iliac arteries, the flow through the celiac artery did. However, in pulsatile flow, three indices of near wall velocity in the iliac arteries were unaffected by celiac artery outflow, while a fourth showed a small effect that can be attributed to differences in minimum velocity. These results indicate that reliable simulations of blood flow in the external iliac arteries can be carried out without including the renal and celiac vessels, provided that the correct infrarenal flow wave is used. They also demonstrate that the flow field downstream of a region, such as a branch, that strongly alters the flow, can be nearly independent of the velocity field entering the region.

Analysis of adenoviral transport mechanisms in the vessel wall and optimization of gene transfer using local delivery catheters

Local delivery devices have been used for adenovirus-mediated gene transfer to the arterial wall for the potential treatment of vascular proliferative diseases. However, low levels of adenoviral gene expression in vascular smooth muscle cells may pose a serious limitation to the success of these procedures in the clinic. In this study, we examined the mechanisms controlling adenoviral transport to the vessel wall, using both hydrogel-coated and infusion-based local delivery catheters, with the goal of enhancing in vivo gene transfer under clinically relevant delivery conditions. The following delivery parameters were tested in vivo: applied transmural pressure, viral solution volume and concentration, and delivery time. We found that viral particles are transported into the vessel wall in a manner consistent with diffusion rather than pressure-driven convection. Consistent with diffusion, viral concentration was shown to be the key variable for viral transport in the vessel wall and thus gene expression in vascular smooth muscle cells. A transduction level of 17.8+/-3.2% was achieved by delivering a low volume of concentrated adenoviral beta-galactosidase solution through an infusion balloon catheter at low pressure without an adverse effect on medial cellularity. Under these conditions, effective gene transfer was accomplished within a clinically relevant time frame of 2 min, indicating that longer delivery times may not be necessary to achieve efficient gene transfer.

Subtype specific regulation of human vascular alpha(1)-adrenergic receptors by vessel bed and age

BACKGROUND

alpha(1)-adrenergic receptors (alpha(1)ARs) regulate blood pressure, regional vascular resistance, and venous capacitance; the exact subtype (alpha(1a), alpha(1b), alpha(1 d)) mediating these effects is unknown and varies with species studied. In order to understand mechanisms underlying cardiovascular responses to acute stress and chronic catecholamine exposure (as seen with aging), we tested two hypotheses: (1) human alpha(1)AR subtype expression differs with vascular bed, and (2) age influences human vascular alpha(1)AR subtype expression.

METHODS AND RESULTS

Five hundred vessels from 384 patients were examined for alpha(1)AR subtype distribution at mRNA and protein levels (RNase protection assays, ligand binding, contraction assays). Overall vessel alpha(1)AR density is 16+/-2.3fmol/mg total protein. alpha(1a)AR predominates in arteries at mRNA (P<0.001) and protein (P<0.05) levels; all 3 subtypes are present in veins. Furthermore, alpha(1)AR mRNA subtype expression varies with vessel bed (alpha(1a) higher in splanchnic versus central arteries, P<0.05); competition analysis (selected vessels) and functional assays demonstrate alpha(1a) and alpha(1b)-mediated mammary artery contraction. Overall alpha(1)AR expression doubles with age (<55 versus > or = 65 years) in mammary artery (no change in saphenous vein), accompanied by increased alpha(1b)>alpha(1a) expression (P< = 0.001).

CONCLUSIONS

Human vascular alpha(1)AR subtype distribution differs from animal models, varies with vessel bed, correlates with contraction in mammary artery, and is modulated by aging. These findings provide potential novel targets for therapeutic intervention in many clinical settings.

Reconstruction of blood flow patterns in human arteries

Local haemodynamic factors in large arteries are associated with the pathophysiology of cardiovascular diseases such as atherosclerosis and strokes. In search of these factors and their correlation with atheroma formation, quantitative haemodynamic data in realistic arterial geometry become crucial. At present no in vivo non-invasive technique is available that can provide accurate measurement of three-dimensional blood velocities and shear stresses in curved and branching sites of vessels where atherosclerotic plaques are found frequently. This paper presents a computer modelling technique which combines state-of-the-art computational fluid dynamics (CFD) with new noninvasive magnetic resonance imaging techniques to provide the complete haemodynamic data in 'real' arterial geometries. Using magnetic resonance angiographic and velocity images acquired from the aortic bifurcation of a healthy human subject, CFD simulations have been carried out and the predicted flow patterns demonstrate the non-planar-type flow characteristics found in experimental studies.

Role of a negative arterial-portal venous glucose gradient in the postexercise state

Prior exercise stimulates muscle and liver glucose uptake. A negative arterial-portal venous glucose gradient (a-pv grad) stimulates resting net hepatic glucose uptake (NHGU) but reduces muscle glucose uptake. This study investigates the effects of a negative a-pv grad during glucose administration after exercise in dogs.

EXPERIMENTAL PROTOCOL

exercise (-180 to -30 min), transition (-30 to -20 min), basal period (-20 to 0 min), and experimental period (0 to 100 min). In the experimental period, 130 mg/dl arterial hyperglycemia was induced via vena cava (Pe, n = 6) or portal vein (Po, n = 6) glucose infusions. Insulin and glucagon were replaced at fourfold basal and basal rates. During the experimental period, the a-pv grad (mg/dl) was 3 +/- 1 in Pe and -10 +/- 2 in Po. Arterial insulin and glucagon were similar in the two groups. In Pe, net hepatic glucose balance (mg x kg(-1) x min(-1), negative = uptake) was 4.2 +/- 0.3 (basal period) and -1.2 +/- 0.3 (glucose infusion); in Po it was 4.1 +/- 0.5 and -3.2 +/- 0.4, respectively (P < 0.005 vs. Pe). Total glucose infusion (mg x kg(-1) x min(-1)) was 11 +/- 1 in Po and 8 +/- 1 in Pe (P < 0.05). Net hindlimb and whole body nonhepatic glucose uptakes were similar.

CONCLUSIONS

the portal signal independently stimulates NHGU after exercise. Conversely, prior exercise eliminates the inhibitory effect of the portal signal on glucose uptake by nonhepatic tissues. The portal signal therefore increases whole body glucose disposal after exercise by an amount equal to the increase in NHGU.

Nitric oxide modulates captopril-mediated angiotensin-converting enzyme inhibition in porcine iliac arteries

The influence of the angiotensin-converting enzyme inhibitor captopril on bradykinin-and angiotensin I-induced responses with special regard to nitric oxide (NO) was studied. Auxometric tension and angiotensin-converting enzyme activity was studied in isolated porcine iliac arteries. Captopril potentiated bradykinin-induced contraction of preparations with intact endothelium; this potentiation was not seen with the kininase I inhibitor mergepta or a bradykinin B(1)-receptor antagonist. Captopril did not affect bradykinin-induced relaxation. The captopril-mediated increase of bradykinin-induced contraction was only seen in preparations with intact endothelium, while captopril did not affect arterial strips treated with Nomega-nitro-L-arginine. Angiotensin I-induced contractions was less reduced by captopril when the strips were pretreated with Nomega-nitro-L-arginine. Both captopril and the NO donor S-nitroso-N-acetyl-penicillamine inhibited angiotensin-converting enzyme activity. An additional reduction in angiotensin-converting enzyme activity was seen when S-nitroso-N-acetyl-penicillamine was added to captopril-treated preparations. In conclusion, captopril increased bradykinin-induced contraction in a NO-dependent manner. This potentiation is probably mediated by the increased metabolism of bradykinin by kininase I, and the additive angiotensin-converting enzyme inhibitory effect of captopril and NO.

Glycemic modulation of insulin/IGF-1 mediated skeletal muscle blood following sympathetic denervation in normal rats

Both insulin and IGF-1 decrease vascular resistance and increase blood flow in skeletal muscle, and it has been suggested that the mechanistic action for insulin may be by increasing autonomic vasodilatory activity. In this study we evaluated the effects of insulin and IGF-1 on blood flow to denervated and non-denervated skeletal muscle as part of a continuing investigation into the mechanism of regulation of cardiovascular responses by these hormones. Normal rats were prepared for measurements of mean arterial pressure (MAP), heart rate (HR) and vascular flow in the left and right iliac artery. Resection of the left lumbar sympathetic chain increased flow (expressed as conductance, flow/MAP) in the denervated left iliac but not in the intact right artery. Subsequent insulin infusion where hypoglycemia was allowed to occur increased conductance in both arteries, but more so in the denervated artery. Similarly, IGF-1 infusion increased conductances in both intact and denervated iliac arteries, and the effect was slightly greater in the denervated artery. Insulin infusion when euglycemia was maintained increased conductance to a similar extent in denervated and intact iliac arteries. Contrastingly, IGF-1 infusion under euglycemic conditions resulted in a much greater increased conductance in the intact iliac. We conclude that both insulin and IGF-1 increase conductance directly and that glycemic status and sympathetic nerve activity modulate these responses. The insulin-induced increase in conductance in the denervated limb under hypoglycemic conditions suggest that hypoglycemic-stimulated epinephrine release may enhance the dilatory response. while the greater response to IGF-1 in the intact vessel under euglycemic conditions may be due to IGF-1 capacity to decrease sympathetic activity leading to an enhanced conductance.

Hemodynamics and wall mechanics after stent placement in swine iliac arteries: comparative results from six stent designs

PURPOSE

To compare the hemodynamics and wall mechanics of swine iliac arteries after placement of six types of stent.

MATERIALS AND METHODS

Stents were placed in the iliac artery of 18 pigs (three pigs each underwent placement with one of six types of stent); 16 untreated pigs served as control animals. Iliac arterial hemodynamics and wall mechanics were measured 4 days after placement.

RESULTS

Four stents (Palmaz-Schatz, Cordis, Warren, NJ; and Strecker, Cragg, and Symphony, Boston Scientific/Vascular, Natick, Mass) caused decreased pulsatile flow rate in the treated and contralateral iliac arteries; one (Memotherm; Bard, Covington, Ga) caused increased flow pulsatility; and one (Wallstent; Schneider, Plymouth, Minn) had no effect. No compliance mismatching was noted for the Cragg, Symphony, and Memotherm stents, whereas a decrease in compliance was noted for the Palmaz-Schatz, Strecker, and Wallstent designs. The Palmaz-Schatz and Strecker stents caused increased arterial wall rigidity, the Symphony and Wallstent designs had no effect, and the Memotherm and Cragg stents caused decreased wall rigidity. Stents made of stiff metal yielded different early results than did stents made of the less rigid nitinol.

CONCLUSION

Soon after implantation, the six stent designs elicited varying changes in blood flow, arterial compliance, and arterial wall mechanics. Contralateral arterial flow also was affected.

Computational blood flow modeling based on in vivo measurements

Study of the relationship between hemodynamics and atherogenesis requires accurate three-dimensional descriptions of in vivo arterial geometries. Common methods for obtaining such geometries include in vivo medical imaging and postmortem preparations (vessel casts, pressure-fixed vessels). We sought to determine the relative accuracy of these methods. The aorto-iliac (A/I) region of six rabbits was imaged in vivo using contrast-enhanced magnetic resonance imaging (MRI). After sacrifice, the geometry of the A/I region was preserved via vascular casts in four animals, and ex situ pressure fixation (while preserving dimensions) in the remaining two animals. The MR images and postmortem preparations were used to build computer representations of the A/I bifurcations, which were then used as input for computational blood flow analyses. Substantial differences were seen between MRI-based models and postmortem preparations. Bifurcation angles were consistently larger in postmortem specimens, and vessel dimensions were consistently smaller in pressure-fixed specimens. In vivo MRI-based models underpredicted aortic dimensions immediately proximal to the bifurcation, causing appreciable variation in the aorto-iliac parent/child area ratio. This had an important effect on wall shear stress and separation patterns on the "hips" of the bifurcation, with mean wall shear stress differences ranging from 15% to 35%, depending on the model. The above results, as well as consideration of known and probable sources of error, suggests that in vivo MRI best replicates overall vessel geometry (vessel paths and bifurcation angle). However, vascular casting seems to better capture detailed vessel cross-sectional dimensions and shape. It is important to accurately characterize the local aorto-iliac area ratio when studying in vivo bifurcation hemodynamics.

A negative arterial-portal venous glucose gradient increases net hepatic glucose uptake in euglycemic dogs

We investigated whether a negative arterial-portal venous (a-pv) glucose gradient, or "portal signal," can increase net hepatic glucose uptake (NHGU) and decrease muscle glucose uptake at euglycemia as it does at hyperglycemia. Twenty 42-h fasted dogs were studied during a basal and two 120-min euglycemic periods (period I and period II). Glucagon was maintained at basal levels, and insulin was raised 3-fold (3xIns, n = 10) or 15-fold (15xIns, n = 10). During period I, dogs received glucose only peripherally. During period II, one-half of the dogs continued the peripheral infusion; the other one-half received glucose intraportally (4 mg. kg(-1). min(-1) and reduced peripheral glucose infusion). A negative a-pv glucose gradient was present during intraportal glucose infusion. All 3xIns and 15xIns dogs had similar NHGU in period I. In period II, it was 2.1 +/- 0.3 (3xIns) and 2.5 (15xIns) mg. kg(-1). min(-1) greater in the presence than in the absence of the portal signal (P < 0.001). The net glucose fractional extraction data paralleled NHGU. In 3xIns, but not in 15xIns, whole body nonhepatic glucose uptake was lower in the presence of the portal signal than in its absence. In conclusion, in hyperinsulinemic, but not hyperglycemic conditions, the portal signal is effective in activating NHGU. The inhibition of nonhepatic glucose uptake, on the other hand, is minimal under euglycemic as opposed to hyperglycemic conditions.

Inhibitory mechanisms by which suramin may attenuate neointimal formation after balloon angioplasty

Restenotic neointimal lesions, a major limitation to coronary angioplasty, develop in response to diverse signals and depend on three properties of activated arterial smooth muscle cells (SMCs): proliferation, migration, and abnormal production of extracellular matrix. Most of the pharmacologic approaches targeting specific pathogenic factors facilitating development of restenosis have failed in clinical trials. Our results indicate that the polysulfonated naphthylurea suramin, a "non-specific drug" that interferes with multiple cellular proteins, inhibits neointimal formation in rabbit iliac arteries after balloon-catheter injury administered throughout the critical period of several weeks after the procedure. In vitro studies aimed at dissecting the mechanism(s) underlying the suramin-dependent effect demonstrated that, in addition to an inhibitory effect on SMC proliferation, suramin inhibited fibronectin and elastin deposition and the migration of SMCs through elastin membranes and into scratch gaps of monolayer cultures. We also demonstrated that suramin causes cell-surface accumulation of the elastin binding protein, a receptor that not only anchors SMCs to the extracellular matrix, but also inhibits SMC response to interleukin-1beta (IL-1beta). We conclude that suramin acts as a multitarget inhibitor of SMC activation and has a therapeutic potential as an agent that may attenuate arterial restenosis after angioplasty.

Pharmacological properties of J-104132 (L-753,037), a potent, orally active, mixed ETA/ETB endothelin receptor antagonist

J-104132 [(+)-(5S,6R, 7R)-2-butyl-7-[2-((2S)-2-carboxypropyl)-4-methoxyphenyl]-5-(3, 4-methylenedioxyphenyl)cyclopenteno[1,2-b]pyridine-6-carboxylic; also referred to as L-753,037] is a potent, selective inhibitor of ETA and ETB endothelin (ET) receptors (e.g., Ki: cloned human ETA = 0.034 nM; cloned human ETB = 0.104 nM). In both ligand-binding and isolated tissue preparation protocols, the inhibition of ET receptors with J-104132 is reversible and competitive. In vitro, J-104132 is a potent antagonist of ET-1-induced accumulation of [3H]inositol phosphates in Chinese hamster ovary cells stably expressing cloned human ETA receptors (IC50 = 0.059 nM), ET-1-induced contractions in rabbit iliac artery (pA2 = 9.70) and of BQ-3020-induced contractions in pulmonary artery (pA2 = 10.14). J-104132 is selective for ET receptors because it had no effect on contractions elicited by norepinephrine or KCl in the vascular preparations. The in vivo potency of J-104132 was assessed using challenges with exogenous ET-1. In conscious mice, 5 nmol/kg i.v. ET-1 causes death. Pretreatment with J-104132 prevents the lethal response to ET-1 when administered i.v. (ED50 = 0.045 mg/kg) or p.o. in fed animals (ED50 = 0.35 mg/kg). In conscious, normotensive rats, pressor responses to 0.5 nmol/kg i.v. ET-1 are inhibited by J-104132 after i.v. (0.1 mg/kg) or p.o. (1 mg/kg) administration. In anesthetized dogs, ET-1 was administered directly into the renal artery or brachial artery to generate dose-response (blood flow) curves, and the inhibitory potency of J-104132 (i.v. infusion) was quantified. J-104132 produced greater than 10-fold shifts in the ET-1 dose-response curves at 0.03 mg/kg/h (renal) and 0.3 mg/kg/h (brachial). Oral bioavailability of J-104132 in rats was approximately 40%. These studies indicate that J-104132 is a selective, potent, orally active antagonist of both ETA and ETB receptors and is an excellent pharmacological tool to explore the therapeutic use of a mixed ETA/ETB receptor antagonist.

Effects of general and selective beta-adrenergic antagonists on insulin-induced cardiac and selected vascular responses in rats

Insulin administration results in vasodilation, decreased mean arterial blood pressure (MAP) and increased conductances (flow/MAP) in various vascular beds. beta-adrenergic blockers antagonize this response, but the mechanism of the interplay between insulin-induced vasodilation and beta-adrenergic antagonism is unknown. In this study, we evaluated the effects of beta-blockade using the selective beta(2) antagonist ICI 118551 or the general beta-antagonist propranolol on insulin-induced cardiac and regional flow responses in normal rats. Insulin-induced responses were also examined following adrenalectomy. Rats were anaesthetized and the femoral vein and artery were cannulated for infusions, sampling or monitoring of MAP and heart rate (HR). The iliac, renal, and superior mesentery arteries were equipped with pulsed-Doppler flow probes. Blood samples were collected at selected intervals. Insulin decreased blood glucose, MAP and increased conductances. Pretreatment with propranolol not only antagonized the insulin-induced decrease in MAP and increased conductance but insulin also then increased MAP and decreased conductances. ICI 11851, like propranolol, antagonized the insulin-induced decrease in MAP and increased iliac and renal artery conductances. Adrenalectomy did not alter the maximum insulin-induced effects on MAP and conductances but prevented the rebound recovery phase. beta-blockade following adrenalectomy had the same effects as beta-blockade alone on the insulin-induced responses. We conclude that the insulin-induced decrease in MAP and the increased flow in the selective vascular beds are modulated by a sympathetic beta(2)-receptor-mediated pathway and this response is not due primarily to the release of adrenal catecholamine.

Daily exercise enhances acetylcholine-induced dilation in mesenteric and hindlimb vasculature of hypertensive rats

The effect of daily spontaneous running (DSR) on endothelial function was examined in spontaneously hypertensive rats (SHR). Following 8-11 weeks of DSR (n=15) or sedentary control (SED, n=15), rats were instrumented with arterial and venous catheters and mesenteric and iliac Doppler ultrasonic flow probes. Hemodynamic responses to vasodilator-mediated substances were determined under two experimental conditions; 1) bolus injection of indomethacin (10 mg/kg) and 4 bolus doses of acetylcholine (0.5-2.0 microg/kg); 2) bolus injection of N(omega)-nitro-L-arginine (5 mg/kg) and 4 bolus doses of nitroglycerin (3-12 microg/kg). Hindlimb vascular conductance decreased more in response to indomethacin in DSR vs. SED rats (-18.3+/-2.8% vs. -10.4+/-2.5%). However, the mesenteric or hindlimb vascular conductance responses to N(omega)-nitro-L-arginine were not different between DSR and SED rats. DSR also enhanced mesenteric and hindlimb vascular conductance responses to acetylcholine. Results suggest that DSR enhances acetylcholine-induced vasodilation in SHR.

Cycloalkanecarboxylic esters derived from lysergol, dihydrolysergol-I, and elymoclavine as partial agonists and antagonists at rat 5-HT2A receptors: pharmacological evidence that the indolo[4,3-fg]quinoline system of the ergolines is responsible for high 5-HT2A receptor affinity

Three series of cycloalkanecarboxylic esters derived from the naturally occurring clavine alkaloids lysergol, dihydrolysergol-I, and elymoclavine were synthesized to study their interaction with 5-HT2A receptors and alpha1-adrenoceptors in rat tail artery and aorta, respectively. Especially cycloalkanecarboxylic esters derived from lysergol showed complex behavior as partial agonists and antagonists of the contractile effect of 5-HT. Within this group, partial 5-HT2A receptor agonist activity was most potent for cyclopropanecarboxylic ester 6a (pKP = 7.67, alpha = 0.21) and decreased as the volume requirement of the alicyclic ring increased. This tendency was echoed in experiments where the compounds were used as antagonists of the contractile effect of 5-HT. From the structure-activity study, the N-1-isopropyl homologue of 6a, compound 6b, emerged as the ligand with the highest affinity for rat 5-HT2A receptors (pA2 = 8.74). For cycloalkanecarboxylic esters derived from dihydrolysergol-I and elymoclavine, no clear structure-affinity relationship could be deduced, although those compounds that had smaller cycloalkyl rings in the acyl portion and an isopropyl substituent at N-1 showed the highest 5-HT2A receptor affinity. On the other hand, cycloalkanecarboxylic esters derived from lysergol, dihydrolysergol-I, and elymoclavine displayed low or marginal affinity at alpha1-adrenoceptors. A further aim of the study was to examine to what extent the complete removal of the acyl portion of the esters would affect 5-HT2A receptor affinity. The parent alcohols of the three series of N-1-isopropyl homologues, 1-isopropyllysergol (1b), 1-isopropyldihydrolysergol-I (2b), and 1-isopropylelymoclavine (3b), displayed higher affinity for 5-HT2A receptors (pA2 = 9.15, 8.50, 9.14) than the corresponding esters. Compounds 1b-3b had no contractile effects by themselves and displayed low affinity at guinea-pig 5-HT1B receptors and rat alpha1-adrenoceptors. The high affinity for rat 5-HT2A receptors was retained when clavines even more simple in structure than 1b-3b, compounds 4b and 5b, were examined as 5-HT2A receptor antagonists. The nanomolar antagonist activity of simple clavines (1b-5b) in the rat suggests that the indolo[4,3-fg]quinoline system of the ergolines is the molecular fragment that is responsible for 5-HT2A receptor affinity, and not the substituent at position C-8.

Thickness, taper, and ellipticity in the aortoiliac bifurcation of patients aged 1 day to 76 years

Lumen area, ellipticity, and wall thickness were measured in the aortoiliac bifurcations obtained at autopsy from 14 patients aged between 1 day and 76 years. The method involved freezing pressure-fixed, stained bifurcations on the stage of a refrigerated microtome and then looking at the block face while sections were removed. Area change was normalized over segment length to produce a value of either taper (narrowing, in mm2/mm), or flare (expansion). The aortoiliac bifurcations were divided into three regions based on the area changes: an apical region corresponding to the bifurcation apex (taper = 2.96 +/- 0.80 mm2/mm), a preapical region (flare = 3.58 +/- 0.87 mm2/mm), and the postapical region (flare = 0.82 +/- 0.80 mm2/mm). Preapical lumen ellipticity showed that the anterio-posterior diameter was always less than the lateral diameter, while the degree of ellipticity increased with age. Average circumferential wall thickness, assessed in polar coordinates, decreased between 0 degree (right lateral) and 120 degrees, while a significant increase in wall thickness was present between 120 degrees and 200 degrees. The most striking difference was found in the 1-day-old, which was very thin posteriorly. This detailed geometric analysis of the aortoiliac bifurcation suggests that taper, flare, and variations in both circumferential and longitudinal wall thickness need to be considered when trying to correlate physical factors in the aorta with the precise location of atherosclerotic lesions and wall remodeling.

Numerical study on the effect of steady axial flow development in the human aorta on local shear stresses in abdominal aortic branches

The three-dimensional flow through a rigid model of the human abdominal aorta complete with iliac and renal arteries was predicted numerically using the steady-state Navier Stokes equations for an incompressible. Newtonian fluid. The model adapted for our purposes was determined from data obtained from cine-CT images taken of a glass chamber that was constructed based on anatomical averages. The iliac arteries had a bifurcation angle of approximately 35 and a branch-to-trunk area ratio of 1.27. whereas the renal arteries had left and right branch angles of 40 and an area ratio of 0.73. The numerical tool FLOW3D (AEA Industrial Technology, Oxfordshire, UK) utilized body-fitted coordinates and a finite volume discretization procedure. Purely axial velocity profiles were introduced at the entrance of the model for a range of cardiac outputs. The four-branch numerical model developed for this investigation produced flow and shear conditions comparable to those found in other reported works. The total wall shear stress distribution in the iliac and renal arteries followed standard trends. with maximum shear stresses occurring in the apex region and lower shear stresses occurring along the lateral walls. Shear stresses and flow rate ratios in the downstream arteries were more effected by inlet Re than the upstream arteries. These results will be used to compare further simulations which take into effect the rotational component of flow which is present in the aortic arch.

Activation of Na+, H+ exchanger produces vasoconstriction of renal resistance vessels

To evaluate the influence of the sodium/proton exchanger (Na+,H+ exchanger) on the constriction of rat resistance vessels and on the iliac artery, the isometric vasoconstrictions of renal resistance vessels and strips from iliac artery derived from Wistar-Kyoto rats were measured using a vessel myograph. The Na+,H+ exchanger was activated by intracellular acidification using propionic acid. Cytosolic pH (pHi) and cytosolic free sodium concentration ([Na+]i) in vascular smooth muscle cells were measured using the fluorescent dye technique. The activation of the Na+,H+ exchanger increased the [Na+]i by 12.4 +/- 1.3 mmol/L (n = 8). The activation of the Na+,H+ exchanger caused a contractile response of the renal resistance vessels (increase of tension, 1.5 +/- 0.1 x 10(-3) N; n = 13) and of the rat iliac artery (increase of tension, 7.5 +/- 0.8 x 10(-3) N; n = 5). The contractile response after activation of the Na+,H+ exchanger was significantly inhibited in the absence of external sodium or in the presence of amiloride, confirming the involvement of the Na+,H+ exchanger. The contractile response after activation of the Na+,H+ exchanger was significantly reduced in the absence of external calcium, after inhibition of calcium channels by nifedipine, and in the presence of an intracellular calcium antagonist 8-(diethylamino-)-octyl-3,4,5-trimethoxybenzoate (TMB-8), indicating that the activation of the Na+,H+ exchanger consecutively caused transplasma membrane calcium influx. On the other hand, the inhibition of the Na+,Ca2+ exchanger by NiCl2 significantly increased the vasoconstriction of renal resistance vessels after activation of the Na+,H+ exchanger. The activation of the Na+,H+ exchanger produces vasoconstriction by an increased cytosolic sodium concentration, inhibition of the Na+,Ca2+ exchanger, and activation of transplasma membrane calcium influx through potential dependent calcium channels.

Visualization of flow patterns from stents and stent-grafts in an in vitro flow-model

RATIONALE AND OBJECTIVES

The authors determine flow characteristics and pressure gradients of different stents and stent grafts in an in vitro flow-model.

METHODS

Five vascular stents (Memotherm, Cragg, two Palmaz P308, Strecker, and Wall) and one stent graft (Cragg EndoPro System 1), equal in length (60 mm) and diameter (10 mm), were deployed in a closed flow-model. The inner diameter of the tube measured 9 mm. Flow at 1.5 L/min, 6 L/min, and 10 L/min was simulated. Flow patterns were visualized by anionic particles illuminated with two Helium-Neon lasers. Laminary flow characteristics and pre-/poststent pressure gradients were determined in either expanded stent, 25% stenosis, or 50% stenosis.

RESULTS

Stent implantation induced a decrease of laminary flow compared with an unstented tube with and without concentric 25% stenosis (P < 0.01) at all flow rates and an increase of pressure gradients compared with an unstented tube for flow rates greater than 1.5 L/min (P < 0.01) (except for Cragg EndoPro System 1 stent, which revealed an increase of the pressure gradient at a flow rate of 1.5 L/min [P < 0.01]). Memotherm stent permitted maximum of laminary flow at all flow rates and stenoses (expanded: 79.50% at 1.5 L/min to 69.90% at 10 L/min; P < 0.01). Memotherm and Palmaz permitted lowest pressure gradients (P < 0.01). All of the endoprostheses demonstrated laminary flow at 50% stenosis.

CONCLUSIONS

The investigated stents and stent grafts showed different severity of flow disturbances and pressure gradients at different graded stenoses. Inadequate stent depolyment bears the risk of creating less laminary flow and pathologic pressure gradients. Because flow disturbances and pressure gradients may influence neointimal hyperplasia, stent design and completeness of stent unfolding are important regarding the appearance of postinterventional restenoses.

Differences of antagonism for a selective alpha1D-adrenoceptor antagonist BMY 7378 in the rabbit thoracic aorta and iliac artery

Based on the affinity of alpha1D adrenoceptor subtype for a selective antagonist BMY 7378, we studied its functional role in rabbit thoracic aorta and iliac artery, and evaluated the subtypes of the alpha1-adrenoceptors that are activated by phenylephrine (a full agonist) and tizanidine (a partial agonist). In thoracic aorta, the concentration response curves of phenylephrine and tizanidine were antagonized by BMY 7378 with low potency (pA2 values 6.68+/-0.06 and 6.67+/-0.06, slopes of Schild plot 1.06+/-0.04 and 1.01+/-0.04, respectively). On the other hand, in iliac artery concentration response curves for phenylephrine were potently antagonized by a low concentration of BMY 7378, and the slope (0.75+/-0.02) of the Schild plot was significantly different from unity. In iliac artery, a concentration response curve of tizanidine was antagonized by BMY 7378 with low potency (pA2 value 6.64+/-0.08, slope of Schild plot 1.01+/-0.05). These results suggest that an alpha1D-adrenoceptor subtype contributes to alpha1-adrenoceptor mediating muscle contraction in iliac artery, but not in thoracic aorta of rabbit, and that it is activated by a full agonist phenylephrine but not by a partial agonist tizanidine.

Matrix metalloproteinase inhibition limits arterial enlargements in a rodent arteriovenous fistula model

BACKGROUND

We administered a specific, nonselective matrix metalloproteinase (MMP) inhibitor (RS-113,456) to examine the effect of MMP inhibition on flow-mediated arterial enlargement in a rodent arteriovenous fistula (AVF) model.

METHODS

Four groups of male Sprague-Dawley rats were created: sham (sham operated; n = 10), control (2.0 mm left common femoral AVF alone; n = 16), vehicle (AVF plus 0.5 mL vehicle orally twice a day; n = 20), and treatment (AVF plus 25 mg/kg RS-113,456 in 0.5 mL vehicle orally twice a day; n = 16). Heart rate, mean arterial pressure, and body weight were recorded on postoperative days 0, 7, 14, and 21. On day 21, AVF patency was confirmed, the infrarenal aorta and common iliac arteries were exposed, blood flow velocity and external diameter were measured, and wall shear stress (WSS) was calculated. Analysis was performed by paired, two-tailed Student t test, one-way analysis of variance, and the Bonferroni/Dunn procedure for post hoc testing.

RESULTS

Heat rate, mean arterial pressure, and weight did not vary at any time between groups. Aortic and left iliac diameter was larger in the AVF groups than in sham groups (P < .001), and control and vehicle groups were larger than treatment groups (P < .0001). Changes in aortic and left iliac flow were also significant (AVF was more than sham and control, and vehicle was more than treatment). No difference in aortic and left iliac artery velocity and WSS or right iliac diameter, velocity, flow, or WSS was observed between groups.

CONCLUSIONS

MMP inhibition diminishes flow-mediated arterial enlargement in the rat AVF model.

A negative arterial-portal venous glucose gradient decreases skeletal muscle glucose uptake

The effect of a negative arterial-portal venous (a-pv) glucose gradient on skeletal muscle and whole body nonhepatic glucose uptake was studied in 12 42-h-fasted conscious dogs. Each study consisted of a 110-min equilibration period, a 30-min baseline period, and two 120-min hyperglycemic (2-fold basal) periods (either peripheral or intraportal glucose infusion). Somatostatin was infused along with insulin (3 x basal) and glucagon (basal). Catheters were inserted 17 days before studies in the external iliac artery and hepatic, portal and common iliac veins. Blood flow was measured in liver and hindlimb using Doppler flow probes. The arterial blood glucose, arterial plasma insulin, arterial plasma glucagon, and hindlimb glucose loads were similar during peripheral and intraportal glucose infusions. The a-pv glucose gradient (in mg/dl) was 5 +/- 1 during peripheral and -18 +/- 3 during intraportal glucose infusion. The net hindlimb glucose uptakes (in mg/min) were 5.0 +/- 1.2, 20.4 +/- 4.5, and 14.8 +/- 3.2 during baseline, peripheral, and intraportal glucose infusion periods, respectively (P < 0.01, peripheral vs. intraportal); the hindlimb glucose fractional extractions (in %) were 2.8 +/- 0.4, 4.7 +/- 0.8, and 3.9 +/- 0.5 during baseline, peripheral, and intraportal glucose infusions, respectively (P < 0. 05, peripheral vs. intraportal). The net whole body nonhepatic glucose uptakes (in mg . kg-1 . min-1) were 1.6 +/- 0.1, 7.9 +/- 1.3, and 5.4 +/- 1.1 during baseline, peripheral, and intraportal glucose infusion, respectively (P < 0.05, peripheral vs. intraportal). In the liver, net glucose uptake was 70% greater during intraportal than during peripheral glucose infusion (5.8 +/- 0.7 vs. 3.4 +/- 0.4 mg . kg-1 . min-1). In conclusion, despite comparable glucose loads and insulin levels, hindlimb and whole body net nonhepatic glucose uptake decreased significantly during portal venous glucose infusion, suggesting that a negative a-pv glucose gradient leads to an inhibitory signal in nonhepatic tissues, among which skeletal muscle appears to be the most important.

Nitric oxide synthase modulates angiogenesis in response to tissue ischemia

We tested the hypothesis that endothelial nitric oxide synthase (eNOS) modulates angiogenesis in two animal models in which therapeutic angiogenesis has been characterized as a compensatory response to tissue ischemia. We first administered L-arginine, previously shown to augment endogenous production of NO, to normal rabbits with operatively induced hindlimb ischemia. Angiogenesis in the ischemic hindlimb was significantly improved by dietary supplementation with L-arginine, compared to placebo-treated controls; angiographically evident vascularity in the ischemic limb, hemodynamic indices of limb perfusion, capillary density, and vasomotor reactivity in the collateral vessel-dependent ischemic limb were all improved by oral L-arginine supplementation. A murine model of operatively induced hindlimb ischemia was used to investigate the impact of targeted disruption of the gene encoding for ENOS on angiogenesis. Angiogenesis in the ischemic hindlimb was significantly impaired in eNOS-/- mice versus wild-type controls evaluated by either laser Doppler flow analysis or capillary density measurement. Impaired angiogenesis in eNOS-/- mice was not improved by administration of vascular endothelial growth factor (VEGF), suggesting that eNOS acts downstream from VEGF. Thus, (a) eNOS is a downstream mediator for in vivo angiogenesis, and (b) promoting eNOS activity by L-arginine supplementation accelerates in vivo angiogenesis. These findings suggest that defective endothelial NO synthesis may limit angiogenesis in patients with endothelial dysfunction related to atherosclerosis, and that oral L-arginine supplementation constitutes a potential therapeutic strategy for accelerating angiogenesis in patients with advanced vascular obstruction.