Human Renal Arteries Research Articles

Contractile responses of the human urinary bladder, renal pelvis and renal artery to endothelins and sarafotoxin S6b

1. 1. Endothelin-1 (ET-1), endothelin-3 (ET-3) and sarafotoxin S6b (SRFTX) produced a concentration-dependent tonic contraction of the human isolated urinary bladder, renal pelvis and renal artery with threshold at nM concentration. 2. 2. In the bladder, the following order of potency was found: ET-1 > SRFTX > ET-3. In the renal pelvis, all peptides displayed similar affinity but, at high concentrations the maximal response was highest for SRFTX followed by ET-1 and ET-3. In the renal artery ET-1 and SRFTX were about equipotent and equieffective while ET-3 produced only a slight and inconsistent (2 out of 5 cases) vasoconstrictor response. 3. 3. As shown previously for the human bladder muscle, the response to ET-1 in the renal pelvis was nifedipine (1 μM)-resistant while a consistent fraction of the response was blocked by nifedipine in the human renal artery. 4. 4. These findings indicate that peptides of the endothelin family exert a potent contractile effect on various human smooth muscles. Participation of dihydropyridine-and voltage-sensitive calcium channels in the contractile response produced by these peptides may vary from one organ to another.

The activity of peptides of the endothelin family in various mammalian smooth muscle preparations

The activity of natural endothelins such as ET-1, ET-2, ET-3 and of sarafotoxin S6b (SRFTX) as compared to that of the C-terminal hexapeptide ET-(16–21) was investigated in several smooth muscle preparations in the presence of indomethacin, captopril, bestatin and thiorphan. In some tissues (rat thoracic aorta, guinea-pig ileum, human urinary bladder, renal pelvis or renal artery), ET-(16–21) had little if any agonist activity. In order preparations (guinea-pig bronchus, rat vas deferens, rabbit pulmonary artery ET-(16–21) was a full agonist. The amidated form of ET-(16–21) was either inactive or less potent than ET-(16–21). These findings provide evidence that at least two receptors exist for peptides of the ET family; these receptors were termed ET A and ET B. ET-(16–21) is a full agonist at ET B receptors while being inactive or weakly active at ET A receptors. The free acid of tryptophan in position 21 plays a key role in the activity of these peptides at ET B receptors.

Flow visualization studies in a mold of the normal human aorta and renal arteries.

To study the flow behavior in regions where hemodynamic effects have been suggested to participate in atherogenesis, we evaluated flow in a mold of the aorta and renal arteries of a previously healthy 27-year-old woman who died of trauma. A birefringent solution (vanadium-pentoxide) was used. When diluted, this material behaves like a Newtonian fluid. This method gives a complete picture of the entire flow field. Zones of flow separation and disturbed flow can be seen and the location and size of disturbed areas observed. Unseparated flow regions downstream from disturbed zones can be properly visualized and the method can be used for pulsatile flow as well as steady flow. During steady flow (only at branch to-trunk flow ratios greater than 0.20), zones of flow separation were observed in the aorta distal to the renal arteries. During pulsatile flow, disturbances were found at nearly all branch-to-trunk flow ratios.

Vascular origin determines plasminogen activator expression in human endothelial cells: Renal endothelial cells produce large amounts of single chain urokinase type plasminogen activator

Positioned at the boundary between intra- and extravascular compartments, endothelial cells may influence many processes through their production of plasminogen activators (PA). Available data have shown that tissue-type plasminogen activator (t-PA) is the major form produced by human endothelial cells. We have compared the molecular forms of PA produced by human endothelial cells from different microvascular and large vessel sources including two different sites within the circulation of the kidney.Using combined immunoactivity assays specific for u-PA and t-PA activity and antigen, we found that both human renal microvascular and renal artery endothelial cells produced high levels of u-PA antigen (60.48 ng/105 cells/24 h and 50.42 ng/105 cells/24 h, respectively) and corresponding levels of u-PA activity after activation with plasmin. Activity was not evident before plasmin activation, showing that the u-PA produced is almost exclusively as single chain form U-PA. In contrast, human omental microvascular endothelial cells and human umbilical vein endothelial cells produced exclusively t-PA (8.80 ng/105 cells/24 h and 2.17 ng/105 cells/24 h, respectively). Neither endothelial cell type from human kidney produced plasminogen activator inhibitor, as determined by reverse fibrin autography and titration assays. Agents including phorbol ester, thrombin, and dexamethasone were shown to regulate the renal endothelial cell production and mRNA expression of both u-PA and t-PA. Among the macro- and microvascular endothelial cells tested, only those from the renal circulation produced high levels of single chain form U-PA, suggesting the vascular bed of origin determines the expression of plasminogen activators.

Cardiovascular and neurohormonal changes following central sympathetic blockade with clonidine in human unilateral renal artery stenosis

The role of central pressor mechanisms in the maintenance of blood pressure in six hypertensive patients with angiographically proven unilateral renal artery stenosis was investigated by studying the haemodynamic and hormonal responses before and after central sympathetic blockade with clonidine. To assess the dependency of blood pressure on the direct effects of angiotensin II, the same patients were studied on a separate occasion after administration of the angiotensin converting enzyme (ACE) inhibitor, captopril. There was a substantial fall in blood pressure after administration of clonidine with a smaller fall after captopril. Clonidine-induced hypotension was accompanied by a fall in cardiac output, through a reduction in the stroke volume and heart rate. Forearm vascular resistance was unchanged. There was a selective decrease in digital skin vascular resistance and plasma noradrenaline, indicating reduced sympathetic activity. Plasma renin activity and aldosterone levels did not fall. After administration of captopril, there was a fall in cardiac output due to a fall in the stroke volume but not in the heart rate. Forearm vascular resistance, digital skin vascular resistance and plasma noradrenaline were unchanged. Plasma renin activity rose and plasma aldosterone fell. We conclude that in our hypertensive patients with renal artery stenosis, clonidine lowered blood pressure by a reduction in central sympathetic activity independently of renin suppression. In these patients captopril had minimal hypotensive effects, indicating a smaller role for the direct vascular effects of angiotensin II.

Endothelium-Dependent Relaxations in Human Arteries

Experiments were designed to study endothelium-dependent relaxations in human renal arteries (N = 13) and peripheral arteries (N = 8) suspended in organ chambers for isometric tension recording. In contracted arterial rings, acetylcholine caused endothelium-dependent relaxations that were not inhibited by indomethacin in either artery but were significantly augmented in the renal artery. Adenosine diphosphate and thrombin caused endothelium-dependent relaxations in renal but not in peripheral arteries. This finding suggests a heterogeneity of endothelium-dependent relaxations in human arteries and indicates that the relaxations are mediated by the release of an endothelium-derived relaxing factor (or factors) rather than the release of prostacyclin.

ヒト腎動脈摘出標本に対するカルシトニン遺伝子関連ペプチドの作用

ヒト腎動脈摘出標本に対するカルシトニン遺伝子関連ペプチドの作用

Haemodynamic Changes during Clonidine Induced Hypotension in Human Renal Artery Stenosis

Haemodynamic Changes during Clonidine Induced Hypotension in Human Renal Artery Stenosis

Neurogenic components of hypertension in human renal artery stenosis.

In renal artery stenosis activation of the renin-angiotensin system elevates blood pressure by direct peripheral effects and probably through stimulation of sympathetic activity, which can be induced by angiotensin-II either centrally or peripherally. In animals specific brain lesions and afferent renal denervation can either attenuate or prevent renovascular hypertension. We investigated the neurogenic mechanisms responsible for hypertension in 21 patients with unilateral renal artery stenosis off drug therapy, by studying the cardiovascular and hormonal effects of Clonidine. The responses to Captopril served as an indicator of the peripheral effects of angiotensin-II. Both oral and intravenous Clonidine lowered blood pressure substantially and for a prolonged period even in patients who had been refractory to multiple antihypertensive drug therapy. Levels of plasma renin activity were unchanged after Clonidine. Plasma noradrenaline levels fell. Pressor responses to infused angiotensin-II were not reduced. These data suggest that Clonidine lowers blood pressure independently of hormonal and peripheral vascular interactions and is consistent with its predominantly central sympatholytic effects. Oral Captopril, unlike Clonidine, had variable hypotensive effects directly related to the basal level of plasma renin activity. The largest reductions were observed in those with the highest level of renin. Our studies indicate that neurogenic mechanisms, probably centrally mediated, have an important and often major role in maintaining hypertension in human renal artery stenosis. These may result from the central effects of angiotensin-II, and/or from increased afferent renal nerve activity, as demonstrated experimentally. The neurogenic components maintaining hypertension in renal artery stenosis are largely dependent on renal ischaemia as revascularisation (by surgery or angioplasty) or nephrectomy, either ameliorates or cures the hypertension in the majority of our patients.

The action of a dopamine (DA1) receptor agonist, fenoldopam in human vasculature in vivo and in vitro.

This study was designed to investigate dopaminergic mechanisms in human vasculature using the selective vascular dopamine receptor agonist fenoldopam in vivo and in vitro. In vivo, forearm blood flow was measured plethysmographically and in vitro isolated rings of human blood vessels from a variety of sites were used for tissue bath studies. Intra-arterial fenoldopam markedly increased forearm blood flow, this effect was antagonised by (R) sulpiride, a vascular dopamine (DA1) antagonist, but not by metoclopramide, a neuronal (DA2) antagonist, or by guanethidine, an adrenergic neurone blocking agent. In vitro, fenoldopam relaxed preconstricted human renal, mesenteric and lumbar arteries, but not saphenous vein in a concentration dependent manner. (RS) sulpiride and SCH 23390 competitively antagonised this effect. These studies demonstrate the presence of a vasodilatory vascular dopamine receptor in man both in vivo and in vitro.

Neuropeptide Y and sympathetic vascular control in man

A parallel increase in systemic plasma levels of neuropeptide Y (NPY)-like immunoreactivity (LI) and noradrenaline (NA) was found during thoracotomy and surgery involving cardiopulmonary bypass in man. Thus, plasma levels of NPY-LI increased from 29 ± 4 pmol/l before anaesthesia to 59 ± 10 after thoracotomy and to 87 ± 8 pmol/l upon cardiopulmonary bypass. The corresponding NA levels increased from 1.3 ± 0.1 nmol/l before anaesthesia to 3.0 ± 0.6 and 4.2 ± 5 nmol/l after thoracotomy and cardiopulmonary bypass, respectively. A significant correlation was found between plasma levels of NPY-LI and NA during the operation but not between NPY-LI and adrenaline. The NPY-LI in human plasma was found to be similar to synthetic porcine NPY on reversed phase high performance liquid chromatography. Human submandibular arteries contained high levels of NPY-LI ( 24 ± 3 pmol/g ). In in vitro experiments on isolated human submandibular arteries, NPY in low concentrations (1000 pmol/l) was found to potentiate the contractile effects of NA or transmural nerve stimulation and to exert vasoconstrictor activity per se in higher concentrations. The calcium-entry antagonist nifedipine abolished both the NPY-induced contractions and the enhancement of NA-evoked contractions. NPY depressed the nerve stimulation-evoked 3H-NA release from human submandibular arteries via a prejunctional mechanism which was resistant to nifedipine. NPY contracted human mesenteric veins and renal arteries, but not mesenteric arteries. In conclusion, NPY seems to be co-released with NA upon sympathetic activation in man. Furthermore, NPY exerts both pre- and postjunctional effects on sympathetic control of human blood vessels.

Activation mechanisms of human renal artery: Effects of KCl, norepinephrine and nitrendipine upon tension development and 45Ca influx

The activation of human vascular smooth muscle by KCl-induced depolarization or norepinephrine and the inhibition produced by nitrendipine were studied in the isolated human renal artery. The contractile response of arterial rings to 80 mM KCl was abolished when extracellular Ca 2+ was removed, and was inhibited by nitrendipine (IC 50 = 10 −8 M). In contrast, a residual, transient contractile response to norepinephrine remained when extracellular Ca 2+ was removed and the norepinephrine-induced contractions obtained in the presence of extracellular Ca 2+ were not blocked by nitrendipine. KCl caused a stimulation of 45Ca influx which was completely prevented by 10 −6 M nitrendipine. Norepinephrine also caused a stimulation of 45Ca influx; however, the norepinephrine-induced 45Ca influx was not prevented by 10 −6 M nitrendipine. These findings are consistent with the concept that depolarization-induced induced activation of the human renal artery is primarily dependent upon a stimulation of Ca 2+ influx; whereas activation by norepinephrine involves the release of intracellular Ca 2+ in addition to the activation of a separate, receptor-operated Ca 2+ influx pathway.

Pulsatile flow of non-Newtonian fluid in distensible models of human arteries.

In addition to biochemical factors, hydromechanical influences are responsible for atherogenesis and deposits of blood platelets at bends and bifurcations of human arteries. Hence the flow patterns were simulated in a true-to-scale three-dimensional bifurcation of a human renal artery model and of an arterial femoralis with Newtonian and non-Newtonian blood like fluid. Investigations were made with steady and pulsatile flow. The velocity profiles (at physiological Re-numbers) were measured after the bifurcations with a laser-Doppler-anemometer. In previous works Newtonian fluids were used to investigate the flow in bends and bifurcations of rigid and elastic simplified models. In this paper, emphasis is placed on the difference between rigid and elastic models and also Newtonian and non Newtonian flow behavior. Differences between Newtonian and non Newtonian fluids may especially be expected to occur after branches where the flow has local strong convective elements such as in reverse zones and flow separation points.

Comparison of Platelet Interaction with Subendothelium of Human Renal and Umbilical Arteries and the Extracellular Matrix Produced by Human Venous Endothelial Cells

Platelet interaction with subendothelium of human renal and umbilical arteries and with the extracellular matrix produced by cultured human venous endothelial cells was compared in flowing citrated blood by using an annular and a rectangular perfusion chamber. The renal arteries were post mortem specimens from adults showing, often pronounced, intimal fibrosis, whereas the umbilical arteries had well organized parallel arranged smooth muscle cells, without elastic membranes. The extracellular matrix obtained after removal of endothelial cells with Triton X-100 was homogenously attached to its substratum. Significantly more platelets adhered to the extracellular matrix than to the subendothelia. This discrepancy was most pronounced in reconstituted blood with plasma from a patient with homozygous severe von Willebrand's disease (subtype III). No differences in platelet adherence and platelet aggregate formation were noted between the subendothelia. Platelet aggregate formation was poor on all surfaces. These data indicate that the extracellular matrix produced by endothelial cells is at least as reactive for the interaction with platelets as subendothelium, probably partly synthesized by smooth muscle cells.

Flow separation in the renal arteries.

To determine the nature of the flow in the proximal portion of the renal arteries, a common site for the development of atherosclerosis, we performed pulsatile flow studies in a clear acrylic mold of a normal human aorta and renal arteries. The mold was developed from a cast of the renal arteries prepared in situ during the autopsy of a 27-year-old woman. Flow in the mold was visualized by the illumination of bouyant particles (100 to 300 mu). A range of branch (renal) to trunk (aorta) flow ratios of 0.053 to 0.350 was studied. Flow separation during systole was considered present when particles near the wall reversed direction. Flow separation occurred throughout systole at the superior aspect of the origin of both the left and right renal arteries at a branch-to-trunk flow ratio of 0.053. As the branch-to-trunk flow ratio increased, flow separation occurred during the deceleration phase of right renal flow. At a branch-to-trunk flow ratio of 0.350, flow separation was no longer present. This suggests that flow separation may occur near the renal ostia if renal flow falls appreciably while aortic flow remains elevated. Because flow separation involves low wall shear, mass transfer across the arterial wall may be adversely affected and possibly contribute to the formation of atheroma.

Adhesion of Platelets to Human Artery Subendothelium: Effect of Factor VIII–von Willebrand Factor of Various Multimeric Composition

The relationship between the multimeric size of factor VIII-von Willebrand factor (FVIII-vWF) and the support of platelet adhesion to subendothelium was studied in an annular perfusion chamber, employing human renal and umbilical arteries. Commercial factor VIII concentrates containing multimers of low molecular weight that had been shown not to correct the bleeding time upon infusion into patients with von Willebrand's disease did not support platelet adhesion in the perfusion chamber. Cryoprecipitate and two experimental FVIII-vWF concentrates containing multimers of high molecular weight supported platelet adhesion. Factor VIII-vWF purified from cryoprecipitate was subdivided into three fractions of different molecular weights (6.0-14.0, 4.0-9.0, and 3.0-7.5 X 10(6) dalton). These fractions appeared to bind equally well and to be equally effective in supporting platelet adhesion. Factor VIII-vWF with multimers of low molecular weight (0.5-1.5 X 10(6) dalton) were prepared by partial reduction. Binding of FVIII-vWF to subendothelium was not impaired, and the support of platelet adhesion appeared to be more resistant to the effect of reduction than the ristocetin cofactor activity. At high shear rate (2,500 sec-1), increased platelet adhesion was observed with partially reduced FVIII-vWF. These data indicate that the ability of FVIII-vWF preparations to correct the bleeding time is reflected in enhanced platelet adhesion to subendothelium in a perfusion chamber. These data also emphasize that multimeric size is not the only factor determining whether FVIII-vWF will support platelet adhesion.

Adhesion of platelets to human artery subendothelium: effect of factor VIII-von Willebrand factor of various multimeric composition

The relationship between the multimeric size of factor VIII-von Willebrand factor (FVIII-vWF) and the support of platelet adhesion to subendothelium was studied in an annular perfusion chamber, employing human renal and umbilical arteries. Commercial factor VIII concentrates containing multimers of low molecular weight that had been shown not to correct the bleeding time upon infusion into patients with von Willebrand's disease did not support platelet adhesion in the perfusion chamber. Cryoprecipitate and two experimental FVIII-vWF concentrates containing multimers of high molecular weight supported platelet adhesion. Factor VIII-vWF purified from cryoprecipitate was subdivided into three fractions of different molecular weights (6.0–14.0, 4.0–9.0, and 3.0–7.5 X 10(6) dalton). These fractions appeared to bind equally well and to be equally effective in supporting platelet adhesion. Factor VIII-vWF with multimers of low molecular weight (0.5–1.5 X 10(6) dalton) were prepared by partial reduction. Binding of FVIII-vWF to subendothelium was not impaired, and the support of platelet adhesion appeared to be more resistant to the effect of reduction than the ristocetin cofactor activity. At high shear rate (2,500 sec-1), increased platelet adhesion was observed with partially reduced FVIII- vWF. These data indicate that the ability of FVIII-vWF preparations to correct the bleeding time is reflected in enhanced platelet adhesion to subendothelium in a perfusion chamber. These data also emphasize that multimeric size is not the only factor determining whether FVIII-vWF will support platelet adhesion.

Flow investigations in a model of a three-dimensional human artery with Newtonian and non-Newtonian fluids. Part I.

Together with biochemical factors, fluid mechanical factors play a role in atherogenesis and the deposition of blood platelets at bends and bifurcations in human arteries. Hence, flow patterns were investigated in a simplified 3-dimensional model of a human renal artery bifurcation using Newtonian (aqueous glycerol) and non-Newtonian (aqueous solution of polyacrylamide) fluids. Studies were carried out in steady as well as pulsatile flow at inflow Reynolds numbers of 498 and 951 with flow rate ratios main tube V1: right branch V4: left branch V3 of 1: 0.25: 0.25 and 1: 0.18: 0.18 respectively. The velocity distribution proximal and distal to the bifurcations was measured using a laser-Doppler anemometer. In steady flow, zones of flow separation and reverse flow were observed distal to the bifurcations. In pulsatile flow using non-Newtonian fluids, there was a significant enlargement of these zones. Differences between the Newtonian and non-Newtonian fluids occurred especially distal to the bifurcations. Shear stresses along all measuring positions were computed from the velocity gradients.

In vitro evidence for dopaminergic receptors in human renal artery.

Effects of dopamine on human renal arteries were pharmacologically investigated in vitro. Norepinephrine (5 X 10(-10)-5 X 10(-5) M) produced concentration-dependent contractions of isolated renal arterial strips, which were significantly depressed by prior administration of phentolamine or phenoxybenzamine. Isoproterenol (4 X 10(-10)-4 X 10(-6) M) concentration dependently relaxed the strips under potassium contracture, but a high dose (4 X 10(-5) M) constricted them. Biphasic responses to isoproterenol were changed to concentration-dependent contractions by prior administration of propranolol, and abolished by propranolol together with phentolamine. Dopamine (5 X 10(-8)-5 X 10(-4) M) produced concentration-dependent contractions of human renal arteries, which were not significantly influenced by propranolol but which were reversed to relaxations by phentolamine. Dopamine-induced relaxations, which were obtained after administration of phentolamine, were not significantly affected by propranolol, but were significantly depressed by combined application of propranolol and haloperidol, or of propranolol and droperidol. Results suggest that isolated human renal arteries have dopaminergic receptors in their smooth muscles which show relaxations of renal arteries after alpha-adrenoceptor blockade.

Noninvasive characterization of renal artery blood flow

Noninvasive characterization of renal artery blood flow variables in the human has not been reported. Using a unique dual-frequency real-time two-dimensional echo Doppler (Duplex scanner) that was calibrated in vitro, we characterized renal artery blood flow patterns in 16 normal subjects (6 females). Calculated mean values of systolic diameter (Ds), maximal spatial average blood velocity (Vmsa), and volume flow rate (Q) were as follows: 4.5 +/- 0.6 mm right, 4.4 +/- 0.6 mm left; 67.6 +/- 9.4 cm . sec-1 right, 69.6 +/- 12.0 cm . sec-1 left; and 403 +/- 127 ml . min-1 right, 395 +/- 98 ml . min-1 left; respectively. Direct linear regression correlation of body surface area (BSA) with Ds and Q were statistically significant (P less than 0.01, r = 0.70; and P less than 0.01, r = 0.72, respectively). In a blind prospective series, six of seven angiographically normal renal arteries were noninvasively identified by normal geometry and blood velocity patterns. One angiographically normal artery was incorrectly classified as mildly stenotic. Eleven angiographically documented abnormal renal arteries were noninvasively identified by their abnormal blood flow patterns and/or geometry. This study suggests that dual-frequency Duplex scanning with careful sample volume control and Doppler audio spectra/blood velocity waveform analysis can be used to characterize blood flow variables in normal and diseased human renal arteries.