Hemodynamics of the renal artery ostia with implications for their structural development and efficiency of flow.

BACKGROUND: Energy losses at tube or blood vessel orifices depend on the extent of flare as measured by the dimensionless ratio of the fillet radius of curvature to diameter (r/D). OBJECTIVE: The goal of this study was to assess the effect of ostial fillet radii on energy losses at the aorta-renal artery junctions since as much as a quarter of cardiac output passes through the kidneys. METHOD: Pressure loss coefficients K for the renal artery ostia as a function of r/D have been determined for representative anatomical variants using finite volume simulations. Estimates of fillet radii in humans from image analysis were employed in simulations for comparison of loss coefficients. RESULTS: Values for K drop 45% as r/D increases over the range 0-1.3. Image analysis indicates that the ostia are not symmetric in humans with (r/D)superior much larger than (r/D)inferior. Simulations show the loss coefficient depends almost entirely on the superior fillet radius. CONCLUSIONS: Superior fillet radii for both renal arteries are similar to the optimal value to reduce energy losses while the inferior radii are not. Ostial asymmetry may have been induced by higher levels of shear stress present on the superior portion of a developing symmetric ostium of small r/D.

A vasoconstrictor response to COX-1-mediated prostacyclin synthesis in young rat renal arteries that increases in prehypertensive conditions.

This study aimed to determine whether prostacyclin (PGI2) functions as an endothelium-derived contracting factor (EDCF) in young rat renal arteries, and, if so, we wanted to examine the underlying mechanism(s) and how it changes in prehypertensive conditions. Vessels from Wistar-Kyoto (WKY) and prehypertensive spontaneously hypertensive rats (SHRs) of 25-28 days of age were isolated for functional and biochemical analyses. Result showed that following NO synthase (NOS) inhibition PGI2 and the thromboxane-prostanoid (TP) receptor agonist U-46619 evoked contractions in young WKY renal arteries that were similar to those in prehypertensive SHRs. Meanwhile, the endothelial muscarinic receptor agonist ACh evoked an endothelium-dependent contraction under NOS-inhibited conditions and a production of the PGI2 metabolite 6-keto-PGF1α; both were sensitive to cyclooxygenase (COX) and/or COX-1 inhibition but higher in prehypertensive SHRs than in young WKYs. Interestingly, in WKY renal arteries PGI2 did not evoke relaxation even after TP receptor antagonism that diminished the contraction evoked by the agonist. Indeed, PGI2 (IP) receptors were not detected in the vessel with Western blot. Moreover, we noted that treatment with the nonselective COX inhibitor indomethacin, which was started at the prehypertensive stage, blunted the elevation of systolic blood pressure and reduced the heart-to-body ratio in SHR within 2 mo of treatment. These results demonstrate that due to scarcity of IP receptors, PGI2, which is derived mainly from COX-1-mediated metabolism, acts as an EDCF in young WKY renal arteries, and it increases in prehypertensive conditions. Also, our data revealed that COX inhibition starting from the prehypertensive stage has an antihypertensive effect in young SHRs.

Postnatal kidney maturation regulates renal artery myogenic constriction.

AIM: Intravascular pressure-induced vasoconstriction (myogenic constriction) is central to renal blood flow autoregulation. At term, kidney maturation is functionally incomplete. Premature neonates are at risk of kidney dysfunction. However, it is unclear whether renal artery myogenic constriction is altered after preterm birth. Here, we compared renal artery myogenic constriction in full-term and preterm pigs during the first week of life. METHODS: We investigated myogenic constriction in small interlobular arteries isolated from the kidneys of pigs delivered at term and at 91% of term (with and without 96 h of neonatal intensive care). RESULTS: Cross-sectional area, media/lumen ratio, and luminal diameter measured under passive conditions were similar in arteries from full-term and preterm pig kidneys. An acute elevation in intravascular pressure from 20 to 100 mm Hg increased arterial wall tension and induced steady-state constriction of the arteries. However, arteries isolated from newly born preterm pigs (within 24 h) developed greater myogenic tone and lower active wall tension compared with arteries from full-term and 4-day-old preterm neonates. Pressure-induced elevation in intracellular Ca2+ was also larger in arteries from newly born preterm pigs compared with full-term and 4-day-old preterm pigs. CONCLUSION: Myogenic constriction is elevated in newly born preterm pigs. Our data also suggests that postnatal kidney maturation may modulate renal blood flow autoregulation.

Neural programming of mesenteric and renal arteries.

There is evidence for developmental origins of vascular dysfunction yet little understanding of maturation of vascular smooth muscle (VSM) of regional circulations. We measured maturational changes in expression of myosin phosphatase (MP) and the broader VSM gene program in relation to mesenteric small resistance artery (SRA) function. We then tested the role of the sympathetic nervous system (SNS) in programming of SRAs and used genetically engineered mice to define the role of MP isoforms in the functional maturation of the mesenteric circulation. Maturation of rat mesenteric SRAs as measured by qPCR and immunoblotting begins after the second postnatal week and is not complete until maturity. It is characterized by induction of markers of VSM differentiation (smMHC, γ-, α-actin), CPI-17, an inhibitory subunit of MP and a key target of α-adrenergic vasoconstriction, α1-adrenergic, purinergic X1, and neuropeptide Y1 receptors of sympathetic signaling. Functional correlates include maturational increases in α-adrenergic-mediated force and calcium sensitization of force production (MP inhibition) measured in first-order mesenteric arteries ex vivo. The MP regulatory subunit Mypt1 E24+/LZ- isoform is specifically upregulated in SRAs during maturation. Conditional deletion of mouse Mypt1 E24 demonstrates that splicing of E24 causes the maturational reduction in sensitivity to cGMP-mediated vasorelaxation (MP activation). Neonatal chemical sympathectomy (6-hydroxydopamine) suppresses maturation of SRAs with minimal effect on a conduit artery. Mechanical denervation of the mature rat renal artery causes a reversion to the immature gene program. We conclude that the SNS captures control of the mesenteric circulation by programming maturation of the SRA smooth muscle.

[Ultrastructural assessment of the role of dysangiogenesis in congenital hydronephrosis].

OBJECTIVE: To confirm the key role of vascular malformation by ultrasound examination and to make a more detailed study of the manifestations of dysnephro- and angiogenesis. SUBJECTS AND METHODS: The study enrolled 34 children aged 3 days to 7 years with congenital hydronephrosis, who were divided into 3 groups in accordance with the degree of renal hemodynamic disorders, the criterion for which was a resistive index (RI). RESULTS: The performed electron microscopic study revealed the signs of malformed vessels of all diameters, as well as hypoplastic changes in the renal parenchyma in children of all ages in all the groups. The most significant ultrastructural signs demonstrating a close correlation between dysangio- and dysnephrogenetic processes are the uniformity of structural failure in the glomerular and arteriolar basement membrane, which shows up in the irregularity of its thickness and obliteration of its layers, as well as the immaturity of endothelial cells of both glomerular and arteriolar capillaries (large sizes and a round shape). The important factor confirming their relationship is a direct correlation between the increased RI in all branches of the renal artery as hypoplastic changes progress in the parenchyma of hydronephrotic kidneys. CONCLUSION: The investigation demonstrated the interdependence of dysangio- and dysnephrotic processes in children with congenital hydronephrosis.

Heterotopic renal transplantation in piglets using vascular closure stapler metallic clips or conventional suturing techniques: comparison of vessel growth and macroscopical study.

BACKGROUND/PURPOSE: Our aim was to perform a macroscopic and imaging (ultrasonographic and angiographic) evaluation of vascular closure stapler (VCS) metallic clips for renal transplantation in growing piglets to assess their role for transplantation surgery in young children. If these techniques are to be useful, it is necessary to prove that their use avoids one of the main pitfalls of conventional sutures in this setting, namely lack of growth in the suture line. METHODS: Twenty-four piglets were used for this study. Animals were subjected to a heterotopic renal autotransplantation when they were 45 days old. The right kidney was moved from its normal location to the cranial area of the iliac fossa. The end-to-side anastomoses between the renal artery and vein and the aorta and vena cava, respectively, were performed using VCS metallic clips in 6 animals. Continuous polypropylene suturing was used in another 6 piglets, and continuous polyglycolic acid suture was used in 6 additional piglets. A control group of 6 animals without renal autotransplantation was also included in the study. All animals were allowed to grow for 6 months, during which time serial angiographic and ultrasonographic studies were carried out to assess the existence of vascular flow disturbances or stenosis. Similarly, angiographic measurements were obtained to document growth at the anastomotic site. Longitudinal growth was evaluated postmortem after the 6-month growing period. RESULTS: Angiography showed significant (P < .001) transverse growth in both arteries and veins belonging to the VCS clips, running absorbable suture, or control groups. No significant difference was observed among the 3 groups. Vascular growth in the running nonabsorbable suture (polypropylene) group, however, was significantly less than in the other 3 groups and did not significantly differ from baseline. Baseline luminal diameters at the anastomotic site as measured by angiography in the VCS group were 3.64 ± 0.40 mm in the artery and 5.30 ± 1.43 mm in the vein. After growth, these values increased to 6.87 ± 0.90 mm and 11.27 ± 2.53 mm, respectively. Significant longitudinal growth was evidenced macroscopically after 6 months in both aorta and vena cava in all groups. On the other hand, significant longitudinal growth in the renal artery and vein were only observed in the control, VCS, and absorbable suture groups. CONCLUSIONS: In this experimental setting, satisfactory macroscopic and angiographic vascular growth results were obtained using the VCS clips, suggesting that this suture could be the technique of choice in pediatric transplantation surgery.

Loss of the VEGF(164) and VEGF(188) isoforms impairs postnatal glomerular angiogenesis and renal arteriogenesis in mice.

Vascular endothelial growth factor (VEGF) is transcribed in the VEGF(120), VEGF(164), or VEGF(188) isoforms, which differ in receptor binding, matrix association, and angiogenic activity. This vascular growth factor has been implicated in the development of the renal vasculature, but the role of the distinct VEGF isoforms remains unknown. In the present report, renal angiogenesis and arteriogenesis were studied in VEGF(120/120) mice, expressing only the short VEGF(120) isoform. In VEGF(120/120) mice, ingrowth and survival of capillaries in glomeruli, remodeling of peritubular capillaries, vascular coverage by pericytes, and branching of renal arteries were all severely impaired, causing abnormal glomerular filtration and impairing renal function. The arterial branching defect might be related to a reduced expression of renin, a presumed renal arterial branching factor. Glomerulosclerosis and tubular dilation possibly resulted from renal ischemia caused by vascular defects. Thus, VEGF(164) and VEGF(188) not only mediate angiogenesis, but they also play an essential role in renal branching arteriogenesis.

The renal glomerulus and vasculature in 'aggregation' chimeric mice.

In glomerular development, the glomerular epithelium is derived from the lower loop of the S-shaped renal vesicle. However, it is unclear whether the capillary endothelium is derived directly by vasculogenesis (e.g. differentiated directly from local metanephric mesenchyme) or whether they are derived by angiogenesis (i.e. derived from pre-existing vasculature in the metanephros). This question has been addressed in other laboratories using surgically created chimeric kidney model systems. In the present study, chimeric kidneys were developed by aggregating the cells from 4- to 8-cell embryos from Mus musculus with ones from Mus caroli and implanting the aggregated embryos into pseudopregnant hosts [Goldowitz D: Neuron 1989;3:705-713]. Species specific DNA clones were used in conjunction with in situ hybridization to identify the species origin of cells. Interspecies aggregate chimeras had varying proportions of renal cells derived from Mus caroli and Mus musculus; however, regions were identified in which the renal tubular and Bowman's capsule or parietal epithelia were from one species while vessel endothelium and cells in the interstitium were from the other species. In those regions, glomeruli always contained an admixture of cells from both species however; many of the glomerular endothelial cells appear to be from the same species as the vessel endothelium and interstitial cells. These findings support the hypothesis that angiogenesis may contribute cells that help form the glomerular capillary endothelium. Most intrarenal arteries contained cells from both species. However a few vessels were found in which the endothelium was derived from one species while the smooth muscle cells were from the other species. This finding suggests that intrarenal arterial development has two cells of origin: the endothelial tube develops and is surrounded by mesenchymal cells that form the tunica media. The aggregation chimeric mouse kidney may become a useful model system for studying in situ aspects of the complex processes involved in kidney development.

The three-dimensional structure of the neonatal mouse kidney as revealed by scanning electron microscopy after KOH treatment.

The shape and arrangement of the developing nephrons were studied three-dimensionally by scanning electron microscopy (SEM) of the neonatal mouse kidney. The specimens were treated with the KOH digestion method in order to remove extracellular connective tissue components, thus enabling the direct observation of the developing nephrons at various stages. At the subcapsular region of the renal cortex, the ureteric ducts were observed as branched tubules with terminal swellings or ampullae. Newly formed blood vessels were often associated with terminals of these ureteric ducts. The cup-shaped renal corpuscles had aggregations of mesangial cells with blood vessels in the groove. At the vascular pole of mature nephrons, extraglomerular mesangial cells were observed as a cellular sheet, which was continuous with the smooth muscle layer of afferent and efferent blood vessels. The present study also demonstrated the shape of the immature podocytes in relation to the endothelial morphology of glomerular capillaries.

[Intrarenal doppler flow analysis in patients with kidney transplantation and stable transplant function]. / Intrarenale Dopplerflussanalysen bei nierentransplantierten Patienten mit stabiler Transplantatfunktion.

AIM OF THE STUDY: Intrarenal arterial Doppler sonography is used in noninvasive monitoring of transplant kidneys with controversial results. With the application of the method on renal transplants with stable function normal values should be generated and pitfalls should be identified. METHOD AND STUDY SUBJECTS: In a prospective study doppler findings in 61 renal transplant patients with stable graft function were compared with measurements in native kidneys of 60 healthy controls. In all kidneys duplex Doppler studies of arcuate/interlobar intrarenal arteries were performed and both the resistance index (RI) as well as the pulsatility index (PI) was determined. RESULTS: The results of our study are summarized: 1. Transplanted kidneys have significantly higher intrarenal arterial flow indices in comparison to native kidneys: RI = 67 +/- 5% in allografts vs. RI = 57 +/- 5% in native kidneys; and PI = 123 +/- 21% in allografts vs. PI = 91 +/- 15% in native kidneys, respectively. 2. RI and PI increase with age in both the native kidneys and the allografts. However, the increase in the transplanted kidney correlates with the age of the recipient but not with the age of the donor. 3. Corresponding to the increase in RI and PI the blood pressure is significantly elevated in the elderly. 4. The degree of external pressure with the transducer on the graft has an impact on the intrarenal arterial Doppler findings and measurements obtained. CONCLUSION: The intrarenal arterial Doppler findings dependent on various extrarenal factors. Using arterial Doppler sonography to evaluate transplant kidneys it is mandatory to take into account factors such as recipient's age and hemodynamic situation. External pressure with the transducer on the graft must be avoided. Once these factors were considered the intrarenal arterial Doppler sonography of kidney transplant is a valuable diagnostic tool.

Altered renal hemodynamics and impaired myogenic responses in the fawn-hooded rat.

The present study examined whether an abnormality in the myogenic response of renal arterioles that impairs autoregulation of renal blood flow (RBF) and glomerular capillary pressure (PGC) contributes to the development of renal damage in fawn-hooded hypertensive (FHH) rats. Autoregulation of whole kidney, cortical, and medullary blood flow and PGC were compared in young (12 wk old) FHH and fawn-hooded low blood pressure (FHL) rats in volume-replete and volume-expanded conditions. Baseline RBF, cortical and medullary blood flow, and PGC were significantly greater in FHH than in FHL rats. Autoregulation of renal and cortical blood flow was significantly impaired in FHH rats compared with results obtained in FHL rats. Myogenically mediated autoregulation of PGC was significantly greater in FHL than in FHH rats. PGC rose from 46 +/- 1 to 71 +/- 2 mmHg in response to an increase in renal perfusion pressure from 100 to 150 mmHg in FHH rats, whereas it only increased from 39 +/- 2 to 53 +/- 1 mmHg in FHL rats. Isolated perfused renal interlobular arteries from FHL rats constricted by 10% in response to elevations in transmural pressure from 70 to 120 mmHg. In contrast, the diameter of vessels from FHH rats increased by 15%. These results indicate that the myogenic response of small renal arteries is altered in FHH rats, and this contributes to an impaired autoregulation of renal blood flow and elevations in PGC in this strain.

Age-related changes in plasma and tissue fatty acid composition in Fischer 344 rats.

Advancing age is associated with increased risk of coronary artery disease. Changes in fatty acid metabolism affect important cellular membrane properties and functions which may contribute to the vascular pathophysiology of aging. This study was designed to investigate the effects of aging on the fatty acid composition of the plasma, liver, aorta, and renal artery in 4-, 15-, and 24-month old Fischer 344 rats, an animal model for aging. With aging, the levels of total polyunsaturated fatty acids (PUFA) increased in the plasma, aorta, and renal artery. The major changes in the liver fatty acid profile were increases in the levels of 18:2n6 and 18:3n3 and a decrease in the levels of 20:3n6 and 20:5n3. The results indicate that significant shifts occur in the levels of n6 and n3 PUFA in the plasma, liver, and vasculature with aging. The alterations in the fatty acid composition may be a pathogenetic mechanism of the vascular changes associated with aging.

Alterations of mRNA levels of alpha 1-adrenoceptor subtypes with maturation and ageing in different rat blood vessels.

1. Alterations of mRNA levels of alpha 1-adrenoceptor subtypes during maturation and ageing were determined by reverse transcription-polymerase chain reaction (RT-PCR) in aortae and renal, pulmonary and mesenteric arteries isolated from 3, 12 and 24-month-old rats. 2. The steady state levels for alpha 1A-, alpha 1B- and alpha 1D-adrenoceptors in aorta declined with maturation and ageing. In renal artery there was a decrease in mRNA for the alpha 1B-adrenoceptor in aged rats. However, in mesenteric and pulmonary arteries there were no changes in mRNA levels for the three subtypes of alpha 1-adrenoceptors as a result of maturation and ageing. 3. The results suggest that expression of alpha 1-adrenoceptors is changed heterogeneously in different blood vessels during maturation and ageing in rats.

Nephrogenesis and renovascular development in angiotensinogen-deficient mice.

Angiotensinogen-deficient mice provide a model to examine the roles of angiotensin II as a renal growth factor in vivo. We monitored nephrogenesis and renovascular development in angiotensinogen-deficient mice from Embryonic Day 13 (E13) to 4 weeks after birth. Northern analysis of homozygote (Atg-/-) mice confirmed the absence of angiotensinogen mRNA in the liver and the kidneys. Embryonic kidneys in Atg-/- mice from E13 to E18 exhibited active nephrogenesis, as also observed in Atg+/- mice and Atg+/+ mice. Furthermore, metanephroi harvested at E12 from Atg-/- embryos showed branching morphogenesis of ureteric bud and tubulogenesis similar to metanephrol from Atg-/- embryos grown with exogenous angiotensin II in serum-free culture. In newborn Atg-/- mice, we observed uniform dilation of the pelvis accompanied by a coarse medulla, which was not noted in Atg+/- or Atg+/+ mice. Hydronephrosis in Atg-/- mice continued, and renal papillae underwent atrophy for the 4 weeks after birth. Another characteristic aspect of the morphology of Atg-/- mice was the thickening of vascular walls as little as 2 weeks after birth. Immunohistochemistry revealed recruitment of renin in hyperplastic vascular smooth muscle cells (VSMC) in Atg-/- mice after 2 weeks. Electron microscopy confirmed that the majority of hyperplastic VSMC contained various sized renin granules with abundant endoplasmic reticulum. In situ hybridization demonstrated that expression of renin mRNA became prominent in parallel with hyperplasia of VSMC, as well as recruitment of renin protein. Furthermore, at 4 weeks, Atg-/- mice expressed alpha-smooth muscle actin in the mesangium, whereas none was ever found in that of Atg+/- mice and Atg+/+ mice. In conclusion, the renin-angiotensin system seems not be essential for nephrogenesis in vivo. Furthermore, hyperplasia of VSMC and expression of the smooth-muscle phenotype in the mesangium are inducible even in the absence of angiotensin II, with hypotension, in vivo.

Renal venous architectonics in domestic swine.

Renal venous architectonics were investigated in 240 kidneys from 120 swines at an age of 1-8 months. The methods used were: preparation, corrosion and X-ray examination. It was established that, in 75% of the cases, v. renalis cranialis and v. renalis caudalis were present. In the rest of the cases (25%), v. renalis intermedia was present. It was also observed that right and left renal veins formed distentions, which enveloped the caudal medial part of each adrenal gland. V. adrenalis (suprarenalis) was not formed as an independent blood vessel. Venous blood from the adrenal gland drains through 2-3 orifices in these distentions. This study describes vv. prelobares, vv, interlobares and vv. arcuatae. Anastomoses were found between them. On that basis this concluded that the renal venous system in domestic swine is not segmented.

Age-related changes of noradrenergic innervation of rat splanchnic blood vessels: a histofluorescence and neurochemical study.

The influence of ageing on the noradrenergic innervation of superior mesenteric artery and vein, renal artery and vein, and portal vein was studied in male Wistar rats by means of catecholamine histofluorescence, image analysis techniques and high pressure chromatography with electrochemical detection. Old age was accompanied by a marked increase in the density of noradrenergic innervation and an increase of noradrenaline levels in superior mesenteric artery, renal artery, and portal vein. In contrast, no significant age-related changes were observed in the density of noradrenergic innervation or in noradrenaline levels in superior mesenteric and renal vein. The present data indicate that, at least in superior mesenteric and renal artery and portal vein, senescence is not accompanied by loss or by lack of change in the noradrenergic innervation as commonly believed to be the case in many vascular trees. On the basis of our findings it cannot be excluded that increased plasma catecholamine levels observed in senescence derive, in part, from perivascular sympathetic endings.

The effect of aging on alpha-adrenoceptors and their responses in rabbits.

The effects of age on alpha-adrenoceptor responses, sensitivity and number were studied in rabbits aged from 1 to 36 months. Three types of investigation were carried out: conscious animal studies, isolated tissue studies and radioligand binding studies. Specific [3H]-prazosin binding decreased with age in both spleen and heart suggesting that the number of alpha 1-receptors declined at least in the tissues studied. The specific binding of [3H]-clonidine to spleen membranes and [3H]-yohimbine to platelets was not affected by age. In vitro responsiveness to alpha-adrenoceptor agonists decreased with age in abdominal aorta and renal artery, while the affinity of adrenoceptors for prazosin (pA2) was not altered. The decrease may be non-specific as responses to potassium were also altered. No change in alpha 2-adrenoceptor mediated platelet aggregation was observed. No change in pressor or depressor responses to full adrenoceptor agonists or to antagonists was observed in vivo. However, responses to clonidine, which is a partial agonist at alpha 1-adrenoceptors, were decreased. While aging influenced alpha-adrenoceptor subtypes differently, there was no direct relation between functional changes and number of receptors.