Extracellular Matrix Analysis of Human Renal Arteries in Both Quiescent and Active Vascular State

In vascular tissue engineering strategies, the addition of vascular-specific extracellular matrix (ECM) components may better mimic the in vivo microenvironment and potentially enhance cell-matrix interactions and subsequent tissue growth. For this purpose, the exact composition of the human vascular ECM first needs to be fully characterized. Most research has focused on characterizing ECM components in mature vascular tissue; however, the developing fetal ECM matches the active environment required in vascular tissue engineering more closely. Consequently, we characterized the ECM protein composition of active (fetal) and quiescent (mature) renal arteries using a proteome analysis of decellularized tissue. The obtained human fetal renal artery ECM proteome dataset contains higher levels of 15 ECM proteins versus the mature renal artery ECM proteome, whereas 16 ECM proteins showed higher levels in the mature tissue compared to fetal. Elastic ECM proteins EMILIN1 and FBN1 are significantly enriched in fetal renal arteries and are mainly produced by cells of mesenchymal origin. We functionally tested the role of EMILIN1 and FBN1 by anchoring the ECM secreted by vascular smooth muscle cells (SMCs) to glass coverslips. This ECM layer was depleted from either EMILIN1 or FBN1 by using siRNA targeting of the SMCs. Cultured endothelial cells (ECs) on this modified ECM layer showed alterations on the transcriptome level of multiple pathways, especially the Rho GTPase controlled pathways. However, no significant alterations in adhesion, migration or proliferation were observed when ECs were cultured on EMILIN1- or FNB1-deficient ECM. To conclude, the proteome analysis identified unique ECM proteins involved in the embryonic development of renal arteries. Alterations in transcriptome levels of ECs cultured on EMILIN1- or FBN1-deficient ECM showed that these candidate proteins could affect the endothelial (regenerative) response.

The renal parenchyma-evaluation of a novel ultrasound measurement to assess fetal renal development: protocol for an observational longitudinal study

INTRODUCTION

Disorders of fetal growth, such as intrauterine growth restriction (IUGR) and large for gestational age (LGA), have been found to have a profound effect on the development of the fetal kidney. Abnormal kidney development is associated with hypertension and chronic kidney disease later in life. This study will use a novel ultrasound measurement to assess the renal parenchymal growth and kidney arterial blood flow in the fetus to evaluate the development of the fetal kidneys and provide an indirect estimate of nephron number. Measurements in normally grown, IUGR and LGA fetuses will be compared to determine if changes in renal parenchymal growth can be detected in utero.

METHODS AND ANALYSIS

This longitudinal, prospective, observational study will be conducted over 12 months in the Ultrasound Department of the Townsville Hospital, Australia. The study will compare fetal renal parenchymal thickness (RPT) and renal artery Doppler flow between IUGR fetuses and appropriately grown fetuses, and LGA fetuses and appropriately grown fetuses between 16 and 40 weeks. The fetal RPT to renal volume ratio will also be compared, and correlations between RPT, renal parenchymal echogenicity, fetal Doppler indices and amniotic fluid levels will be analysed.

ETHICS AND DISSEMINATION

This study was approved by the Townsville Health District Human Research Ethics Committee. The study results will form part of a thesis and will be published in peer-reviewed journals and disseminated at international conferences.

Variations of the origin of renal arteries in the fetus identified on power Doppler and 3D sonography

PURPOSE

To investigate anatomic variations of renal arteries (RAs) using 2-dimensional (2D)/3D power Doppler sonography (PDUS) in normal fetuses and in fetuses with renal anomalies.

METHODS

The origin, direction, and distribution of RAs were studied in 120 fetuses without renal malformations using 2D/3D PDUS. Studies were performed between 14 and 17 weeks of gestation age on 64 male and 56 female fetuses. PDUS of the RAs was also performed in 12 fetuses with renal anomalies.

RESULTS

In 117/120 fetuses, a single RA was found to originate from each side of the abdominal aorta. The origin of the right RA from the abdominal aorta was superior to, at the same level as, and inferior to that of the left RA in 47% (55/117), 25.5% (30/117), and 27.5% (32/117) of the cases, respectively. An accessory right RA was found in 3 cases. Bifurcation of the right RA was found in 2 cases. There were no variations of the origin of renal vessels in 69% of the cases (83/120), whereas the remaining 31% (37/120) had 1 or several variation patterns. Variations in renal vessels were found in 8 of the 12 fetuses with renal malformations: accessory artery in 3 cases, origin of the right RA from the iliac artery in horseshoe kidney and in 2 cases with pelvic kidney, and bifurcation in 2 of the fetuses with double collecting system.

CONCLUSIONS

Variations in origin and distribution of fetal RAs are frequently observed in normal pregnancies. The majority of renal malformations are associated with such vascular variations.

Renal artery variations: embryological basis and surgical correlation

Understanding anatomy of the vascular variations of kidney is essential for the clinician to perform procedures such as renal transplantation, interventional radiological procedures and renal vascular operations more safely and efficiently. In order to facilitate the clinical approaches, we studied renal arterial pattern in 50 formalin-fixed cadavers, on 100 kidneys. We observed prehilar multiple branching patterns in 11 (11.66%) cases, duplication of renal artery in eight (8.33%) cases and superior polar artery in seven (6.66%) cases. In the present study findings discussed with its clinical correlation.

Suprarenal gland-arterial supply: an embryological basis and applied importance

Variation arterial anatomy of suprarenal gland is significant for radiological and surgical interventions. Knowledge of anomalous suprarenal artery is required to avoid complications in surgical procedure. Arterial architecture of human suprarenal gland was studied in sixty-eight cadavers of adult male and female. In all cases, superior suprarenal artery on right side was normal in origin but on left side, 24% showed anomalous origin. The incidence of anomalous origin of middle suprarenal artery on right side was 47% and on left side 6%. Anomalous origin of inferior suprarenal artery on the right side was 29% and left side 35%. The superior suprarenal artery was present in all subjects. However, there was absence of right middle suprarenal artery in 29% and left inferior suprarenal artery in 35% subjects. The most variable group was inferior suprarenal artery. The study result is being described to report anomalous origin of suprarenal arteries in the light of surgical, radiological and embryological significances. Present study findings suggest, thorough knowledge of anomalous arterial anatomy of suprarenal gland is required for surgical and radiological interventions of retroperitoneal organs of upper abdomen to avoid complications.

Origins of the gonadal artery: embryologic implications

The gonadal arteries are paired vessels that usually originate from the abdominal aorta at the level of second lumbar vertebra. In 5-20% of cases, the gonadal artery has a high origin (superior to L2) and in 5-6% of cases it originates from the main or accessory renal artery. The latter is referred to here as an aberrant gonadal artery. Ninety-eight kidneys of 50 healthy potential renal transplant donors were prospectively studied by conventional angiography. The renal artery, either main or accessory, was detected and individually injected to highlight their perihilar divisions and possible extrarenal branches. The gonadal arteries were recorded if they originated from the renal arteries. We found that 39% (n = 38) of kidneys had at least one accessory renal artery. In 14 sides (14% of kidneys), the gonadal artery (11 right and 3 left) originated from the renal artery, either main (n = 5) or accessory (n = 9). Ten out of 14 kidneys with an aberrant gonadal artery had an associated accessory renal artery. In nine cases, the gonadal artery originated from the accessory renal artery, and in one case, although it originated from the main renal artery, the same kidney had an accessory arterial supply. The results of this study demonstrate that aberrant gonadal arteries tend to originate from kidneys that possess an accessory arterial supply. We hypothesize that aberrancies of the gonadal artery are a part of a common embryologic error resulting in the persistence of the future accessory renal arteries. We believe that this study is the first to hypothesize and study such an association with these arterial anomalies of the renal pedicle.

Multiple anomalies involving testicular and suprarenal arteries: embryological basis and clinical significance

Variations in the origin of arteries in the abdomen are very common but with the invention of new operative techniques within the abdominal cavity, the anatomy of abdominal vessels has assumed much more clinical importance. During routine dissection of the abdominal cavity, we came across multiple arterial anomalies involving testicular and suprarenal arteries. On the right side, there was double testicular artery (medial and lateral) and the right inferior suprarenal artery aroused from the medial testicular artery. The right inferior phrenic artery (IPA) and middle suprarenal artery took origin from a common trunk just above the origin of right renal artery (RRA). On the left side, the left testicular artery was arching over the lower tributary of the left renal vein proper (LRVP). Apart from the developmental and morphological interest in arching gonadal arteries, they are of practical importance from a clinical and surgical viewpoint. The embryological and clinical significance of above variations has been described.

Bilateral prehilar multiple branching of renal arteries: a case report and literature review

Proper knowledge of variations of the arteries supplying the kidney is essential not only to the anatomists but also to the surgeons. In the present paper we are reporting a case of bilateral early and multiple branching of the renal arteries. The origin of the 2 renal arteries was normal but soon after their origin they ended by giving rise to multiple branches. Most of these branches entered the kidney through the hilum. However, on both sides, one of the branches (superior polar artery) passed superolaterally to reach the upper pole of the kidney. The superior polar artery also gave rise to the inferior suprarenal artery. Further, related literature review is done and the urological implications of these variations in renal surgeries are discussed.

An investigation of the origin, location and variations of the renal arteries in human fetuses and their clinical relevance

We investigated the origin, localizations and anatomic variations of the renal artery (RA) in human fetuses with the aim of determining the distribution of these variations according to lateralization and gender. In total, 90 fetuses of spontaneous abortion (45 males, 45 females) with no congenital malformations were included to the study. The abdominal aorta and its branches were dissected after latex solution colored with red ink had been injected into the vessels from the thoracic aorta. In all, 180 RA dissections were performed bilaterally in 90 cases and the anatomic variations were photographed. Right and left RAs were found to originate from the following levels according to the columna vertebralis, respectively: 3.8% and 1.9% lower T12, 67.3% and 25.0% upper L1, 9.6% and 28.8% mid L1, 15.3% and 40.3 lower L1, 3.8% and 3.8% upper 1/3 part of L2 vertebra. The right RA originated from the lateral part and anterolateral wall of the abdominal aorta in 73.0% and 26.9% of cases while the lateral and anterolateral wall origin percentages of left RA were 90.3% and 9.6%, respectively. The origin site of the right RA from the abdominal aorta was superior to, at the same level with, and inferior to that of the left RA in 53.8%, 34.6% and 11.5% of the cases, respectively. There were no variations in 75% of the cases whereas the remaining 25% had several variation patterns. The presented morphological results are as follows: A single hilar artery in 75% of the cases, double hilar arteries in 11.1%, an inferior polar artery in 10.5%, and a superior polar artery in 3.3% of specimens studied. Anatomical variations were observed more frequently among male fetuses and on the right side. Knowledge of RA variations is important for surgeons in performing many procedures and may help to avoid clinical complications, especially, during radiological examination and/or surgical approaches in the abdominal region.

Analysis of renal artery hemodynamics in normal fetuses using the color Doppler method

OBJECTIVE

From analysis of fetal renal artery hemodynamics, we attempted to reveal renal glomerular and tubular function in normal fetuses during pregnancy.

DESIGN

The study included 36 cases of normal fetuses from the 20th to the 40th week of gestation; V(max) (the systolic peak velocity of main renal artery), V(mean) (time averages of trace of peak velocity) blood flow were initially measured between 20 and 24 weeks of gestation and every 4 weeks thereafter. The measurement was performed a total of five times in a longitudinal study. In addition, the blood flow waveform was concurrently examined.

RESULTS

The V(max) was 22.02 +/- 0.50 cm/s at 20-24 weeks of gestation. This standard value (100%) was found to increase for each group as follows: 125.2, 149.1, 156.1, and 181.5%. Furthermore, using 20-24()weeks of gestation as the standard, the V(mean) increased after the 37th week of gestation: 186.7%, respectively. At 20-24 weeks of gestation, the blood flow wave forms consisted of 43.2% type I (only systolic waveforms), and 56.8% type II (both systolic and diastolic waveforms). Type III waveforms (waveforms that extended beyond the diastolic to the next systolic component) were not recognized. In the 33- to 36-week group, 82.6% of the waveforms were type II, and in the 37- to 40-week group, 76.2% of the waveforms were type III.

CONCLUSIONS

The V(max) and V(mean) of the renal artery in normal fetuses exhibit a similar rate increase when 20-24 weeks of gestation is compared to 37-40 weeks of gestation. The blood flow waveforms changed as pregnancy progresses; thus, it was inferred that this finding was related to the development of the renal glomerular and renal tubular function.

Normative values of Doppler velocimetry of five major fetal arteries as determined by color power angiography

OBJECTIVE

To produce normograms of Doppler indices of major fetal arteries and their ratios relative to the ascending aorta in a cohort of appropriately grown for gestational age fetuses.

METHODS

Prospective longitudinal study of 70 women with appropriately grown for gestational age fetuses between 24 and 38 weeks' gestation attending the Fetal Growth Clinic of a large UK teaching hospital. Doppler velocimetry of the middle cerebral (MCA), umbilical (UmA) and renal arteries (RA) and the ascending (AAO) and descending (DAO) aortas were studied using color power angiography. Ratios of the Doppler indices [pulsatility index (PI), resistance index (RI), systolic/diastolic (S/D) ratio] were then calculated using the ascending aorta as the reference numerator for the other four vessels to produce normograms. Regression analysis was performed to determined the significance, if any, of the changes in these ratios with gestation.

RESULTS

The normograms of the various Doppler indices were similar for the middle cerebral artery, ascending and descending aortas. There was an initial rise to a peak between 30 and 32 weeks and then a gradual return to values at 38 weeks similar to those at 24 weeks' gestation. In the renal artery, the indices showed very little variation with gestation. However, there was a gradual fall in the indices with gestation in the umbilical artery. The ratios of the various indices relative to that of the ascending aorta demonstrated an increase with gestation. The changes with gestation were statistically significant for the ratios of the indices from the ascending aorta to those of the middle cerebral, renal and umbilical arteries but not for those of the descending aorta.

CONCLUSIONS

The vascular resistance in the five fetal arteries decreased towards the end of pregnancy and the ratios of their indices relative to those of the ascending aorta decreased from 24 to 38 weeks' gestation. Early subtle changes in circulation in compromised fetuses may be identified early from deviations in these normograms.

Comparative anatomical study of the kidney position in amniotes using the origin of the renal artery as a landmark

The anatomical relationship between the kidney position and its arterial supply was investigated in 21 mammals, 1 bird, and 3 reptiles (n = 1 for each species) and in 43 human cadavers. The following observations were made. (1) Although the right kidney was located caudal to the left kidney in 29 out of 43 human cadavers (67.4%), the origin of the right renal artery from the aorta was located cranial to the origin of the left renal artery in 36 human cadavers (83.7%). Therefore, the relative positions of the kidneys do not correspond with the relative origins of the renal arteries in humans. (2) Among the mammals that were examined, the position of the kidney and the branching level of the renal artery on the right side were usually cranial to those on the left side. (3) In the bird and most reptiles that were examined, kidneys were typically located in the pelvic region and were supplied by segmental arterial branches. These results suggest that the right kidney and its arterial supply are generally located cranial to the left kidney in phylogeny of mammals. While the presence of a human accessory renal artery in 9 out of 86 sides (10.5%) and a cranial origin of the left renal artery relative to the right renal artery in 7 out of 43 cadavers (16.3%), shows some variation in the arterial supply to the kidneys, the origin of the renal arteries can generally be used as phylogenetic landmarks indicating the relative positions of the kidneys. Hence, from an ontological perspective, the human right kidney may be initially situated cranial to the left kidney during the early stages of development. Thereafter, the human right kidney may shift downwards secondary.

Rare case of right accessory renal artery originating as a common trunk with the inferior mesenteric artery: A case report

Dissection of a male cadaver revealed several vascular abnormalities in the abdominal cavity, notably of the renal circulation. In particular, three renal arteries were observed on the right side and two on the left. On the right side, one accessory renal artery originated as a common trunk with the inferior mesenteric artery. Additional variations included a left inferior phrenic artery originating from the celiac trunk, bilateral testicular veins emptying into renal veins, and the left testicular artery arising from the left renal artery. The possible embryonic development of these branching patterns and their clinical significance are discussed briefly.

Doppler blood flow velocity waveforms in the fetal renal arteries: variability at proximal and distal sites in the right and left arteries

OBJECTIVE

To investigate variability in pulsatility/resistance indices and absolute velocities of blood flow in fetal renal arteries dependent on side and sampling site within each vessel.

METHODS

Doppler blood flow measurements of pulsatility index (PI), resistance index (RI) and peak systolic velocity (PSV) and end-diastolic velocity (EDV) were performed in the renal arteries of 27 fetuses between 236 and 247 days of gestation. Velocity waveforms were sampled in both the right and left renal arteries at two different sites: proximally, close to the aorta, and distally, before any major visible bifurcation of the vessels. The intraobserver variation was measured in 15 additional fetuses.

RESULTS

Mean values of PI and RI were similar in the right and left renal arteries and at the proximal and distal sampling sites of these arteries. Mean PSV and EDV were higher at the proximal compared to the distal site on both sides. For all parameters the 95% limits of agreement between measurements made in the right and left arteries and at proximal and distal sites were wide but tended to be narrower for the left renal artery and at the distal site. Intraclass correlation coefficients for intraobserver variability were 0.88, 0.89, 0.83 and 0.81 for PI, RI, PSV and EDV, respectively.

CONCLUSIONS

It is important to standardize the precise site at which Doppler blood flow velocity waveform measurements are made in the renal arteries of the fetus. On the basis of our observations, we suggest that the left renal artery is the preferred vessel for sampling and that measurements should be made in the renal arterial trunk away from the aorta and before any visible branches.

Reduced uteroplacental blood flow alters renal arterial reactivity and glomerular properties in the rat offspring

Fetal malnutrition and hypoxia may modify organ system maturation and result in cardiovascular diseases in the adult. We tested whether intrauterine stress (IUS) leads to persistent alterations of renal biology. In rats, intrauterine stress was induced by ligation of the uterine arteries at day 17 of pregnancy. Renal arteries of the 21-day-old male offspring were isolated to study pharmacological reactivity. Kidneys were dissected to analyze renal structure and beta-adrenoceptor expression. At 21 days of age, half of the animals underwent unilateral left nephrectomy. At the age of 12 weeks, rats were instrumented for blood pressure monitoring, blood sampling, and renal function measurements. After IUS, litter size and birth weight were reduced, whereas the hematocrit was increased. Renal arterial responses to beta-adrenergic stimulation and sensitivity to adenylyl cyclase activation were increased, along with the renal expression of beta2-adrenoceptors. At 21 days and at 6 months of age, the number and density of the glomeruli were reduced, whereas their size was increased. The filtration fraction and urinary albumin concentration were increased 12 weeks after intrauterine stress. In control rats, removal of the left kidney at 21 days of age did not affect kidney function and blood pressure. However, after IUS, the remaining right kidney failed to compensate for the loss of the left kidney, and blood pressure was increased. In conclusion, prenatal stress transiently modifies renal arterial reactivity and results in long-lasting adverse effects on renal structure and function and on renal compensatory mechanisms.

Digital analysis of the volume of the human foetal suprarenal arteries

Vascularisation of an organ is an index of its metabolic activity. The suprarenal glands are of crucial importance in the development of pregnancy. No data were found by the authors to describe the volume of the human foetal suprarenal arteries throughout pregnancy. The study was designed to form a database of human foetal suprarenal arterial volume in relation to foetal age and sex. Digital images were obtained at 4-week intervals of the suprarenal arteries of 30 foetuses aged between 12-40 Hbd. The arteries were primarily filled with LBS latex. A unique form of software was designed to assist in incorporating vector graphics, spliced functions of Bezier, into the analysis. The arteries contoured by the geometric curves were calculated for their initial, average and terminal diameter, length and volume. The measurements were compared in relation to foetal age and sex at 4-week intervals. Foetal age was assessed by means of calculation from the last menstrual period, manual measurement of foot length and ultrasonagraphic measurement of femoral length. The suprarenal arteries in human foetuses are of strongly individual variation both in their origin and quantity. The volume of the arteries appears constant in the group analysed.

Digital analysis of the dynamics of the arterial supply to the human foetal kidneys

Variations in the renal arteries in human individuals and foetuses have already been well studied. Contemporary trends in visualisation techniques focus on the evaluation of the dynamic parameters of blood flow in the vessels (speed, pulsatility, resistance). Most of these data have been obtained by the means of Doppler ultrasound (Fig. 1, 2). The authors have not found any anatomical database containing information about variability in the volume of the foetal renal arteries. The aim of the study is to design a database for variation in foetal renal artery volume in relation to foetal age and sex. The material consisted of digital images of the renal arteries filled with LBS-latex taken from 30 foetuses aged 12-19 Hbd. Digital analysis of the arteries was made with a unique form of software. The program is a 2D vector graphic editor using spliced functions of Bezier. Foetal age is estimated according to the last menstrual period and measurement of manual foot length and femur length (FL) as determined by ultrasound.

Growth dynamics of the renal and suprarenal arteries in human foetuses

The kidneys and suprarenal cortex are of common embryonic origin. The suprarenal gland and kidney have a common pathway in angiogenesis. Each of the organs is of key importance for intrauterine and individual development, yet they vary greatly in growth dynamics throughout pregnancy. The authors compared the arterial supply of these organs quantitatively in respect to foetal age and sex.

Making a zebrafish kidney: a tale of two tubes

The kidney can be thought of as the pairing of two tubes: an epithelial tube (the nephron), carrying filtered blood and engaged in ion and water transport; and endothelial tubes (the blood vessels), delivering blood and carrying away recovered solute. The development of the nephron presents several interesting questions. How does an epithelial tube form and how is it patterned into functionally distinct components and segments? What guides the interaction between the vasculature and kidney epithelia? How are epithelial cell shape and lumen diameter maintained, and what goes wrong when kidney tubules balloon into cysts? Here, I outline the progress that has been made in answering these questions using the zebrafish pronephros as a simple, accessible model of nephron development.

Intrauterine growth restriction is accompanied by decreased renal volume in the human fetus

OBJECTIVE

Intrauterine growth-restricted fetuses are at risk for the development of adult hypertension and related cardiovascular diseases. Congenital oligonephropathy has been postulated as the primary mechanism. The objective of our study was to determine whether ultrasonically obtained in utero measurements of renal volume or renal artery Doppler blood flow differ between fetuses that are intrauterine growth restricted and fetuses that are not.

STUDY DESIGN

The study population consisted of women who were referred for a prenatal ultrasound evaluation at a large community medical center. The women were divided into two groups: women with fetal biometry that was consistent with intrauterine growth restriction and women with biometry within normal range. Information was collected on maternal demographics and other factors known to affect fetal growth. We performed detailed fetal renal anthropomorphic and Doppler blood flow measurements in addition to standard fetal biometric measurements on all patients, specifically comparing renal volume and renal artery flow data between the two groups.

RESULTS

No differences were observed in maternal age, race, parity, or fetal gestational age. Renal volume in the intrauterine growth-restricted fetuses was 31% (95% CI, 20%-40%), which was less than that in the group of fetuses that were not intrauterine growth restricted after an adjustment was made for gestational age. The ratio of renal volume to estimated fetal weight was 15% (95% CI, 1%-26%), which was less than the same ratio in the fetuses that were not intrauterine growth restricted. There were no differences seen in the renal artery Doppler measurements.

CONCLUSION

Intrauterine growth restriction appears to be associated with a decrease in fetal renal volume. Because renal volume is a likely proxy for nephron number, this study supports the hypothesis that intrauterine growth restriction may be linked to congenital oligonephropathy and potentially to hypertension in later life.

Precaval right renal artery: description and embryologic origin

OBJECTIVES

To describe our experience with precaval right renal arteries and discuss a theory of development of this unusual vascular variant. The right renal artery typically passes dorsal to the inferior vena cava and is thought to represent a consistent anatomic relationship.

METHODS

Three cases of precaval renal arteries were identified during laparoscopic and endourologic procedures. The intraoperative and radiologic anatomic findings were recorded. The embryologic origins of the kidney and renal artery were reviewed to postulate a mechanism for the precaval location of a renal artery.

RESULTS

In all cases, the precaval renal artery was an accessory vessel to the lower pole. Computed tomography demonstrated the location of the accessory artery ventral to the vena cava; the superior "main" renal artery was dorsal to the vena cava. In addition, bifid collecting systems (ie, pelves) were present, and the renal contours suggested nearly complete fusion of two renal moieties, with normal location and rotation of the kidney. No other cases of precaval renal arteries were recorded in urologic operative reports during the past 5 years at the University of California, San Francisco.

CONCLUSIONS

The precaval renal artery is a rare but important variant of renal vascular anatomy. Several associated findings on computed tomography (bifid collecting system, enlarged kidney) may suggest its presence. The embryologic origin is likely due to the late, incomplete division of the ureteral bud during the eighth week of gestation. The renal artery to the lower pole develops and persists after the posterior cardinal vein has become the inferior vena cava but before gonadal descent.

Morphostructural changes of the kidney microvasculature during the prenatal period in Bubalus bubalis

The microcirculation of the foetal kidney was studied in the buffalo using light (LM) and scanning electron microscopy (SEM). The primordial glomerules originated from the peripheral zone of the metanephros at the stage of 8 cm CRT. The glomerular capillaries started to differentiate at the stage of 10-15 cm CRT. They were sparse and showed a few primordial pores. In addition, they began to make contacts with primordial podocytes. At the stage of 40-60 cm CRT, the renal microcirculation showed a complex and almost completely organized morphology.

Fetal hemodynamics

Starting in the left cardiac ventricle the reader is taken on a guided tour on a fetal erythrocyte as measured by Doppler ultrasound. Up in the ascending aorta we move through the aortic isthmus to the descending aorta and the internal umbilical arteries, which fuse around the umbilical cord. With fresh oxygen from the placenta our erythrocyte moves in an accelerating continuous flow along the umbilical vein to the ductus venosus. After having reached the left ventricle again it now passes through a coronary artery to the right atrium and eventually the ductus arteriosus or the pulmonary circulation. Concepts of pulsatility, impedance and resistance are presente in the context of their clinical applicability in Doppler waveforms of various fetal vessels.

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.

Angiopoietin-2 is a site-specific factor in differentiation of mouse renal vasculature

Angiopoietin-1 (Ang-1) stimulates endothelial and vascular network differentiation through the Tie-2 receptor tyrosine kinase, while Ang-2 modulates this activation in embryo and tumor growth. The nephrogenic pattern of Ang-2 was documented in a mouse strain that expresses the LacZ reporter gene driven by the Ang-2 promoter. Heterozygous animals were healthy with morphologically normal kidneys, and they were examined after X-gal staining. At embryonic days 10.5 (E10.5) and E12.0, transgene expression was absent in the mesonephros and metanephros. At E14.0, expression was noted in the metanephric artery and its major branches. At E19.0 and in neonatal kidneys, expression was maintained in larger renal artery branches, extending to arcuate and smaller cortical vessels. Histologically, transgene expression was located in multiple layers of vessel wall cells, extending further from the endothelium than alpha-smooth muscle actin. The mesangium of immature glomeruli also expressed LacZ. In the first 3 postnatal weeks, a new pattern became evident, with intense X-gal staining in the inner stripe of the outer medulla, where a subset of thin descending limbs of loops of Henle expressed the transgene. This dynamic and developmentally regulated pattern indicates that Ang-2 is an early marker of the renal pericyte and vascular smooth muscle lineage and is also an epithelial-derived growth factor. Because Tie-2 is widely expressed by differentiating renal endothelia, this study is consistent with the hypothesis that Ang-2 has roles in kidney vascular maturation.

Fetal renal artery flow and renal echogenicity in the chronically hypoxic state

The object of this study was to investigate the fetal renal arterial blood flow in normal and hyperechogenic kidneys during the third trimester of gestation. The pregnancies screened were all chronically hypoxic. Depending on the etiology of the intrauterine chronic hypoxia, the cases were divided into two study groups. Group I comprised 120 pregnant women with pregnancy-associated hypertension and/or proteinuria. Group II consisted of 87 pregnancies with intrauterine growth retardation. Both study groups included pregnant women from the third trimester. Hyperechogenic renal medullae were detected in 15 out of 120 cases with pregnancy-associated hypertension and/or proteinuria, and in 22 fetuses of the 87 pregnancies involving intrauterine growth retardation. Fetal renal hyperechogenicity appears to be an indicator of fetal arterial circulatory depression, correlated with pathological changes in the resistance index for the fetal renal arteries. The fetal renal arterial blood flow resistance index was significantly lower in hyperechogenic cases. This may also be an in utero indication of subsequent intrauterine and neonatal complications, such as cesarean section because of fetal distress (43%), treatment in a neonatal intensive care unit (51%) or increased perinatal mortality (5.4%, as compared with 0.8-1.0% in the normal population). Detailed ultrasound and Doppler examinations of renal parenchyma and arteries appear to be useful methods in the prenatal diagnosis of reduced renal perfusion and of intrauterine hypoxia to detect possible pathological fetal conditions in utero.

Maternal cocaine abuse and fetal renal arteries: a morphometric study

The purpose of the present study was to evaluate the pathological findings and perform morphometric analysis of the renal arteries of fetuses exposed to cocaine in utero. The control group consisted of 22 stillborn fetuses of unknown etiology whose mothers' urine was negative for cocaine or any other vasoactive substances. The study group comprised 29 stillborn fetuses whose mothers' urine was positive only for cocaine on the day of admission. Sections of fetal kidneys (4 microm), stained with hematoxylin and eosin and periodic acid-Schiff reagent, were examined under light microscopy (x40) to identify interlobular arteries. Morphometric analysis of these arteries was performed using a self-assembled system with a touch-sensitive screen as an interactive peripheral. Their inner and outer circumferences were measured by outlining them on the screen with a stylus. The radius (r) was calculated from the measurement of the circumference (2.pi.r). The difference of the radii of the outer and inner circumferences was the thickness of the arterial wall. The interlobular arterial thickness was significantly greater (P<0.001) in the cocaine-exposed group (mean 15.46+/-5.8 microm, 2SD) compared with the normal (mean 9.03+/-3.96 microm, 2SD). There was a significantly (P<0.001) positive relation with advancing gestational ages in both groups. The circumferences of the lumen of the arteries showed a significant (P<0.05) relation with advancing gestational ages in the normal group only. In the cocaine-exposed group, the arterial lumen circumference (mean 167.88+/-17.58 microm, 2SD) was significantly (P<0.001) smaller than in the normal group (mean 227.73+/-6.82 microm, 2SD). Thus, maternal cocaine abuse is associated with thickening of the interlobular arterial wall of the fetal kidney and narrowing of the lumen.

Predictive value of serial middle cerebral and renal artery pulsatility indices in fetuses with oligohydramnios

OBJECTIVE

To determine if unexplained changes in the amniotic fluid index or pulsatility indices of the fetal renal, middle cerebral, or umbilical artery are predictive of perinatal outcome in pregnancies complicated by oligohydramnios.

METHODS

Changes in amniotic fluid measurements and fetal vessel velocimetry in patients with oligohydramnios were evaluated for correlation with fetal outcome. Fourteen fetuses with oligohydramnios underwent serial sonography evaluating the amniotic fluid index and fetal middle cerebral, renal, and umbilical velocimetry. Matched controls and neonatal outcomes were obtained.

RESULTS

Change in amniotic fluid index and in renal artery pulsatility index were inversely correlated. Change in the middle cerebral artery pulsatility index was different in infants with normal outcome compared to infants with adverse outcome

CONCLUSIONS

Serial velocimetry of the middle cerebral artery may identify fetuses with oligohydramnios at risk for adverse outcomes.

The application of color power angiography to the longitudinal quantification of blood flow volume in the fetal middle cerebral arteries, ascending aorta, descending aorta, and renal arteries during gestation

OBJECTIVE

This study was undertaken to determine by means of color power angiography the longitudinal changes in the diameters and the flow volumes of 4 major fetal arteries during gestation.

STUDY DESIGN

The middle cerebral artery, the ascending aorta, the descending aorta, and the renal arteries in 81 appropriate-for-gestational-age fetuses were examined longitudinally between 24 and 38 weeks' gestation by means of color power angiography. In addition to measurement of the diameters of these arteries, Doppler velocimetry was performed. Flow volume was calculated from the cross-sectional areas of the arteries and the velocity integral of the Doppler waveforms.

RESULTS

The mean (+/-SD) gestational age at delivery and birth weight were 39.8 +/- 1. 6 weeks and 3326 +/- 345 g, respectively. The diameters and flow volumes of all the arteries increased significantly as gestational age advanced. Flow volume increased from 39 +/- 19.0 mL/min to 140 +/- 63.9 mL/min in the middle cerebral artery, from 216.2 +/- 77.6 to 937.4 mL/min in the ascending aorta, from 124.4 +/- 76.6 to 390.0 mL/min in the descending aorta, and from 27.5 +/- 16.8 to 80.3 +/- 57.3 mL/min in the renal arteries. When blood flow volume was adjusted to milliliters per kilogram body weight, an initial significant fall in blood flow was seen in all the vessels to a minimal level at 30 weeks' gestation; blood flow rose thereafter, although not significantly, until term. The ratios of flow volume in the ascending aorta to those in the other vessels increased with gestation, with the highest ratio being that between the ascending aorta and the renal arteries.

CONCLUSION

Identification of fetal arteries with color power angiography is easy and highly sensitive. The distributions of blood flow in various fetal arteries exhibited regional differences, with significantly more blood flow to the brain. These normative baseline values may be useful in the diagnosis of congenital cardiac anomalies and also in the diagnosis and monitoring of fetuses with intrauterine growth restriction.

Variations in ovarian arteries in fetuses and adults

The present studies were carried out on 80 female fetuses and adults, aged 20 to 28 weeks and 18 to 90 years, respectively. Attention was paid to the place of origin of ovarian arteries from the aorta or renal artery, the location of these vessels in relation to the trunk of inferior vena cava, and to their courses relative to the renal veins. Four most frequently encountered types of ovarian artery courses were identified, and subsequently the discovered variations of basic types were described.

[The renal arterial pedicle in the human fetus]

To analyze the incidence of renal arteries variations during the fetal period and compare these findings with previous findings in adults, we studied the renal arterial pedicle in 70 human fetuses ranging in age from 13 to 36 weeks postconception. The fetuses were injected through the right common carotid artery with a red polyester resin to fill in the arterial tree enabling the identification and dissection of the small fetal arteries. The renal arteries were analyzed considering their number, origin, direction and site of penetration. Among the 70 fetuses studied, 30 (42.8%) presented at least one kidney with renal artery variations. In 6 fetuses the variation was bilateral. Among the total of 140 renal pedicles studied, 36 presented arterial variations (25.7%). We did not find statistically significant difference between right and left kidneys and between male and female fetuses. In the present study we did find kidneys with more than 2 arteries, probably because we did not study kidneys with any kind of development anomaly. Even kidneys with malrotations of the vertical axis were removed from the study.

[Accessory renal arteries in human fetuses]

Using conventional anatomical methods, renal arteries of 140 human fetuses were studied. It was found (21.1%) that the accessory renal arteries occurred in a three-fold manner: 1. as single arteries (19.2%), 2. as double arteries (2.1%) and 3. as triplex arteries (0.7%). More often they originated from the right part of the circumference of the abdominal aorta, mainly in the female fetuses. These arteries penetrated the following segments of the kidney: the inferior (12.9%), the superior (2.3%), the anterior inferior (2.8%), the posterior (2.1%) and the anterior superior (1.5%). They crossed the renal pelvis more often in front (12.2%) than from behind of it (5%). The frequency of the occurrence of the accessory arteries depends not from the age of the fetus.

Doppler velocimetry of the fetal middle cerebral and renal arteries: interobserver reliability

Using color and pulsed Doppler ultrasonography, the interobserver reliability of measurements in the fetal circulation was evaluated in 41 pregnancies of 25 to 39 weeks' gestation. Two observers recorded flow velocity waveforms from the middle cerebral and renal arteries for measurement of peak systolic, minimum diastolic, and mean velocities, pulsatility index, and resistive index. Intraclass correlation coefficient of reliability was calculated by analysis of variance. Substantial interobserver agreement was found for pulsatility index and minimum diastolic velocity in both arteries. Therefore, these measurements have the greatest clinical applicability.

Blood flow velocity waveforms of the abdominal arteries in appropriate- and small-for-gestational-age fetuses

The aim of this study was to describe flow velocity waveforms of abdominal arteries in the appropriate- and small-for-gestational-age fetus. Splenic artery, superior mesenteric artery, hepatic artery and renal artery velocity waveforms were obtained from 57 appropriate-for-gestational-age and nine small-for-gestational-age fetuses with color flow Doppler ultrasonography. The pulsatility index was used to quantify the arterial waveforms. Repeated measure analysis of variance indicated significant differences in the pulsatility index values in both the appropriate-for-gestational-age and small-for-gestational-age fetuses. A multiple comparison test revealed a significantly lower value for the pulsatility index in the splenic artery when compared to that of the other vessels for both the appropriate- and small-for-gestational-age fetuses. In the small-for-gestational-age fetuses, a lower pulsatility index value was observed at the superior mesenteric artery level when compared to the renal artery. Because of its lower frequency of successful insonation, the hepatic artery was not considered for the analysis. In the normal fetus, the splenic artery had the lowest pulsatility index when compared to the other arteries we investigated. This difference remained in small-for-gestational-age fetuses, reflecting a lower vascular resistance at the fetal spleen in both normal and small-for-gestational-age fetuses. It appears that in small-for-gestational-age fetuses the renal artery has a higher pulsatility index than the superior mesenteric artery, suggesting a preferential distribution of blood flow to the bowel.

Fractal geometric analysis of the renal arterial tree in infants and fetuses

Fractal geometry is a useful method of quantitating the space-filling properties of complex objects and has a particular advantage in pediatric pathology because it is independent of organ size. The fractal dimensions of angiographic images of 44 renal arterial trees from 23 consent pediatric autopsies were measured by the box-counting method. The mean fractal dimension was 1.64 and all values were greater than the topological dimension (one), indicating that the renal arterial tree in fetuses and infants has a fractal element to its structure. There was no significant association with size of the kidneys, confirming the size-independent nature of the fractal dimension. There was no significant association with age of the subject, and the mean value was not significantly different from values obtained in studies of adult kidneys, suggesting that the degree of branching, at a lobar and lobular level, does not increase after about the 21st week of gestation. The results are compatible with a diffusion-limited aggregation model of development.

Fetal renal artery and umbilical artery Doppler flow and fetal urine output

The object of this study was to determine if a correlation exists between the resistance index (RI) of the umbilical artery, the RI of the fetal renal artery, and hourly urine output by fetuses of normal pregnancies. Doppler flow study of the fetal renal artery and the umbilical artery was performed in 110 fetuses between 19 and 40 weeks' gestation. Color and pulse wave Doppler was used to obtain the flow velocity waveforms. The RI of the flow velocity waveforms was calculated. Fetal bladder volume was calculated by transverse, anteroposterior, and longitudinal diameters obtained from coronal and transverse sonographic images of the fetal urinary bladder. The difference in bladder volume at 30-minute intervals was used to determine hourly urine output. Gestational age has a positive linear association with fetal urine output (P < 0.01). The RI of the fetal renal artery has a negative linear association with gestational age (P < 0.05). The RI of the umbilical artery decreased with an increase in gestation age (P < 0.01). There was a significant correlation between the RI of the umbilical artery (P < 0.01) and the fetal renal artery (P < 0.05) and hourly urine output by the fetus. The RI of the fetal renal artery decreased with gestational age. Hourly urine output of the fetus increased with gestational age. The RI of the umbilical artery and the fetal renal artery had a significant correlation with fetal urine output.

Hourly fetal urinary production rate and blood velocity waveforms in the fetal renal artery relative to fetal heart rate pattern and fetal eye movements in normal pregnancies at 30-32 weeks of gestation

In 14 normal pregnancies at 30-32 weeks of gestation, bloodflow velocity waveforms in the fetal renal artery and fetal micturition were studied in relation to fetal heart rate pattern (FHRP) and fetal eye movements. PI in the fetal renal artery was significantly lower in the presence of FHRP-B and eye movements separately and in combination compared with FHRP-A and absent eye movements separately and in combination. Fetal urinary output was higher in the absence of fetal eye movements. There was an inverse relationship between renal artery PI and fetal heart rate. However, since mean fetal heart rate in the various state variables was not essentially different, no standardization for heart rate was necessary. No correlation existed between renal artery PI and fetal urinary production rate. It can be concluded that in the normal fetus at 30-32 weeks of gestation, renal artery PI demonstrates a significant reduction in the presence of FHRP-B and fetal eye movements separately and in combination, suggesting reduced downstream impedance at renal level. However, the decrease in fetal micturition in the presence of fetal eye movements, suggests that reduced urinary output is determined by changes in fetal central nervous system activity rather than by changes in fetal renal perfusion.

[Doppler ultrasound evaluation of fetal renal arteries in normal pregnancy]

Normal values of the pulsatility index in the fetal renal arteries in a group of 65 uncomplicated pregnancies were established. The measurements were obtained between 28 and 40 weeks of gestation. The values of pulsatility index may be used as a reference for further investigation of pathologic pregnancies.

[Normal values of color Doppler ultrasound in pregnancy]

In addition to the flowmetrie of aorta fetalis and a. umbilicalis, color flow mapping enables the examination of the renal and middle cerebral arteries in the assessment of the fetal blood circulation. The resistance and pulsatility-indices of aorta fetalis, umbilical artery, renal artery and middle cerebral artery were calculated in a prospective examination of a normal study group of 123 pregnant women. Moreover, ratios were established from the pulsatility-indices of renal artery and aorta fetalis, renal artery and umbilical artery, middle cerebral artery and aorta fetalis, middle cerebral artery and umbilical artery. By the use of these ratios, we hope to detect more reliably changes in the fetal blood circulation.

[Correlation between reduced amniotic fluid volume and Doppler spectra of fetal blood vessels at term]

The aim of this study was to determine, whether foetuses with reduced amniotic fluid in other-wise uncomplicated pregnancies at term show signs of redistribution of blood flow analogous to foetuses with intrauterine growth retardation. In 33 pregnancies > or = 37 gestational weeks with the largest pocket of amniotic fluid < 2 cm, flow velocity waveforms were recorded for the umbilical artery, middle cerebral artery and renal artery and compared with those of foetuses of the same gestational age and normal amniotic fluid volume. No difference was found in the resistance index (umbilical artery and middle cerebral artery), the pulsatility index (renal artery), or for the cerebral-placental ratio between these two collectives. We conclude, that Doppler examination of foetal vessels does not help to clarify the phenomenon of decreasing amniotic fluid volume during the final period of gestation. We suggest, that the decrease is not caused by renovascular changes, but has intra- or extrarenal causes.

Behavioural states and Doppler velocimetry of the renal artery in the near term human fetus

Transition of fetal behavioural state 1F to 2F coincides with cardiovascular changes measured by Doppler velocimetry e.g. a decrease in pulsatility index (PI) in the internal carotid arteries and in the descending aorta, indicating redistribution of blood flow. Recently, we reported a considerable reduction in fetal urine production rate of 47% during fetal behavioural state 2F as compared to 1F. It was suggested that this reduction is caused by an increase in renal vascular resistance during 2F. Using Doppler ultrasound, flow velocity waveforms (FVW) of fetal renal arteries were recorded during behavioural states 1F and 2F. Fetal behavioural states 1F and 2F were assessed by recording fetal heart rate pattern, eye movements and body movements. The PI of the renal artery FVWs were calculated as an index of renal vascular resistance to blood flow. Fifteen healthy pregnant women between 36 and 40 weeks gestational age were studied and the relationship between fetal renal vascular resistance to blood flow and behavioural states was determined. We found that PI values in the renal arteries did not change relative to behavioural state 1F and 2F. These findings suggest that renal vascular resistance to blood flow is not appreciably different in 1F and 2F. This is in contrast with urine production rate which is almost reduced by half during 2F in the near term fetus.

Effects of maternal administration of 3% carbon dioxide on umbilical artery and fetal renal and middle cerebral artery Doppler waveforms

OBJECTIVE

The null hypothesis is that umbilical, middle cerebral, and renal artery pulsed Doppler velocity waveforms in the normal term fetus may be affected during short-term maternal inhalation of 3% carbon dioxide gas mixture.

STUDY DESIGN

Seventy-two observations were made on 14 term fetuses before and during maternal 3% carbon dioxide gas mixture inhalation. The umbilical, middle cerebral, and renal arteries of these fetuses were sampled with pulsed Doppler velocity waveforms and recorded on a strip chart at a preset speed of 50 mm/sec. Doppler waveforms were analyzed for differences in the systolic peak to end-diastolic velocity ratio for these three vascular beds. Peak flow velocity and time velocity integral were also analyzed for the cerebral and renal vascular beds. The data were analyzed with the paired t test.

RESULTS

A significant decrease in the systolic-to-diastolic-velocity ratio of the middle cerebral artery occurred with 3% carbon dioxide inhalation (p < 0.02). The other vascular beds had no demonstrable change.

CONCLUSION

Transient maternal breathing of 3% carbon dioxide gas mixture selectively causes a decrease in resistance in the fetal cerebral circulation.

Doppler ultrasonographic assessment of fetal renal artery blood flow velocity waveforms in intrauterine growth retarded fetuses

Thirty-two blood flow velocity waveforms of the fetal renal artery, umbilical artery and fetal middle cerebral artery were recorded by a pulsed Doppler ultrasound from 28 to 38 gestational weeks in 32 intrauterine growth-retarded (IUGR) fetuses without structural defects. The nonstress test (NST) was performed on the day of pulsed Doppler ultrasonographic examination to assess fetal well-being. Of the 32 fetuses, the pulsatility index (PI: peak systolic velocity minus end diastolic velocity over mean velocity) values in the fetal renal artery were in the normal range in 26 measurements (81.3%), high in 2 (6.3%) and low in 4 (12.5%). The resistance index (RI: peak systolic velocity minus end diastolic velocity over peak systolic velocity) values in the umbilical artery and fetal middle cerebral artery were determined simultaneously in all the patients examined. Of the 12 fetuses with high RI values in the umbilical artery and low RI values in the fetal middle cerebral artery, the PI values in the fetal renal artery were within the normal range in 11 measurements (91.7%) and high in 1 (8.3%). Of the 9 fetuses with loss of fetal heart rate baseline variability in NST, the PI values in the fetal renal artery were within the normal range in 7 measurements (77.8%), high in 1 (11.1%) and low in 1 (11.1%). These data suggest that fetal renal blood flow may not change under the condition of chronic hypoxic state, although the NST shows fetal distress and the pulsed Doppler ultrasound reveals a brain sparing effect in the fetal middle cerebral artery. It is hypothesized that the fetal renal blood flow is controlled by an autoregulation mechanism for oxygen delivery presumably located in the renal artery.