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Renal cortical blood-flow distribution was measured by means of radiolabeled microscopheres in eight kidneys from 4 pigs of mixed Yorkshire and Danisk landrace. We found a pronounced intracortical variation in the perfusion pattern of 28 sections of outer cortex. Three consequetive flow determinations with an interval of 45 minutes showed that the heterologous perfusion pattern was plastic, changing between the flow-determinations. In addition, we found a significantly reduced perfusion in the renal poles, compared to the rest of the outer cortex. It is speculated that the reduced polar perfusion is a contributing aetiological factor to the increased incidence of polar scar formation secondary to reflux nephropathy.

The isolated and perfused cortical collecting tubule of the rabbit was examined by differential interference contrast microscopy in order to characterize the morphologic response of this nephron segment to peritubular hypotonicity. Computer-assisted, morphometric procedures were developed to obtain measurements of cell volume and lateral intercellular space geometry from interference contrast images of perfused nephron segments. Following dilution of the bath from 290 to 190 mOsm in the absence of antidiuretic hormone (T = 25 degrees C), the cells swelled rapidly to a new steady-state volume which was maintained for at least 20 to 30 min and which was about 90% of that predicted for ideal osmometric behavior. The increase in cell volume was accomplished entirely by bulging of the cells into the lumen; lateral space width and outside tubule diameter were unaffected by peritubular hypotonicity. In addition, the swelling of the cells was associated with an apparent swelling of intracellular organelles, e.g., nuclei and mitochondria. Our results indicate that cells of the mammalian collecting tubule swell without the capacity for significant volume regulation at 25 degrees C and without the cytoplasmic vacuolation and dilation of the lateral intercellular spaces observed following the onset of antidiuretic hormone-dependent volume reabsorption (E. Ganote , J. Grantham , H. Moses, M. Burg and J. Orloff , J. Cell Biol. 36:355, 1968).

Silicone rubber injections of methyl salicylate-cleared rat kidneys were performed. In 50 of 56 injections of superficial nephrons with their accompanying blood supply, the efferent vessel and early proximal tubule were closely approximated. In 18 of 21 tubular injections filling through the pars recta, the proximal tubule folded upon itself with early and late proximal segments, in close contact, located over their parent glomerulus, and the midproximal segments separate and located over their parent interlobular artery. The distribution of blood was serially through the early-late proximal region above the glomerulus via a long unbranched efferent vessel, via branches over the capsular surface, via capillaries down through the midproximal region, then into the interlobular vein. The observed anatomical pattern of the superficial nephron appears to permit direct functional interactions between the juxtaposed early and late proximal tubule, and in turn may effect midproximal function via the distribution of blood (modified by early proximal) from the efferent vessel to midproximal convolutions. In addition, the relationship between specific segments of the proximal tubule and specific portions of the postglomerular peritubular blood supply may be important in determining the distribution of peritubular physical forces to these nephrons.

The manatee kidney is composed of several closely apposed lobes. These are formed by cortical folds (plicae corticales) that completely isolate the medullae, except where the medullae of adjacent lobes are partially fused. The cortex is continuous; its folds usually are separated, but only partially, by interlobar septa extending from the renal capsule. The cortex makes up approximately 57% of renal mass in adults and 68% in the calf. There are about 3 million glomeruli per kidney. The average is somewhat less than that expected of an adult eutherian of equal mass. The glomeruli, however, are large; they form 7.38% +/- 1.33 of cortical mass, which is above that for at least ten unrelated adult eutherians. The number of glomeruli per gram of cortex is considerably greater in the calf than in the adult. The medullae are about 43% of renal mass. The cortico-medullary thickness ratio is 0.08 to 0.24. All terminal collecting ducts open at a crater (cratera cribrosa) of varying depth. Hair-pin loops occur at all levels of medulla, and apparently all loops bend at their thick segment. Cortical loops occur in the medullary rays. Vascular bundles were evident at the cortico-medullary border and thin tubules extended into the medulla from the central ends of the medullary rays (cortical) in seven out of the nine kidneys. The renal pelvis is separated from the central ends of the cortical folds by delicate fascia through which pass the interlobar vessels. There are no fornices and no infundibula. The collagenous tissue of the pelvic wall extends across most of the pelvic surface of the outer medulla.

Terminology of the cortex of the kidney is discussed and some new terms are suggested. Observations are described on 50 kidneys which have been injected and variously dissected. These include descriptions of the medulla, papillae and calyces. Some developmental, radiological and surgical aspects are mentioned and suggestions for further study are made.

The renal morphology of three species of desert dwelling Perognathus rodents were compared to Dipodomys and two species of sympatric cricetid rodents. Perognathus has a highly adapted unipolar kidney capable of urine concentration up to 7,500 mOsm/KgH2O. Two major modifications were observed in these kidneys. (1) There is elongation of both the inner and outer medulla. When the thickness of the regions in P. penicillatus are factored by kidney weight it is found that the outer medulla is 3.8 and the inner medulla is 2.2 times greater in length than the extensively studied Dipodomys merriami. (2) There is great variance in glomerular size with approximately 20% of the glomeruli being very large and located in the juxta medullary region. These glomeruli are 1.5--1.6 times greater in diameter than the more numerous superficial glomeruli. These structural modifications are quantitated and the functional implications are discussed particularly in relation to urine concentrating ability in these desert inhabitants.

Renal cortex visualization and dynamic renal computed tomography (CT) were carried out by bolus injection of contrast medium. In vivo renal cortex visualization showed that renal cortex volume and cortex thickness are both inversely correlated with age. The percentage volumes of cortex and columns of Bertin are correlated inversely in non renal-failure subjects. Percentage volumes of cortex tend toward low values in renal failure and status after renal transplantation. In analyzing dynamic renal CT curves, the corticomedullary junction time is a good index of mild impairment of renal function.

Auranofin, a gold-containing compound, was administered to Charles River CD-1 mice for 18 months to assess its possible carcinogenicity. The mice were dosed orally with 1.0, 3.0, or 6.0 (increased to 9.0 on Day 294) mg/kg/day. Each dose group and each of two control groups contained 110 males and 110 females. Survival was greater than 70% at the end of the study. No effect of the treatment on neoplastic or nonneoplastic lesions was found. This is in contrast to the results reported in rats. Auranofin in rats produced a heavy metal nephropathy characterized by acute coagulative necrosis, subacute renal cortical fibrosis, chronic cytomegaly and karyomegaly, and finally renal cortical neoplasia (adenomas and adenocarcinomas). The lack of effect of auranofin on tumor incidence in mice suggests the findings in rats may be species specific.

Experiments were undertaken to substantiate the hypothesis that the mechanism of the direct effect of ouabain on the renal excretion of electrolytes is the result of inhibition of the transport enzyme, (Na+, K+)-ATPase. In dogs hydrated with saline, an injection of 3H-ouabain into the unilateral renal artery produced a continuing marked increase in excretion of water and sodium from the kidney, but not from the counter kidney. At maximal diuresis -- 90 min after ouabain injection, both kidneys were removed to assay microsomal ATPase activity and determine radioactivity distributed in subcellular structures. It was demonstrated that 3H-ouabain was deposited in the microsome fraction obtained from the injected kidney in concentrations ranging from 10(-7) to 10(-6) M/kg wet weight and (Na+, K+)-ATPase activity of this fraction was inhibited as compared with that of the microsomal fraction obtained from the counter kidney. Since (Na+, K+)-ATPase activity of renal microsomes was significantly inhibited in vitro by more than 10(-7) M of ouabain, ouabain concentration in microsomes obtained from the injected kidney was considered to be sufficient to inhibit ATPase activity. These findings indicate that ouabain diuresis under the present condition is closly related to direct inhibitory effect of ouabain on (Na+, K+)-ATPase activity of microsomes in tubular cells.

The kidney of the okapi is of the medullary crest type and is divided transversely into six lobes by encroachments of cortex into medulla. These lobes are demarcated externally by furrows. The collecting ducts open at the apex of the truncated medullary crest. The pelvis part of the kidney, or pars pelvina renis, is the entire inner medulla and is the only part exposed to the pelvic urine. The pelvis has 10 interlobar vascular eminences and extends peripherally along-side the interlobar vessels as 10 fornices. The vascular eminences are buttressed by 12 free-edged semilunar eminences, which form pouches across 12 intervascular eminences. At each pole a vascular eminence supplies blood vessels to a dorsal and a ventral intervascular eminence. The extrahilar portion of the renal vein consists mainly of a thick coat of longitudinal muscle. In the renal sinus this heavy muscular coat is absent. The tributaries of this vein open via conspicuous nonmuscular valves. The cortex is about 85% of the renal mass and has about 2.89 X 10(6) glomeruli, which form 4.85% of the cortical mass. The filtering surface of a glomerulus is 0.088 mm2, making the total filtering surface of one kidney 0.219 m2. The number of glomeruli per kidney falls into the line which relates number of glomeruli to adult body weight from mouse to elephant and is expressed by log N = 0.59 log W + 3.2 or by N - 1.585W0.59 where N is the number of glomeruli in one kidney and W the adult body weight.

Our recent morphological studies showed that basement membranes isolated from renal tubules tended to collapse and form folded sheets while glomerular basement membranes were more resilient. In an effort to study the shapes of various isolated basement membranes in undissociated tissues, a method was developed to remove all cellular elements and leave the extracellular matrix and associated basement membranes intact. Accordingly, transplant quality human kidneys were harvested, perfused with Collin's medium and transported to the laboratory on ice. The renal cortex was then peeled away by blunt dissection, further minced to 2 mm3 and placed in 1 mM EDTA (with gentle intermittent stirring) for 72 h at 4 degrees C. Solubilization of cellular materials was carried out by successive washings with 3% Triton X-100, 0.025% DNAse and 1-4% sodium deoxycholate (all with gentle stirring or shaking at 22 degrees C). Each solution contained 0.1% sodium azide. At the level of fine structure, glomerular, tubular, Bowman's capsular and peritubular capillary basement membranes all maintained their respective shapes and did not collapse. Glomerular basement membrane was particularly striking in this regard and exhibited an open, lobulated form that closely resembled its in vivo histoarchitecture. Moreover, when the acellular tissue blocks were prepared for scanning electron microscopic observation, the glomerular basement membranes exposed at the surface of the block showed a remarkable structural rigidity. These basement membranes were free-standing, convoluted electron-dense sheets, continuous with highly folded central mesangial regions. It seems significant that glomerular basement membranes maintain their in vivo conformation irrespective of the presence of other extracellular matrix components while removal of these materials by organ subfractionation results in folding and general shapelessness of tubular basement membrane. It is possible that in addition to its unique role in filtration, glomerular basement membrane may also serve to preserve glomerular shape, regardless of changing cell populations or alterations in hydrostatic pressures.

The hamster renal pelvis has been studied by means of low-power light microscopy, scanning electron microscopy and morphometric analyses. The results of this study are highly suggestive that the contact of pelvic urine with the other medulla as well as with the inner medulla may be an important aspect of final urine formation. The outer medulla constituted nearly 50% of the total pelvic surface area, with the inner stripe of the outer medulla more than twice the pelvic surface area of the outer stripe of the outer medulla. The large outer medullary pelvic surface area was accounted for by the elaboration of the upper pelvic walls into peripelvic columns, opercula ("secondary pyramids"), fornices and secondary pouches. A thin simple-squamous to low cuboidal pelvic epithelium separated pelvic urine from outer medullary parenchyma. The inner medulla which constituted about one quarter of the total pelvic surface area was covered by a cuboidal to columnar pelvic epithelium which appeared morphologically similar to the papillary collecting duct epithelium. Tubules and capillaries of the inner medulla did not appear as closely juxtaposed to the pelvic epithelium as did those of the outer medulla. Cortical tissue comprised only 11.7% of the total pelvic surface area and was covered by transitional epithelium similar to that of ureter and bladder. The previously reported impermeability of this epithelium suggests that pelvic urine contact with the cortex is unimportant in final urine formation. The rich layer of smooth muscle under the transitional epithelium probably functions to move urine into and out of the pelvis during pelvic peristalsis, which has been observed in vivo.

We have demonstrated a significant, directionally dependent, anisotropic, echogenicity from the cortices of two sheep kidneys and a normal human cadaver kidney. The anisotropy corresponds to the relationship of the sound field to the medullary rays and interlobular arteries. At 7.5 MHz, the backscatter from specimens of cortex of a sheep kidney was 4.7 +/- .7 dB (mean +/- SEM) greater in parts of the cortex where the field was perpendicular to these structures as opposed to where it was parallel to them. In addition, we measured the angular distribution of this anisotropy and compared it to the 5 dB inclusion angle of the 5 MHz linear array that was used in measurements on the whole kidney specimens. The transducer inclusion angle was 10 degrees +/- 2 degrees, while the angular distribution was 34 degrees +/- 22 degrees and 23 degrees +/- 11 degrees (mean +/- SD) for the intact sheep and human kidney, respectively, demonstrating some variation of the medullary rays from perfect specular reflectors. This anisotropy should be visible in standard diagnostic scanning, and its recognition could increase ultrasound's sensitivity for the detection of renal disease.

The sensitivity and detection limit for measurements of the concentration of cadmium in the kidney cortex of man in vivo have been investigated using the technique of X-ray fluorescence. An 11 GB1 241Am source was used to generate the characteristic K alpha X-rays of cadmium. The variation in the sensitivity for the detection of cadmium at various locations in a kidney has been studied. Because of the pronounced variation in sensitivity with depth in tissue, a measurement could be made selectively in the kidney cortex. The minimum detectable Cd concentration varies between 20 and 40 micrograms g-1 for distances between the skin and the kidney surface of 30 to 40 mm; this distance has a measured uncertainty of +/- 3 mm which gives rise to an uncertainty of +/- 30% in the estimated Cd concentration. The mean absorbed dose to the kidney during such a measurement is about 0.6 mGy. The X-ray fluorescence method is more advantageous than the alternative neutron capture gamma ray analysis technique as far as the total irradiation of the patient is concerned. The cadmium concentrations in the kidneys of five exposed persons were found to lie between 30 and 143 micrograms g-1.

The relative kidney weight (1.44% greater than 1.15% greater than 1.07%) and the GFR (44 greater than 39 greater than 35 ml/min . m2) are higher in adult males than in adult females or in orchiectomized males. In contrast, GFR based on kidney weight is smallest in healthy males (1.02 less than 1.22; 1.22 ml/min . g). Only the cortex tissue seems to be increased in males, because its width (1.67 mm) is greater than in females (1.26 mm), while medullary width is identical (2.4 mm) in both sexes. Enlargement of the cortex in males can be accounted for by the nonglomerular tissue, because glomerular diameters (120 micrometers) do not differ and the number of glomeruli in representative sections is lower than in females. Cuboidal cell transformation of the outer layer of Bowman's capsule was observed in 60% of the glomeruli of the males and in 5% of the females. It might be an indicator for hyperplasie of the proximal tubular cells in the males.

Certain quantitative data on stereological indices reflecting the canine kidney tissue element parameters are presented.

The distal tubule, which includes the thick ascending limb (TAL), the macula densa, and the distal convoluted tubule (DCT), and the collecting duct are structurally heterogeneous, thus reflecting the functional heterogeneity that is also present. As the TAL ascends from medulla to cortex, the surface area of the apical plasma membrane increases while that of the basolateral membrane decreases. The structure of the DCT resembles that of the medullary TAL. An excellent correlation exists between structure, Na-K-ATPase activity, and NaCl reabsorptive capacity in the distal tubule. The collecting duct is subdivided into the initial collecting tubule (IC), and cortical (CCD), outer medullary (OMCD), and inner medullary (IMCD) collecting ducts. Between the distal tubule and the collecting duct is a transition region termed the connecting segment or connecting tubule (CNT). Considerable structural heterogeneity exists along the collecting duct within the two major cell populations, the intercalated cells and the principal cells. In the CNT, the ICT, and the CCD, potassium loading and mineralocorticoids stimulate Na-K-ATPase activity and cause proliferation of the basolateral membrane of CNT cells and principal cells, thus identifying the cells responsible for mineralocorticoid-stimulated potassium secretion in these regions. Finally, at least two morphologically distinct populations of intercalated cells exist, types A and B. In the rat, type A predominates in the CNT and the OMCD and is believed to be responsible for H+ secretion, at least in the OMCD. Type B predominates in the CCD, where it may be involved in bicarbonate secretion.

The site of localization of [(3)H]gentamicin within mouse kidney is shown to be the proximal renal tubule by coincidence of the radioactivity, as visualized by autoradiography, and the mucopolysaccharide-rich microvilli characteristic of proximal convoluted tubules, as visualized by histochemical staining.

Clearance experiments were carried out in fetal, young, and adult pigs undergoing salt loading. Kidney sections were histologically examined and the proximal tubular length, glomerular volume, and number of glomeruli were estimated. Between days 48 and 55 of gestation, the significant increase in glomerular filtration rate was proportionately higher than the concentration increase in water, total solutes, and sodium reabsorption. During this period, neither the proximal tubular length nor the glomerular volume of the juxtamedullary nephrons changed significantly. The main morphologic change took place in the superficial cortex, where new glomeruli attached to very short tubules differentiated. From day 55 to birth, the increase in water, total solutes, and sodium filtered loads was proportionately smaller than the concomitant increase in tubular reabsorption. During this phase, the major morphologic change was the significant lengthening of the proximal tubules of the juxtamedullary and superficial nephrons. These findings suggest that for water, sodium, and total solutes the maturation of superficial nephrons is accompanied by a phase of functional glomerular preponderance. Despite the differentiation of the superficial nephrons, renal handling of normally filtered glucose did not change significantly. Functional glomerulotubular coupling for water, sodium, and total solutes took place soon after birth.

Collins' solution is an excellent medium for kidney preservation by simple cold storage before transplantation. Efforts by Sacks et al. to improve this technique by modifying the composition seemed promising. A comparison between ability of these two media to preserve the tubular cell was attempted. The viability of the tubular cells was evaluated by measuring the 125 I Hippuran uptake in cortex slices taken from kidneys preserved for 24 and 48 hr in the respective solutions. Kidneys exposed to as well as kidneys not exposed to warm ischaemia were used. Collins' solution was found to be superior in protecting the cell function. Nonetheless intracellular oedema during preservation was greater after preservation in this solution as compared with cells preserved in Sacks' solution.

The architecture of the desert rodent Psammomys obesus has been studied by means of standard histologic procedures and by single nephron injections. As other rodent kidneys (rat, mouse), the Psammomys kidney consists of two types of nephrons, 66% short looped and 34% long looped nephrons. The cortex is composed of 4 to 5 layers of glomeruli, which lie closely put together, the glomeruli often touch each other. The superficial and the midcortical glomeruli give rise to short looped neophrons, the juxtamedullary to long looped nephrons. In the strongly developed medulla the inner stripe shows the most striking pattern. It consists of two distinct compartments, that of the giant vascular bundles and that of the interbundle regions. The giant vascular bundles consist of about 8 to 14% arterial vasa recta and 39 to 47% venous vasa recta; furthermore they include the thin descending limbs of the short loops of Henle which amount to 44 to 51% of the bundle structures. The tubules of the interbundle regions surround the bundles in a regular pattern. The inner zone is almost completely surrounded by the renal pelvis; the long broad papilla protrudes into the ureter. The thin descending limbs of short looped nephrons traverse the inner stripe inside the giant vascular bundles. Leaving the bundles they turn back within the inner stripe; their ascending limbs lie in the interbundle region. Both limbs of the long loops of Henle run in the interbundle region, together with the ascending limbs of the short loops and the collecting ducts. The long loops penetrate deeply the inner zone. Many bends are found near the tip of the papilla. The renal pelvis has a very specialized form. It penetrates the inner stripe with many complexely shaped extensions, which surround the giant vascular bundles. Large parts of the bundles with their thin walled structures are thus separated from the pelvic urine only by a single layer of cuboidal epithelium. The possible functional importance of the described specializations of the Psammomys kidney (giant vascular bundles, large inner zone, special shape of the renal pelvis) for the urine concentrating and urea recyclng mechanisms is discussed.

A prospective renal ultrasound study of 134 newborns (49 prematures weighing less than 2500 g and 85 more mature babies) was undertaken to investigate factors associated with increased renal cortical echogenicity (RCE). Increased RCE was seen in 39 (29 per cent) babies. It was significantly related to body weight, age, medical status, blood urea nitrogen, and serum creatinine. In view of the interdependence of these factors, however, multivariate analysis was performed, which revealed that age was the most important factor associated with increased echogenicity (r = -0.46), and the other factors had only small independent effects, increasing the multiple r to 0.56. The authors conclude that an infant's immaturity is the most important determinant of increased RCE.

The response to progressive volume expansion with isotonic saline was studied in sham-operated (CS) rats and in rats with reduced nephron mass after unilateral removal of cortical tissue (CX) or amputation of the kidney poles (NX). Glomerular filtration rate (GFR) in CS kidneys was not statistically different from that in control kidneys. CX and NX kidneys had GFR values markedly lower than control and CS kidneys. CX kidneys had FENa similar to that of control and CS kidneys until very high rates of urine flow were reached (volume expansion greater than 15% of body weight), when it was greater in CX than in CS or control kidneys (25 +/- 14% vs. 11 +/- 2%; p less than 0.05). The same relationship was found between NX kidneys and their controls: FENa only exceeded the values in control kidneys at high rates of urine flow. A defect in free water reabsorption was present in CX when compared to CS and control kidneys, while NX kidneys had TcH2O values which were not different from control kidneys. This different response of CX and NX kidneys suggests that the behavior of CX kidneys cannot be attributed simply to a nonspecific reduction of renal mass. Instead, these results suggest a heterogeneity of nephron function between superficial short-loop nephrons and deep long-loop nephrons primarily with respect to water handling.

Inability to demonstrate the renal corticomedullary junction (CMJ) on magnetic resonance (MR) images has been reported in connection with several medical renal diseases. T1-weighted spin echo pulse sequences have been advocated to demonstrate a signal intensity difference between cortex and medulla. This study was undertaken to determine which of several T1-weighted spin echo (SE) and gradient echo (GE) sequences are better for delineation of the CMJ. The MR studies were performed at 0.5 Tesla on 27 normal volunteers. Multi-slice axial images of both kidneys were obtained in all subjects at each of the following five pulse sequences: SE 250/20, SE 500/30, SE 900/30, and GE 300/15 with 80 degrees and 64 degrees flip angles. Contrast/noise ratios were calculated for the signal intensity differences between cortex and medulla; the average standardized contrast/noise ratios ranked as follows: GE 300/15/80 degrees = 3.01 +/- 0.74, GE 300/15/64 degrees = 2.72 +/- 0.74, SE 250/20 = 2.02 +/- 0.33, SE 500/30 = 1.96 +/- 0.51, and SE 900/30 = 1.71 +/- 0.39. In addition, the five sequences for each patient were randomized and the images were independently ranked for delineation of CMJ by three MR radiologists. The cumulative subjective ranking for all observers from best to worst is as follows: SE 500/30, GE 300/15/80 degrees, GE 300/15/64 degrees, SE 900/30, SE 250/20. Although better contrast/noise ratios are achieved with the GE sequences and the more T1-weighted SE sequences, as a practical matter this does not seem to be the only significant factor when compared with the visual image evaluation by independent observers.(ABSTRACT TRUNCATED AT 250 WORDS)

Using computerized tomography (CT scan), it was demonstrated that the renal cortex of the graft was thinner in the contact area with the psoas muscle than in the rest of the kidney and that its function in the local area appeared somewhat decreased. These findings might be related to the importance of the perirenal fat in shielding the kidney from mechanical pressure.

The pattern, distribution, and extent of the lymphatic circulation in the canine renal cortex was studied with light and electron microscopy, in two groups of animals, one with and one without ipsilateral ureteric obstruction for 3 days. Recognition of lymphatics in tissue sections was facilitated by mild dilatation, induced in both groups by ligation of the renal collecting vessels for 4 to 6 hours, and by retrograde injection of tracer in a third group. Of 77 lymphatics present in 180 blocks from six kidneys, approximately one third were intralobular, the remainder being primarily associated with interlobular blood vessels. The cross-sectional area of interlobular lymphatics was almost twice that of intralobular lymphatics. The relationships of these lymphatics were analyzed quantitatively. Intralobular lymphatics had primary relationships with terminal arteries, arterioles, renal corpuscles, and tubular elements. Both inter- and intralobular lymphatics had secondary relationships with a small proportion of all components of the cortical parenchyma including juxtaglomerular complexes. The most common association was between lymphatics and elements of the vascular tree. Morphometric analysis was used to obtain volume density data on the composition of the renal cortex. The volume density of lymphatics was 0.0026 in ureter-obstructed kidneys and 0.0017 in nonobstructed kidneys. The cross-sectional surface area of lymphatics in ureter-obstructed kidneys was significantly larger than those in nonobstructed kidneys. The volume density of other cortical components was found to be in good agreement with published data. From the volume density data, it was concluded that the volume of lymph in the renal cortex, under conditions of mild lymphatic dilatation, was about 1% that of the volume of blood in the cortical peritubular capillaries.

1. Total renal blood flow and its distribution within the renal cortex of the conscious rabbit were studied with radioactive microspheres of 15 and 25 mum diameter. 2. The reliability of the microsphere technique was influenced by microsphere diameter and number (dose). The optimum microsphere diameter for determination of flow distribution in the rabbit kidney was 15 mum and dose 100-150 000 spheres. 3. Spheres of 15 mum nominal diameter were randomly distributed within the renal cortex of adult rabbits. The larger spheres in batches nominally 15 mum in diameter in young rabbits and 25 mum diameter in adult rabbits were preferentially distributed to the superficial cortex. 4. In adult rabbits 15 mum diameter spheres lodged in glomerular capillaries. Larger spheres occasionally lodged in interlobular arteries causing intrarenal haemorrhage. 5. Microspheres of 15 mum caused a decrease in renal clearance of creatinine and of p-amino-hippurate when the total injection dose was about 200 000 spheres. These effects were greater when the injection dose was increased to 500 000 spheres. 6. The reduction in total renal blood flow observed with large doses of spheres largely reflected decreased outer cortical flow, as measured by a second injection of spheres, and confirmed by a decrease in p-aminohippurate extraction. 7. The reproducibility of multiple injection studies was limited by these intrarenal effects of microspheres. 8. Total renal blood flow measured in six rabbits in acute experiments by the microsphere technique was 107 plus or minus 12 (mean plus or minus SD) ml/min and by p-amino-hippurate clearance was 100 plus or minus 10 ml/min. 9. Total renal blood flow in twelve conscious, chronically instrumented rabbits was 125 plus or minus 11 ml/min, of which 92 plus or minus 6 ml/min was distributed to the superficial cortex and 33 plus or minus 4 ml/min to the deep cortex.

Freshly harvested kidneys from New Zealand white rabbits, Sprague-Dawley white rats, rhesus monkeys, and transplant-quality human kidneys were used in this study. Minced renal cortical tissue blocks (less than 2 mm3) were treated with 1 mM EDTA, 3% Triton X-100, 0.025% DNAse, and 4% sodium deoxycholate in an effort to remove all cellular elements and leave the extracellular matrix (ECM) intact. These preparations showed remarkable structural preservation and all components of the ECM, including basement membranes (BMs), maintained their in vivo histoarchitectural relationships. By light microscopy, at least four major BM types were recognizable, including Bowman's capsular BM (BCBM), tubular BM (TBM), glomerular BM (GBM), and peritubular capillary BM (PTCBM). Scanning electron microscopy demonstrated that, despite the lack of supporting interstitium, GBMs in human, monkey, and rat (and rabbit to a lesser degree) exhibit intrinsic structural rigidity such that their convoluted spheroidal shapes are maintained following cell removal. Transmission electron microscopy showed that major BM types are morphologically heterogeneous and vary markedly within and between species. Randomized measurements showed that isolated BM thicknesses (lamina densa only) compared favorably with those reported in cellular preparations. Mean thicknesses of GBMs were within normal ranges in all species with or without power transformations to reduce right-sided skew of distribution curves. In all species, thickness of BCBM greater than TBM greater than GBM greater than PTCBM. The striking morphologic heterogeneity of major BM types demonstrated in the acellular renal cortex is not surprising in view of recent biochemical analyses that show that BMs derived from different sources are compositionally disparate. We conclude that BMs should be evaluated and characterized individually and that morphologic definition of isolated BMs necessary prior to further analysis.

Although each of the major experimental techniques applied to the study of renal physiology has provided its fair share of new information, the technique of in vitro microperfusion of nephron segments is notable for two major contributions. First, it has supplied a more direct and controlled means of studying epithelial transport processes, some of which already have helped us to understand certain aspects of kidney function and others of which have yet to find their application in unraveling the mysteries of the kidney. Second, in the process of delineating these transport characteristics, it has served to emphasize the epithelial specialization present in the kidney, providing functional counterparts to the already recognized anatomic heterogeneity present in the kidney. In this second role microperfusion has spawned the application of biochemical analysis of the hormonal responses of various nephron segments and contributed to the impetus for work in culturing the various cell types present in each nephron segment. This review outlines the functional characteristics of the 11 major segments of the nephron, incorporating what has been learned from some of the biochemical work on hormone response and correlating the latter with transport events.

We have studied the effects of two diuretics, selective for renal cortical (furosemide) and inner medullary (vasopressin antagonist) water handling, in rat kidney at 1.5 T and find that furosemide completely dissipates the cortical-inner medullary T2 gradient whereas the vasopressin antagonist has little effect. This phenomenon appears to be related to changes in luminal water content. We also demonstrate the feasibility of obtaining live mouse kidney images with a resolution of 100 x 100 x 700 micrometers at 9.4 T.

The contents of sodium, potassium, magnesium and urea equally increases from the renal cortex to medulla in desert birds. This process is due, mainly, to the countercurrent multiplior of the medulla and, under natural conditions, depends on the length of medullar cone and the number of Henle's loops.

Intrarenal anatomy including cortex, medulla, and arcuate vessels can be demonstrated with gray scale ultrasonography by using higher frequencies, appropriately focused transducers, and simple sector scans. We have defined this anatomy in three cadaver kidneys, in in vivo normotopic and transplanted kidneys, and in a fetal kidney in utero. The normal cortex is echogenic. The normal medulla is sonolucent and has a characteristic appearance distinguishing it from renal cystic disease. The arcuate vessels can be recognized as a discrete high level echo at the corticomedullary junction and serve as a marker for the evaluation of renal cortical thickness. The ability to identify and characterize intrarenal anatomy should aid in the discovery of smaller renal lesions and in the diagnosis of medical renal disease.

Anatomical studies of rat kidneys revealed the presence of a unique population of juxtamedullary glomeruli (JMG) located at the inside cortical surface apposed to the pelvic lining and arcuate veins. These "superficial" JMG were exposed by longitudinally bisecting the kidney, reflecting the papilla, removing the pelvic mucosa, and transecting the venous walls. A microperfusion system was developed to allow blood perfusion of these nephrons via arcuate arteries. At a perfusion pressure of 100 mmHg, with most of the preglomerular pressure drop being localized to the terminal afferent arteriolar segment. In subsequent studies, blood hematocrit was reduced to approximately 30% with physiological solutions devoid of or containing albumin, and rats were treated with a converting enzyme inhibitor. In these conditions, single nephron glomerular filtration rate averaged 34 +/- 4 nl/min (low plasma colloid osmotic pressure, PCOP) and 23.3 nl/min (maintained PCOP). Proximal tubule reabsorption ranged from 17 to 29%. In conclusion, the integrity of nephron function is maintained in this model, which may provide further insights into the dynamics of filtration and reabsorption processes of juxtamedullary nephrons.

The ultrasound appearances of the neonatal and adult kidney contrast dramatically. In the normal kidney of a newborn infant, the echogenicity of the renal cortex equals that of the liver. To determine the morphological reasons for the unique and specific sonographic findings, we performed a quantitative anatomic analysis of the components of the kidney on autopsy specimens from four neonates. Our analysis reveals that the glomeruli occupy proportionally a much greater volume of the renal cortex during the first two months of life (18% as compared with 8.6% in the adult). Other anatomic differences include the greater proportional volume of the cellular component of the glomerular tuft in the neonate, and the location of 20% of the loops of Henle within the neonatal cortex rather than in the medulla. The increased number of anatomical structures, and thus interfaces, undoubtedly accounts for the increased echogenicity. The neonatal kidney often demonstrates prominent and hypoechoic renal pyramids. This may be explained by the larger volume of medulla in the neonatal kidney, which results in a ratio of cortex to medulla of 1.64:1 in the neonate as compared with a ratio of 2.59:1 in the adult. There is also a noted lack of echogenicity in the renal sinus region in neonates. Anatomically this is secondary to the absence of renal sinus adipose tissue in the kidney of the neonate.

The distal tubule, which includes the thick ascending limb (TAL), the macula densa, and the distal convoluted tubule (DCT), and the collecting duct are structurally heterogeneous, thus reflecting the functional heterogeneity that is also present. As the TAL ascends from medulla to cortex, the surface area of the apical plasma membrane increases while that of the basolateral membrane decreases. The structure of the DCT resembles that of the medullary TAL. An excellent correlation exists between structure, Na-K-ATPase activity, and NaCl reabsorptive capacity in the distal tubule. The collecting duct is subdivided into the initial collecting tubule (ICT), and cortical (CCD), outer medullary (OMCD), and inner medullary (IMCD) collecting ducts. Between the distal tubule and the collecting duct is a transition region termed the connecting segment or connecting tubule (CNT). Considerable structural heterogeneity exists along the collecting duct within the two major cell populations, the intercalated cells and the principal cells. In the CNT, the ICT, and the CCD, potassium loading and mineralocorticoids stimulate Na-K-ATPase activity and cause proliferation of the basolateral membrane of CNT cells and principal cells, thus identifying the cells responsible for mineralocorticoid-stimulated potassium secretion in these regions. Finally, at least two morphologically distinct populations of intercalated cells exist, types A and B. In the rat, type A predominates in the CNT and the OMCD and is believed to be responsible for H+ secretion, at least in the OMCD. Type B predominates in the CCD, where it may be involved in bicarbonate secretion.

Physiological studies of glomerular function in the rat have been much advanced by the accessibility of superficial glomeruli for micropuncture in a mutant strain, the Munich Wistar (MW) rat. An important parameter studied in this way is the glomerular ultrafiltration coefficient, or Kf. Kf is the product of hydraulic permeability and of the effective filtration surface area. Confounding factors are the variation in anatomical glomerular filtration surface in the rat with body weight (BW) and with the anatomical position of the glomerulus. To establish appropriate anatomical values for the interpretation of Kf in the MW rat, we have carried out a morphometric study by electron microscopy of two groups of relatively mature male MW rats, of approximately 200 g and approximately 300 g BW respectively. We find that superficial cortical (SC) and midcortical (MC) glomeruli of MW rats of approximately 200 g BW have relatively low glomerular volumes and anatomical filtration surface areas, but that MW rats of approximately 300 g BW have larger SC and MC glomeruli of similar size to juxtamedullary (JM) glomeruli, and anatomical filtration surface areas comparable to values usually assumed in physiological studies. We ascribe this contrast between SC glomeruli of MW rats of approximately 200 g and approximately 300 g BW respectively to the maturation of SC glomeruli.

With the use of new sonographic technology, we have observed that the echogenicity of kidneys is often equal to that of the liver in patients in whom there is no evidence of renal disease; this observation conflicts with the generally accepted notion that a normal kidney is always less echogenic than the liver. In order to reassess renal echogenicity as an indicator of disease, three experienced radiologists blindly reviewed the sonograms of the right kidney and liver in 153 patients. The prevalence of renal disease was 26% (40/153). Accepted sonographic criteria for abnormal renal echogenicity (kidney echogenicity greater than or equal to liver) were neither sensitive (62%) nor specific (58%) for renal disease, with a positive predictive value of 35%. Most of these inaccuracies occurred because 43 (72%) of 60 patients in whom renal echogenicity was equal to that of liver had normal renal function. If stricter criteria for abnormality were adopted (kidney echogenicity greater than liver), specificity (96%) and positive predictive value (67%) rose; however, sensitivity was only 20%. We conclude that renal echogenicity equal to the echogenicity of liver is not a good indicator of disease. Use of stricter criteria (kidney echogenicity greater than liver) provides a specific but insensitive test.