Functional heterogeneity of nephrons. I. Intraluminal flow velocities

A comprehensive review on advancements in tissue engineering and microfluidics toward kidney-on-chip

This review provides a detailed literature survey on microfluidics and its road map toward kidney-on-chip technology. The whole review has been tailored with a clear description of crucial milestones in regenerative medicine, such as bioengineering, tissue engineering, microfluidics, microfluidic applications in biomedical engineering, capabilities of microfluidics in biomimetics, organ-on-chip, kidney-on-chip for disease modeling, drug toxicity, and implantable devices. This paper also presents future scope for research in the bio-microfluidics domain and biomimetics domain.

Odd E. Hanssen and the Hanssen method for measurement of single-nephron glomerular filtration rate

In the middle of the twentieth century, the suspicion that deep and superficial nephrons might serve different functions created a demand for measurement of single-nephron glomerular filtration rate (SNGFR). Rather unexpectedly, the answer came from Odd E. Hanssen (1917-1964), a Norwegian physician working on his own in the Department of Pathological Anatomy, University of Oslo, with minimal support and no interaction with renal physiologists. In 1963, after nearly 10 years of work, he presented the ferrocyanide method, allowing simultaneous estimates of SNGFR in a large number of nephrons in all layers of the kidney. This review first describes his early visions of the method and the elaborate and extremely time-consuming studies in mice to verify the technique. As a byproduct came valuable information on the relationship between nephron size and SNGFR, glomerular intermittency, and the emptying of the tubules on filtration stop. Hanssen died from a cerebral hemorrhage in 1964, and for several years the method seemed entirely forgotten. Fortunately, Andrew Baines took up the use of ferrocyanide in 1963-1964 while working on his thesis in Toronto, but his first publication came in 1969 from Saclay, France, in collaboration with Christian de Rouffignac. Modifications allowing determination of absolute SNGFR were worked out by de Rouffignac and by Jaime Coehlo in New York. Thereafter, the "Hanssen method" spread rapidly, and in the early 1980s about 50 reports had been published from 17 laboratories in 9 countries. The distribution of SNGFR in mammals, birds, and fish was described, as well as the response to water and salt loads, vasoactive substances, hormones, varying perfusion pressure, blood loss, etc. Finally, after mentioning two recent methods inspired by the Hanssen technique but using other filtration markers, the review concludes that most of our present knowledge on SNGFR distribution and regulation has been obtained by the method developed by Hanssen 40 years ago.

Long-term effects of 24-hr unilateral ureteral obstruction on renal function in the rat

To characterize the pattern of recovery following release of unilateral ureteral obstruction of 24-hr duration, rats were studied with whole kidney clearance techniques, 3 hrs, 8, 14, and 60 days after release. The single nephron glomerular filtration rate (SNGFR) of superficial and juxtamedullary nephrons was estimated with a modification of Hanssen's technique in rats studied 8 and 60 days after ureteral release. The whole kidney glomerular filtration rates (GFR) were decreased markedly 3 hrs after relief of obstruction, but gradually increased and by 14 days, the GFR of the postobstructed kidney (POK) and the contralateral kidney (CK) were comparable. This recovery of GFR was not a consequence of a homogeneous improvement in SNGFR. At 8 days, more than 15% of superficial and juxtamedullary nephrons were not filtering in the POK. This decrease in the percent of filtering nephrons persisted to 60 days post release, indicating a permanent loss of nephron units. The SNGFR of the residual nephrons of the POK was significantly greater than that of the CK at 8 and 60 days following ureteral release. Thus, acute unilateral ureteral obstruction results in a permanent loss of filtering nephrons, which is offset by hyperfiltration of those remaining. Abnormalities in renal tubule function persisted beyond the time (14 days) when whole kidney GFR had returned to normal. These abnormalities were in distal tubule function. Urine osmolality was consistently lower at all time intervals post release, as was net acid excretion. The results of the present study suggest that these abnormalities are a consequence of the reduction in the number of filtering juxtamedullary nephrons and/or to abnormalities in collecting duct function.

Disparity between surface and deep nephron function early after renal ischemia

Experiments were performed using a variety of methods to assess the functional status of different nephron populations following 45 min of renal ischemia in the rat. Micropuncture techniques revealed that SNGFR and reabsorption in the surface nephrons are only modestly reduced after ischemia, whereas kidney GFR and reabsorption are more severely affected. Determinations of bolus velocity with the Hanssen technique or of glomerular blood flow with the microsphere method confirmed that both were highest in the surface nephrons, lower in the middle nephrons and lowest of all in the juxtamedullary nephrons after ischemia. It is concluded that surface nephron function is well-maintained following ischemia and that it is the functional deficiency of the deeper nephrons that is predominantly responsible for the impairment in whole kidney function. Although the pathogenic mechanism is not yet clear, neither tubular obstruction nor tubular leakage in the deeper nephrons seems to be involved. The present findings suggest that micropuncture of the surface nephrons is a technique of questionable validity for studying this type of acute renal failure, they explain the inability of the kidney to concentrate the final urine, and they predict a more pronounced deficiency in medullary than in outer cortical blood flow.

A geometric model of the rat kidney

Firstly details are collected concerning the required parameters of a simple linear regression in order to evaluate statistically results of measurements, which can also be present in the form (chii, yi +/- SDi). In this way lines of regression are determined for connections between the kidney weight and the body weight, between the lengths of the proximal tubules (and the proximal convolution) of the three various types of nephron and the kidney weight, between the length of the distal convoluted tubule, likewise the number of glomerula, and the kidney weight and finally between the single nephron filtration rate and the length of the proximal tubule. Starting from a model body weight for the rat of 200 g and considering the percentage of thin segments in the tissue of the renal pyramid, a loop of Henle with a length of 8.1 mm for the thin part and a length of 2.4 mm for the ascending thick limb was calculated for the model nephron from the lengths of the loops of the three types of nephrons. In contrast to former model formulations concerning the collecting duct system, the tree-like branched structure was considered for the first time and a linear approximation to the relation between both the circumference line and the cross section area and the lenggh of the collecting ducts was determined. The geometric model relates only to the tubular system and takes no notice of the blood vessels.

Effect of dietary sodium intake on the intrarenal distribution of nephron glomerular filtration rates in the rat

Redistribution of single nephron glomerular filtration rate (SNGFR) between superficial (S) and juxtamedullary (JM) nephrons is thought to participate in the renal adaptation to different levels of dietary sodium intake. This possibility was examined using the Hanssen technique which measures SNGFR as the 14 C-ferrocyanide content of microdissected nephrons factored by the mean plasma concentration following a 12-second infusion. Rats from the same litter were placed on a low-sodium (0.8 mEq/day) or a high-sodium (9 mEq/day) diet. The distribution of SNGFR was measured as the S/JM (mean of S nephrons/mean of JM nephrons) SNGFR ratio. In spite of an eightfold change in sodium excretion, there was no significant change in the S/JM SNGFR ratio (low sodium - high sodium: -0.0033 ± 0.048 [ SE ], P > 0.9). Seven rats that were not littermates were maintained on a standard diet but drank saline (13 mEq sodium/day); carotid and ureteral catheterization and the duration of the diet (3-14 weeks) had no effect on the S/JM SNGFR ratio ( P > 0.1), which was similar to that of nine rats maintained on a standard diet with water for drinking (3 mEq sodium/day). The value of the S/JM SNGFR ratios were 0.77 and 0.83, respectively. These variations in dietary sodium intake appeared to have no detectable effect on the intrarenal SNGFR distribution.

Restoration and maintenance of glomerular filtration by mannitol during hypoperfusion of the kidney

Glomerular filtration (GF) during progressive reduction of renal perfusion pressure by aortic clamping was studied in hydropenic rats and in rats infused with isotonic saline, hypertonic saline, or mannitol. As judged by visual observation of Lissamine green movements in superficial nephrons. GF was absent in hydropenic or saline-loaded rats at 40 mm Hg aortic pressure, but continued in some nephrons of all rats infused with mannitol and of some rats infused with hypertonic saline. Urine flow persisted only in rats infused with mannitol. By use of the qualitative Hanssen technique, it was found that all glomeruli in superficial and deep portions of the cortex were perfused at 40 mm Hg in all groups of rats. By the same method. GF continued in 1% of nephrons in hydropenic rats, 12% of nephrons in isotonic saline-loaded rats, and 78% of nephrons in rats infused with mannitol. By means of a quantitative Hanssen technique, GF was 5.8 nl/min per nephron in mannitol-infused rats and not measurable (< 0.5 nl) in hydropenic rats. Superficial and deep nephrons were similar in both qualitative and quantitative studies. Although urine flow did not persist in rats infused with hypertonic saline, GF was detected in four of seven studies by the Hanssen method (mean, 9.1 nl/min per nephron). In additional experiments, mannitol infused after perfusion pressure had already been lowered to 40 mm Hg in hydropenic rats reestablished urine flow and GF (mean, 9.8 nl/min). Furosemide, isotonic and hypertonic saline did not restart urine flow; however, GF (Lissamine green) was restarted by hypertonic saline. We conclude that mannitol can maintain or reestablish by an extratubular mechanism GF which otherwise would not occur during renal hypoperfusion. Hypertonic saline has a similar effect on GF in some cases, but urine flow is not maintained, implying complete reabsorption of filtrate.

Effect of renal vasodilatation on the distribution of cortical blood flow in the kidney of the dog

Studies were performed to evaluate the validity of using the radioactive microsphere technique to measure regional blood flow in the renal cortex. A technique was developed in which the renal cortex was divided into four equal zones, and the fractional and absolute distribution of blood flow in these zones was determined. It was consistently found that approximately 70% of the renal blood flow was distributed to the two outer cortical zones with the remaining 30% going to the two inner cortical zones. In addition, there was a reproducible pattern of distribution of blood flow in different areas of the same kidney after a single injection of microspheres and in the same area of the kidney after multiple injections of microspheres. Using this method, the distribution of renal blood flow was determined before and during the intrarenal administration of either acetylcholine (40 mug/min) or bradykinin (5 mug/min). Both agents decreased the per cent of blood flow to outer cortical zone 1, caused no change in zone 2, and increased the fractional blood flow in inner cortical zones 3 and 4. When this data was evaluated in terms of total blood flow, there was no change in zone 1, an increase in zone 2 commensurate with the change in total blood flow, and a marked increase in inner cortical zones 3 and 4 which accounted for 60 and 65% of the increase in total blood flow during acetylcholine and bradykinin administration, respectively.Therefore, the natriuresis of renal vasodilatation is associated with a redistribution to inner cortical nephrons.