Micropuncture studies on the filtration rate of single superficial and juxtamedullary glomeruli in the rat kidney

Summary Single nephron filtration rates of superficial and juxtamedullary nephrons were determined in high and low sodium rats. Single nephron GFR was calculated from TF/P inulin and tubular flow rate in superficial nephrons and single juxtamedullary GFR from corresponding data in long loops of Henle. In low sodium rats superficial nephron GFR was 23.5±6.4 (SD)×10^–6 ml/min×g KW, juxtamedullary nephron GFR was 58.2±13.6 and total kidney GFR (C _In) was 0.94±0.16 ml/min×g KW. Using these single nephron values, total kidney GFR and a total number of 30,000 glomeruli per kidney, the number of superficial and juxtamedullary glomeruli was calculated to be 23,267 and 6,733, respectively. During high sodium diet superficial nephron GFR increased to 38.1±11.3 and single juxtamedullary GFR decreased to 16.5±6.6, total kidney GFR increasing to 1.01±0.24. Calculation again revealed the same distribution of the two nephron types. End-proximal TF/P inulin in superficial nephrons was 2.36±0.36 in low sodium and 2.31±0.28 in high sodium rats. Loops of Henle TF/P inulin and intratubular flow rate were inversely related: the highest TF/P inulin values and lowest intratubular flow rates were found in the descending limb. These data quantify the distribution of superficial and juxtamedullary nephrons on a functional basis and suggest a mechanism by which the kidney adjusts sodium excretion by altering the contribution of each nephron type to total kidney GFR.Supported by the Deutsche Forschungsgemeinschaft and the U.S. Department of the Army, through its European Research Office.     

Adaptive changes of juxtamedullary glomerular filtration in the remnant kidney

The participation of surviving juxtamedullary nephrons in the adaptive changes of glomerular filtration that occur in response to loss of functioning nephron mass was examined by direct micropuncture of the rat renal papilla. The solitary remnant kidney (RK) in rats with an 85% reduction of renal mass demonstrated strikingly elevated values for single nephron glomerular filtration rate (SNGFR) in both superficial (46.1±3.2 nl/min) and juxtamedullary (73.5±6.1 nl/min) nephrons in comparison to respective values observed in normal hydrophenic rats (superficial SNGFR=15.0±1.9nl/min,P<0.001, and juxtamedullary SNGFR=30.2±3.2 nl/min,P<0.001). In RK rats, the proximal portions of both superficial and juxtamedullary nephrons exhibited a marked increase in absolute fluid reabsorption as well as a markedly enhanced delivery of fluid to more distal portions of the nephron. These observations indicate that similar, not preferential, functional adaptations in glomerular filtration occur concommitantly in both superficial and juxtamedullary nephrons consequent to reduction of renal mass.     

Function of juxtamedullary nephrons in normotensive and chronically hypertensive rats

Summary The function of juxtamedullary nephrons was investigated by micropuncture of long loops of Henle at the exposed papilla in normal rats and in the untouched kidney of rats with experimental hypertension (unilateral Goldblattclip). With increasing blood pressure (range from 90–190 mm Hg) a continuous rise in juxtamedullary single nephron glomerular filtration rate was observed. Juxtamedullary single nephron GFR averaged 60×10^–6 ml/min/g K.W. in the control group (mean arterial blood pressure 116 mm Hg) and 114×10^–6 ml/min/g K.W. in the hypertensive group (mean arterial blood pressure (164 mm Hg). There was no change in superficial single nephron GFR (30×10^–6 ml/min/g K.W.) but a slight increase in total kidney GFR from 1.07 to 1.28 ml/min g K.W. In both the normotensive and the hypertensive animals, tubular fluid-to-plasma (TF/P) inulin ratio and intratubular flow rate in the descending limb of the long loops of Henle were not statistically different from those found in the ascending limb. Intratubular flow rate in the hypertensive rats was twice as high as in the controls; the mean TF/P inulin ratios in the two groups did not differ from each other. Appearance time of lissamine green in the long loops of Henle and in the collecting ducts was shortened in the hypertensive animals. It is concluded that there is no autoregulation of glomerular filtration rate in juxtamedullary nephrons. The increased juxtamedullary GFR may contribute to the elevated urinary excretion of the unclipped kidney in hypertensive rats.This paper was presented before the German Physiological Society, Mainz, March 1969 [11].     

The effect of experimental alterations in urine concentration on nephron filtration rate

Summary Experiments were performed to clarify the cause of the dependency of juxtamedullary nephron filtration rate (JN-GFR) on the diuretic state of the animal. Using the ferrocyanide technique of de Rouffignacet. al. [5] the distribution of nephron filtration rates was determined during selective modification of final urine osmolarity by papillary superfusion with concentrated or isotonic solutions. Papillary superfusion with a 2000 mosmolar solution led to a mean urine osmolarity of 1848±78 mOsm/l. JN-GFR displayed a mean increase of 66.6% over the superficial nephron filtration rate (SN-GFR). When the superfusion fluid was isotonic urine osmolarity averaged 754±53 mOsm/l and JN-GFR increased by a mean of only 26.3% over the SN-GFR. Using the micropuncture technique it was shown that SN-GFR in a given animal was not altered when the superfusion fluid was interchanged. We conclude therefore that the change in the percentage increase in GFR from superficial to juxtamedullary nephrons is caused by a change of juxtamedullary nephron filtration rate. Since plasma ADH concentration was not altered this effect appears to be elicited by the changed medullary solute concentration rather than by a vasomotor action of the antidiuretic hormone.This work was supported by the Deutsche Forschungsgemeinschaft.     

Influence of water-diuresis or saline volume expansion on deep nephron tubuloglomerular feedback

We have recently demonstrated the existence of a tubuloglomerular feedback mechanism in juxtamedullary nephrons in rat kidneys during antidiuresis. In the present experiments, we have investigated the influence of water-diuresis on Munich Wistar rats and in homozygote Brattleboro rats. We have also observed the effect of saline volume expansion on the tubuloglomerular feedback of juxtamedullary nephrons in Munich Wistar rats. For comparison, the feedback mechanism was also studied in surface nephrons during water-diuresis in Munich Wistar rats. Measurements of flow rate in the descending limb of Henle and single nephron glomerular filtration rate (GFR) using micropuncture at the renal papilla were performed, while the ascending limb was microperfused at varying perfusion rates with a modified Ringer solution. In surface nephrons early proximal flow rate, single nephron GFR and stop-flow pressure was measured during microperfusion of the end-proximal loop. No significant changes were measured in surface nephrons during water-diuresis: the tubular flow rates, feedback responses, stop-flow pressure and stop-flow pressure changes were similar to those during anti-diuresis. In juxtamedullary nephrons, Henle loop flow rate increases during water-diuresis but the feedback-mediated flow and single nephron GFR response curves obtained during microperfusion were unaltered compared to controls. Together, these results indicate that the feedback could be more activated during water-diuresis than during control conditions. On the other hand, during saline volume expansion, reduced tubuloglomerular feedback sensitivity was found as shown earlier for surface nephrons. The reduction of tubuloglomerular feedback sensitivity therefore seems to be important in maintaining salt-, but not water-balance.     

Number of nephrons in hypertrophic kidneys after unilateral nephrectomy in young and adult rats

Summary The number of functional nephrons in hypertrophied kidneys was determined in adult non diuretic rats which had been uni-nephrectomized either before 45 days (NY) or after 90 days (NO). This number was calculated by dividing the whole kidney GFR by the single nephron GFR, measured either by micropuncture or the¹⁴C-ferrocyanide infusion technique. Kidney weight was greater in NY rats (1.48±0.08 g SE) than in NO rats (1.23±0.10). In micropuncture experiments on NO rats the number of nephrones (34300±1600) was similar to that of normal adult rats. In NY rats this number was significantly greater (44100±1800,P<0.001).The ferrocyanide technique gave similar results (NO rats: 34800±2100; NY rats: 43900±3600) and indicated that the ratio of superficial to juxtamedullary SNGFR was not altered in the hypertrophied kidneys.The length of microdissected proximal tubules was increased in hypertrophied kidneys of both NY and NO rats and this increase affected thepars recta andpars convoluta equally.Single nephron GFR and F/P Inulin in late proximal and early distal tubules were similar in NO and NY rats.In conclusion, our results demonstrate that when uni-nephrectomy is performed on young rats, the compensatory hypertrophy of the remaining kidney is the result of an increase in both the size and the number of nephrons.     

Phosphate reabsorption in juxtamedullary nephron terminal segments

Summary Adult Munich Wistar rats undergoing mild salt diuresis (NaCl 20 g·l^–1, 0.1 ml·min^–1) were injected with tracer doses of³H-Inulin and³²P-sodium phosphate in thin descending and ascending limbs of Henle's loop, collecting ducts accessible at the surface of the papilla and early distal superficial tubules. Kidneys were prepared for simultaneous papillary microinjection and urinary flow collection. Expressed in percent of the amounts injected, unidirectional phosphate reabsorption fluxes were 5±1% and 3±1% for injections into early distal superficial tubules and collecting ducts, respectively. By contrast, the flux was 21.7±3% for injections into either the descending or ascending thin limbs of juxtamedullary nephrons. We conclude from these results that in the rat, a significant amount of phosphate is reabsorbed by the juxtamedullary distal tubules and/or the subsequent arcades connecting the juxtamedullary distal tubules to the collecting ducts.     

Experimental Papillary Necrosis of the Kidney: I. Morphologic and Functional Data

Papillary necrosis was produced in rats by a single intravenous injection of bromoethylamine hydrobromide (BEA). The earliest changes as seen by light microscopy were necroses of the limbs of Henle and eosinophilic droplets in collecting ducts. Complete necrosis of the papilla took place between 4 and 7 days and the dead papilla was usually sequestered completely by 21 days. Cortical changes occurred secondary to papillary necrosis. Tubular atrophy and loss was greatest in the deeper parts of the central cortex, the more superficial nephrons frequently being spared. The perihilar cortex was the least involved. This distribution was considered to be related to the respective lengths of the limbs of Henle, nephrons with limbs extending into the papilla being those undergoing change. Increased urine output occurred during the first day and continued thereafter. There was a profound defect in concentrating ability.     

Evidence for tubuloglomerular feedback in juxtamedullary nephrons of young rats

To determine whether the filtration rate of juxtamedullary nephrons is regulated by tubuloglomerular feedback (TGF), we developed two micropuncture techniques suitable for the papilla of young rats. One consisted of measuring the tubular flow in descending limbs of Henle loops (VDLH) while the ascending limbs of the loop of Henle (ALH) were perfused at various rates with three different solutions: modified Ringer, artificial Henle loop solution, and Ringer containing 10(-4) M furosemide. SNGFR was also measured in several juxtamedullary nephrons. The other protocol consisted of measuring the tubular stop-flow pressure (PSF) in descending limbs of the loop of Henle upstream to a wax block. Distal to the block Ringer was perfused at various rates through ALH. Our results provide the first evidence of a TGF response in juxtamedullary nephrons. VDLH and SNGFR decreased during Ringer perfusion to 42 +/- 4 and 44 +/- 4% of their values at zero perfusion. The same pattern was observed using Henle loop solution as perfusate, whereas with furosemide VDLH did not change. The maximal decrease in PSF was 14.1 +/- 1.4 mmHg. The perfusion rate necessary to induce a half-maximal PSF decrease was 9.1 +/- 0.9 nl/min. Similar micropuncture techniques were used in proximal tubules of surface nephrons in these rats, which in comparison to the deep nephrons showed smaller feedback responses. The mechanism seems to be active at physiological nephron flow rates in both nephron populations. Thus, TGF can exert its effect on GFR of the whole kidney by acting in both deep and surface nephrons.     

Impaired glomerular permselectivity for albumin in chemically medullectomized WKY rats

Chemical renal medullectomy with 2-bromo-ethylamine hydrobromide (BEA) has been used to study the importance of the renal medulla in blood pressure regulation. However, conclusive evidence as to whether BEA treatment affects the glomerular barrier is lacking. In the present study, the effects of BEA upon glomerular permselectivity for albumin were studied using isolated kidneys (IPK) perfused at a low temperature (8 °C) to inhibit tubular reabsorption of proteins. Sixteen WKY rats (W_B) received an i.v. injection of BEA (150 mg kg^-1) while 10 rats served as controls (W_C). Volume balance, urinary osmolality and creatinine clearance (GFR) were measured in metabolic cages. Acute paired experiments (n=9) were performed 5–7 weeks after BEA. The rats were anaesthetized and the total in vivo albumin excretion was recorded. The kidneys were then isolated and perfused for measurements of inulin clearance (GFR) and fractional albumin clearance without tubular reabsorption of protein. The nine BEA treated rats showed polyuria and hypoosmotic urine. In vivo GFR was lower in the BEA treated groups when measured with creatinine clearance (459±22 vs. 213±41 μL min^-1 100 g^-1 body wt, P<0.001), while GFR was not significantly changed in the IPK (W_C=135±27, W_B=92±14 μL min^-1 100 g^-1 body wt, n.s.) when perfused at identical pressures. The fractional albumin clearance was increased three times in the BEA group (W_B=9.6±3.4J, P<0.05). Moreover, albumin excretion in vivo was similar in the two groups despite low GFR in the BEA group. We conclude that BEA treatment affects glomerular permselectivity for albumin.     

ATPase activity in macula densa cells of the rabbit kidney

Na-K- and Mg-activated ATPase activities were determined in maculae densae and glomeruli dissected from both superficial and juxtamedullary nephrons of normal rabbits, using an ultramicro method including a cycling reaction. Activities were expressed as P_i generated per macula densa or per glomerulus and normalized for tissue volume. Results indicate that the mean volume of superficial and juxtamedullary macula densa samples was not statistically different, while glomeruli from deep nephrons had sample volumes that were 29% larger than those from superficial nephrons (P<0.001). Correcting for volume both superficial and juxtamedullary macula densa samples had an Na-K-ATPase activity of 0.37±0.21 fmol · h^–1 · (m³)^–1. Mg-ATPase activity in both pools was also similar [0.41±0.07 and 0.52±0.1 fmol · h^–1 · (m³)^–1]. Na-K-ATPase activity in macula densa cells is estimated to be about 1/40th the activity of surrounding cortical thick ascending limb cells. Total glomerular ATPase per unit volume was significantly higher in glomeruli from superficial than from deep nephrons [0.41±0.04 vs. 0.28±0.04 fmol · h^–1 · (m³)^–1 P<0.05]. There was no statistically significant activity of Na-K-ATPase in either superficial or deep glomeruli. These results suggest that in contrast to previous reports, the macula densa contains Na-K-ATPase, but at a low level relative to surrounding tubular cells. Further, in normal rabbits, this activity is invariant in superficial and juxtamedullary samples.     

Micropuncture studies on the dog kidney

Summary Micropuncture studies were carried out on the dog kidney in order to delineate the response of micropuncture parameters to changes in blood pressure within and below the autoregulatory range. By the use of chloralose anaesthesia and carotid sinus denervation elevations in systemic blood pressure were induced, while the use of Regitine permitted the induction of lower BP levels both in the lower part of the autoregulatory range and to frankly hypotensive levels. The results indicate a constancy of intratubular function (TF/P inulin, transit time, single nephron GFR, intratubular pressure) so long as blood pressure remained within the autoregulatory range, supporting the concept of a preglomerular site for autoregulation. During hypotension the single nephron GFR decreased, the transit time was prolonged, but the end proximalTF/P inulin did not change significantly. These changes in tubular function corresponded to a fall in total GFR, RBF, and filtration fraction. The fall in single nephron GFR was greater than the corresponding fall in total GFR suggesting that during hypotension the filtrate of the punctured superficial nephrons is less well protected than that of other nephrons in the dog kidney.Supported in part by a Medical Research Fellowship of the Medical Research Council of Canada.     

Technical problems in the micropuncture determination of nephron filtration rate and their functional implications

Summary The theory of a functional coupling between distal tubular fluid composition and glomerular filtration rate implies that the blockade of flow at a proximal site should lead to a marked increase of GFR. This potential alteration of steady state GFR was studied by comparing the influence of sampling from distal or proximal sites on the filtration rate of identical nephrons. During antidiuresis an average GFR of 25.2 nl/min±7.5 S.D. was found in distal collections, while proximally collected samples gave an average GFR of 34.5 nl/min±8.4 S.D. This difference of 9.3 nl/min is highly significant (p<0.001). During saline diuresis a mean nephron GFR of 41.6 nl/min±5.0 was found by distal sampling and of 45.3 nl/min±5.4 by proximal sampling (p>0.05). The proximal-distal difference in nephron GFR is interpreted to indicate the operation of a tubulo-glomerular feedback control system. Thus, a true steady-state GFR probably cannot be obtained by proximal fluid collection.Even in the presence of high intratubular pressures and unusually short oil blocks no evidence of sample contamination by retrograde fluid flow past an injected oil block was obtained.The application of a counter-pressure to the sampling pipette which has been recommended by Gertzet al. [5] as a means to standardize fluid collections, was found to lead to abnormally high intratubular pressures. The reason for this finding appears to be an unexpectedly high and inconstant tip resistance to flow during fluid flow into the pipette.     

Single nephron glomerular filtration rate ratios of superficial,intercortical and juxtamedullary nephrons in rats during development

Summary In 20, 40 and 60-day-old rats the filtration rate was studied, using Baines modification of Hanssen's Na₄Fe(¹⁴CN)₆ method enabeling the determination of single nephron glomerular filtration rate (SNGFR) ratio between superficial (S), intercortical (I) and juxtamedullary (J) nephrons. The proximal tubule lengths were determined as well. A close correlation was obtained between age and S/I, I/J and S/J of proximal tubule lengths and between age and I/J, S/J¹⁴C-activities of ferrocyanide. Presented findings confirm the data on the increasing role of superficial nephrons in the course of postnatal development of rat.     

The effect of antidiuretic hormone on the distribution of nephron filtration rates in rats with hereditary diabetes insipidus

Summary The effect of antidiuretic hormone on the distribution of nephron filtration rates was studied in rats with hereditary diabetes insipidus using the Hanssen method for determination of nephron filtration rates as modified by de Rouffignacet al. [18]. Conversion of water diuresis to antidiuresis by infusion of ADH resulted in a moderate, but highly significant increase in the filtration rate of the juxtamedullary nephrons, while the nephrons of all other cortex regions filtered at an unaltered rate. A mechanism based on the action of ADH on distal nephron water permeability is proposed as an explanation: water inflow into the medulla very likely decreases when water diuresis is converted to antidiuresis. This occasions a rise in medullary osmolality which then causes an increase in the apparent viscosity of the blood flowing through the vasa recta. This is responsible for a rise in juxtamedullary postglomerular resistance which results in an increase in the effective filtration pressure and thus in the juxtamedullary nephron filtration rate. The results suggest that an increased juxtamedullary filtration rate participates in the establishment and maintenance of the inner medullary solute gradients, possibly as a consequence of an increased solute delivery to the ascending limbs of the long loops of Henle.This work was supported by the Deutsche Forschungsgemeinschaft.On leave from the University of Melbourne as a recipient of a scholarship from the Deutscher Akademischer Austauschdienst.     

Heterogeniety in regulation of glomerular function

The aim was to study differences in filtration driving forces and glomerular filtration rates between superficial and deep nephrons when urine flow rate was altered at the macula densa region. In young rats stop-flow pressures and single nephron glomerular filtration rates (SNGFR) were measured in the superficial proximal tubules and in the loops of Henle in the papilla. SNGFR was also measured with a modified Hanssen technique. The stop-flow pressures of superficial nephrons amounted to 30.9±0.8 mmHg (mean ± SE) and those of juxtamedullary nephrons to 52.2±1.6 mmHg. In the stop-flow condition the net driving filtration forces were calculated to be about 19 mmHg and 50 mmHg for the superficial and deep glomeruli, respectively. In free flow conditions both net driving forces were calculated to be 19 mmHg. The micropuncture technique gave a SNGFR value for superficial nephrons of 29.6±2.9 and for deep nephrons of 84.1±8.5 nl±min^-1 g^-1 kidney weight (KW). With a modified Hanssen technique the corresponding values were 25.8±3.3 and 27.7±2.9 nl. min^-1.g^-1KW. The tubuloglomerular feedback mechanism is considered to have a powerful regulatory influence on the glomerular filtration rate of deep nephrons.     

Anatomical and functional heterogeneity of nephrons in the rabbit: Microdissection studies and SNGFR measurements

Summary The single nephron glomerular filtration rate (SNGFR) was determined in superficial (S) and juxtamedullary (JM) nephrons of 10 anesthetized rabbits by the¹⁴C ferrocyanide infusion technique. The length of the proximal tubules and the volume of the glomeruli were also determined for the same nephrons. SNGFR was higher in JM than in S: 28.6±3.4 versus 22.6±3.0 nl/min,P<0.001. In JM nephrons, glomeruli were larger than in S: 1.3±0.1 versus 0.9±0.1 nl,P<0.001, whereas there was no difference between proximal tubule length in either category (S, 8.7±0.3 and JM, 8.9±0.5 mm). In 6 out of 8 animals, SNGFR was significantly correlated to glomerular volume. Lack of correlation was observed between SNGFR and length of proximal tubule in all animals but one. These results show that the rabbit, as well as small rodents and the dog, has a higher SNGFR in juxtamedullary than superficial glomeruli. Although this functional difference is not related to the length of the proximal tubule in each individual animal, the ratio between the mean SNGFR value and the mean length of the proximal tubule in superficial rabbit nephrons is similar to the ratio found in other species.     

Single glomerular filtration rate of superficial and Juxta-medullary nephrons in the rat during different types of arterial hypertension

Summary The single nephron glomerular filtration rate (SNGFR) of superficial (S) and juxtamedullary (JM) nephrons were measured using¹⁴C-ferrocyanide infusion technique in rats under 3 different states of hypertension: acute hypertensions obtained either by bilateral carotid clamping (CC) or by contralateral renal ischemia (CI), and chronic Goldblatt hypertension. The juxtaglomerular index (JGI) was determined on the experimental kidneys.During acute hypertensions the JGI was normal, the granularity being more marked for the superficial than for the deep cortex. SNGFRs were higher in the JM (CC=39.2±3.4 SE nl/min; CI=41.0±4.5) than in the S (CC=30.3±2.5 CI=30.3±3.0) nephrons. These values are not different from those of normal rats. In the untouched kidney of Goldblatt rats the JGI was equal to zero. There was a general increase in SNGFRs. This increase was more marked for the S than for the JM nephrons, and the SNGFRs equalized in these two categories of nephrons (S=73.0±8.4; JM=74,7±8.2).From these observations, it is suggested that the renin content of the juxtaglomerular apparatus may play some role in the absolute value and intrarenal distribution of SNGFRs.This work was supported in part by a grant D.G.R.S.T. No. 7172 2726.Chargé de recherches à l'INSERM.     

Functional and morphologic maturation of superficial and juxtamedullary nephrons in the rat.

The development of single nephron glomerular filtration rate (SNGFER) was studied in both superficial and juxtamedullary nephrons in rats in relation to concomitant morphologic maturation. These experiments were carried out in rats between 23 and 91 days of age (between 36 nad 275 g body weight) with the [14C]ferrocyanide infusion technique. 2. SNGFR of the superficial and juxtamedullary nephrons increased with body weight, glomerular volume and proximal tubular length. 3. The ratio SNGFR of the superficial (S) nephrons/SNGFR of the juxtamedullary (JM) nephrons rose from 0-60 in the 40-60 g rats to 0-84 in the adult rats, demonstrating the centrifugal functional maturation of the nephrons. 4. The S/JM ratio for both glomerular volume and tubular length was constant and averaged 0-72+/--0-12 and 0-81+/-0-05, respectively, indicating that while the increase in SNGFR was greater for S than for JM nephrons, this was not accompanied by concomitant disproportionate increases of glomerular volume and/or proximal tubular length between these nephron categories during development in the rat.     

Tubuloglomerular feedback and autoregulation of glomerular filtration rate in Wistar-Kyoto spontaneously hypertensive rats

Experiments were done in Wistar-Kyoto spontaneously hypertensive rats (SHR) to examine the efficiency of autoregulatory adjustments of kidney and nephron filtration rate (GFR) to acute changes in blood pressure (BP) over a broad blood pressure range. When BP of the SHR was reduced from 158±7 to 118 ±3 mm Hg by aortic clamping, kidney-GFR remained unchanged from 1.19±0.11 to 1.17±013 ml·min^–1·g^–1 kidney weight (KW), respectively. Single nephron GFR (SNGFR) measured at early distal tubule sites was similarly unchanged with the same BP change, 27.9±1.5 vs. 24.9±2.1 nl·min^–1·g^–1 KW (P>0.10). Proximal and distal estimates of SNGFR were significantly different from each other at high BP (7 nl·min^–1·g^–1,P<0.025), but were not different at low BP (2.0 nl·ml^–1·g^–1,P>0.10). Studies assessing tubuloglomerular feedback activity were done with orthograde perfusion of the loop of Henle using recollections of early proximal flow rate (EPFR) as an index of change of glomerular filtration rate. A change in perfusion rate from 0 to 45 nl·min^–1 induced a reduction in early proximal flow rate of 40.5 ±4.5%. Juxtaglomerular renin activity of superficial nephrons was 36.2±4.3 in the SHR, a value insignificantly different from 23.7±4.4 ng Angiotensin II amide·0.1 ml^–1·h^–1. 5 glomeruli^–1 in normal controls (P>0.05). The SHR appears to behave as a normal animal with respect to tubologlomerular feedback and autoregulatory renal vascular adjustments. Like normal rat models, the SHR demonstrated dependence on maintenance of distal filtrate delivery to achieve single nephron GFR autoregulation.Financial support for these studies and for Dr. Ploth were made available by funds from the Deutsche Forschungsgemeinschaft