Tubuloglomerular feedback in rat kidneys of different renin contents

Decreased tubuloglomerular feedback response in high-fat diet-induced obesity

Obesity increases the risk of renal damage, but the mechanisms are not clear. Normally, kidneys autoregulate to keep the glomerular capillary pressure (PGC), renal blood flow, and glomerular filtration rate in a steady state. However, in obesity, higher PGC, renal blood flow, and glomerular filtration rate are noted. Together, these may lead to glomerular damage. PGC is controlled mainly by afferent arteriole resistance, which, in turn, is regulated by tubuloglomerular feedback (TGF), a vasoconstrictor mechanism. High fat-induced obesity causes renal damage, and this may be related to increased PGC. However, there are no studies as to whether high-fat diet (HFD)-induced obesity affects TGF. We hypothesized that TGF would be attenuated in obesity caused by HFD feeding (60% fat) in Sprague-Dawley rats. Sprague-Dawley rats fed a normal-fat diet (NFD; 12% fat) served as the control. We studied 4 and 16 wk of HFD feeding using in vivo renal micropuncture of individual rat nephrons. We did not observe significant differences in body weight, TGF response, and mean arterial pressure at 4 wk of HFD feeding, but after 16 wk of HFD, rats were heavier and hypertensive. The maximal TGF response was smaller in HFD-fed rats than in NFD-fed rats, indicating an attenuation of TGF in HFD-induced obesity. Baseline PGC was higher in HFD-fed rats than in NFD-fed rats and was associated with higher glomerulosclerosis. We conclude that attenuated TGF and higher PGC along with hypertension in HFD-fed obese Sprague-Dawley rats could explain the higher propensity of glomerular damage observed in obesity.NEW & NOTEWORTHY Reduced tubuloglomerular feedback, higher glomerular capillary pressure, and hypertension in combination may explain the higher glomerular damage observed in high-fat diet-induced obesity.

Renal autoregulation in health and disease

Intrarenal autoregulatory mechanisms maintain renal blood flow (RBF) and glomerular filtration rate (GFR) independent of renal perfusion pressure (RPP) over a defined range (80-180 mmHg). Such autoregulation is mediated largely by the myogenic and the macula densa-tubuloglomerular feedback (MD-TGF) responses that regulate preglomerular vasomotor tone primarily of the afferent arteriole. Differences in response times allow separation of these mechanisms in the time and frequency domains. Mechanotransduction initiating the myogenic response requires a sensing mechanism activated by stretch of vascular smooth muscle cells (VSMCs) and coupled to intracellular signaling pathways eliciting plasma membrane depolarization and a rise in cytosolic free calcium concentration ([Ca(2+)]i). Proposed mechanosensors include epithelial sodium channels (ENaC), integrins, and/or transient receptor potential (TRP) channels. Increased [Ca(2+)]i occurs predominantly by Ca(2+) influx through L-type voltage-operated Ca(2+) channels (VOCC). Increased [Ca(2+)]i activates inositol trisphosphate receptors (IP3R) and ryanodine receptors (RyR) to mobilize Ca(2+) from sarcoplasmic reticular stores. Myogenic vasoconstriction is sustained by increased Ca(2+) sensitivity, mediated by protein kinase C and Rho/Rho-kinase that favors a positive balance between myosin light-chain kinase and phosphatase. Increased RPP activates MD-TGF by transducing a signal of epithelial MD salt reabsorption to adjust afferent arteriolar vasoconstriction. A combination of vascular and tubular mechanisms, novel to the kidney, provides for high autoregulatory efficiency that maintains RBF and GFR, stabilizes sodium excretion, and buffers transmission of RPP to sensitive glomerular capillaries, thereby protecting against hypertensive barotrauma. A unique aspect of the myogenic response in the renal vasculature is modulation of its strength and speed by the MD-TGF and by a connecting tubule glomerular feedback (CT-GF) mechanism. Reactive oxygen species and nitric oxide are modulators of myogenic and MD-TGF mechanisms. Attenuated renal autoregulation contributes to renal damage in many, but not all, models of renal, diabetic, and hypertensive diseases. This review provides a summary of our current knowledge regarding underlying mechanisms enabling renal autoregulation in health and disease and methods used for its study.

Telmisartan improves endothelial dysfunction and renal autoregulation in Dahl salt-sensitive rats

Hypertensive vascular disorders are characterized by endothelial dysfunction. Loss of renal autoregulation causes glomerular hypertension. However, the relationship between the autoregulatory response and glomerular damage has not been well examined. We examined the contributions of uncoupled endothelial nitric oxide synthase (eNOS) in hypertensive renal disease, and the relationship between the degree of autoregulation impairment and glomerular injury. We also investigated the effects of telmisartan on eNOS coupling and renal autoregulation. Male Dahl salt-sensitive hypertensive (DS) rats (14-week old) fed an 8% salt diet were used to examine endothelial dysfunction and impaired renal autoregulation caused by glomerular hypertension. Some DS rats were treated with telmisartan (3.0 mg kg(-1) day(-1)), an angiotensin receptor blocker, for 2 weeks. Increased superoxide production and decreased nitric oxide production, as detected by fluorescent indicator perfusion methods, were observed in the glomeruli and arterioles of hypertensive DS rats. Telmisartan improved the imbalance of superoxide and nitric oxide in the glomeruli and arterioles. Decreased serum tetrahydrobiopterin levels and coupled eNOS seen in the DS rat kidney were improved with telmisartan treatment. The endothelial relaxation reaction was impaired in DS rat aortic arteries. Autoregulatory capacity in response to step changes in perfusion pressure was also impaired in DS rat kidney. Treatment with telmisartan improved these abnormalities. Endothelial dysfunction in the glomeruli and impaired renal autoregulation, which may cause glomerular sclerosis, were observed in DS rat kidney. Telmisartan treatment improves these dysfunctions in hypertensive renal disease.

Aldosterone antagonism attenuates obesity-induced hypertension and glomerular hyperfiltration

This study examined the importance of aldosterone (ALDO) in mediating changes in renal function and increased mean arterial pressure (MAP) during the development of dietary-induced obesity in chronically instrumented dogs. Mean arterial pressure, heart rate (HR), and cardiac output (CO) were recorded 24 hours per day in lean dogs (n=7) before and after administration of an ALDO antagonist, eplerenone (EP) (10 mg/kg twice daily), for 10 days. After 10 days of EP treatment, the dogs (n=7) were given a supplement of cooked beef fat for 5 weeks while EP was continued. An untreated group (n=6) was fed a high fat diet for 5 weeks and used as control (C). In lean dogs, EP decreased MAP from 89+/-4 to 84+/-4 mm Hg and glomerular filtration rate from 67.4+/-6.8 to 53.2+/-4.9 mL/min while inducing a small negative Na+ balance (-42+/-12 mEq). Plasma renin activity increased from 0.4+/-0.1 to 2.7+/-0.7 ng AI/mL per hour and plasma K+ increased from 4.8+/-0.1 to 6.1+/-0.3 mEq/L. After 5 weeks of a high fat diet, body weight increased 45% to 53% in EP and C obese dogs. In C dogs, MAP increased by 16+/-3 mm Hg, compared with only 7+/-1 mm Hg in EPLE dogs. Compared with untreated dogs, the EP dogs had smaller increases in CO (18+/-4.6% versus 43+/-1.5%), HR (33+/-5% versus 60+/-3%), glomerular filtration rate (19+/-5% versus 38+/-6%), and cumulative Na+ balance (138+/-35 mEq versus 472+/-110 mEq) after 5 weeks of a high fat diet. Thus, EP markedly attenuated glomerular hyperfiltration, sodium retention, and hypertension associated with chronic dietary-induced obesity. These observations indicate that ALDO plays an important role in the pathogenesis of obesity hypertension.

Increased availability of nitric oxide leads to enhanced nitric oxide dependency of tubuloglomerular feedback in the contralateral kidney of rats with 2-kidney, 1-clip Goldblatt hypertension

The contralateral kidney of 2-kidney, 1-clip hypertensive (2K1C) rats is unable to escape the renal vasoconstrictive and sodium-retaining effects of increased circulating angiotensin II levels. Evidence is accumulating that renal function is relatively preserved by enhanced influence of NO in the contralateral kidney. In this study, we investigated (1) whether the high NO dependency of renal hemodynamics in the contralateral kidney is due to increased availability of NO or increased sensitivity to NO and (2) whether elevated NO activity dampens the actions of angiotensin II to enhance tubuloglomerular feedback (TGF) responses in the nonclipped kidney of 2K1C rats. To estimate whether the available NO is increased, the NO clamp technique was applied in rats that underwent sham operation (n=6) and in the contralateral kidney of 2K1C Sprague-Dawley rats (3 weeks old; 0.25-mm silver clip; n=6). During systemic infusion of nitro-L-arginine (L-NNA; 50 microg/kg. min(-1)), sodium nitroprusside (SNP) was infused in the renal artery and the rate was adjusted so that renal vascular resistance (RVR) was restored to baseline levels. In sham rats, RVR increased during L-NNA treatment from 17.2+/-2.0 to 33.0+/-3.6 U (P<0.01) and was restored to baseline values during SNP infusion (17.1+/-2.3 U); 9. 2+/-1.8 nmol/min of SNP was needed to restore RVR to baseline values. In 2K1C rats, RVR increased during L-NNA treatment from 16.7+/-1.1 to 53.4+/-3.5 U (P<0.01). This increase of RVR was significantly larger than in sham rats. RVR was restored to baseline values during SNP infusion (17.4+/-0.9 U); 26.0+/-4.3 nmol/min of SNP was needed to restore RVR to baseline values (P<0.05 versus sham). Furthermore, maximum TGF responses were assessed before and during late proximal tubular infusion of L-NNA in the kidneys of sham rats and the nonclipped kidneys of 2K1C rats. Control maximum TGF responses were 4.7+/-0.7 and 5.1+/-0.4 mm Hg in sham and 2K1C rats, respectively. During intraluminal L-NNA infusion, maximum TGF responses were 15. 4+/-0.9 mm Hg in sham rats and 22.2+/-2.5 mm Hg in 2K1C rats (P<0.05 versus sham). Finally, urinary NO(2)+NO(3) excretion in the nonclipped kidney was significantly higher than in the clipped kidney (P<0.05). In conclusion, (1) as assessed using the NO clamp, ambient intrarenal NO levels are increased in the contralateral kidney of 2K1C rats and (2) the NO dependency of the TGF system is enhanced. These experiments indicate that adaptations in NO activity lead to relatively low TGF responsiveness, which will offset the simultaneous sodium-retaining actions of angiotensin II on proximal tubular reabsorption and TGF responsiveness.

Modulation of tubuloglomerular feedback by angiotensin II type 1 receptors during the development of Goldblatt hypertension

It has been suggested that the increased levels of angiotensin II (Ang II) in the contralateral kidney of two-kidney, one clip (2K1C) Goldblatt hypertensive rats act to enhance tubuloglomerular feedback responsiveness and proximal tubular reabsorption and thereby exert a substantial sodium-retaining influence on the nonclipped kidney. The current study investigated the Ang II dependency of tubuloglomerular feedback responsiveness in the nonclipped kidney during the early stages of development of 2K1C hypertension. Stop-flow pressure feedback responses were assessed in the nonclipped kidney of 2K1C rats during control conditions and after systemic administration of the Ang II type 1 receptor antagonist losartan (10 mg/kg). In 1-week clipped and sham-operated rats, losartan administration decreased mean arterial pressure (from 143 +/- 6 to 123 +/- 2 mm Hg, P < .01, and from 129 +/- 2 to 106 +/- 5 mm Hg, P < .01, respectively) and attenuated the magnitude of the maximal feedback responses (from -12.9 +/- 1.2 to -3.0 +/- 0.3 mm Hg, P < .01, and from -13.2 +/- 1.5 to -3.6 +/- 1.1 mm Hg, P < .01, respectively). The decreases in mean arterial pressure were not significantly different in sham-operated and 1-week clipped rats. In 3-week clipped rats, mean arterial pressure was further elevated (163 +/- 6 mm Hg) compared with sham-operated rats (134 +/- 4 mm Hg, P < .01).(ABSTRACT TRUNCATED AT 250 WORDS)

Pathophysiology of altered renal function in renal vascular hypertension

It is now clear that specific angiotensin-dependent mechanisms contribute importantly to the pathophysiology of hypertension (HT) and altered renal function in models of two-kidney, one-clip (2-K, 1-C) HT in rats. The discovery of specific antagonists for angiotensin-converting enzyme and the newer angiotensin receptor and kinin receptor antagonists have allowed delineation of the contributions of these hormones to altered renal function in these models. The focus of interest in most of these studies has been the nonclipped kidney, which would be expected to ameliorate elevated blood pressure by exhibiting a pressure diuresis and natriuresis in the environment of systemic HT. Antagonism of the renin-angiotensin system in rat models of renal vascular HT indicates that the effects of angiotensin attenuate renal hemodynamic and excretory behavior, particularly in the nonclipped kidney. Furthermore, angiotensin attenuates the efficiency of autoregulation of renal hemodynamics in the nonclipped kidney. Function of the clipped kidney appears to be both angiotensin and perfusion pressure dependent. Evidence that inhibition of angiotensin reverses or improves these altered hemodynamic and excretory functions indicates that angiotensin may contribute importantly to the pathophysiology of HT in these models by altering or impairing the ability of the nonclipped or "normal" kidney to excrete sodium and volume. The precise roles of altered activity of vasodilator hormones to contribute to these alterations of renal function remains to be defined.

Renal response to volume depletion and expansion in Milan hypertensive rats

In previous studies on Milan hypertensive (MHS) rats, we found an impaired tubuloglomerular feedback (TGF) response before, during and after development of hypertension. In the present study MHS rats and rats of the Milan normotensive strain (MNS) were investigated after 24 hours of volume depletion (VD) and subsequently after 5% isotonic volume expansion (VE) with respect to whole kidney function, interstitial hydrostatic (P(int)) and oncotic (IIint) pressures, stop-flow pressure characteristics of TGF and changes in early proximal flow rate in response to increased loop of Henle flow. MHS rats had higher mean arterial blood pressure (Pa) than MNS rats (129 vs. 101 mmHg) both after VD and after subsequent VE. No difference in glomerular filtration rate (GFR) was found. Both strains had a low urine flow rate (approximately 1.5 microliters min-1) during VD, which increased fourfold after VE. The interstitium was significantly more dehydrated in MHS, as indicated by a more negative net interstitial pressure (P(int)-IIint than in MNS (-1.3 +/- 0.3 vs. +/- 0.0 +/- 0.5 mmHg) after VE. The TGF mechanism was more activated in MHS during volume depletion, as indicated by a larger drop in stop-flow pressure (Psf) in response to loop of Henle perfusion (7.1 +/- 0.7 vs. 4.7 +/- 0.2 mmHg, P less than 0.05). However, during VD the loop of Henle flow that elicited half maximal response in Psf, the turning point (TP), was equally low in MHS and MNS (13.5 +/- 0.6 and 14.3 +/- 0.4, respectively).(ABSTRACT TRUNCATED AT 250 WORDS)

Tubular sodium handling and tubuloglomerular feedback in compensatory renal hypertrophy

Tubular sodium handling and tubuloglomerular feedback (TGF) activity were assessed in established compensatory renal hypertrophy in Sprague Dawley rats. Hyperfiltration at the level of the single nephron was confirmed 4-6 weeks following a reduction in renal mass. TGF activity, determined as the difference between late proximal and early distal measurements of single-nephron glomerular filtration rate (SNGFR), was significantly increased in compensatory renal hypertrophy, being 7.8 +/- 1.0 vs 23.3 +/- 1.9 vs 25.5 +/- 2.6 nl/min (P for analysis of variance less than 0.05) following sham operation, unilateral nephrectomy, and 1 1/3 nephrectomy, respectively. Enhanced net tubular Na transport was also observed, with total Na reabsorption up to the late proximal site being 1.8 +/- 0.2 vs 2.7 +/- 0.1 vs 3.1 +/- 0.3 nmol/min (P less than 0.05), and to the early distal site being 3.4 +/- 0.5 vs 5.8 +/- 0.6 vs 7.9 +/- 0.8 nmol/min (P less than 0.05) in the three animal groups respectively. Comparison of proximal tubular length demonstrated a 71.9 +/- 8.1% increase in uninephrectomised vs sham-operated animals. This increase was proportionately greater than the increase in proximal Na reabsorption (50.0 +/- 4.0%) observed in the corresponding animal groups. Concurrent electron microprobe experiments in uninephrectomised and sham-operated animals demonstrated that the proximal tubular intracellular Na concentration was significantly lower following uninephrectomy (16.8 +/- 0.6 vs 18.9 +/- 0.5 mmol/kg wet weight, P less than 0.01), in association with evidence of reduced basolateral Na/K-ATPase activity.(ABSTRACT TRUNCATED AT 250 WORDS)

Afferent arteriolar responsiveness to altered perfusion pressure in renal hypertension

The present study was performed to determine the role of afferent arterioles in the impaired autoregulatory response shown to occur in the contralateral kidney of Goldblatt hypertensive rats. The responsiveness of juxtamedullary afferent arterioles to alterations in perfusion pressure was studied in the nonclipped kidney of two-kidney, one clip hypertensive and sham-operated rats. Systolic pressure, 5-6 weeks after clipping, averaged 184 +/- 6 mm Hg in the hypertensive rats (n = 16) and 121 +/- 3 mm Hg in the sham-operated control rats (n = 7). By using the in vitro blood-perfused juxtamedullary nephron technique, afferent arterioles were directly visualized, and their inside diameters were measured by videomicroscopic methods. In sham-operated kidneys perfused with blood from normotensive rats, afferent arteriolar diameter averaged 22.8 +/- 1.8 microns at a renal arterial perfusion pressure of 151 +/- 1 mm Hg and increased to 24.8 +/- 1.8 microns when perfusion pressure was reduced to 110 +/- 2 mm Hg. Conversely, in hypertensive kidneys perfused with blood from either hypertensive or normotensive rats, the afferent arterioles failed to vasodilate and actually exhibited a slight decrease in diameter from 24.6 +/- 1.3 to 23.0 +/- 2.3 microns in response to the same reduction in perfusion pressure. Vasodilator capability, however, could be demonstrated in response to verapamil and sodium nitroprusside, which increased afferent diameter in both the sham-operated and hypertensive groups of rats. Thus, unlike arterioles from normotensive rats, juxtamedullary afferent arterioles from two-kidney, one clip Goldblatt hypertensive rats fail to vasodilate after a reduction in perfusion pressure.(ABSTRACT TRUNCATED AT 250 WORDS)

Angiotensin influences on tubuloglomerular feedback mechanism in hypertensive rats

The tubuloglomerular feedback (TGF) mechanism was evaluated in the nonclipped kidney of Goldblatt hypertensive rats from both stop flow pressure (SFP) and single nephron glomerular filtration rate (SNGFR) responses to step increases in late proximal perfusion rate from 0 to 40 nl/min. During control conditions, increases in late proximal perfusion rate produced flow dependent decreases in SFP and SNGFR with maximal values of 10.2 +/- 1.0 mm Hg and 12.9 +/- 2.5 nl/min, values similar to those obtained in normal rats. During ACE inhibition (MK 422; 0.6 mg/kg/hr), arterial pressure decreased from 168 +/- 8 to 137 +/- 7 mm Hg and there was a marked attenuation in the magnitude of SFP feedback responses (delta = 2.5 +/- 0.3 mm Hg). SNGFR feedback responses, however, were not significantly impaired. Direct decreases in renal arterial pressure reduced control SFP but SFP feedback responses were maintained, indicating that the attenuated SFP feedback responses during ACE inhibition were not due to decreased arterial pressure. Superimposed infusion of angiotensin II during ACE inhibition partially restored SFP feedback responses. In contrast, norepinephrine infusion did not result in a similar restoration of SFP feedback sensitivity. These results indicate that the nonclipped kidney of Goldblatt hypertensive rats has an intact TGF mechanism as assessed from SFP and SNGFR feedback responses. Furthermore, ACE inhibition attenuates SFP but not SNGFR feedback responses, and systemic angiotensin II infusions can restore SFP feedback responsiveness towards normal.

Glomerular prostaglandin production in diabetic rats with renovascular hypertension

A rat model combining two-kidney, one-clip (2K1C) renovascular hypertension and streptozotocin-induced diabetes mellitus was used to assess the pathogenetic significance of vasodilator prostaglandins in diabetic glomerular injury. Glomeruli isolated from normotensive diabetic rats produced greater than normal amounts of PGE2 and 6-keto PGF1 alpha under in vitro incubation conditions. In 2K1C hypertensive-diabetic rats, glomeruli from unclipped kidneys (which are prone to accelerated diabetic glomerular injury) produced similarly elevated amounts of PGE2 and 6-keto PGF1 alpha, which significantly exceeded the levels produced by glomeruli from clipped kidneys (which are relatively protected from glomerular injury), despite exposure to a similar diabetic environment. In contrast, glomeruli from both unclipped and clipped kidneys of 2K1C hypertensive-non-diabetic rats produced normal amounts of PGE2 and 6-keto PGF1 alpha. These results suggests a correlation between vasodilator prostaglandin metabolism and susceptibility to diabetic glomerular injury, and illustrate that enhanced glomerular prostaglandin production is not an invariable metabolic consequence of hyperglycemia or insulin deficiency. The data also demonstrate that hemodynamic as well as metabolic factors may influence glomerular prostaglandin metabolism in experimental diabetes mellitus.

Increased tubuloglomerular feed-back mediated suppression of glomerular filtration during acute volume expansion in rats

1. Volume expansion is currently believed to change the intrinsic properties of the juxtaglomerular apparatus such that the sensitivity of the tubuloglomerular feedback (TGF) mechanism is reduced, thus allowing glomerular filtration rate, and hence salt and water excretion, to rise. Recent studies conflict with this view and indeed the older literature reveals that the rise in glomerular filtration rate (GFR) under these conditions is far more modest than would be expected if TGF control were eliminated. 2. To investigate this problem, TGF control of filtration rate was examined by measuring single-nephron glomerular filtration rate (SNGFR) during loop of Henle perfusion at varying rates in rats under control conditions, after acute, moderate (4% of body weight), iso-oncotic volume expansion and in rats treated with antibodies to atrial natriuretic peptide (ANP) prior to the acute volume expansion. 3. With TGF control of filtration interrupted by filtrate collection from the proximal tubule, SNGFR in the expanded rats was massively increased compared with controls, although SNGFR measured in the distal tubule, and hence with TGF control intact, was only modestly increased, as was whole-kidney filtration rate. Loop perfusion at increasing rates up to 30 nl min-1 progressively decreased SNGFR in controls, and in the expanded rats the range over which control was exerted extended up to 60-80 nl min-1. For changes in loop flow around the spontaneous operating point, the sensitivity of the TGF mechanism, defined as delta SNGFR/delta loop flow, was similar in both groups. Treatment of rats with ANP antibodies prior to volume expansion substantially blunted the changes in renal salt and water excretion and the increase in SNGFR seen in the absence of loop perfusion. 4. These results are not consistent with a diminution of TGF function after volume expansion, rather with an enhancement. The latter is best accounted for by vasodilation of preglomerular resistance vessels on volume expansion, a result predicted by calculations from a model based on the serial arrangement of preglomerular and TGF-controlled vascular resistance elements and the established pharmacological actions of ANP.

Renal parenchymal involvement in essential hypertension

This article has reviewed the involvement of the kidney as a target organ of essential hypertension. Since Bright first made the association of renal disease and hypertension in 1836, the nature of this relationship has been debated. Although there is evidence implicating abnormalities of renal function in the pathogenesis of essential hypertension, hypertension frequently precedes histologic evidence of alterations in renal structure. Nephrosclerosis, or hardening of the kidney, is the term used to describe the histologic changes occurring in the kidney as the result of hypertension. It can be though of as an acceleration of the normal aging process of the renal vasculature. Glomerular and tubular changes have been traditionally thought to be ischemic in origin. Experimental evidence supports the notion that, as renal function is lost, intraglomerular hypertension develops and may be responsible for additional nephron loss in hypertension. This idea may have therapeutic implications for hypertensive patients with renal insufficiency in that agents that reduce both systemic and intraglomerular pressure may be preferable. Hemodynamically, early hypertension is often characterized by normal peripheral and renal vascular resistance and an increased cardiac output. In established hypertension, cardiac output is usually normal, and peripheral and renal vascular resistances are increased. Renal blood flow is reduced, glomerular filtration rate is maintained, and the filtration fraction rises. In the absence of an accelerated malignant phase, renal failure is uncommon in essential hypertension. Males and blacks are most sensitive to the vascular damage of essential hypertension. Essential hypertension remains an important cause of end-stage renal disease, especially in blacks. Atherosclerotic obstruction of the renal arteries may be a more common cause of renal failure in patients with essential hypertension than has been previously recognized. There are few sensitive markers of early renal involvement in essential hypertension. Several studies of sensitive markers are promising and may detect patients who are prone to renal injury and deserve more aggressive treatment. Malignant hypertension is characterized pathologically by vascular changes of proliferative endarteritis and fibrinoid necrosis. Fortunately, its frequency is decreasing because of early identification and effective treatment of essential hypertension. Effective treatment of severe and malignant hypertension clearly leads to stabilization (and occasionally improvement) of renal function.(ABSTRACT TRUNCATED AT 400 WORDS)

Glomerular filtration effects of acute volume expansion: importance of chloride

The present studies were done to determine the effect on GFR of acute volume expansion (AVE) using solutions of various sodium salts and to explore if degree of tubuloglomerular feedback (TGF) activation plays a role in any GFR differences. Free-flow micropuncture and inulin clearance studies were combined to investigate anesthetized Munich-Wistar rats expanded to 10% body weight with isotonic solutions of NaCl, Ringers bicarbonate (RB), NaHCO3, Na acetate (NaAc) and Na2SO4 as well as euvolemic controls. In the clearance studies, AVE yielded per gram kidney weight GFR's greater than control (1009 +/- 51 microliter/min) in the NaCl and RB (chloride expanded) groups (1397 +/- 89 and 1389 +/- 64) microliter/min, respectively, P less than 0.05 vs. control) but not in the NaHCO3, NaAc, and Na2SO4 (non-chloride expanded) groups. Proximal minus distal single nephron GFR determinations (P-D), an estimate of the degree of TGF, were less than control 13.2 +/- 2.1 nl/min) in the NaCl and RB groups (4.1 +/- 0.7 and 5.3 +/- 1.9 nl/min, respectively, P less than 0.05 vs. control) but were not significantly different from control in any of the non-chloride expanded groups. Early distal (ED) fluid flow correlated positively with P-D in all groups. ED chloride concentration but not TCO2 nor osmolality correlated with P-D for all groups. The correlation was negative for control and chloride expanded groups and positive for non-chloride expanded groups.(ABSTRACT TRUNCATED AT 250 WORDS)

Myosin content and vasoconstrictive ability of the proximal and distal (renin-positive) segments of the preglomerular arteriole

The PAP-technique and antibodies to myosin were used to demonstrate the prerequisites for vasoconstriction in the juxtaglomerular part of the preglomerular arteriole as compared with its proximal segment in rats and mice. In contrast with the myosin-positive/renin-negative proximal part of the afferent arteriole no myosin-like activity could be demonstrated in its distal, renin-positive part. In accordance, no thick myofilaments were found in fully differentiated juxtaglomerular epithelioid cells replete with mature secretory granules. Stimulation of the renin-angiotensin system was followed by an increase of the renin-positive/myosin-negative portions of the preglomerular arteriole. Marked interspecies and internephron variations in the length of this vessel segment under control and stimulated conditions were observed. The juxtaglomerular part of the preglomerular arteriole close to the macula densa seems therefore to have only limited capabilities for vasoconstriction. This finding may be of importance regarding the tubulo-glomerular feedback, a mechanism allegedly triggered by the so-called 'macula densa-signal'. It is suggested that this non-contractile segment of the afferent arteriole may represent the renal vascular receptor responsible for the increase of renin secretion during pressure reduction. Unlike the afferent arterioles, most of the efferent arterioles showed the highest level of their weak but distinct myosin-like immunoreactivity in the juxtaglomerular region, indicating some efferent juxtaglomerular vasoconstrictive ability.

Changes in single nephron renin release are mediated by tubular fluid flow rate

In vivo renin release from single nephrons microperfused with artificial tubular fluid was studied in recollection experiments. Renin concentration was measured in systemic arterial plasma (A-PRC) and in either early proximal tubular fluid (TFR), or in plasma from the welling point of the efferent arteriole (SV-PRC) belonging to the microperfused nephron. Micropuncture collections were controlled to maintain the proximal intratubular pressure equal to the control free-flow pressure. Increasing the Henle loop flow rate from 12 to 18, or to 34 nl/min, was followed by a significant decrease in TFR, while reducing the flow rate from 12 to 6 nl/min caused a significant increase in TFR. Similarly, increasing the Henle loop free-flow rate by 6 to 8 nl/min depressed SV-PRC, while reducing the flow rate by fluid aspiration at 8 to 10 nl/min caused a significant increase in SV-PRC. These data indicate: that renin release, to a significant part at least, occurs into the vascular lumen of the afferent arteriole: that modest changes in early distal flow rate may control renin release from the JG-cells; and that increasing the flow rate depresses renin release, and vice versa. It is suggested that the renin system is directly involved in an additional TGF mechanism controlling postglomerular vascular resistances.

Relation of glomerular injury to preglomerular resistance in experimental hypertension

A semiquantitative glomerular damage index (GDI) was determined for overall (O), superficial (S), and juxtamedullary (JM) glomeruli in four models of experimental hypertension in the rat to assess the severity and distribution of injury in light of present day knowledge of glomerular hemodynamics. After a four week period of similar hypertension, comparison of Group 1 (renal ablation) with Group 2 (aortic ligature) revealed OGDIs of 0.420 +/- 0.064 (SEM) vs. 0.062 +/- 0.019, P less than 0.0001, SGDIs of 0.250 +/- 0.071 vs. 0.035 +/- 0.007, P less than 0.0089, and JGDIs of 0.455 +/- 0.071 vs. 0.155 +/- 0.036, P less than 0.002. Within Group 1 the SGDI and JMGDI were not significantly different but within Group 2 the SGDI was less (P less than 0.005) than the JMGDI. Arterial/arteriolar damage was comparable in both groups. After an eight week period of similar hypertension, comparison of Group 3 (deoxycorticosterone-saline) with Group 4 (stroke-prone spontaneously hypertensive rats) showed OGDIs of 0.301 +/- 0.065 vs. 0.128 +/- 0.023, P less than 0.025, SGDIs of 0.289 +/- 0.096 vs. 0.072 +/- 0.015, P less than 0.044, and JMGDIs of 0.394 +/- 0.083 vs. 0.307 +/- 0.062, NS. Within Group 3 the SGDI and JMGDI were not significantly different, but within Group 4 the SGDI was less (P less than 0.002) than the JMGDI. Vascular damage in the two groups was comparable. Taking into account known physiologic data, the findings are consistent with the idea that increased preglomerular resistance is protective of glomeruli, whereas decreased resistance with increased pressure and/or flow is injurious.(ABSTRACT TRUNCATED AT 250 WORDS)

The morphological basis of fluid balance in the interstitium of the juxtaglomerular apparatus

The morphological basis of fluid balance in the interstitium of the juxtaglomerular apparatus (JGA) was reevaluated in rats, mice and Tupaia. Three ultrastructural features in the region of the vascular pole of the renal corpuscle are described that may be important for the fluid balance in this region: (1) podocyte foot processes in the parietal layer of Bowman's capsule, (2) endothelial fenestrations in the wall of the incoming afferent arteriole, both facing Goormaghtigh and epithelioid cells, and (3) the mesangial-type lining of the glomerular stalk. With respect to the relevant pressure gradients, this morphology may provide the basis of bulk-fluid flow directed to the interstitium of the JGA including the Goormaghtigh cell field. Thus, the fluid balance in the lacis area and, consequently, the tubulo-glomerular feedback mechanism, probably does not solely depend upon the reabsorptive transport of the macula densa. Similar considerations may be valid for the humoral control of renin secretion from juxtaglomerular epithelioid cells.

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.

Treatment of hypertension in renal disease

Experimental and clinical evidence are summarized that support the hypothesis that enhanced transmission of systemic hypertension to the adapted glomerulus in the setting of reduced nephron mass may be responsible for accelerated vascular and glomerular damage in the hypertensive stage of parenchymal renal disease in man. In experimental models of hypertension associated with reduced renal mass, the kidney appears to be damaged directly by transmission of pressure rather than primarily through vasoconstriction and ischemia. When hypertension is combined with models of glomerular disease, vascular and glomerular injury are aggravated. It is proposed that adaptive glomerular hemodynamic alterations which occur in parenchymal renal disease magnify the transmission of increased pressure and flows when hypertension supervenes. Accelerated vascular and glomerular damage and functional deterioration result. According to this hypothesis, control of systemic hypertension and minimization of hydraulic stress on the diseased glomerulus become critical to the management of chronic renal disease and the prevention of progressive renal insufficiency.

Hemodynamic basis for glomerular injury in rats with desoxycorticosterone-salt hypertension

Micropuncture and/or morphologic studies were performed in seven groups of uninephrectomized (UNX) adult male Munich-Wistar rats. Control groups 1, 3, and 6 received standard (24% protein) chow and tap water. Groups 2, 4, and 5 received weekly injections of desoxycorticosterone pivilate (DOC) and 1% saline for drinking, groups 2 and 4 were fed standard chow, and Group 5 a diet containing 6% protein. Group 7 received DOC, salt, and standard chow for 3 wk followed by withdrawal of DOC and salt for an additional 6 wk. 10-14 d after UNX, groups 1 and 2 exhibited similar single nephron glomerular filtration rates (SNGFR) and initial glomerular plasma flow rates (QA). Group 2 had higher mean arterial pressure (AP) and glomerular capillary hydraulic pressure (PGC) than group 1. 3-4 wk after UNX, group 4 exhibited further elevations in AP and PGC as compared with groups 2 and 3. SNGFR and QA were similar in groups 3 and 4, but these average values were greater than typical for normal rats. Group 4 also demonstrated increased urinary protein excretion. Morphologic evaluation of glomeruli in groups 2 and 4 revealed mesangial expansion and focal intraglomerular hemorrhage whereas glomeruli of groups 1 and 3 were essentially normal. Values for AP and PGC in group 5 were not different than group 3 but significantly lower than group 4. QA and SNGFR were lower in group 5 (low protein) than in groups 3 and 4. Furthermore, proteinuria and glomerular structural lesions were abolished in group 5. Morphologic studies performed in groups 6 and 7 showed that early DOC-SALT lesions progress to focal glomerular sclerosis. These studies suggest that continued elevations in glomerular capillary flows and pressures predispose to glomerular injury in this model of systemic arterial hypertension.

A functional role for the tubuloglomerular feedback mechanism

Ever increasing evidence exists that the tubuloglomerular feedback system exerts a major influence on overall renal function. Several examples are potentially pertinent to clinical medicine in which there is reasonable evidence that activation or suppression of tubuloglomerular feedback mechanisms contribute significantly to alterations in normal renal physiology. However, in most examples reported, the feedback mechanism is one of several influences acting in concert to determine the final nephron filtration rate, its respective determinants, and the relationship of filtration to the rate of tubular reabsorption. A more complete understanding of all the factors which influence and modify the functional role of tubuloglomerular feedback mechanisms will aid our understanding significantly and the consequent therapy of a variety of altered physiologic conditions.

The effect of intraarterial infusion of prostacyclin on the tubuloglomerular feedback control in the rat

Effects of intraarterial prostacyclin (PGI2) infusions on interstitial hydrostatic and oncotic pressures and on the tubuloglomerular feedback (TGF) control of glomerular filtration rate (GFR) were studied in rat kidneys. The hilar lymph flow rate was used as a measure of interstitial hydrostatic pressure and the lymph protein concentration was used for interstitial oncotic pressure estimation. In the micropuncture experiments the stop-flow pressure technique was employed for determining the TGF characteristics, i.e. stop-flow pressure (PSF), maximal reduction of PSF (delta PSF) and turning point (TP), defined as the end-proximal flow rate at which 50% of delta PSF was obtained. Non-hypotensive doses of PGI2 (50 to 100 ng X kg-1 B.W. X min-1) infused in 30 min evoked an increase in urine and lymph flow rates and a decrease in lymph protein concentration, but did not affect GFR. delta PSF was reduced (9.9 +/- 1.0 mmHg versus 4.7 +/- 2.2 mmHg) and TP increased (22 +/- 2 nl/min versus 34 +/- 2 nl/min), but the PSF was unaffected. These changes were seen during the infusion period and during the immediate post-infusion control period of 30 min. Our data indicate that non-hypotensive doses of PGI2 in some way can affect the renal interstitial pressure and the TGF control system.

A model study of the tubuloglomerular feedback mechanism: effector site and influence on renal autoregulation

The effector site of the macula densa tubuloglomerular feedback mechanism was determined with a mathematical model of glomerular ultrafiltration. The feedback response was found to be mediated by an increase in the hydraulic resistance of the afferent arteriole, possibly accompanied by a slight decrease in the ultrafiltration coefficient of the glomerular membrane. The contribution of the tubuloglomerular feedback mechanism to the autoregulation of renal blood flow and GFR during increased arterial blood pressure was evaluated with a mathematical model of the kidney. The tubuloglomerular feedback system of the superficial nephron was found to be a less efficient regulator of renal blood flow and GFR than the remainder of the autoregulatory mechanism.

Formation and activation of renin in vivo

Active and acid activated renin was measured in glomeruli of rats obtained by microbiopsy and in rat plasma. Sodium depletion increased total and active renin in the juxtaglomerular apparatus and approximately one third of the renin was in an inactive form in sodium depletion. Sodium loading decreased active and total renin and there was no inactive renin present. In plasma changes in a similar direction occurred for active and total renin but in sodium depletion there was no inactive renin present while with sodium loading approximately 40% was in the inactive form. Haemorrhage caused a release of active renin in both sodium states and did not alter the renin content of the J.G.A. Increased delivery of sodium chloride to the macula densa increased the active renin content of J.G.A. but did not alter the total renin content. These results are compatible with two different roles of the renin angiotensin system. One being concerned with intrarenal regulation of glomerular filtration and renal blood flow and the other with maintenance of vascular tone. The conversion of inactive renin to active renin being of particular importance in the regulation of G.F.R.

Influence of replacement of chloride by sulphate upon urine excretion and glomerular filtration rate in blood perfused isolated dog kidneys

Tubular reabsorption was inhibited in isolated dog kidneys by the progressive substitution of plasma chloride by sulphate. In the absence of antidiuretic hormone activity, urine output remained unchanged owing to an equivalent decrease in glomerular filtration rate. This equilibrium was demonstrated under conditions of "saline natriuresis" and was not disturbed by furosemide. Although the impairment of glomerular filtration rate was accompanied by a decrease of total renal blood flow, the equilibrium was not disrupted by angiotensin antagonism. Sodium excretion was enhanced by low plasma chloride concentrations in the absence, but not in the presence of furosemide. The results are not compatible with a specific role of osmolality, sodium or chloride concentrations in the tubular fluid in the adjustment of glomerular filtration. Simultaneous changes in blood flow and tubular flow resistances might explain the results. It is suggested that, in contrast to the mechanism of tubulo-glomerular feedback found in individual nephrons of hydropenic animals, this intrarenal mechanism might serve to protect the organism against sodium loss under conditions of high intake.

The early phase of experimental acute renal failure. V. The influence of suppressing the renin-angiotensin system

Experiments were conducted to determine whether suppression of the renin-angiotensin-system and inhibition of the tubuloglomerular feedback response offer protection from acute renal failure, as found in chronically-salt loaded animals. The juxtaglomerular renin activity and tubuloglomerular feedback response were inhibited acutely, by saline expansion, or chronically, by DOCA-treatment with saline drinking fluid or salt diet, by high salt diet alone, or by inducing two-kidney Goldblatt hypertension. The chronic pretreatment procedures depressed juxtaglomerular renin to 16, 7, 13 and 4% of control, respectively, inhibited the feedback response to 53, 37, 56, and 38% of control, respectively, but conferred no benefit in the first hours following a nephrotoxin or ischaemia. In contrast, the acute treatment procedure reduced juxtaglomerular renin activity to only 56% and lowered the feedback response to only 71%, but improved renal function after the nephrotoxin, although not after ischaemia. It is concluded that since severe restrictions of renin activity and tubuloglomerular feedback are not protective, neither is primarily involved in generating the functional restrictions early in acute renal failure. The restoration of renal function by saline expansion accompanied only a modest depression of these two systems and suggests that the beneficial effect may result more from volume expansion or diuresis than from suppression of renal renin or inhibition of tubuloglomerular feedback.

Feedback regulation of nephron filtration rate during pharmacologic interference with the renin-angiotensin and adrenergic systems in rats

Tubuloglomerular feedback has been defined as a mechanism in which changes in distal tubular sodium chloride delivery induce changes in glomerular arteriolar resistance. Experiments were performed in rats to test the hypothesis that the alterations in vasomotor activity are controlled by local hormonal mechanisms. Early proximal flow rate (EPFR), used as an index of filtration rate, was assessed at loop perfusion rates of 10 and 40 nl/min and during zero loop flow before and during intravenous administration of agents which interfere with the reninangiotensin or adrenergic systems. During infusion of the angiotensin (A) antagonists [Sar1,Ile8-]-AII or [Me2,Gly1,Ile8]-AII at doses ranging from 4.8 to 30.6 micrograms/kg . min, feedback response, expressed as percent change of EPFR during loop flow elevation from 3 to 40 nl/min, fell from a mean of 47.6 +/- 3.3% to 33.2 +/- 2.9% (P less than 0.05). Likewise, after administration of the converting enzyme inhibitor SQ 20881 in a dose ranging between 5.5 and 34.0 mg/kg, feedback response decreased from 48.5 +/- 2.1% to 25.9 +/- 1.9% (P less than 0.001) and returned to 43.1 +/- 5.1% after the inhibitory effect of SQ 20881 on the pressure response to angiotensin I had disappeared. Luminal application of [Sar1,Thr2]-AII (5mM) or of SQ 20881 (5 or 10 mM) had no effect on the feedback response. A significant reduction in the feedback response was noted also during intravenous infusion of propranolol (46.4 +/- 3.2% vs. 29.0 +/- 2.8%, P less than 0.001), whereas 6-OH-dopamine, reserpine, or phenoxybenzamine had no detectable effect. Our results are in agreement with the concept that the renin-angiotensin system may mediate feedback-induced resistance changes. In addition, circulating catecholamines may, in some unknown manner, act as modulators of the feedback response.

Studies on the tubulo-glomerular feedback system in the rat. The mechanism of reduction in filtration rate with benzolamide

The specific mechanism whereby superficial nephron glomerular filtration rate (sngfr) is reduced after the administration of benzolamide, a carbonic anhydrase inhibitor with a primary inhibitory effect in the proximal tubule, have been examined by measuring pertinent pressures, flows, and glomerular permeabilities in the hydropenic Munich-Wistar rat, a strain with surface glomeruli. Because benzolamide decreases absolute proximal reabsorptive rate, the rate of delivery of tubular fluid to the distal nephron should be at least transiently increased and may reduce sngfr by activating the tubulo-glomerular feedback system. Sngfr fell from 29.2+/2.0 to 2.1+/3.1 nl/min (P less than 0.01) after benzolamide (group 1), a percentage reduction equal to kidney glomerular filtration rate and similar to sngfr obtained in collections from distal tubules. Separate studies (group 2) revealed that if transient increases in distal nephron delivery were prevented by insertion of a long oil block in proximal tubules before control, the decrease in sngfr was prevented (30.3+/1.0 vs. 30.3+/1.8 nl/min, P greater than 0.9). In paired "unblocked" nephrons in the same rats, sngfr fell in group 2 (33.0+/1.0 vs. 25.2+/2.3 nl/min, P less than 0.01). In "blocked" nephrons in which sngfr reduction was prevented, the rate of fluid leaving the proximal tubule increased from 16.9+/ to 23.1+/1.0 nl/min (P less than 0.01). In group 1 studies in which sngfr fell and transient increases in flow out of the last segment of the proximal tubule (distal delivery) (approximately equal to 8 nl/min) were not prevented, steady-state distal delivery was unchanged by benzolamide (13.9+/1.1 vs. 14.2+/2.2 nl/min). Also, sngfr returned toward control, pre-benzolamide values, when a proximal oil block was placed for 15 min and the rate of distal delivery reduced after benzolamide administration, which suggests that this activation was reversible. These data suggest that activation of tubulo-glomerular feedback by transient increases in distal delivery was responsible for decreases in sngfr. Analysis of all determinants of glomerular ultra-filtration revealed that the efferent mechanism leading to reduced sngfr after benzolamide was decreased nephron plasma flow (101+/13 vs. 66+/13 nl/min, P less than 0.01). Hydrostatic pressure and the glomerular permeability coefficient did not contribute to reductions in sngfr with benzolamide. Because the rate of distal delivery remained constant in spite of large changes in both sngfr and absolute proximal reabsorptive rate, it is suggested that the rate of distal delivery may be the physiologic entity that is regulated by the tubulo-glomerular feedback system via alterations in sngfr.

Influence of age on the renal renin response to a high salt intake in the rat

Saline drinking combined with DOCA-treatment was found to decrease renal renin in weanlings at a higher rate than in adult rats, with a comparable saline consumption level. The decrease was not potentiated by uninephrectomy.

Factors controlling the release of renin. A micropuncture study in the cat

Blood was collected by micropuncture from the efferent arteriole and superficial venules of the cat's kidney. Blood samples were also collected from the femoral artery and the renal vein. The blood renin concentrations (ng A1 m1-1 2h-1) in a basal state were 37.2 +/- 3.5 (S.E.M.) (n equal to 60) (artery), 32.5 +/- 5.2 [7] (efferent arteriole), 53.5 +/- 4(116) (superficial venule), 54.2+/- 5.4 (43) (renal vein). The corresponding values after haemorrhase were 389 +/- 98 (21), 345 +/- 115 (6), 963 +/- 208 (37), 907 +/- 290 (17), ng A1 m1-1 2h-1. The efferent arteriolar renin did not differ from that in the artery but the concentrations in superficial venular blood and renal vein were higher than arterial concentration. Thus renin entered the circulation between the efferent arteriole and the superficial venule. The blood renin concentration of different superficial venules at a steady arterial renin concentration varied markedly. Into certain venules there appeared to be little or no renin secretion, into others a marked renin secretion, suggesting a heterogeneity of renin secretion by the different nephrons. When the flow of tubular fluid to the macula densa of a group of nephrons was blocked, the renin concentration fell and was significantly less than the renin concentration in venules draining non blocked nephrons and less than in the renal vein. These results suggest that the juxtaglomerular apparatus of the nephrons do not release renin in a synchronous fashion. The release appears to be episodic and is inhibited when flow to the macula densa is ceased. This implies that a high sodium concentration at the macula densa stimulates renin release.

Distal Tubule [Na+] and juxtaglomerular apparatus Renin activity in uranyl nitrate induced acute renal failure in the rat. An evaluation of the role of tubuloglomerular feedback

It has been previously demonstrated that single neophron filtration rate, whole kidney glomerular filtration rate and total renal blood flow decreased by 30-35% 6 h after uranyl nitrate induced acute renal failure in the rat. In order to evaluate a role of the renin-angiotensin system in the initiating phase (0-6 h) of this model of acute renal failure determinations of plasma renin activity, superficial (S) and deep (D) juxtaglomerular apparatus (JGA) renin activity and distal nephron [Na+] were obtained. Plasma renin activity increased from the control value of 1.5 +/- 0.3 (S.E.M.) to 2.9 +/- 0.4 ng/ml/h (P less than 0.005) at 6 h. Mean renin activity in S- and D-JGA's of control rats was 6.99 +/- 0.41 and 2.67 +/- 0.21 ng/JGA/h, respectively. After uranyl nitrate, renin activity in S-JGA's increased to 13.62 +/- 0.80 ng/JGA/h (P less than 0.001) at 2 h and remained elevated, 12.56 +/- 0.90 and 12.75 +/- 0.87 ng/JGA/h at 4 and 6 h. D-JGA renin activity increased (P less than 0.05) to 7.04 +/- 0.53, 6.23 +/- 0.31 and 3.44 +/- 0.33 ng/JGA/h at 2, 4 and 6 h after uranyl nitrate. Distal tubule [Na+], 27 samples in 6 rats, increased from a mean control value of 53.7 +/- 1.2 mEq/l to 116.9 +/- 2.5 mEq/l, 24 samples in 6 rats (P less than 0.001). Prompt increases in JGA renin activity were observed in the initiating phase of acute renal failure, suggesting a role for the renin-angiotensin system in the pathophysiology of this nephrotoxic model. The association of increased JGA renin activity and increased distal [Na+] is consistent with a role for the tubuloglomerular feedback mechanism in the initiating phase of uranyl nitrate induced acute renal failure in the rat.