Effect of sodium balance on intrarenal distribution of blood flow in normal man

Visualization of the intrarenal distribution of capillary blood flow

This study describes a modified technique to fill the renal vasculature with a silicon rubber (Microfil) compound and obtain morphologic information about the intrarenal distribution of capillary blood flow under a variety of conditions. Kidneys and cremaster muscles of rats were perfused in vivo with Microfil using a perfusion pressure equal to the animal's mean arterial pressure at body temperature. Microfil did not alter arteriolar diameter or the pattern of flow in the microcirculation of the cremaster muscle. The modified protocol reproducibly filled the renal vasculature, including; glomerular, peritubular, and vasa recta capillaries. We compared the filling of the renal circulation in control rats with that seen in animals subjected to maneuvers reported to alter the intrarenal distribution of blood flow. Infusion of angiotensin II, hypotension, volume expansion, and mannitol- or furosemide-induced diuresis redistributed flow between renal cortical and medullary capillaries. The advantage of the current technique is that it provides anatomical information regarding the number, diameter, and branching patterns of capillaries in the postglomerular circulation critical in determining the intrarenal distribution of cortical and medullary blood flow.

The use of microcomputed tomography to study microvasculature in small rodents

Appropriate nephron function is dependent on the intrarenal arrangement of blood vessels. The preferred and primary means to study the architecture of intrarenal circulation has been by filling it with opaque substances such as india ink, radio-opaque contrast material, or various polymers for study by light or scanning electron microscopy. With such methodologies, superficial vessels may obscure deep vessels and little quantitative information may be obtained. Serial-section microtomy has not been practical because of problems relating to alignment and registration of adjacent sections, lost sections, and preparation time and effort. Microcomputed tomography (micro-CT) overcomes such limitations and provides a means to study the three-dimensional architecture of filled vessels within an intact rodent kidney and to obtain more quantitative information. As an example of micro-CT's capabilities, we review the use of micro-CT to study the alterations in renal microvasculature caused by the development of liver cirrhosis after chronic bile duct ligation. In this example, micro-CT evidence shows a selective decrease in cortical vascular filling in the kidney, with a maintenance of medullary vascular filling. These changes may contribute to the salt and water retention that accompanies cirrhosis. These results indicate that micro-CT is a promising method to evaluate renal vascular architecture in the intact rodent kidney relative to physiological and pathological function.

Microcomputed tomography of kidneys following chronic bile duct ligation

BACKGROUND

In hepatic cirrhosis, renal sodium and water retention can occur prior to decreases in renal blood flow (RBF). This may be explained in part by redistribution of the intrarenal microcirculation toward the juxtamedullary nephrons. To appreciate this three-dimensional spatial redistribution better, we examined the intrarenal microcirculatory changes using microcomputed tomography (micro-CT) in rats subjected to chronic bile duct ligation (CBDL).

METHODS

Six kidneys from control rats and eight kidneys from rats that had undergone CBDL for 21 days were perfusion fixed in situ at physiological pressure, perfused with silicon-based Microfil containing lead chromate, embedded in plastic, and scanned by micro-CT. The microvasculature in the reconstructed three-dimensional renal images was studied using computerized image-analysis techniques. To determine the physiological condition of the rats, parallel experiments were conducted on six control and six CBDL rats to measure mean arterial pressure (MAP), RBF, glomerular filtration rate (GFR), urine flow (UF) rate, and sodium excretion by conventional methods.

RESULTS

The percentage of vasculature in the renal cortex from CBDL rats was significantly decreased (10.8 +/- 0.4% vs. 16.8 +/- 2.7% control values). However, the vascular volume fractions of the medullary tissues were not significantly altered. There were no significant differences in the number of glomeruli between groups (36,430 +/- 1908 CBDLs, 36,609 +/- 3167 controls). The CBDL rats had a similar GFR than the controls but a reduced MAP, RBF, UF, and sodium excretion.

CONCLUSIONS

The results indicate that after CBDL, there is a selective decrease in cortical vascular filling, which may contribute to the salt and water retention that accompanies cirrhosis.

High doses of furosemide in children with acute renal failure. A preliminary retrospective study

The diuretic effect of high doses of furosemide alone and furosemide plus mannitol was analysed retrospectively in 30 children with acute renal failure. In 10 children (Group 1) renal failure developed mainly during glomerulonephritis, and in 20 children (Group 2) the cause was gastroenteritis. The diuretic effects of furosemide and furosemide plus mannitol were evaluated measuring the 24-hour urine volume at the time of anuria, oliguria or normal diuresis. The highest mean single intravenous doses of furosemide were 6.5 and 14 mg/kg in Groups 1 and 2, respectively; the highest average daily doses were 10.1 and 25.5 mg/kg, respectively. A broad relationship was observed between single i.v. dose and diuretic response following administration of furosemide (1.2 to 30.8 mg/kg). In both groups of patients a statistically significant negative linear correlation was found between the daily intravenous dose of furosemide and the 24-hour urine volume. Calculations based on the obtained regression equations showed that the expected 24-hour urine volumes corresponding to daily diuresis normal for age could be obtained after administration of daily 2.8 to 1.4 mg/kg furosemide in Group 1 and 9.3 to 2.3 in Group 2. It is therefore suggested that the total daily dose of furosemide should not exceed 100 mg in children with acute renal failure. Administration of furosemide plus mannitol did not result in higher daily diuresis as compared to 24-hour urine volume obtained when furosemide was given alone. Furosemide was well tolerated. Electrolyte disturbances, especially in Group 2, were the most frequent side effects due to high doses of furosemide.

Moderate sodium restriction in hypertensive subjects: renal effects of ACE-inhibition

It has been suggested that AII-mediated renal mechanisms limit the efficacy of moderate sodium restriction in the lowering of blood pressure (BP) in hypertension. We therefore studied renal hemodynamics and sodium handling in nine essential hypertensives in balance on 200 and on a 50 mmol sodium diet, before and during ACE-inhibition (enalapril 10 mg bid for 8 days) in a cross-over fashion. BP was similar on 50 and 200 mmol Na before enalapril, the fall in BP during enalapril was significantly more pronounced on 50 mmol Na. On 50 mmol Na, GFR and filtered Na were significantly lower, and tubular reabsorption was significantly higher than on 200 mmol Na. GFR increased during enalapril in 50 but not on 200 mmol Na. Consequently, the differences in GFR and filtered load elicited by sodium restriction were no longer present during ACE-inhibition. In contrast, the differences in tubular reabsorption between 50 and 200 mmol Na persisted during enalapril. In conclusion, moderate sodium restriction, not affecting BP, can elicit a renal hemodynamic response. As this response is blunted by ACE-inhibition it is probably mediated by AII. This blunting may contribute to the increased sodium sensitivity of BP during ACE-inhibition. The adaptation of tubular sodium reabsorption is not affected by ACE-inhibition.

Reduction of proteinuria by indomethacin in patients with nephrotic syndrome

Immediate and longer-term (five-day) effects of indomethacin on proteinuria and renal function were examined in a group of nephrotic subjects with glomerular filtration rates (GFR) that ranged from near normal to moderately impaired. The modifying role of the patients' sodium/volume (S/V) status on renal prostaglandin inhibition was systematically evaluated by renal clearance and balance studies. After patients were S/V-depleted for five days, indomethacin (75 mg/d) decreased protein excretion by 45%. The decrement in proteinuria was greater than 2 times greater than the fall in creatinine clearance and was unrelated to baseline clearance. In acute clearance studies, 75 mg indomethacin administered orally immediately reduced protein excretion, effective renal plasma flow (CPAH), GFR (C inulin), Na, K, and free water excretion. Indomethacin responsiveness (reduced proteinuria) correlated with the change in PGE2 excretion. The effect of indomethacin on protein excretion and renal hemodynamics was apparent, but blunted, when dietary Na intake was increased to 200 mEq/d. Mean BP increased during indomethacin therapy only when patients were S/V-expanded.

Renal concentrating ability in obesity. Effect of modified fasting and the supplementation of T3, sodium chloride and carbohydrate

The renal concentrating ability (RCA) was studied in 30 obese subjects before and after modified fasting (MF) and T3 supplementation, and during hypocaloric-carbohydrate refeeding. We also studied the effect of sodium supplementation on the RCA during MF. Modified fasting induced a low T3-high rT3 state ("sick euthyroid"). During T3-supplementation plasma T3 levels increased but were in the normal range for normal weight controls. Plasma sodium, potassium, and calcium remained within the normal range during all study periods. After MF (14 days) the mean maximal urinary osmolality was significantly lower compared to prefast values both after dehydration alone (706 +/- 12 mosm/kg H2O v 975 +/- 14, P less than 0.001) and after dehydration plus sc vasopressin administration (676 +/- 19 v 899 +/- 17, P less than 0.001). After 14 days MF followed by 14 days MF + T3-supplementation plasma urea, urinary urea excretion, and the creatinine clearance were significantly greater than after MF alone as was the RCA (764 +/- 15 v 652 +/- 25, P less than 0.002). Sodium chloride supplementation increased RCA (P less than 0.02) but no additive effect of T3 and sodium chloride supplementation was observed. Severe dietary salt restriction induced a significant decline in RCA (P less than 0.005). Refeeding with carbohydrate increased plasma T3 from 79.9 +/- 7.7 to 97 +/- 7.5 ng/100 mL (NS) and decreased plasma rT3 from 0.33 +/- 0.02 to 0.27 +/- 0.02 ng/mL, (P less than 0.02); no significant change in RCA was observed.(ABSTRACT TRUNCATED AT 250 WORDS)

Are non-modulating patients with essential hypertension a distinct subgroup? Implications for therapy

In 40 to 50 percent of the essential hypertensive population, a high intake of sodium does not increase renal blood flow. These patients have been called "non-modulators" since their adrenal and renal vascular responses to angiotensin II are not modified by changes in sodium intake. To determine if these patients form a distinct subgroup, the frequency distribution of four characteristics that have been reported to be abnormal in non-modulators were analyzed: aldosterone secretory response to acute volume depletion, plasma aldosterone response to angiotensin II infusion, plasma renin activity response to saline infusion, and renal blood flow response to salt loading. All four characteristics had a bimodal distribution in patients with hypertension. The effect of angiotensin converting enzyme inhibition on two of these abnormalities was also reviewed. In both cases--aldosterone secretory response to angiotensin II and renal blood flow response to salt loading--converting enzyme inhibition restored the abnormal responses towards normal values in non-modulators without altering the responses in normotensives or modulators. Indeed, the correction of the abnormal renal blood flow response to salt loading through converting enzyme inhibition may explain how converting enzyme inhibitors normalize blood pressure in 50 percent of the patients in whom the renin-angiotensin system is suppressed by an unrestricted, typically high, intake of salt. In summary, non-modulators are a distinct subset of the hypertensive population. Converting enzyme inhibition corrects the abnormalities that may be responsible for their hypertensive condition and, therefore, may be a specific form of therapy for these patients.

Correction of abnormal renal blood flow response to angiotensin II by converting enzyme inhibition in essential hypertensives

In 40-50% of patients with essential hypertension, a high sodium intake does not increase renal blood flow (RBF). These patients have been defined as nonmodulators because sodium intake does not modulate renal and adrenal responsiveness to angiotensin II (AII). To define the role of AII in mediating this altered responsiveness, we assessed the effect of a converting enzyme inhibitor (enalapril) on RBF and its responsiveness to AII in 25 patients with essential hypertension--10 modulators and 15 nonmodulators--and 9 normotensive controls. After 5 d of a 200-meq sodium intake, the nonmodulators did not increase RBF, whereas the normotensives (79 +/- 28 ml/min per 1.73 m2) and modulators (75 +/- 26 ml/min per 1.73 m2) did (P less than 0.025). Arterial blood pressure did not change in the modulators with the salt loading, whereas in the nonmodulators, blood pressure rose (P less than 0.004). After enalapril administration for 66 h, there was a significant difference (P less than 0.01, Fisher Exact Test) in the blood pressure response in the two hypertensive subgroups. In the modulators, there was no change; in the nonmodulators, despite the high salt diet, a blood pressure reduction occurred. In parallel, basal RBF and RBF responsiveness to AII were not changed after converting enzyme inhibition in the normotensive control (n = 9) or the hypertensive modulators (n = 10). Conversely, in the nonmodulators (n = 14), the basal RBF increased significantly (83 +/- 25 ml/min per 1.73 m2; P = 0.01), the increment being indistinguishable from the response to salt loading in normal subjects. Furthermore, renovascular responsiveness to infused AII was also significantly enhanced (P = 0.027) in the nonmodulators, suggesting that enalapril-induced increase in RBF reflected a fall in intrarenal AII levels, and not an increase in prostaglandins or kinins, which would have blunted the renal response to AII. Thus, short-term converting enzyme inhibition corrected abnormalities in sodium-mediated modulation of renal vascular responsiveness to AII. The close quantitative relation of the increase in RBF with sodium loading in normal subjects and modulators, and with converting enzyme inhibition in nonmodulators, viewed in the context of the effectiveness of enalapril only in the latter, and parallel shifts in sensitivity to AII, raises the intriguing possibility that converting enzyme inhibition reversed the failure of the renal blood supply to respond to sodium loading. Thus, converting enzyme inhibitors may reduce blood pressure specifically in this subset of patients with essential hypertension, who are sodium sensitive by way of mechanisms more closely related to local than systemic activity of the renin-angiotensin system.

Renal and systemic hemodynamics in sustained essential hypertension

Cardiac output (CO), renal blood flow (RBF), calf blood flow (CBF), and hepatic blood flow (HBF), glomerular filtration rate (GFR), and dopamine beta hydroxylase (D beta H) activity were studied in 198 men (67 normotensive controls and 131 hypertensive patients) of the same age with sustained uncomplicated essential hypertension. In the hypertensive men, the RBF and the RBF/CO ratio were significantly decreased (p less than 0.001). The RBF and RBF/CO ratio were negatively correlated with age (p less than 0.01), blood pressure (p less than 0.01), and D beta H activity (p less than 0.01). None of these relationships were observed with CBF and HBF. The observed decreases in RBF and the RBF/CO ratio in hypertensive men were reversed after administration of clonidine and alpha-methyldopa (p less than 0.01), but not after administration of propranolol. The study provides evidence that the reduction of renal perfusion in essential hypertension is partly reversible and related to an abnormality in the adrenergic system control.

Renal adaptation to sodium deprivation. Effect of captopril in the rat

Dietary sodium restriction is associated with a rapid decrease in urinary sodium excretion and achievement of a new sodium balance within three to five days. In addition, renal vasoconstriction and progressive activation of intrarenal systems with vasoconstrictor (renin-angiotensin) or vasodilating (kallikrein-kinin and prostaglandins) properties are observed. The relationship between sodium homeostasis and the renin-angiotensin system was assessed through the use of captopril in the rat. Treatment with captopril, before and during a six-day period after suppression of dietary sodium, was associated with sodium wasting (urinary sodium always exceeded sodium intake during the observation period); in addition, the normal increase in urinary aldosterone was blunted by about 80 percent. When captopril treatment was given for six days to rats maintained on long-term sodium restriction (at least four weeks) urinary sodium increased, although transiently; at the end of the study, renal vasodilatation together with a redistribution of glomerular blood flow to nonsuperficial glomeruli was observed. These studies indicate that captopril administration markedly blunts the renal and systemic adaptations to a reduced sodium intake in the rat. They suggest that the renin-angiotensin system is probably indispensable in preventing sodium loss when dietary sodium is suppressed.

Defect in the sodium-modulated tissue responsiveness to angiotensin II in essential hypertension

In normal subjects, dietary sodium intake modulates renovascular, adrenal, and pressor responses to infused angiotensin II (AII). To examine the hypothesis that this modulation is abnormal in some patients with essential hypertension, we studied 18 hypertensives and 9 normal subjects twice--during dietary sodium restriction and during loading. Paraaminohippurate (PAH) clearance was used to assess renal plasma flow. AII was infused in graded doses (0.3-3.0 ng/kg per min). Plasma aldosterone, cortisol, renin activity, AII, sodium, potassium, and PAH clearance were measured at the onset and end of each AII dose. During dietary sodium repletion, eight of the subjects with essential hypertension showed a normal renovascular response (greater than 125 ml/min per 1.73 m2) to AII infusion (3 ng/kg per min). The decrement in renal blood flow in these normal responders (NR) was 168 +/- 10, which was comparable to the range in normotensive subjects (206 +/- 25 ml/min per 1.73 m2). All of the remaining hypertensive patients, designated abnormal responders (AbR), had lower (less than 125) renal blood flow responses to the same dose of infused AII (mean decrement: 84 +/- 11 ml/min per 1.73 m2) compared with the NR and normotensive subjects. Renal blood flow responses to all AII doses were statistically greater on a high-vs.-low salt diet in the NR (P less than 0.001, chi-square) and normotensives (P = 0.004, chi-square) but sodium intake had no effect on this response in the AbR. Basal renal blood flow in NR increased significantly (P less than 0.001, paired t test) with dietary sodium repletion, from 491 +/- 36 (low salt) to 602 +/- 40 ml/min per 1.73 m2 (high salt), but was almost identical in the AbR on differing dietary sodium intakes (429 +/- 24 vs. 425 +/- 26 ml/min per 1.73 m2). The adrenal responses to sodium intake and infused AII also differed in the two subgroups. In the NR, the adrenal response to AII was significantly greater (P = 0.011, Wilcoxon signed rank test) after sodium restriction. In contrast, there was no significant difference in the aldosterone response to AII infusion between the low and high sodium diets in the AbR. Thus, a substantial subgroup of essential hypertensives has an abnormality in responsiveness to AII in two systems central to volume homeostasis: the kidney and adrenal. They fail to modulate their renal blood flow and aldosterone responses to AII with changes in dietary sodium intake. Moreover, basal renal blood flow does not increase appropriately with increased sodium intake. These abnormalities, which may be due to an increased local production of AII or a defect in the AII receptors in these three target tissues, could contribute to the elevated blood pressure.

Renal hemodynamics and the renin--angiotensin system in cirrhosis: relationship to sodium retention

Renal hemodynamics and the renin-angiotensin-aldosterone system were investigated in 15 cirrhotic patients without renal failure on controlled sodium intake of 140-160 mEq/day and related to the degree of sodium retention as measured by urinary sodium excretion. Fourteen patients were free of clinical ascites when studied. The distribution of renal blood flow was measured by the noninvasive technique of computerized radioisotope renography. In 11 patients, outer cortical renal plasma flow, expressed as a percentage of total effective renal plasma flow, was directly proportional to sodium excretion (P less than or equal to 0.01). Three patients with severe sodium retention (UNa.V less than or equal to 10 mEq) had estimated outer cortical renal plasma flows of less than or equal to 274 ml/min/1.73 M2 as compared to eight cirrhotics with better (UNa.V greater than or equal to 50 mEq) sodium tolerance (mean = 438 ml/min/1.73 M2). A significant inverse correlation (P less than or equal to 0.01) existed between outer renal cortical blood flow and plasma renin activity. No significant relationship was observed between glomerular filtration rate, total effective renal plasma flow, plasma aldosterone concentration and sodium excretion. These results provide further evidence that a renal vascular abnormality exists in cirrhosis, and that diminished outer cortical renal perfusion is related to the elevated renin levels and sodium intolerance observed in cirrhotic patients.

Effects of positive end-expiratory pressure on renal function

The effects were studied positive end-expiratory pressure (PEEP) on renal function in eight patients with acute respiratory failure, requiring mechanical ventilation. On application of PEEP + 10 cm H2O, central venous pressure increased, systolic blood pressure decreased, urine flow and PAH-clearance were reduced, while inulin clearance remained stable. There was a marked increase in fractional sodium reabsorption and a concurrent decrease in fractional osmolal excretion. Fractional free-water clearance and the ratio UOsm/POsm did change.

Effects of steady-state plasma vasopressin levels on the distribution of intrarenal blood flow on electrolyte excretion

1. In order to evaluate the effects of arginine vasopressin (AVP) on the distribution of intrarenal blood flow and on electrolyte excretion, steady-state plasma AVP levels (4-8, 19-1, 44-3, and 100-6 micro u./ml.) were produced in anaesthetized dogs, which were hydrated to minimize endogenous anti-diuretic hormone (ADH) release. 2. The urinary excretion of sodium and potassium increased without change in their filtered loads during AVP infusion. 3. Measurement by the 133xenon washout method revealed diphasic blood flow shifts, as a function of the plasma AVP level, between compartment 1 (outer cortex) and compartment 2 (inner cortex and outer medulla) without change in compartment 3 (inner medulla). 4. In a separate study, the radioactive microsphere (15 micronm) method was used with a plasma AVP levels of 19-8 micronu./ml. Blood flow (expressed as % flow/g tissue) decreased in the outer cortex and increased in the inner cortex. 5. Total renal blood flow did not change during infusion of AVP. However, the values measured by 133xenon were lower than those measured by the microsphere method. 6. There was agreement between these two independent methods that blood flow shifted from outer to inner cortex, with no change in total renal flow, at similar plasma AVP levels (19-1 and 19-8 micronu./ml.). The relationship of these intrarenal circulatory changes to the increased electrolyte excretion is discussed.

Shock and the kidney: pathophysiology and pharmacological support

This article reviews current knowledge as to the physiological mechanisms that control renal vascular resistence. The contribution of both extrinsic and intrinsic neuro-humoral regulation of both blood flow and glomerular filtration rate are described. The changes that occur both to the renal blood flow and glomerular filtration rate in the pathophysiological situation of "pre-renal uraemia" as well as "acute tubular necrosis" are described. Within this setting pharmacological manoeuvres that may improve both renal blood flow and glomerular filtration rate are discussed. In addition, the indications for and general principles of haemo-and peritoneal dialysis are described.

Effects of angiotensin II and noradrenaline on intrarenal haemodynamics in the rat

The haemodynamic effects of angiotensin II and noradrenaline were studied in the rat kidney. These pressors were given by intravenous infusion in stepwise increasing doses. Intrarenal haemodynamics were analyzed by the 133xenon washout technique, 85krypton autoradiography and silastic casting of the renal vascular tree. Angiotensin II induced significant changes in intrarenal haemodynamics before any changes in systemic blood pressure were detected. The decrease in mean renal blood flow (2.91 ml.min-1.g-1 in controls, 1.76 ml.min-1.g-1 in rats given 50 mug of angiotensin II.kg-1.h-1) reflects a reduction in component I blood flow rate (from 3.9 to 2.9 ml.min-1.g-1) as well as a decrease in the fraction of total renal blood flow supplied to component I of the washout curve (from 84% to 62%). With noradrenaline an increase in total renal resistance occurred simultaneously with the elevation of mean arterial blood pressure. The resulting reduction in mean renal blood flow (from 2.76 ml.min-1.g-1 in controls to 1.55 ml.min-1.g-1 in rats given 1000 mug of noradrenaline kg-1.h-1) reflects a decrease in component I blood flow rate with lower infusion rates and a drop in component I flow fraction (from 82% to 52%) whith higher doses. In contrast to canine kidneys, no evidence for a patchy cortical vasoconstriction was found in the rat. Using autoradiography it was possible to attribute component I to the renal cortex and subcortical area of the kidney.

Renal intracortical blood flow distribution, function and sodium excretion in response to saline loading of anesthetized and unanesthetized dogs

In order to study the effect of anesthesia on the canine response to saline loading, experiments were performed on 10 dogs, first while awake and then during pentobarbital anesthesia. Individual kidney function and intrarenal blood flow response to saline loading (7.5% body weight) were measured in each condition and all data are reported as the average of a single kidney. CIN is considerably reduced under anesthesia (24.7 +/- 3.2 vs. 43.2 +/- 3.9 ml/min, P less than 0.01). A directionally similar reduction of PAH clearance was noted (89 +/- 17 vs. 122 +/- 13 ml/min). The natriuretic response to saline loading of the dogs reached 290 +/- 61 muEq/min while awake, but only 70 +/- 27 muEq/min while anesthetized. No measurable increase of CIN or CPAH occurred in response to saline loading either in the anesthetized or unanesthetized state. The natriuresis was entirely due to a rise of CNA/GFR in both circumstances. The change of CNA/GFR in response to saline load was also appreciably larger while awake (1.2 leads to 4.7% vs. 0.7 leads to 1.8%). Although the fraction of blood flow to the outermost quarter of the kidney was initially the same (31 +/- 3 vs. 29 +/- 3%) awake or anesthetized, the changes with saline loading were in the opposite direction and the values reached were significantly different (37 +/- 3, awake, vs. 27 +/- 3%, P less than 0.05). We conclude that while increased outer cortical blood flow is not necessary for natriuresis, it may occur during sodium loading and may facilitate sodium excretion.

Effect of variation in dietary NaCl intake on total and fractional renal blood flow in the normal and mercury-intoxicated rat

We studied the effect of different chronic (3-4 weeks) dietary salt intakes on intrarenal hemodynamics of normal and mercury-intoxicated rats. Cardiac output (CO), total renal blood flow (RBF), and the zonal perfusion rate in the outer cortex (OC) and inner cortex (IC) were measured by the radioactive microsphere method. The distribution of cortical blood flow was calculated as the distribution index (DI), which reflects the ratio OC/IC. Rats were placed on a high salt diet (group I), intermediate salt diet (group II), or low salt diet (group III). For each group control rats (subgroup A) and mercury-intoxicated rats (subgroup B) were studied. No effect of the different salt intakes on the DI could be detected. The DI in group IA was 2.35 +/- 0.14; in IIA, 2.40 +/- 0.16; and in IIIA, 2.38 +/- 0.09 (P greater than 0.05). After mercury injection RBF changed from 5.32 +/- 0.36 ml/g.min(-1) (IIA) to 3.31 +/- 0.20 ml/g.min(-1), IIB and from 4.32 +/- 0.11ml/g.min(-1) (IIIA) to 1.98 +/- 0.10 ml/g.min(-1) (IIIB) P less than 0.01). The DI was lowered to 1.53 +/- 0.06 (IIB) (P less than 0.05) and to 1.16 +/- 0.10 (IIIB) (P less than 0.01). In both IIB and IIIB a marked elevation of the blood urea was noted (IIB = 97 +/- 9 MG/100 ML AND IIIB = 182 +/- 25 mg/100 ml). In group IB no effect on RBF, OC, IC, or DI could be observed (for all values, P greater than 0.05) despite similar histological renal lesions. Group IB rats also had normal blood urea levels (31 +/- 6 mg/100 ml;P greater than 0.05). We conclude (1) that variations in dietary salt intake appear to have no detectable effect on the intracortical blood flow distribution; and furthermore (2) that the mercury-induced acute renal failure (ARF) is characterized hemodynamically by a total renal and preferential outer cortical ischemia and that chronic salt loading prevents the ARF while preserving normal renal perfusion.

Intrinsic differences in various segments of the proximal convoluted tubule

Until recently it has not been possible to compare directly the function of superficial and juxtamedullary nephrons. The present studies, using in vitro microperfusion, were designed to examine whether functional differences exist between proximal convoluted tubule segments of superficial and juxtamedullary nephrons. Electrophysiological studies showed that major differences exist between the relative chloride and sodium permeabilities of these segments. In the 1st mm of the superficial proximal convoluted tubule, the permeability to sodium was greater than that to chloride, whereas in the 2nd mm of the superficial proximal convoluted tubule and all later segments, the permeability to chloride was greater than that to sodium. The juxtamedullary proximal convoluted tubule was found to differ from the superficial proximal convoluted tubule in two respects: first, the relative permeabilities to chloride and sodium did not differ in the various segments of the juxtamedullary proximal convoluted tubule; second, the permeability to sodium was greater than to chloride throughout. When perfused with a solution lacking glucose and amino acids, the superficial and juxtamedullary convolutions exhibited the same transepithelial potential change, a reversible decrease to less than -- 1 mV. It thus appears that in both convolutions there exists electrogenic sodium transport coupled to the transport of these organic solutes. This differs from pars recta of both of these nephrons, which have been shown to exhibit electrogenic sodium transport independent of organic solutes. However, when perfused with a solution lacking glucose and amino acids but also containing high chloride and low bicarbonate concentrations, the superficial convolution developed a significantly more positive potential than the juxtamedullary. This difference reflects greater relative chloride permeability in the superficial proximal convolution. These studies show that intrinsic functional differences exist between proximal convoluted tubules obtained from the superficial and juxtamedullary nephron populations.

The role of the kidney in essential hypertension

1. Many forms of human and experimental hypertension begin with compromised renal function. Essential hypertension may be another such case. 2. The kidneys of subjects with essential hypertension excrete normal amounts of salt and water at higher-than-normal renal perfusing pressures. Other overt signs of renal dysfunction are few; renal disease is excluded by definition. However, renal blood flow and glomerular filtration rate are usually less than normal in essential hypertension. 3. Renal afferent resistance can be calculated from arterial pressure, renal blood flow, and an estimate of glomerular capillary pressure. These calculations indicate that afferent resistance is increased to two or more times normal in essential hypertension. 4. It is not clear whether afferent constriction causes hypertension or results from it. The ability of high pressure to produce vascular damage points to the latter. But, most essential hypertensives show low-to-normal plasma renin levels and a marked afferent dilation after saline loading. These observations do not suggest nephrosclerosis: they are consistent with a causal role for afferent constriction. 5. We can speculate that, in essential hypertension, there is a defect in one of the mechanisms that sets afferent resistance. Afferent constriction could result from extrinsic influences (neural or humoral) or something totally within the kidney, such as abnormal handling of information from the macula densa. 6. The effect of afferent constriction on salt-and-water excretion would theoretically be offset by elevated arterial pressure so that the actual salt-and-water excretion would be normal, but only so long as the arterial pressure remained elevated.

The starved kidney: a defect in renal concentrating ability

The renal tubular responsiveness to antidiuretic hormone was assessed in seven obese patients during starvation and feeding by an overnight dehydration test followed by exogenous vasopressin. All seven subjects showed a mean reduction of one-third in their maximum urinary osmolality on day 4 of starvation. Thes- data show that the renal tubule is partially insensitive to antidiuretic hormone at a time when it is also insensitive to mineralocorticoids.?Author

Renal intracortical blood flow distribution, function, and sodium excretion in unanesthetized dogs following vena caval ligation

We studied the renal function and the intrarenal blood flow of nine dogs whose thoracic inferior vena cava had been previously ligated (caval dogs) and nine other dogs. Following preparative surgery which included placement of a left atrial catheter, a femoral artery catheter, and bilateral ureteral catheters, the caval dogs gained an average of 2.1 kg of fluid weight, whereas the normal dogs gained no weight. Although neither the caval dogs' blood pressure (114 plus or minus 7 vs 120 plus or minus 4 mm Hg) nor their inulin clearance (0.64 plus or minus 0.06 vs. 0.79 plus or minus 0.06 ml/min g-1 kidney weight) was significantly reduced, their estimated renal blood flow (Cpah/[1-hematocrit]) was considerably lower (2.30 plus or minus 0.24 vs. 3.25 plus or minus 0.15 ml/min g-1). During the clearance study, the caval dogs' excretion of sodium (79 plus or minus 18 vs. 158 plus or minus 17 muEq/min) and their fractional clearance of sodium (2.0 plus or minus 0.4 vs. 3.4 plus or minus 0.5%) were reduced. Studies with microspheres failed to demonstrate a selective decrease in blood flow. However, comparison studies of nine other dogs (five caval and four normal) demonstrated that microsphere results were less reproducible in caval dogs than they were in normal dogs. We have concluded taht reduced blood flow is the only consistent alteration of renal function in this edematous animal model and that previous suggestions of altered distribution are not supported by these studies.

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.

The effect of chronic sodium loading and sodium restriction on plasma prostaglandin A, E, and F concentrations in normal humans

It has been suggested that prostaglandins may be involved in the control of sodium homeostasis. Prostaglandin A and prostaglandin E have been shown to increase renal blood flow and urinary sodium excretion and prostaglandin A has been shown to stimulate aldosterone release. The purpose of this study was to determine the effect of chronic sodium loading and sodium restriction on plasma prostaglandin A, E, and F concentrations. SEVEN NORMAL HUMAN VOLUNTEERS WERE PLACED ON THREE SODIUM INTAKE DIETS: (a) ad lib. sodium intake, (b) high sodium intake, and (c) low sodium intake. Plasma prostaglandin A, E, and F concentrations were measured by radioimmunoassay. Mean prostaglandin A levels on the ad lib. diet were 1.60 ng/ml. Prostaglandin A levels decreased 49% to 0.82 ng/ml on the high sodium intake and increased 34% to 2.14 ng/ml on the low sodium intake. Prostaglandin A levels increased 161% on the low sodium diet in comparison with levels on the high sodium diet. Plasma prostaglandin E and F concentrations did not change significantly during variation in sodium intake. These results show that dietary sodium content markedly effects plasma prostaglandin A levels and that prostaglandins may play a role in the physiologic mechanism of sodium homeostasis.

Intrarenal blood flow in congestive heart failure

Intrarenal blood flow distribution was measured by the 133 xenon washout technic in 10 patients with heart disease who were studied at time of left and right heart catheterization. Renal washout curves were analyzed by computer using a weighted least-squares nonlinear regression technic. In three patients with heart disease without edema the compartment I blood flow rates (outer cortex) were not significantly different from those found in nine normal kidney donors. In seven patients with hemodynamic evidence of heart failure and clinical edema the compartment I flow rates were significantly lower than those of the normal control group and of a group of sodium-depleted hypertensive patients. The rate constants of isotope removal from more central regions of the kidney (compartments II and III) were not depressed to a similar degree. Infusion of furosemide into the renal artery induced diuresis in eight studies which was accompained by preferential increases in compartment I flow rates in six. The data suggest that preferential vasoconstriction of renal cortical vessels may contribute to increased sodium retention by the kidneys and to edema formation in patients with congestive heart failure.

A weighted least-squares technique for the analysis of kinetic data and its application to the study of renal xenon washout in dogs and man

A computer program was written in PL/1 to successively fit the sum of two, three, and four exponential terms to data by an iterative least-squares technique, using a combination of the steepest-descent and the Newton-Raphson methods for convergence. Each data point was weighted by the reciprocal of its variance, assuming that the errors followed a Poisson distribution. A compartment, i.e., an exponential term, was declared nonsignificant if it did not significantly reduce the least-squares error about the fitted line as judged by an F test. Validity of the data was assessed by a "runs" test and by the frequency with which data points fell outside the 95% confidence range. Results of the analysis showed that (1) 9 of 12 normal human kidney 133 Xe washout curves were best described by a four-compartment model, (2) 18 of 38 studies in patients with essential hypertension yielded a four-compartment curve with significant reduction in compartment-1 flow, (3) nine patients with congestive heart failure all had three-compartment washout curves, (4) two patients with oliguric renal failure had washout curves described best by a two-exponential equation (one of these patients responded to an injection of furosemide with the appearance of a third, more rapid compartment). Obviously, this form of analysis can be easily applied to other sets of data which are described by nonlinear equations.

Effect of variation in dietary NaCl intake on the intrarenal distribution of plasma flow in the rat

The effect of dietary variation in sodium chloride intake on the intrarenal distribution of plasma flow was investigated in rats using the antiglomerular basement membrane antibody technique. Rats were placed on a liquid diet containing either 9.86 (n = 9) or 0 (n = 9) mEq NaCl/daily portion for 2 wk. Labeled antibody was injected and the diets were reversed. After an additional 2 wk period, antibody labeled with a different radionuclide was injected and the animals were sacrificed. Fractional plasma flow distribution was then calculated for each dietary period. No change in flow to any cortical region could be detected. In six additional awake rats on identical dietary regimen, total plasma flow was estimated by the clearance of hippuran-(131)I. No change in this parameter occurred with changes in NaCl intake. We conclude, therefore, that no change in either total renal plasma flow or intracortical distribution of plasma flow occurs with wide variations in dietary sodium chloride intake in the rat. The implications of this constancy of regional plasma flow are discussed with reference to presumed concomitant alterations in the intrarenal distribution of nephron filtration rate.

Effect of methylprednisolone on renal function and the zonal distribution of blood flow in the rat

The effect of acute and chronic administration of methylprednisolone on renal function was studied in rats with clearance and micropuncture techniques. Although acute administration did not influence renal function, chronic administration for 4 days caused a marked increase in glomerular filtration rate and PAH clearance. The rise in the reabsorption of sodium under these conditions was associated with a disproportionate increase in filtration rate and renal blood flow in deep portions of the cortex. There was no evidence of altered fractional sodium reabsorption in the proximal segment of surface nephrons by micropuncture analysis or in the ascending limb by clearance studies during a water or a solute diuresis.

Renal vascular response to salt restriction in normal man. Evidence against adrenergic mediation

The role of the sympathetic nervous system in the renal vasoconstriction induced by sodium restriction has been assessed in normal man in balance on a 10-mEq sodium intake. Renal blood flow was measured with radioxenon injected into the renal artery. Phentolamine infused into the renal artery at rates of up to 3 mg/min did not increase net renal perfusion or alter its intrarenal pattern. That dose of phentolamine was at least 30 times the threshold for significant blockade of the renal vascular effects of a large dose of epinephrine injected intra-arterially. The results suggest strongly that neither circulating catecholamines nor the sympathetic nerves play a central role in the renal vascular response to salt restriction in normal man.