A micropuncture study of renal salt and water retention in chronic bile duct obstruction

Obstructive jaundice and perioperative management

The causes of obstructive jaundice are varied, but it is most commonly due to choledocholithiasis; benign strictures of the biliary tract; pancreaticobiliary malignancies; and metastatic disease. Surgery in patients with obstructive jaundice is generally considered to be associated with a higher incidence of complications and mortality. Therefore, it poses a considerable challenge to the anesthesiologist, surgeons, and the intensive care team. However, appropriate preoperative evaluation and optimization can greatly contribute to a favorable outcome for perioperative jaundiced patients. This article outlines the association between obstructive jaundice and perioperative management, and reviews the clinical and experimental studies that have contributed to our knowledge of the underlying pathophysiologic mechanisms. Pathophysiology caused by obstructive jaundice involving coagulopathies, infection, renal dysfunction, and other adverse events should be fully assessed and reversed preoperatively. The depressed cardiovascular effects of obstructive jaundice are worth noticing because it has complicated mechanisms and needs to be further explored. Alterations of anesthesia-related drugs induced by obstructive jaundice are varied and clinicians should be aware of the possible need for a decrease in the anesthetic dose. Recommendations concerning the perioperative management of the patients with obstructive jaundice including preoperative biliary drainage, anti-infection, nutrition support, coagulation reversal, cardiovascular evaluation, perioperative fluid therapy, and hemodynamic optimization should be taken.

Hormonal regulation of salt and water excretion: a mathematical model of whole kidney function and pressure natriuresis

We present a lumped-nephron model that explicitly represents the main features of the underlying physiology, incorporating the major hormonal regulatory effects on both tubular and vascular function, and that accurately simulates hormonal regulation of renal salt and water excretion. This is the first model to explicitly couple glomerulovascular and medullary dynamics, and it is much more detailed in structure than existing whole organ models and renal portions of multiorgan models. In contrast to previous medullary models, which have only considered the antidiuretic state, our model is able to regulate water and sodium excretion over a variety of experimental conditions in good agreement with data from experimental studies of the rat. Since the properties of the vasculature and epithelia are explicitly represented, they can be altered to simulate pathophysiological conditions and pharmacological interventions. The model serves as an appropriate starting point for simulations of physiological, pathophysiological, and pharmacological renal conditions and for exploring the relationship between the extrarenal environment and renal excretory function in physiological and pathophysiological contexts.

Aquaporin-1 and aquaporin-2 urinary excretion in cirrhosis: Relationship with ascites and hepatorenal syndrome

Several experimental models of cirrhosis have shown dysregulation of renal aquaporins in different phases of liver disease. We investigated the urinary excretion of both aquaporin-1 and aquaporin-2 in patients with cirrhosis at different stages of the disease. Twenty-four-hour urine was collected from 11 healthy volunteers, 13 patients with compensated cirrhosis (without ascites), and 20 patients with decompensated cirrhosis (11 with ascites without renal failure and 9 with hepatorenal syndrome). Aquaporin-1 and aquaporin-2 excretion was analyzed by immunoblotting. Urinary aquaporin-2 excretion was reduced in patients with cirrhosis compared to healthy subjects. A progressive decrease in urinary aquaporin-2 excretion was observed as the severity of cirrhosis increased, from compensated cirrhosis to cirrhosis with ascites and hepatorenal syndrome. Patients with hyponatremia had lower urinary aquaporin-2 excretion than patients without hyponatremia. Vasopressin plasma level did not correlate with aquaporin-2 excretion. There were no differences between healthy subjects and patients with cirrhosis with or without ascites in urinary excretion of aquaporin-1, but urinary aquaporin-1 excretion of those with hepatorenal syndrome was extremely low. In conclusion, patients with cirrhosis appear to exhibit a decreased abundance of renal aquaporin-2 and therefore lower water permeability in the collecting tubules. This may represent an adaptive renal response to sodium retention, with expansion of extracellular fluid volume and dilutional hyponatremia observed in those who have cirrhosis with ascites. Finally, aquaporin-1 does not appear to play a role in the progressive dysregulation of extracellular fluid volume in cirrhosis.

Vitamin E prevents renal dysfunction induced by experimental chronic bile duct ligation

BACKGROUND

The mechanisms by which prolonged cholestasis alters renal hemodynamics and excretory function are unknown but may be related to increased oxidative stress, with subsequent formation of lipid peroxidation-derived products (e.g., F2-isoprostanes) and endothelin (ET). We investigated whether antioxidant therapy prevents chronic bile duct ligation (CBDL)-induced alterations in systemic and renal hemodynamics, and reduces F2-isoprostane and ET levels.

METHODS

Sprague-Dawley rats were placed on either a normal or a high vitamin E diet for 7 days and then underwent either CBDL or sham surgery. They were then maintained on their respective diets for 21 more days, at which time the physiologic studies were performed.

RESULTS

Thirty-three percent of the CBDL rats died by day 21. The remaining rats had a lower mean arterial pressure (MAP), renal blood flow (RBF), glomerular filtration rate (GFR), and sodium and water excretion than control rats. CBDL rats had higher portal pressure, renal venous pressure, and renal vascular resistance (RVR). These changes were associated with increased levels of systemic and renal venous F2-isoprostanes and ET. Vitamin E normalized MAP, RBF, GFR, RVR, and sodium and water excretion, and improved the 21-day survival without altering portal or renal venous pressures. Surprisingly, vitamin E did not alter the systemic levels of F2-isoprostanes but markedly reduced their levels in the renal venous circulation.

CONCLUSION

Vitamin E improves MAP and renal function in CBDL rats, and selectively decreases renal levels of oxidative stress and ET, suggesting that local redox balance is implicated in CBDL-induced renal dysfunction.

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.

Dysregulation of renal aquaporins and Na-Cl cotransporter in CCl4-induced cirrhosis

BACKGROUND

Severe hepatic cirrhosis is associated with abnormal renal water retention.

METHODS

Semiquantitative immunoblotting was employed to investigate the abundance of the major renal aquaporins (water channels) and sodium-dependent cotransporters in kidneys from control rats and rats with cirrhosis secondary to chronic CCl4 inhalation.

RESULTS

The cirrhotic rats had ascites and manifested a water excretion defect detected by a standard water-loading test. The abundance of aquaporin-1 (the major aquaporin in the proximal tubule) was increased, an effect markedly accentuated in high-density membrane fractions prepared by differential centrifugation. Differential centrifugation studies demonstrated a redistribution of aquaporin-2 from high-density to low-density membranes, compatible with increased trafficking of aquaporin-2 to the plasma membrane. The abundance of aquaporin-3, but not aquaporin-2, was increased in collecting ducts of rats with CCl4-induced cirrhosis. The Na-K-2Cl cotransporter of the thick ascending limb showed no change in abundance. However, the abundance of the thiazide-sensitive Na-Cl cotransporter of the distal convoluted tubule was markedly suppressed in cirrhotic rats, possibly contributing to a defect in urinary dilution.

CONCLUSIONS

In this model of cirrhosis, the development of a defect in urinary dilution may be multifactorial, with contributions from at least four abnormalities in transporter regulation: (1) an increase in the renal abundance of aquaporin-1, (2) a cellular redistribution of aquaporin-2 in the collecting duct compatible with trafficking to the plasma membrane without an increase in total cellular aquaporin-2, (3) an increase in the renal abundance of aquaporin-3, and (4) a decrease in the abundance of the thiazide-sensitive cotransporter of the distal convoluted tubule.

Renal expression of aquaporins in liver cirrhosis induced by chronic common bile duct ligation in rats

Semiquantitative immunoblotting was used to investigate the expression levels of the four major renal aquaporins, the Na-K-2Cl cotransporter of the thick ascending limb, the type 3 Na-H exchanger, and the Na-K-ATPase in kidneys from rats with cirrhosis secondary to common bile duct ligation (CBDL). These rats had significant water retention and hyponatremia. In contrast to models of cirrhosis induced by carbon tetrachloride, aquaporin-2 expression in CBDL-induced cirrhosis was decreased. Thus, these results show that in the setting of extracellular fluid volume expansion, excessive water retention with hyponatremia can occur in the absence of increases in aquaporin-2 abundance. In addition, the expression levels of the two basolateral collecting duct aquaporins (aquaporin-3 and -4) were decreased in CBDL rats relative to sham-operated control rats. Similarly, the Na-K-2Cl cotransporter of the thick ascending limb and the type 3 Na-H exchanger showed decreases in expression. In contrast, the expression levels of aquaporin-1 and the all subunit of the Na-K-ATPase were not decreased. Thus, dysregulation of multiple water channels and ion transporters may play a role in water balance abnormalities associated with CBDL-induced cirrhosis in rats.

Interaction between prostanoids and nitric oxide in the control of tubular function in rats with chronic bile duct ligation

Recent work indicates that both nitric oxide and cyclooxygenase products play an important role in the renal alterations of liver cirrhosis, although the interactions between them have not been completely established. The purpose of this study was to assess the effect of simultaneous blockade of nitric oxide synthase and cyclooxygenase in rats with chronic bile duct ligation and in control, sham-operated rats. Compared with control rats, chronic bile duct ligation rats, 23-25 days after surgery, showed a decreased mean arterial pressure, natriuresis, and kaliuresis, without differences in glomerular filtration rate, and an increased urinary nitrite excretion. Nitric oxide synthesis inhibition by administration of NG-nitro-L-arginine methyl ester induced, in control rats, an increase in mean arterial pressure, without significant changes in natriuresis or glomerular filtration rate. In chronic bile duct ligation rats, NG-nitro-L-arginine methyl ester induced an increase in mean arterial pressure, natriuresis, and kaliuresis, together with a reduction in urinary nitrite excretion and an increase in prostaglandin E2 excretion. Cyclooxygenase inhibition with indomethacin induced in both experimental groups a marked inhibition in urinary prostaglandin E2 excretion without significant changes in Na+ or K+ excretion, and a significant increase in urinary nitrite excretion in control rats. NG-Nitro-L-arginine methyl ester in addition to indomethacin prevented the indomethacin-induced increase in nitrite excretion and dramatically reduced sodium excretion in both experimental groups. Thus, the present study suggests that both nitric oxide and cyclooxygenase products interact in the control of urinary sodium excretion and that each system is activated in the absence of the other one.Key words: kidney, biliary cirrhosis, nitric oxide synthase, cyclooxygenase.

Hepatic denervation ameliorates sodium and water retention in experimental cirrhosis in rats

Increased activity in the hepatic sympathetic nervous system may exacerbate salt and water retention in patients with liver cirrhosis. The aim of this study was to evaluate sodium and water homeostasis in rats with cirrhosis induced by diethylnitrosamine and to investigate the influence of hepatic denervation in this model. Animals were randomized into three groups: diethylnitrosamine-treated rats with (N = 13) and without (N = 8) hepatic denervation and control rats (N = 8). Rats were fed a normal salt diet (0.23% sodium ad libitum). The 24-hr measurements for sodium balance, water balance, and creatinine clearance were performed every two weeks for 12 weeks after surgery. Diethylnitrosamine-induced cirrhosis was confirmed histologically. The cumulative change in sodium balance in the innervated diethylnitrosamine-treated rat increased progressively and was significantly higher than the control during the last four weeks of the study. Meanwhile, rats with hepatic denervation showed significantly smaller changes in cumulative sodium balance at week 12 than those in the innervated group. The cumulative changes in water balance in the innervated group were significantly greater at weeks 10 and 12 than those of the denervated and control group, which remained unchanged throughout the study. Creatinine clearance in the innervated group decreased at weeks 10 and 12 by approximately 70% from baseline (P < 0.05); in contrast, it did not change significantly in the denervated group and control group throughout the study. These results demonstrated that hepatic denervation ameliorates sodium and water retention as well as glomerular function in cirrhosis model in rats.

Sodium retention and hepatic function following partial portal vein ligation in the rat

Recent studies have suggested that the development of sodium retention in experimental cirrhosis in the rat occurs when hepatic function, measured by the aminopyrine breath test, decreases below a critical threshold. The present study evaluated the relationship between renal sodium handling and hepatic function and determined whether sodium retention occurs following partial portal vein ligation. Sodium balance, urine volume, creatinine clearance and the aminopyrine rate constant of elimination, on a constant sodium intake, were evaluated daily, from 1 day before surgery to 5 days after surgery, in both sham-operated (n = 6) and partially portal vein-ligated rats (n = 14). In the partially portal vein-ligated group, sodium retention occurred in 9 rats between 1 and 4 days after surgery, accompanied by a 45% reduction in the aminopyrine rate constant of elimination. Spontaneous natriuresis occurred within 5 days after surgery, and was associated with an increase in the aminopyrine rate constant of elimination from 0.94 +/- 0.07 x 10(-2) min-1 on the last day of sodium retention to 1.36 +/- 0.06 x 10(-2) min-1 on the day of diuresis (P < 0.05). In contrast, creatinine clearance did not change throughout the study. There was a negative curvilinear association between sodium balance and the aminopyrine rate constant of elimination (r = 0.70, P < 0.001). In the five rats without sodium retention, there was no change in the aminopyrine rate constant of elimination and creatinine clearance over the 5 days.(ABSTRACT TRUNCATED AT 250 WORDS)

Rat renal functions during the first days post-bile duct ligation

Renal functions during the early stage of hepatic damage before ascites formation were studied in adult female rats. Tubular and hemodynamic parameters were analyzed for 12 days after common bile duct ligation. The fractional excretion of water, sodium, and potassium increased from control values at every day studied. Glomerular filtration rate and renal plasma flow were found to be diminished on the fourth day. Renal plasma flow remained decreased while glomerular filtration rate was recovered on the sixth day after common bile duct ligation. Filtration fraction in both experimental groups (4 and 6 days) was higher than in control animals. These observations suggested a preferential efferent arteriole vasoconstriction that could be responsible for a blood flow redistribution to the medulla. This fact might cause the sodium diuresis with diminished urine-to-plasma osmolalities ratio. The onset of cortical vasoconstriction was confirmed by dopamine infusion to bile duct-ligated rats 4 days postsurgery. Hemodynamic and tubular parameters recovered to control values during dopamine administration. All the data point out diuresis and natriuresis as the earliest renal abnormalities in bile duct-ligated rats. This phenomenon could be associated not only to the cortical vasoconstriction proposed but also to another systemic modification associated to liver damage.

Renal function in obstructive jaundice in man: cholangiocarcinoma model

Renal function with respect to water clearance and renal hemodynamics was studied in 15 patients with obstructive jaundice due to cholangiocarcinoma. The results were compared with those of the control normal subjects. There was no change in renal function in the patients with mild to moderate jaundice, with total serum bilirubin from 8.0 to 15.1 mg/dl. Increased urinary sodium excretion and decreased free water and negative water clearances were observed in the patients with severe jaundice with total serum bilirubin from 27.0 to 40.4 mg/dl and normal serum albumin. Renal blood flow was normal, but creatinine clearance was decreased. In severely jaundiced patients with serum bilirubin from 30.5 to 40.1 mg/dl and hypoalbuminemia urinary sodium excretion, free water clearance, negative water clearance, renal blood flow and creatinine clearance were decreased. There was salt and water retention in this group. The findings suggest that in severe jaundice there is inhibition of sodium chloride reabsorption in the thick ascending limb of Henle's loop. ADH and increased hydraulic conductivity of the collecting tubules possibly contribute to decreased free water clearance. In severely jaundiced patients with hypoalbuminemia this salt losing effect is converted to salt retention by increased proximal tubular reabsorption of sodium.

Phenobarbital influences the development of sodium retention in liver disease induced by bile duct ligation in the rat

The onset of sodium retention in phenobarbital/carbon tetrachloride-induced cirrhosis in rats is preceded by a linear decrease in hepatic function as assessed by the aminopyrine rate constant of elimination. Sodium retention occurs when liver function decreases below a critical aminopyrine rate constant of elimination threshold of 1 min-1 x 10(-3). The objective of this study was to investigate this relationship in a different experimental model of cirrhosis in rats and to learn whether alteration of drug-metabolizing activity by hepatic enzyme induction changes the threshold for urinary sodium retention. Cirrhosis was induced in untreated and phenobarbital-treated rats by bile duct excision. Liver function, assessed by the aminopyrine breath test, and urinary sodium excretion on a constant salt diet were measured weekly for up to 4 wk. In untreated rats, the aminopyrine breath test rate constant of elimination was reduced by about 40% within 1 wk of surgery. Aminopyrine rate constant of elimination then decreased more slowly, but linearly. Urinary sodium excretion was initially unchanged, but sodium retention occurred after 2.5 wk and was maintained until the end of the experiment. Phenobarbital-treated rats had greater initial aminopyrine rate constant of elimination, but we saw a similar fall in aminopyrine rate constant of elimination of about 40% within 1 wk of bile duct excision to a value still above baseline aminopyrine rate constant of elimination of untreated controls. Aminopyrine rate constant of elimination remained at a plateau for 3.5 wk without changes in urinary sodium excretion. After 3.5 wk, a sudden decrease in aminopyrine rate constant of elimination was associated with the sudden onset of sodium retention.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal failure complicating obstructive jaundice

Postoperative acute renal failure in patients with obstructive jaundice remains a clinically significant complication. Acute renal failure occurs in approximately 9 percent of patients requiring surgery for relief of obstructive jaundice, and contributes to eventual mortality in 76 percent of those who develop it. The overall mortality rate for patients undergoing surgery for obstructive jaundice is 16 percent. Despite advances in perioperative care, these figures have changed very little over the past 25 years. This article describes the clinical association between jaundice and renal failure and reviews the studies that have contributed to the delineation of the possible underlying pathophysiologic mechanisms, as well as possible preventive measures which have been developed as a result of these investigations. With increased awareness of the potential risk of developing postoperative acute renal failure, the institution of prophylactic measures may result in an improvement in the mortality rate seen after surgery for obstructive jaundice.

The pathogenesis of renal sodium retention and ascites formation in Laennec's cirrhosis

This chapter critically reviews our current understanding of the pathogenesis, clinical syndrome, and therapy of the disturbances of renal sodium handling, renal perfusion, and glomerular filtration rate that occur in patients with Laennec's cirrhosis. Avid renal sodium reabsorption, a characteristic feature of cirrhosis, occurs independent of moderate changes in renal function and precedes the onset of ascites. The initiation of sodium retention may be a direct consequence of the hepatic disease process and may also result from defective intravascular filling. In the presence of ascites the most important sodium retaining signal is a defective intravascular volume. The principal effectors of renal sodium retention and vasoconstriction are stimulation of the renin-angiotensin-aldosterone axis and augmentation of renal sympathetic nerve activity. Deficient production of natriuretic hormone(s) and endogenous renal vasodilators, such as prostaglandins and kinins, also contributes to the sodium retention and renal hypoperfusion seen in cirrhosis. The hepatorenal syndrome is an extreme imbalance in these renal vasoconstrictor and vasodilator forces. In the therapy of ascites in Laennec's cirrhosis, abstention from alcohol, sodium restriction, and cautious diuresis are the principal therapeutic measures. A grave prognosis accompanies the diagnosis of the hepatorenal syndrome although recoveries have been reported.

Effect of hypoxemia on sodium and water excretion in chronic obstructive lung disease

To determine the role of hypoxemia in the pathogenesis of impaired sodium and water excretion in advanced chronic obstructive lung disease, 11 clinically stable, hypercapneic patients requiring long-term supplemental oxygen were studied. The renal, hormonal, and cardiovascular responses to sodium and water loading were determined during five-and-a-half-hour studies on a control day (arterial oxygen tension = 80 +/- 6 mm Hg) and on an experimental day under hypoxic conditions (arterial oxygen tension = 39 +/- 2 mm Hg). Hypoxemia produced a significant decrease in urinary sodium excretion but did not affect urinary water excretion. Hypoxemia also resulted in concomitant declines in mean blood pressure, glomerular filtration rate, and filtered sodium load. Renal plasma flow and filtration fraction were unchanged whereas cardiac index rose. On the control day, plasma renin activity and norepinephrine levels were elevated whereas aldosterone and arginine vasopressin levels were normal; none of these four hormones was affected by hypoxemia. Renal tubular function did not appear to be altered by hypoxemia as there was no significant change in fractional reabsorption of sodium. The concurrent decreases in glomerular filtration rate, filtered sodium load, and mean blood pressure at constant renal plasma flow suggest that the reduction in urinary sodium excretion was due to an effect of hypoxemia on glomerular function, possibly related to impaired renovascular autoregulation.

Failure of changes in intracapillary pressures to alter proximal fluid reabsorption

To determine the role that peritubular capillary oncotic and hydraulic pressures play in regulating urinary sodium excretion in the euvolemic state, experiments were carried out in rats under conditions which altered these pressures without volume expanding the animal. In cross-circulation experiments, the donor rat was expanded with plasma or Ringer's solution while the recipient rat remained euvolemic. Micropuncture measurements in the euvolemic recipients demonstrated significant increases in efferent plasma flow rate (QEA), capillary hydraulic pressure (Pc), and decreases in mean capillary oncotic pressure (pi c). There were no changes in nephron GFR (SNGFR), absolute proximal reabsorption (APR), or UNaV. In additional studies, peritubular oncotic pressure was lowered markedly by plasmapheresis of the experimental animal. Large decreases in pi c were produced without any change occurring in SNGFR, APR, or UNaV. Measurements of interstitial hydraulic pressure (Pi) with a subcapsular pressure pipet revealed that Pi was unaltered under all of these conditions but rose markedly in rats undergoing a saline-expansion diuresis. Our findings indicate that APR and UNaV can remain constant despite large changes in pi c, Pc, and QEA in nonexpanded animals. Furthermore, the changes in pi c, Pc, and QEA induced in the euvolemic non-diuretic rats were the same as those in the saline-expanded diuretic rats. We conclude that under euvolemic experimental conditions, urinary sodium excretion and APR do not correlate with intracapillary pressures or flow rates in the renal cortex. The only difference found between the nondiuretic and diuretic rats was a rise in Pi in the latter group.

Effect of short-term bile duct ligation on peripheral blood steroids, urinary PGE2 and the rate of sodium excretion in male rabbits

Short-term bile duct ligation in male rabbits resulted in a significant reduction in the rate of sodium excretion after saline challenge (10 ml/kg/hr for 4 hr, P less than 0.03). The reduction in the sodium excretory rate (14.3 +/- 7.8 to 6.3 +/- 5 mu-equiv/min, P less than 0.03) was associated with an increased urinary PGE2 excretion (200.9 +/- 174 to 731.8 +/- 1039.8 pg/min, P less than 0.01) without significant change in serum aldosterone and cortisol concentrations. Serum progesterone concentration increased (37.2 +/- 15.6 to 119.2 +/- 34.6 ng/dl, P less than 0.01) whereas serum 17-hydroxyprogesterone concentration declined after bile duct ligation suggesting the development of a 17-hydroxylase enzymatic block.

Hormonal abnormalities affecting sodium and water balance in acute respiratory failure due to chronic obstructive lung disease

The pathogenesis of edema and hyponatremia associated with chronic obstructive lung disease (COLD) is poorly understood. In ten edematous COLD patients with acute respiratory failure (ARF), we monitored plasma renin activity (PRA), aldosterone (PA), and antidiuretic hormone (arginine vasopressin, AVP) for six days. Six patients receiving supplemental oxygen and antibiotics had near normal PRA, PA, and AVP, and diuresed Na+ and H2O and lost weight; only one patient was hyponatremic (PNa+ less than 130 mEq/L). On the same therapy, nonresponders (n = 4), with persistently elevated PRA, PA, and AVP, demonstrated no loss of Na+, H2O, or weight; three patients were hyponatremic. The PRA and PA correlated inversely with sodium loss; AVP correlated inversely with free water clearance. These studies suggest that in patients with COLD, edema, and ARF (1) lack of sodium diuresis may be contributed to by secondary hyperaldosteronism; and (2) hyponatremia can be explained by inappropriately elevated plasma AVP.

Selective deep nephron hyperfiltration in uninephrectomized spontaneously hypertensive rats

Studies were carried out to determine the effect of uninephrectomy (UNX) on single nephron hemodynamics and proteinuria in the spontaneously hypertensive rat (SHR). Four groups were studied: two-kidney SHR and normotensive WKY controls; SHR + UNX and WKY + UNX. UNX was performed at age 8 to 10 weeks. Blood pressure and protein excretion were measured periodically, and micropuncture experiments of cortical nephrons were carried out at age 32 to 40 weeks. Systolic blood pressure was not significantly different between SHR and SHR + UNX. Protein excretion increased markedly in the SHR + UNX 6 months after UNX, as compared with the other three groups. In cortical nephrons, single nephron glomerular filtration rate (SNGFR) and plasma flow entering the glomeruli (SNPF) was lower in SHR + UNX than in WKY + UNX. Glomerular hydraulic pressure (PG) during stopped flow was closely comparable in all groups, rising only 2 mm Hg after UNX. SNGFR was measured in juxtamedullary (JM) nephrons 2 months after UNX, a stage before heavy proteinuria developed. We found that JM SNGFR was approximately 50% higher in SHR + UNX than in WKY + UNX. The observations suggest that following ablation of renal mass, superficial cortical glomeruli are not exposed to excessively high pressure or flow rates in the SHR. In contrast, JM glomeruli undergo a disproportionate rise in SNGFR, presumably associated with excessively high PG and/or blood flow.(ABSTRACT TRUNCATED AT 250 WORDS)

The role of tubuloglomerular feedback in acute impairment of renal function in obstructive jaundice

Acute renal functional impairment not infrequently accompanies liver dysfunction and, particularly with bile duct obstruction, may be extremely severe. Recent studies suggest that tubuloglomerular feedback (TGF) activated by circulating non-electrolyte factors which occur during liver dysfunction may contribute to the intense renal vasoconstriction thought to be central to the functional renal impairment. In this study, serum from two patients with obstructive jaundice (OJ) and renal impairment, and from rats with OJ due to bile duct ligation were either dialysed or treated with furosemide, known to block electrolyte-mediated TGF. These sera, when perfused into loops of Henle in rat nephrons, induced a significant fall of 28% in stop-flow pressure, an indirect measure of glomerular capillary pressure thus implying arteriolar vasoconstriction. These findings are consistent with the hypothesis that circulating, non-electrolyte factors, which stimulate TGF, occur in cases of obstructive jaundice and that these may contribute to the renal impairment.

Pathogenesis of sodium and water retention in edematous disorders

Edema is a collection of fluid within the body's interstitial space which occurs when there is an alteration of the Starling forces which control transfer of fluid from the vascular compartment to surrounding tissue spaces. Generalized edema results when altered Starling forces affect all capillary beds, such as occurs in cardiac failure, cirrhosis, and nephrotic syndrome. Common to these conditions is the development of increased total body sodium and water content. The kidneys play an essential role in the retention of this sodium and water. In this article we shall discuss the signals the kidneys receive for sodium and water retention in these edematous disorders (afferent mechanisms). We shall also examine the means by which the kidney responds to these signals and retains sodium and water (efferent mechanisms). As shall become apparent these edematous states may share many of the same afferent and efferent mechanisms for sodium and water retention.

Body fluid homeostasis in congestive heart failure and cirrhosis with ascites

The urinary excretion of salt and water in man is regulated by a variety of renal and extrarenal mechanisms that respond to changes in dietary sodium intake as well as to alterations in the holding capacity of the vascular and interstitial compartments. Changes in extracellular fluid volume are detected by volume sensors located in the intrathoracic vascular bed, the kidney and other organs. These sensing mechanisms gauge the adequacy of intravascular volume relative to capacitance at various sites within the circulation. Congestive heart failure and cirrhosis with ascites are two disease states of man in which a hemodynamic disturbance within a given circulatory subcompartment is perceived by these sensing mechanisms and results in renal sodium retention. While the primary disturbance in both of these conditions originates outside the kidney, a variety of renal effector mechanisms respond to the perceived circulatory disturbance and result in enhanced tubule reabsorption of salt and water. These effector mechanisms involve physical adjustments in renal microvascular hemodynamics, tubule fluid composition and flow rate and transtubular ion gradients. These in turn are partially regulated by a variety of neural and humoral pathways including the renin-angiotensin-aldosterone axis, prostaglandins, and kinins.

Resistance to diuretics: emphasis on a pharmacological perspective

Resistance to diuretics occurs frequently in clinical settings. Most attention to this phenomenon has been directed toward the pathophysiology of the disease state, with little focus on the pharmacology of the diuretics themselves. This review summarises the pathogenesis and emphasises the pharmacological determinants of response to diuretics, including absorption, delivery to the kidney, and response to amounts of diuretic reaching the site of action. In normal subjects, overall response to organic acid diuretics such as frusemide (furosemide) is determined by the total amount of drug delivered into the urine (reflecting amounts of drug reaching the intraluminal site of action), the time course of delivery, and the relationship between amounts of drug reaching the urine and response (the dynamics of response). The conditions of azotaemia, inhibition of synthesis of prostaglandins, and the oedematous disorders of congestive heart failure, cirrhotic liver disease and nephrotic syndrome are examined in the above context. In azotaemic subjects, delivery of organic acid diuretics to their intraluminal site of action is inhibited by accumulated endogenous organic acids which compete for transport into the nephron at the organic acid secretory site of the proximal tubule. Whether the dynamics of response are changed has not been investigated. During inhibition of synthesis of prostaglandins, and in the oedematous disorders, there appear to be no changes in handling of frusemide; i.e. bioavailability, total drug delivered into the urine and the time course of delivery are comparable with that in normal subjects unless concomitant renal dysfunction exists. Resistance in these conditions is therefore due to a change in the dynamics of response.

Mechanisms of altered renal perfusion in the early stage of obstructive jaundice

Mechanisms responsible for renal hemodynamic alterations were studied in jaundiced (by bile-duct ligation) rabbits (BDL) 10 days after ligation of the biliary tract, in comparison with sham-operated rabbits (SO). Arterial hematocrit, plasma volume, blood pressure, abdominal inferior vena cava pressure, and heart rate were not significantly different between the BDL and SO groups. Cardiac output in BDL rabbits decreased to approximately 73% of the value for SO rabbits. Renal blood flow and GFR were reduced to 64 and 61%, respectively. Reductions in blood pressure and renal blood flow, caused by bleeding (8 ml/kg of body wt), were more marked in the BDL group than they were in the SO group. In the BDL group, the recovery of blood pressure following blood infusion was slower and the mortality was higher, There was no significant increase in the renovascular sensitivity to exogenous noradrenaline or angiotensin II in the BDL group. The findings indicate that the early stage of obstructive jaundice in rabbits was characterized by altered renal perfusion partly due to reduced cardiac output and by incrased liability to hemorrhagic hypotension.

A micropuncture study of renal sodium retention in nephrotic syndrome in rats: evidence for increased resistance to tubular fluid flow

Micropuncture studies were carried out in surface nephrons of rats with nephrotoxic-serum (NTS)-induced nephrotic syndrome during a period of active sodium and water retention. It was found that hydrostatic pressure and tubular diameter were increased in the proximal tubules (13.4 +/- 0.2 vs. 10.4 +/- 0.2 mm Hg; 31.3 +/- 0.9 vs. 18.4 +/- 0.7 mu), whereas pressure and tubular diameter were normal in the distal tubules. Single nephron glomerular filtration rate (SNGFR) was decreased and fractional reabsorption of fluid was markedly increased in the proximal tubules (74.1 vs. 61.7%). The increased pressure gradient between the proximal and distal tubules suggests a condition of increased resistance to flow between the proximal and distal tubules. Microinfusion of proximal tubules with an isotonic "equilibrium" solution led to little or no rise in intratubular pressure in normal rats but it led to a significant rise in nephrotic rats. When proximal tubules of normal rats were infused with a solution containing 100 mg/100 ml albumin, pressure rose to levels observed in nephrotic rats. The mechanism of the increased resistance to flow appeared to be related, therfore, to the presence of protein in the tubular fluid. Sodium retention in the nephrotic animals might be attributed to the reduction in GFR. In other types of renal disease in animals and man with comparable or greater reductions in GFR, sodium retention does not occur, however, and fractional excretion of sodium in the urine is increased in proportion to the reduction in GFR. Thus, the rise in proximal fractional reabsorption secondary to impaired fluid flow could be an important factor in the sodium retention of this disease.

Renal sodium retention during volume expansion in experimental nephrotic syndrome

We have studied sodium retention during volume expansion in rats with autologous immune complex nephropathy (AICN), a model of nephrotic syndrome (NS) in which GFR after volume expansion was not different from that in adjuvant-injected controls (C). AICN rats developed heavy proteinuria (298 +/- 27 vs. less than 10 mg/day), hypoalbuminemia (2.14 +/- 0.15 vs. 3.08 +/- 0.12 g/100 ml) and hypercholesterolemia (181 +/- 22 vs. 58 +/- 4 mg/100 ml). After saline, there were no significant differences in blood pressure (119 +/- 2 vs. 114 +/- 2 mm Hg), renal plasma flow (4.9 +/- 0.41 vs. 4.1 +/- 0.28 ml/min), inulin clearance (1.37 +/- 0.06 vs. 1.55 +/- 0.10 ml/min), or SNGFR (47 +/- 2 vs. 53 +/- 4 nl/min). Sodium excretion, however, was significantly lower in NS rats (4.7 +/- 1.1 vs. 9.2 +/- 1.2 muEq/min). Proximal sodium reabsorption was decreased in NS rats (35 +/- 2 vs. 41 +/- 2%, 2.5 +/- 0.2 vs. 3.3 +/- 0.2 nEq/min). Sodium delivery into the loop, however, was equal in NS and C, since the slightly lower filtered load in NS rats offset the depression in proximal reabsorption. Sodium reabsorption by the loop and by the distal convoluted tubules were equal in NS and C. Thus, sodium delivered into the cortical collecting ducts was the same in both groups (0.33 +/- 0.17 vs. 0.34 +/- 0.07 nEq/min; 4.5 +/- 0.6% of filtered sodium vs. 4.4 +/- 0.3%). The percent of filtered sodium excreted in the urine, however, was significantly lower in the NS rats, 2.18 +/- 0.48% vs. 4.0 +/- 0.58%. We conclude that antinatriuresis in this model of NS is determined beyond the superficial late distal convoluted tubule. The inability to excrete the sodium load during volume expansion is due to either enhanced reabsorption by the collecting duct or to abnormal function in deep nephrons.