Influence of sodium balance on the ability of diuretics to inhibit tubular reabsorption. A study of factors that influence renal tubular sodium reabsorption in man

Enteral Sodium Chloride Supplementation and Fluid Balance in Children Receiving Diuretics

The use of sodium chloride (NaCl) supplementation in children being prescribed diuretics is controversial due to concerns that supplementation could lead to fluid retention. This is a single-center retrospective study in which fluid balance and diuretic dosing was examined in children prescribed enteral NaCl supplements for hyponatremia while receiving loop diuretics. The aim of this study was to determine whether significant fluid retention occurred with the addition of NaCl. Fifty-five patients with 68 events were studied. The median age was 5.2 months, and 82% were hospitalized for cardiac disease. Daily fluid balance the seven days prior to NaCl supplementation was lower than the seven days after, with measurement of: median 17 mL/kg/day (7–26) vs. 22 mL/kg/day (13–35) (p = 0.0003). There was no change in patient weight after supplementation (p = 0.63). There was no difference in the median loop diuretic dose before and after supplementation, with the diuretic dose in furosemide equivalents of 3.2 mL/kg/day (2.3–4.4) vs. 3.2 mL/kg/day (2.2–4.7) (p = 0.50). There was no difference in the proportion of patients receiving thiazide diuretics after supplementation (56% before vs. 50% after (p = 0.10)). NaCl supplementation in children receiving loop diuretics increased calculated fluid balance, but weight was unchanged, and this was not associated with an increase in diuretic needs, suggesting clinicians did not consider the increase in fluid balance to be clinically significant.

Diuretic Resistance in Heart Failure

Decompensated heart failure accounts for approximately 1 million hospitalizations in the United States annually, and this number is expected to increase significantly in the near future. Diuretics provide the initial management in most patients with fluid overload. However, the development of diuretic resistance remains a significant challenge in the treatment of heart failure. Due to the lack of a standard definition, the prevalence of this phenomenon remains difficult to determine, with some estimates suggesting that 25-30% of patients with heart failure have diuretic resistance. Certain characteristics, including low systolic blood pressures, renal impairment, and atherosclerotic disease, help predict the development of diuretic resistance. The underlying pathophysiology is likely multifactorial, with pharmacokinetic alterations, hormonal dysregulation, and the cardiorenal syndrome having significant roles. The therapeutic approach to this common problem typically involves increases in the diuretic dose and/or frequency, sequential nephron blockade, and mechanical fluid movement removal with ultrafiltration or peritoneal dialysis. Paracentesis is potentially useful in patients with intra-abdominal hypertension.

Distal convoluted tubule

The distal convoluted tubule (DCT) is a short nephron segment, interposed between the macula densa and collecting duct. Even though it is short, it plays a key role in regulating extracellular fluid volume and electrolyte homeostasis. DCT cells are rich in mitochondria, and possess the highest density of Na+/K+-ATPase along the nephron, where it is expressed on the highly amplified basolateral membranes. DCT cells are largely water impermeable, and reabsorb sodium and chloride across the apical membrane via electroneurtral pathways. Prominent among this is the thiazide-sensitive sodium chloride cotransporter, target of widely used diuretic drugs. These cells also play a key role in magnesium reabsorption, which occurs predominantly, via a transient receptor potential channel (TRPM6). Human genetic diseases in which DCT function is perturbed have provided critical insights into the physiological role of the DCT, and how transport is regulated. These include Familial Hyperkalemic Hypertension, the salt-wasting diseases Gitelman syndrome and EAST syndrome, and hereditary hypomagnesemias. The DCT is also established as an important target for the hormones angiotensin II and aldosterone; it also appears to respond to sympathetic-nerve stimulation and changes in plasma potassium. Here, we discuss what is currently known about DCT physiology. Early studies that determined transport rates of ions by the DCT are described, as are the channels and transporters expressed along the DCT with the advent of molecular cloning. Regulation of expression and activity of these channels and transporters is also described; particular emphasis is placed on the contribution of genetic forms of DCT dysregulation to our understanding.

Update in diuretic therapy: clinical pharmacology

All diuretics except spironolactone exert their effects from the lumen of the nephron. Thus, to exert an effect, they must reach the urine. Pharmacokinetics (PK) describes this access. Different edematous disorders can affect access to this site of action and therein affect response to a diuretic. In addition, once a diuretic reaches the site of action, a response ensues. The characteristics of this response that can be affected by a patient's clinical condition are described by the pharmacodynamics (PD) of a diuretic. To understand the mechanisms of abnormal response to a diuretic one must dissect its PK and PD in different edematous disorders. For example, in patients with renal insufficiency, the mechanism of poor diuretic response is PK. In contrast, in patients with cirrhosis or in those with congestive heart failure, it is PD. In patients with nephrotic syndrome, both PK and PD are operative. These different mechanisms mandate differences in therapeutic strategy, as explained in this article.

Effects of the rate and composition of fluid replacement on the pharmacokinetics and pharmacodynamics of intravenous torasemide

The effects of differences in the rate and composition of intravenous fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of torasemide were evaluated in rabbits. Each rabbit received 2-h constant intravenous infusion of 1 mg kg−1 torasemide with 0% replacement (treatment 1, n = 6), 50% replacement (treatment 2, n = 9), 100% replacement with lactated Ringer's solution (treatment 3, n = 8), and 100% replacement with 5% dextrose in water (treatment 4, n = 6). Total body (4.53, 5.72, 10.0 and 4.45 mL min−1 kg−1 for treatments 1–4, respectively) and renal clearance (1.44, 1.87, 6.78 and 1.72 mL min−1 kg−1) of torasemide, and total amount of unchanged torasemide excreted in 8-h urine (Ae 0–8 h: 694, 780, 1310 and 1040 μg) in treatment 3 were considerably faster and greater compared with treatments 1, 2 and 4. Although the difference in Ae 0–8 h between treatments 1 and 3 was only 88.8%, the diuretic and/or natriuretic effects of torasemide were markedly different among the four treatments. For example, the mean 8-h urine output was 101, 185, 808 and 589 mL for treatments 1–4, respectively, and the corresponding values for sodium excretion were 10.1, 20.6, 89.2 and 29.9 mmol, and for chloride excretion were 14.5, 27.9, 94.0 and 37.2 mmol. Although full fluid replacement was used in both treatments 3 and 4, the 8-h diuretic, natriuretic and chloruretic effects in treatment 3 were significantly greater compared with treatment 4, indicating the importance of the composition of fluid replacement. Both treatments 1 and 4 received no sodium replacement, however, the 8-h diuretic, natriuretic and chloruretic effects were significantly greater in treatment 4 compared with treatment 1, indicating the importance of rate of fluid replacement for the diuretic effects. Therefore, the 8-h diuretic, natriuretic and chloruretic effects were significantly greater in treatment 3 compared with treatments 1, 2 and 4, indicating the importance of full fluid and electrolyte replacement. Some implications for the bioequivalence evaluation of dosage forms of torasemide are discussed.

Furosemide dynamics in conscious rabbits: modulation by angiotensin II

The aim of this study was to investigate the effects of an infusion of angiotensin II (50 ng/kg/min) on furosemide pharmacodynamics and kinetics in the conscious rabbit. The protocol included a 90-minute phase to estimate the glomerular filtration rate and the renal plasma flow, followed by a 60-minute phase where 5 mg/kg (n = 12) or 10 mg/kg (n = 9) of furosemide were administered. During the pre-furosemide phase, compared to control rabbits, angiotensin II increased natriuresis and diuresis. In the presence of angiotensin II, the furosemide-induced natriuresis decreased, that is, it was 174 +/- 14 versus 95 +/- 25 mumol/min (p < 0.05) and 187 +/- 17 versus 89 +/- 21 mumol/min (p < 0.05) for the 5 and the 10 mg/kg doses, respectively. The infusion of angiotensin II decreased renal plasma flow without modifying the glomerular filtration rate, thus the filtration fraction was increased. Angiotensin II increased the area under the furosemide plasma concentrations as a function of time since it decreased its systemic clearance. However, furosemide urinary excretion rate was not altered and its renal clearance decreased slightly without reaching statistical significance. It is concluded that angiotensin II decreases the response to furosemide and the mechanism underlying this effect is related to the pharmacodynamics rather than the kinetics of the diuretic.

Effects of the rate and composition of fluid replacement on the pharmacokinetics and pharmacodynamics of intravenous bumetanide

The effects of differences in the rate and composition of intravenous (i.v.) fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of bumetanide were evaluated with rabbit as the animal model. Each rabbit received a 4-h constant i.v. infusion of bumetanide at 1 mg/kg with 0% replacement (treatment I, n = 8), 50% replacement (treatment II, n = 6), and 100% replacement (treatment III, n = 7) with lactated Ringer's solution, in addition, another group of rabbits received 100% replacement with 5% dextrose in water (D-5-W, treatment IV, n = 4). Some pharmacokinetic parameters, such as the apparent volume of distribution at steady-state, mean residence time, and terminal half-life, remained relatively unchanged in all four treatments. Renal clearance and urinary excretion rate of the drug in treatments I-III were essentially the same, but were considerably higher than those in treatment IV. In spite of the similarities in kinetic properties (approximately 40% difference between lowest and highest values), the diuretic and/or natriuretic effects of bumetanide were markedly different among the four treatments. For example, the mean 8-h urine output values were 189, 317, 2170, and 306 mL for treatments I-IV, respectively, the corresponding 8-h sodium excretion values were 9.19, 16.5, 88.8, and 15.7 mmol, and the chloride excretion values were 10.8, 33.7, 77.4, and 11.7 mmol. Except for treatment III, diuresis and/or natriuresis were time dependent, generally decreasing with time until reaching a low plateau during later hours of infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Responses to low dose intravenous perindoprilat infusion in salt deplete/salt replete normotensive volunteers

1. Intravenous ACE inhibitor therapy appears to have a role in the treatment of acute heart failure and early after myocardial infarction. Practical experience with intravenous administration with activation of renin is limited. We report responses to perindoprilat (Pt, 0.67 mg) or placebo (P) infused over 4 h in normotensive male volunteers (n = 12, 19-28 years, 53-77 kg) with double-blind, placebo controlled salt depletion (SD) or salt repletion (SR) as a model of the activated renin system. 2. Salt depletion caused no significant fall in serum sodium (P, 139.4 +/- 2.4; Pt, 138.3 +/- 1.9) compared with salt replete preparation (P, 139.9 +/- 1.2; Pt, 139.7 +/- 0.9) but elevation of plasma renin activity 2-3-fold. Pretreatment baseline systolic blood pressure following salt depletion (P, 121 +/- 9.3/71 +/- 7.9; Pt, 121.5 +/- 9.6/69 +/- 8.1) was higher than following salt replete preparation (P, 114 +/- 9.5/61 +/- 7.2; Pt, 116.9 +/- 6.9/67 +/- 7.2). 3. Baseline corrected supine SBP fell significantly and to a similar extent following active treatment regardless of activation of the renin system (SD, -14.6 +/- 9.5/-9.4 +/- 6.4; SR, -12 +/- 14/-10.1 +/- 6.6) compared with placebo (SD, -6.1 +/- 6/-3.7 +/- 5.6; SR, -4.7 +/- 10/-1.3 +/- 6.5). Heart rate was unchanged.(ABSTRACT TRUNCATED AT 250 WORDS)

Plasma renin activity in alcoholic liver disease

PURPOSE AND PATIENTS AND METHODS

The relationship of plasma renin activity (PRA) to indices of circulatory filling and other possible determinants of renin secretion was studied in 31 men with alcoholic liver disease. Characteristics of patients with normal and increased PRA values were examined. Significant differences guided subsequent simple and multiple regression analysis.

RESULTS

Supine PRA was increased (greater than 2.4 ng/mL/h on a 200 mEq/d intake of sodium, ranging as high as 33 ng/mL/h) in 14 of 57 studies. Nonascitic patients with elevated PRA values were significantly younger than those with normal PRA values. Among patients without ascites, the plasma atrial natriuretic factor concentration correlated inversely with PRA. Ascitic patients with elevated PRA values had a significantly reduced serum sodium concentration, urinary sodium excretion, creatinine clearance, and arterial pressure. Systemic vascular resistance, plasma norepinephrine and caffeine concentrations, and left atrial volume were similar in patients with and without increased PRA values. Univariate followed by multiple regression analysis identified age and plasma atrial natriuretic factor concentration as significant independent correlates of PRA in patients without ascites (R2 = 0.54). Serum sodium concentration and urinary sodium excretion were significant correlates of PRA in patients with ascites (R2 = 0.80).

CONCLUSION

The associates of PRA in alcoholic liver disease are diverse and potentially complex. Age and plasma atrial natriuretic factor concentration are important in patients without ascites. In patients with ascites, tubular delivery of sodium to the macula densa, as modified by the filtered load and proximal reabsorption, appeared to be a principal association of PRA. Indices of circulatory filling did not emerge as clearly independent associations of PRA. Increased PRA values in patients with ascites may be an effect of sodium retention rather than part of its cause.

Mechanism of impaired natriuretic response to furosemide during prolonged therapy

The mechanism of the diuretic braking phenomenon was studied in nine male hypertensive patients by assessing the diurnal pattern of renal sodium (Na) excretion during furosemide therapy, and the response to a test dose of furosemide (10 to 15 mg hr-1 i.v.) infused alone and with chlorothiazide (500 mg bolus i.v.). Patients were studied after one month of twice-daily administration of: placebo (P): chlorothiazide 500 mg (C); furosemide 40 mg (F); furosemide with spironolactone (100 mg b.i.d.) for the last 36 hours (F + S; N = 6). During F therapy, furosemide-induced natriuresis was followed by six hour periods of decreased UNaV. Diuretic therapy with F or C for one month reduced BP, but did not alter body weight, plasma volume (PV), glomerular filtration rate or PAH clearance. After P, the test infusion of furosemide increased fractional Na excretion (FENa) by +10.5 +/- 0.7%; this increment was reduced after therapy with F (+8.9 +/- 0.7%; P less than 0.05), C (+8.5 +/- 1.0%; P less than 0.01), or F + S (+8.9 +/- 0.9%; P less than 0.05). Renal furosemide excretion was greater (P less than 0.05) after F and C treatments (133 +/- 10 micrograms.min-1 and 130 +/- 13 micrograms.min-1, respectively) compared with P (94 +/- 9 micrograms.min-1). After P, a test dose of chlorothiazide given during furosemide infusion increased FENa further (+7.5 +/- 1.2%); this increment was greater after therapy with F (+10.1 +/- 1.4%; P less than 0.01) and F + S (+11.3 +/- 0.8%; P less than 0.05) but not after C (+6.3 +/- 1.5%; P greater than 0.1).(ABSTRACT TRUNCATED AT 250 WORDS)

Furosemide pharmacokinetics and pharmacodynamics in health and disease--an update

The literature on furosemide pharmacokinetics and pharmacodynamics is critically reviewed, concentrating on those papers published subsequent to the 1979 reviews of this topic. Intravenous and oral data are presented for healthy volunteers and for patients with various disease states. It is the latter populations about which the majority of the studies have been published since 1979. Inter- and intraindividual variations in bioavailability are discussed, as are data on the metabolism of furosemide to its glucuronide conjugate. Published studies examining the relationship between furosemide pharmacodynamics and pharmacokinetics are also evaluated. The literature is reviewed through June 1988.

Effects of the rate and composition of fluid replacement on the pharmacokinetics and pharmacodynamics of intravenous furosemide

Effects of differences in the rate and composition of intravenous fluid replacement for urine loss on the pharmacokinetics and pharmacodynamics of furosemide were evaluated using the dog as a model animal. Each of six dogs received 8-hr constant intravenous infusion of 20 mg (15 mg used in one dog) of furosemide with 0% replacement (treatment I), 50% replacement (treatment II), and 100% replacement (treatment III) with lactated Ringer's solution, as well as with 100% replacement with 5% dextrose in water (treatment IV). Most pharmacokinetic parameters, such as plasma clearance, steady-state volume of distribution, mean residence time, and terminal half-life, were essentially the same in all four treatments. Renal clearances and urinary excretion rates of the drug in treatments II-IV were essentially the same, but about 20% higher than those in treatment I. In spite of the similarities in kinetic properties, diuretic and/or natriuretic effects from furosemide were markedly different among the four treatments. For example, mean 10-hr urine outputs were 646, 1046, 3156, and 1976 ml and mean 10-hr sodium excretions were 87.0, 142, 383, and 97.2 mmole for treatments I-IV, respectively. Except for treatment III, diuresis and/or natriuresis were found to be time-dependent, generally decreasing with time until reaching a low plateau during later hours of infusion. The present findings also showed that no fluid replacement and 100% replacement with 5% dextrose solution both produced the same degree of severe acute tolerance in natriuresis, indicating the insignificance of water compensation in tolerance development; in treatment II, where neutral sodium balance was achieved, the development of acute tolerance in diuresis and natriuresis can mainly be attributed to negative water balance under this special condition; at steady state the hourly diuresis and natriuresis could differ up to about ten times between treatments. Some implications for the kinetic/dynamic relationship or modeling, in the clinical use, and in the bioequivalence evaluation of dosage forms are discussed.

Clinical pharmacologic implications in diuretic selection

Logical and comprehensive diuretic therapy is based on a sound knowledge of renal physiologic principles. Knowledge of the sites within the nephron at which the currently available diuretics work and their modes of action provide the clinician with a basis upon which to arrive at therapeutic decisions. True diuretic resistance is uncommon, but when it occurs, sequential nephron blockade can frequently reverse the refractoriness initially exhibited by the patient.

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.

Reabsorption of sodium in the proximal renal tubule in cirrhosis of the liver

Proximal tubular reabsorption was examined in patients with liver cirrhosis and ascites by a variety of indirect methods. Maximal diluting ability, urine flow rate, and free water clearance were reduced. During frusemide administration V/GFR was lower than in normal control subjects, indicating that proximal fractional reabsorption is enhanced in liver cirrhosis. This, by reducing Na delivery to the loop of Henle, impairs maximal urine osmolality. Mannitol, by reducing proximal reabsorption, restores availability of Na to the loop and urine concentrating ability during osmotic diuresis, whereas volume expansion with dextran was ineffective. This could be due to a persistent increase in renal vascular resistance preventing the rise in interstitial pressure responsible for driving fluid back into the proximal tubular lumen.

Sodium intake and furosemide administration in hypertensive patients with renal insufficiency

The effects of various levels of sodium intake and loop diuretic (furosemide) administration upon arterial pressure and renal function were studied in 11 patients with impaired renal function and essential hypertension. The patients were hospitalized in a metabolic ward and continued taking their usual antihypertensive medications. After a stabilization period, all patients followed the following regiments for 5 to 7 days: period I, 20 mEq sodium diet without diuretic administration; period II, 80 mEq sodium diet and furosemide, 80 mg daily; and period III, 200 mEq sodium diet and furosemide, 240 mg daily. Supine diastolic pressure was lower (P is less than 0.05) during period II than during period I and both supine and standing systolic and diastolic pressures were significantly lower in period III than in period I (P is less than 0.01). No significant differences in the renal clearance of inulin were noted between any of the study periods. In patients with essential hypertension and impaired renal function, consumption of a moderate or liberal sodium diet combined with administration of a loop diuretic agent (furosemide) appears to result in better control of arterial pressure without significant changes in renal function than does strict sodium restriction without diuretic administration.

Renal consequences of valvular heart disease

Three aspects of potential renal involvement in patients with valvular heart disease are discussed. These include (1) disturbances in renal salt and water handling and their implications with respect to diuretic management; (2) the hemodynamic effects of angiographic contrast agents with identification of potentially dangerous effects on the kidneys; and (3) the histologic patterns of bacterial endocarditis in the kidney and their similarity to those of immunologically mediated disease.

Abolition of the renin-releasing action of frusemide by acute renal denervation in dogs

1. The effects of infusions of frusemide at low (0.05-0.1 mg.kg-1.min-1) and high (0.5-2.0 mg.kg-1.min-1) rates were studied on renin secretion and urinary outputs of sodium and potassium in anaesthetized dogs in which one kidney was removed and the remaining kidney was either innervated or denervated. 2. When the kidney was innervated, low rates of infusion of frusemide did not significantly affect renin secretion if urinary volume and sodium losses were replaced. Without replacement of urinary losses, renin secretion increased at sodium deficits of 0.7-0.9 mmol.kg-1 in the presence of elevated rates of sodium and potassium excretion. 3. High rates of infusion of frusemide caused an immediate increase in renin secretion from innervated kidneys which was not related to urinary losses. 4. Denervation of the kidney increased the urinary outputs of sodium and potassium while it decreased the rate of renin secretion to one-tenth of the resting value. 5. Denervation of the kidney abolished the renin-releasing action of frusemide at both low and high infusion rates even when the sodium deficit amounted to 4.3 mmol.kg-1. 6. Constriction of the aorta producing a fall of 10-30 mmHg in perfusion pressure raised the rate of renin secretion from denervated kidneys to control levels and partially restored the renin-releasing action of frusemide at high infusion rates. 7. The findings indicate that frusemide has a site of action apart from the macula densa in mediating renin release.

Relationship between glucose and sodium excretion in the new-born dog

1. The relationship between renal glucose and sodium excretion was studied in thirty-three new-born dogs aged 1-14 days and in ten adult dogs.2. Glucose was infused into the animals at rates sufficient to produce an amount of filtered glucose at least 1.5 times the tubular transport of glucose (saturating glucose load). In both puppies and adults tubular glucose reabsorption at saturating glucose loads varied directly with the glomerular filtration rate (r = 0.54 and 0.73 respectively, P < 0.01 for both).3. In the puppy, as the fraction of filtered sodium excreted (C(Na)/C(In)) increased from 0.05 to 0.45, the ratio, renal tubular glucose transport divided by glomerular filtration rate at saturating glucose loads, (T(G)/GFR)(m), decreased from 3.7 to 1.7 mg/ml. (r = -0.75, P < 0.01). In the adult C(Na)/C(In) was below 0.08 in all experiments and (T(G)/GFR)(m) was within the 95% confidence limits predicted by regression analysis of the data from puppies. Although mean (T(G)/GFR)(m) was greater in the adult than in the puppy (P < 0.01), when puppies had C(Na)/C(In) similar to that for adults, they had (T(G)/GFR)(m) values equivalent to that for the adult.4. There was excellent correlation between glucose excretion and water excretion for both adult and new-born dogs (r = 0.93 and 0.87, respectively). However, for any glucose loss, water loss was greater in the puppy than in the adult (P < 0.01).5. During the control period total sodium excretion (per gram kidney) and C(Na)/C(In) were similar in the new-born and adult dog. However, during glucose loading, the puppies excreted more sodium and had a higher C(Na)/C(In) than did the adult, although glucose excretion was greater in the adult than in the puppy (P < 0.01 for all comparisons).6. Glomerular blood flow, as measured by radioactive microspheres, was redistributed towards inner cortical nephrons during glucose loading in the puppy. There was no such redistribution of glomerular blood flow in the adult.7. Sodium reabsorption beyond the proximal tubule was blocked with ethacrynic acid and chlorothiazide. In the puppy, the increase of C(Na)/C(In) following a glucose load was the same whether the glucose load followed control or distal blockade collections, suggesting that reductions of sodium reabsorption following a glucose load probably came from the proximal tubule. C(Na)/C(In) during glucose loading plus distal blockade was significantly (P < 0.01) higher in the puppy (0.598) than in the adult (0.280), indicating that glucose diuresis produced a greater inhibition of proximal tubular sodium reabsorption in the new-born than in the adult dog. These results support the hypothesis that the high sodium excretion rate during glucose diuresis in the new-born dogs appears to be due to the greater sensitivity of the neonatal proximal tubule to the osmotic effect of glucose. When presented with a glucose osmotic load the new-born dog diminishes net proximal sodium reabsorption more than does the adult and thus depresses tubular glucose reabsorption to a greater extent. The lower values of maximal glucose transport rates found in new-born animals may be related, therefore, to the higher fractional sodium excretion rates during glucose diuresis rather than to a diminished intrinsic glucose transport capacity in the new-born kidney.

Acute effect of prednisolone on renal handling of sodium

The effect of prednisolone on renal handling of sodium (Na) was studied in rats under three experimental conditions: 1) hydropenia, 2) water diuresis, and 3) distal tubular blockade (DTB). Prednisolone, 0.25 mg/100 g per hr, was infused directly into left renal artery and urine was collected separately from each kidney. Predominantly unilateral increases in urine flow (V) and Na excretion were noticed in all experiments during prednisolone infusion. In the hydropenic rats the maximal increments on the infused side were, for V (mean ± SD), from 9.3 ± 1.5 to 21.4 ± 0.8 μl/min (P < 0.001); for C_Na/C_In, from 0.28 ± 0.11 to 2.97 ± 0.71 % (P < 0.005); and for TH2Oc/CIn, from 2.93 ± 2.26 to 5.32 ± 1.92% (P < 0.05). In the rats with water diuresis, the maximal increases were, for V/C_In, from 5.87 ± 1.97 to 10.1 ± 6.0% (P < 0.005); for C_H2O/C_In, from 4.09 ± 0.68 to 6.00 ± 0.44% (P < 0.0005); and for C_Na/C_In, from 0.22 ± 0.07 to 0.70 ± 0.38% (P < 0.01). In DTB-rats the maximal increases were for V from 48.6 ± 9.0 to 72.7 ± 14.1 μl/min (P < 0.0005) and for C_Na/C_In from 9.42 ± 2.97 to 20.23 ± 7.34% (P < 0.005). In the contralateral kidney these changes were less pronounced. These observations suggest that prednisolone depresses directly Na reabsorption. The association of natriuresis with augmented TH2Oc/CIn and C_H2O/C_In during hydropenia and water diuresis, respectively, and the increases in V and C_Na/C_In during DTB, all are consistent with inhibition of Na reabsorption in the proximal tubule.

Effect of chronic bile duct obstruction on renal handling of salt and water

Renal sodium reabsorption and the concentrating and diluting abilities of the kidney were evaluated in the same trained mongrel dogs before and after chronic common bile duct ligation (BDL). Glomerular filtration rate (GFR) and C(PAH) were not altered by BDL. The natriuretic response to a standardized infusion of 0.45% solution of NaCl was markedly blunted by BDL (P < 0.01); calculated distal sodium delivery was significantly less in experiments after BDL than in control studies. Furthermore, the fractional reabsorption of sodium at the diluting segment for any given rate of distal delivery was enhanced by BDL. Similarly, C(H2O)/100 ml GFR for a given sodium delivery was higher after BDL than control values. Maximal urinary concentration (Uosm-max) was lower after BDL, and the mean Uosm-max for the whole group of animals was 60% of the control value (P < 0.001). Mean maximal T(H2O)/100 ml GFR after BDL was not different from control values; however, T(c) (H2O)/100 ml GFR for a given Cosm/100 ml GFR was lower after BDL in three dogs only. The sodium content of the inner part of renal medulla after BDL was significantly lower than the values obtained in control animals. The excretion of an oral water load in the conscious state was impaired after BDL; although all animals excreted hypotonic urine, urinary osmolality was usually higher after BDL than in control studies. Maximal urinary concentration and the excretion of an oral water load were not affected by sham operation. These studies demonstrate that chronic, common bile duct ligation is associated with (a) enhanced sodium reabsorption both in the proximal and diluting segments of the nephron, (b) a defect in attaining maximal urinary concentration, (c) diminished sodium content in the renal papilla, and (d) impaired excretion of a water load. The results suggest that decreased distal delivery of sodium may underlie the abnormality in the concentrating mechanism and in the inability to normally excrete a water load. In addition, antidiuretic activity despite adequate hydration, may contribute to the impaired water diuresis. Chronic, common bile duct ligation appears to provide a readily available and reproducible model for the study of liver-kidney functional interrelationship.