Evidence that an acute increase in glomerular filtration has little effect on sodium excretion in the dog unless extracellular volume is expanded

Single nephron glomerular filtration rate measured by linescan multiphoton microscopy compared to conventional micropuncture

Renal micropuncture, which requires the direct access to the renal tubules, has for long time been the technique of choice to measure the single nephron glomerular filtration rate (SNGFR) in animal models. This approach is challenging by virtue of complex animal preparation and numerous technically difficult steps. The introduction of intravital multiphoton microscopy (MPM) offers another approach to the measure of the SNGFR by mean of the high laser-tissue penetration and the optical sectioning capacity. Previous MPM studies measuring SNGFR in vivo relied on fast full-frame acquisition during the filtration process obtainable with high performance resonant scanners. In this study, we describe an innovative linescan–based MPM method. The new method can discriminate SNGFR variations both in conditions of low and high glomerular filtration, and shows results comparable to conventional micropuncture both for rats and mice. Moreover, this novel approach has improved spatial and time resolution and is faster than previous methods, thus enabling the investigation of SNGFR from more tubules and improving options for data-analysis.

Integrated control of Na transport along the nephron

The kidney filters vast quantities of Na at the glomerulus but excretes a very small fraction of this Na in the final urine. Although almost every nephron segment participates in the reabsorption of Na in the normal kidney, the proximal segments (from the glomerulus to the macula densa) and the distal segments (past the macula densa) play different roles. The proximal tubule and the thick ascending limb of the loop of Henle interact with the filtration apparatus to deliver Na to the distal nephron at a rather constant rate. This involves regulation of both filtration and reabsorption through the processes of glomerulotubular balance and tubuloglomerular feedback. The more distal segments, including the distal convoluted tubule (DCT), connecting tubule, and collecting duct, regulate Na reabsorption to match the excretion with dietary intake. The relative amounts of Na reabsorbed in the DCT, which mainly reabsorbs NaCl, and by more downstream segments that exchange Na for K are variable, allowing the simultaneous regulation of both Na and K excretion.

A review of nutritional factors in hypertension management

Hypertension is a major health problem worldwide. Its attendant morbidity and mortality complications have a great impact on patient's quality of life and survival. Optimizing blood pressure control has been shown to improve overall health outcomes. In addition to pharmacological therapies, nonpharmacological approach such as dietary modification plays an important role in controlling blood pressure. Many dietary components such as sodium, potassium, calcium, and magnesium have been studied substantially in the past decades. While some of these nutrients have clear evidence for their recommendation, some remain controversial and are still of ongoing study. Dietary modification is often discussed with patients and can provide a great benefit in blood pressure regulation. As such, reviewing the current evidence will be very useful in guiding patients and their physician and/or dietician in decision making. In this review article of nutritional factors in hypertension management, we aim to examine the role of nutritional factors individually and as components of whole dietary patterns.

[Renal physiology]

The kidneys are responsible for the urinary excretion of uremic toxins and the regulation of several body systems such as intra and extracellular volume status, acid-base status, calcium and phosphate metabolism or erythropoiesis. They adapt quantitative and qualitative composition of the urine to keep these systems in balance. The flow of plasma is filtered in the range of 120 mL/min, and depends on the systemic and renal hemodynamics which is subject to self-regulation. The original urine will then be modified in successive segments of the nephron. The proximal nephron is to lead the massive reabsorption of water and essential elements such as sodium, bicarbonates, amino-acids and glucose. The distal nephron includes the distal convoluted tubule, the connector tube and the collecting duct. Its role is to adapt the quality composition of urine to the needs of the body.

Insulin-like growth factor I administration induces fluid and sodium retention in healthy adults: possible involvement of renin and atrial natriuretic factor

OBJECTIVE

Growth hormone induces fluid and sodium retention. The underlying mechanism is, however, incompletely understood. A possible mediator could be IGF-I. To investigate the impact of IGF-I administration on body fluid distribution and sodium homeostasis in healthy subjects, we examined normal subjects during six days IGF-I treatment and during a six-day control period.

DESIGN AND MEASUREMENTS

Eight normal male subjects aged 23-30 years were randomised to receive IGF-I 50 microg/kg subcutaneously thrice daily during a six day study period, and to a six day control period. After each study period, extracellular volume and plasma volume (ECV, PV) were determined using 82Br and 125I-albumin. Blood samples, urinary sodium excretion, and bioimpedance were measured every second day of each study period.

RESULTS

Serum IGF-I (microg/l) increased during active treatment (control, 293 +/- 9; IGF-I, 628 +/- 42; P < 0.01). ECV (l) was expanded by IGF-I (control, 18.42 +/- 0.28; IGF-I, 19.72 +/- 0.50; P < 0.05) whereas PV (l) remained unaffected (control, 3.76 +/- 0.11; IGF-I, 3.80 +/- 0.16; n.s.). Likewise, bioimpedance and body weight were unchanged by IGF-I. Plasma renin (mU/l) increased but not significantly during IGF-I (control, 28.7 +/- 2.7; IGF-I, 39.9 +/- 4.3; P = 0.08), and plasma aldosterone was unaffected by IGF-I. N-Terminal proANF (pmol/l) was suppressed during IGF-I administration (control, 422 +/- 32; IGF-I, 330 +/- 20; P < 0.05). Diurnal sodium excretion (mmol) was reduced during IGF-I administration (control, 151 +/- 8; IGF-I, 124 +/- 7; P < 0.05).

CONCLUSION

IGF-I treatment causes fluid and sodium retention. This may be mediated by increased renin release and suppression of atrial natriuretic factor. The present data suggest that the fluid and sodium retaining effect of GH is at least partly mediated through IGF-I.

Mechanisms of tubular sodium chloride transport

Extracellular fluid volume is determined by sodium and its accompanying anions. There are control mechanisms which regulate sodium balance in the body. These include high and low pressure baroreceptors, intrarenal baroreceptors, renal autoregulation, tubuloglomerular feedback, aldosterone, and numerous other physical and hormonal factors. Sodium transport by the nephron involves active and passive processes which occur in several different nephron segments. Mechanisms of cotransport, Na(+)-H+ exchange, antiporters and ion-specific channels are all utilized by the nephron to maintain sodium balance. These regulatory factors and transport mechanisms for sodium in the kidney will he discussed in detail.

Sodium and water homeostasis

Disorders of sodium and water homeostasis are common occurrences in pediatric practice. They reflect distinct problems in the regulation of total body sodium balance and water distribution, respectively. Each of these groups of disorders has separate afferent and efferent mechanisms that are activated during disease states. Optimal therapy of children with fluid and electrolyte problems requires accurate delineation of the ECF volume and water distribution disturbance and the design of therapeutic regimens that account for each component of the clinical condition.

Renal regulation of salt balance: a primer for non-purists

The greater than 40-fold range of voluntary salt intake in humans requires corresponding adjustments in renal excretion to maintain balance. Although many mechanisms have been implicated in the regulation of salt output by the kidney, surprisingly little consideration has been given to their quantitative significance and possible interaction. This survey summarizes the effects of changes in glomerular filtration rate, proximal peritubular physical factors, and plasma concentrations of aldosterone and atrial natriuretic factor (ANF), singly and in combination, on the level of salt excretion. Contrary to expectation, even large increases in filtration or decreases in proximal reabsorption have only minor natriuretic effects, due to constancy of fractional reabsorption in downstream nephron segments. Lack of aldosterone release increases salt excretion as much or more than the upstream mechanisms, whereas ANF-induced inhibition of reabsorption in the medullary collecting duct has the largest effect. It may be concluded, therefore, that the potency of these natriuretic factors increases with distance along the nephron, even though each is operating on a progressively small tubular load. However, none of the mechanisms, in isolation, is sufficient to explain salt balance over the range of voluntary intake. Combination of factors demonstrates synergism rather than simple additivity, resulting in more than enough reserve capacity for salt excretion.

Renal hemodynamic response to intrarenal infusion of calcitonin gene-related peptide in dogs

The renal hemodynamic and excretory effects of intrarenal infusions of synthetic beta-human calcitonin gene-related peptide (beta-hCGRP) were examined in normal sodium replete dogs (Group 1, n = 6), in sodium replete dogs pretreated with indomethacin (Group 2, n = 6), and in sodium deplete dogs (Group 3, n = 5). In all groups of anesthetized dogs beta-hCGRP was infused at 5 and 10 ng.kg-1.min-1 for 50 min periods each. In the sodium replete group, beta-hCGRP infusions strikingly increased renal blood flow, but this response was markedly attenuated in the other 2 groups. During beta-hCGRP infusions, the clearance of creatinine also increased significantly in the sodium replete and deplete groups, but not in the indomethacin pretreated animals. No consistent changes in urinary sodium excretion or plasma renin activity were observed with beta-hCGRP infusions in any of the 3 groups of dogs. These results indicate that beta-hCGRP is a potent renal vasodilator and can increase renal blood flow and glomerular filtration. The data also suggest that the renal hemodynamic actions of beta-hCGRP are partially mediated by renal prostaglandins, and that the vasodilatory effects of beta-hCGRP may be antagonized by high circulating levels of endogenous angiotensin II in sodium-volume depletion. Finally, beta-hCGRP does not appear to have significant actions on urinary sodium excretion or plasma renin activity under the experimental conditions of the present study.

Atrial natriuretic peptide in volume expansion-induced natriuresis in man

The role of atrial natriuretic peptide (ANP) in the extracellular volume expansion (ECVE) induced natriuresis was examined in normal man under basal conditions and following dopamine blockage. Hypotonic ECVE was induced by drinking of 20 ml/kg tap water and subsequent intravenous infusion of 2 1 0, 9% saline over a period of 4 hours. This maneuver caused an increase in the plasma concentrations of ANP from 25.8 +/- 3.4 (means +/- SEM) to 59.7 +/- 6.7 fmol/ml. There was a dissociation between ANP response and urinary sodium excretion. A transient rise in glomerular filtration rate (GFR), plasma dopamine and a continuous decrease in plasma renin activity, aldosterone, vasopressin, and noradrenaline were observed. The natriuretic response to ECVE was blunted during dopamine blockade by metoclopramide, but plasma ANP, renin activity, catecholamine and vasopressin levels were not affected. However, plasma aldosterone rose. Our data are compatible with the concept that intrarenal dopamine and raised plasma concentration of ANP contribute to the natriuretic response to ECVE, but these hormonal changes do not completely explain the underlying mechanisms.

Site of the action of a synthetic atrial natriuretic peptide evaluated in humans

The renal site of the natriuretic effect of human, atrial natriuretic peptide (hANP) was studied using clearance techniques in eight salt-loaded normal volunteers undergoing maximal water diuresis. Lithium was used as a marker of proximal sodium reabsorption. According to a two-way, single blind, crossover design, hANP (Met12-(3-28)-eicosahexapeptide, (2 micrograms/min) or its vehicle (Ve) were infused for two hours, followed by a two-hour recovery period. Blood pressure, heart rate and insulin clearance remained unchanged. During hANP infusion, the filtration fraction increased slightly from 19.6 to 24.3% (P less than 0.001), fractional water excretion rose transiently at the beginning of the infusion. Fractional excretion of sodium increased markedly from 2.2% to 7.4% (P less than 0.001) but remained unchanged with Ve. ANP increased fractional excretion of lithium slightly from 46 to 58% (P less than 0.01), while it remained stable at 47% during Ve. The distal tubular rejection fraction of sodium calculated from sodium and lithium clearances rose markedly from 4.7 to 13% (P less than 0.001) and returned to 6.2% at the end of the recovery period. Thus, under salt loading and water diuresis conditions, hANP infusion did not alter GFR, but reduced proximal reabsorption of sodium, and markedly enhanced the fraction of sodium escaping distal tubular reabsorption, suggesting that hANP-induced natriuresis is due, for an important part, to inhibition of sodium reabsorption in the distal nephron.

The dopamine receptor antagonist haloperidol blocks natriuretic but not hypotensive effects of the atrial natriuretic factor

Studies were performed on anesthetized male Münich-Wistar rats to investigate the influence of the dopamine (DA) receptor antagonist haloperidol on the natriuretic response to infusion of a synthetic atrial natriuretic factor. The whole kidney glomerular filtration rate (GFR), urinary excretion of electrolytes, and arterial blood pressure (BP) were therefore measured in groups of animals pretreated with haloperidol or vehicle and given a continuous intravenous infusion of atrial natriuretic peptide (ANP; 28 amino acids). Forty-five minutes of ANP infusion at 10 micrograms h-1 kg-1 body wt did not increase GFR (change from 1.14 +/- 0.08 to 1.15 +/- 0.05 ml min-1 g-1 kidney wt). Sodium excretion (UNaV) increased more than four-fold from 0.037 +/- 0.008 to 0.165 +/- 0.070 mumol min-1 g-1 kidney wt (P less than 0.01). Potassium excretion (UKV) increased by 86% (P less than 0.001) and the urine flow rate (V) increased transiently by 63% (P less than 0.05) and did not differ from the control value during the last 15 min of ANP infusion. The urinary sodium concentration (UNa) increased almost three-fold, while BP decreased by 14%. There was no change in urine osmolality. In animals pretreated with haloperidol (1 mg kg-1 body wt), 45 min of ANP infusion did not significantly alter GFR (from 1.10 +/- 0.08 to 0.98 +/- 0.09 ml min-1 g-1 kidney wt). The UNaV did not increase significantly (change from 0.026 +/- 0.006 to 0.030 +/- 0.009 mumol min-1 g-1 kidney wt). The UKV was not elevated by ANP infusion.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparison of the natriuresis and chloruresis associated with glomerular hyperfiltration induced by atrial natriuretic factor or glucagon

The impact on renal sodium chloride reabsorption of an acute increase in glomerular filtration rate (GFR) induced by atrial natriuretic factor (ANF) or glucagon was examined in the conscious rat. These hormones have no direct effect on proximal solute transport and have opposite effects on distal transport. ANF and glucagon increased GFR to a comparable extent (2.0 +/- 0.2 to 3.5 +/- 0.4 ml/min, p less than 0.01, and 1.9 +/- 0.1 to 3.3 +/- 0.1 ml/min, p less than 0.001, respectively). While most (95-97%) of the increment in filtered sodium chloride was reabsorbed, a small portion (3-5%) escaped tubular reabsorption. Absolute sodium and chloride urinary excretion rates increased similarly in response to each hormone, by two- to three-fold. Slightly imperfect load-dependent sodium chloride reabsorptive response by the nephron, despite opposite direct effects on distal nephron transport, may account for the observed natriuresis and chloruresis associated with the acute glomerular hyperfiltration induced by ANF or glucagon administration.

Interaction of nonsteroidal anti-inflammatory drugs with antihypertensive and diuretic agents. Control of vascular reactivity by endogenous prostanoids

Indomethacin and some other nonsteroidal anti-inflammatory drugs partially antagonize the blood pressure lowering effect of drugs used to treat hypertension. They can also produce a mild elevation of blood pressure in normotensive individuals. The elevated arterial pressure caused by these agents is associated with increases in the vascular resistance of mainly the renal and splanchnic beds. This may be due to direct inhibition of the synthesis of vasodilator prostanoids, or it may be due to indirect potentiation of the action of the sympathetic nervous system or of angiotensin II. Nonsteroidal anti-inflammatory drugs also cause renal retention of sodium and this probably contributes to their hypertensive effects. In humans, the sodium retention may involve increased reabsorption in the proximal tubule. Although a direct tubular action is possible, these drugs may change proximal sodium reabsorption by their vascular effects. However, the exact mechanism is not understood. These interactions are clinically significant and may complicate the treatment of common diseases.

Atrial natriuretic factor--a new hormone affecting kidney function

A family of biologically active peptides (atrial natriuretic factor - ANF) has recently been identified in mammalian heart atria. The peptides derive from a common 152 amino acid precursor and at least 1% of total messenger RNA activity is specific for the factor. When injected intravenously ANF is hypotensive and natriuretic. Data indicate that atrial natriuretic factor represents a newly discovered hormone involved in the regulation of blood pressure and volume. Cellular release of ANF does not require the activation of the adenylate cyclase system, but is associated with receptor-mediated activation of the cellular polyphosphoinositide mechanism. The natriuretic effect includes increased glomerular filtration rate and specific inhibition of normal sodium reabsorption from the medullary collecting duct. The mechanism of this transport inhibition is not yet known.

Metabolic control of renal vascular resistance and glomerulotubular balance

Renal vascular resistance (RVR) and glomerulotubular balance were examined in isolated rat kidneys perfused at 100 mm Hg with 10 mM lactate (L) or 10 mM pyruvate (P) or 5 mM glucose (G) either alone or with a mixture of 20 amino acids (13.5 mM, AA); albumin oncotic pressure 24 +/- 1 mm Hg. RVR was L greater than P greater than G = AA. Vasodilation by G and AA was additive. Proximal tubular sodium-cotransport was evaluated from fractional reabsorption (FR) of phosphate (Pi), G, and L. FR Pi was 91% in AA, 86% in P, 72% in L, and 67% in G. Combining AA or P with L or G increased FR Pi to 89 to 90%. FRs of G and L by G and L perfused kidneys were 83 and 78%, respectively, and were increased to 97 to 99% by combining G or L with AA or P. P and AA also increased FR sodium and FR water when combined with L or G or when combined with each other. GFR correlated positively with FR sodium and FR water. AA combined synergistically with L to increase gluconeogenesis. These results indicate that, compared with pyruvate or AA, neither glucose nor lactate alone is a good energy source for proximal tubular reabsorption, that synergistic interactions between AA or pyruvate and lactate or glucose augment GFR by increasing proximal tubular reabsorption, and that the vasodilating effects of glucose and AA are not related directly to their effects on GFR.

Short-term protein loading in assessment of patients with renal disease

The effect of short-term protein loading on the glomerular filtration rate in normal persons and patients with renal disease was evaluated. Previous studies have demonstrated that in healthy subjects, protein loading results in an increased glomerular filtration rate. By determining the glomerular filtration rate preceding (baseline glomerular filtration rate) and following (test glomerular filtration rate) oral protein loading, it was possible to define (1) the filtration capacity (test glomerular filtration rate) and (2) the renal reserve (test glomerular filtration rate - baseline glomerular filtration rate) of the kidney. In normal persons, filtration capacity averaged 157 +/- 13 ml per minute and renal reserve 34 ml per minute. The test glomerular filtration rate was reproducible and independent of protein intake, whereas baseline glomerular filtration rate was significantly influenced by diet. Patients with renal disease were found to have a reduced renal reserve and/or a diminished filtration capacity. The reduction in filtration capacity appears to correlate with the damage sustained by the organ. It is suggested that an abnormal response to protein loading in renal disease may herald the fall in the baseline glomerular filtration rate and the rise in plasma creatinine level.

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.

Renal functional reserve in humans. Effect of protein intake on glomerular filtration rate

This study was designed to investigate the effect of protein intake on glomerular filtration rate, and to demonstrate and evaluate the functional reserve of the kidney. Normal subjects ingesting a protein diet had a significantly higher creatinine clearance than a comparable group of normal subjects ingesting a vegetarian diet. A progressive increment in protein intake in normal volunteers resulted in a significant increase in creatinine clearance. Diurnal variations in creatinine clearance were found. These daily variations correlated well with the periods of food intake. The capacity of the kidney to increase its level of function with protein intake suggests a renal function reserve. In short-term studies, the effect of a protein load on glomerular filtration rate was evaluated. Normal subjects showed an increase in glomerular filtration rate two and a half hours after protein load to a maximal glomerular filtration rate of 171.0 +/- 7.7 ml per minute. In patients with a reduced number of nephrons, renal functional reserve may be diminished or absent.

Glucocorticoid accelerates renal functional maturation in fetal lambs

Renal function was measured in seven premature lambs delivered spontaneously after a fetal injection of betamethasone, four near term lambs delivered via cesarean section after a fetal injection of a placebo and in ten spontaneously delivered full term lambs. Glomerular filtration rates were significantly higher in the premature betamethasone treated than in the near term placebo treated and the full term lambs. Fractional sodium excretions were significantly lower in the betamethasone treated preterm than the placebo treated near term lambs. This suggests that glucocorticoid accelerates renal glomerular and possibly tubular maturation. As in the lung, fetal administration of glucocorticoid stimulates functional maturation of the kidney.

Body fluid homeostasis in man. A contemporary overview

In the steady state, urinary excretion of sodium is closely matched to dietary salt intake. Given rigorous defense of extracellular fluid osmolality, it is the quantity of sodium in the extracellular fluid that determines the volume of this compartment. Changes in extracellular fluid volume are detected by volume sensors located in the intrathoracic vascular bed, kidney and other organs. These mechanoreceptors gauge the adequacy of intravascular volume, relative to capacitance, at various sites within the circulation. The perception of a change in the normal relationship between intravascular volume and circulatory capacity evokes a host of renal effector mechanisms that lead ultimately to physiologically appropriate changes in urinary sodium excretion. These effector mechanisms involve physical adjustments in the glomerular filtration rate, renal microvascular hemodynamics and peritubular capillary Starling forces, tubule fluid composition, flow rate and transtubular ion gradients. Neural and humoral pathways are also involved and, among the latter, angiotensin II, aldosterone, prostaglandins and kinins have been studied extensively. The continuous interaction between these sensor and effector mechanisms serves to ensure near-constancy of the extracellular fluid volume, a condition essential for optimal circulatory performance.

Renal hemodynamics and volume homeostasis during pregnancy in the rat

We believe that in pregnant rats, GFR is elevated at term, whereas renal plasma flow appears not to be increased. The mechanism for this increment is unclear, as is the specific time during gestation when renal hemodynamics increase. Rats increase their salt appetite and significantly positive sodium balance occurs, which is most pronounced during the last week of gestation. The retained sodium is distributed in part to the products of conception and in part to the mother, particularly in increasing her extracellular fluid volume. Although chronic volume expansion is present, absolute tubular sodium reabsorption remains elevated. The mechanism for this elevated tubular reabsorption appears no to be related to aldosterone because reduction or inhibition of this mineralocorticoid does not affect sodium balance significantly.

Control of renal function in isovolemic hemodilution or in vagotomized, infused rats

In male Sprague-Dawley rats cardiac output (CO) was increased 0.16 ml/min x g body weight and inulin clearance was increased 2.2 ml/min x g kidney weight either by isovolemic hemodilution with 6% albumin solution or by isohemic expansion to 133% of control blood volume. Despite similar changes in CO and glomerular filtration (GFR), hemodilution caused a much smaller rise in renal excretion at a much later time than did volume expansion. Therefore, in addition to simultaneous changes in CO and GFR and afferent factor indicating a state of expanded extracellular fluid volume was required for normal diuresis and natriuresis. This might have been mean central venous pressure (CVP). In further experiments, volume expansion in vagotomized or non-vagotomized rats led to nearly identical changes in water-, sodium- and potassium excretion in both groups. The only other measured parameter that showed identical behaviour in the two groups was CVP. It was concluded that CVP is an important contributor to body fluid control mechanisms even after vagotomy.

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.

Renal action of cholera toxin: I. Effects on urinary excretion of electrolytes and cyclic AMP

The infusion of cholera toxin (CT), 4 mug/min, into one renal artery of normal and thyroparathyroidectomized (T-PTX) dogs produced ipsilateral increments in the excretion of Na, K, Ca, Mg and Cl. Phosphate excretion increased from both kidneys, but more from the infused kidney in intact dogs. Unilateral phosphaturia occurred in T-PTX dogs studied five or more days after T-PTX. The changes in electrolyte excretion appeared 40 to 80 min after initiation of CT infusion and the maximal effects were noted after 100 to 140 min. The effects of CT on electrolyte excretion could not be accounted for by changes in glomerular filtration rate or renal plasma flow. Urinary cyclic adenosine monophosphate (AMP) increased from both kidneys but slightly more from the infused kidney. Adenylate cyclase activity of cortex and outer medulla of the infused kidney was 109 to 142% higher than that of the control kidney. The results indicate that CT decreases the net transport of various electrolytes by the renal tubule. This effect is probably mediated by the activation of renal adenylate cyclase(s) sensitive to the enterotoxin.