The relationship between peritubular capillary protein concentration and fluid reabsorption by the renal proximal tubule

Open microfluidic coculture reveals paracrine signaling from human kidney epithelial cells promotes kidney specificity of endothelial cells

Endothelial cells (ECs) from different human organs possess organ-specific characteristics that support specific tissue regeneration and organ development. EC specificity is identified by both intrinsic and extrinsic cues, among which the parenchyma and organ-specific microenvironment are critical contributors. These extrinsic cues are, however, largely lost during ex vivo cultures. Outstanding challenges remain to understand and reestablish EC organ specificity for in vitro studies to recapitulate human organ-specific physiology. Here, we designed an open microfluidic platform to study the role of human kidney tubular epithelial cells in supporting EC specificity. The platform consists of two independent cell culture regions segregated with a half wall; culture media are added to connect the two culture regions at a desired time point, and signaling molecules can travel across the half wall (paracrine signaling). Specifically, we report that in the microscale coculture device, primary human kidney proximal tubule epithelial cells (HPTECs) rescued primary human kidney peritubular microvascular EC (HKMEC) monolayer integrity and fenestra formation and that HPTECs upregulated key HKMEC kidney-specific genes (hepatocyte nuclear factor 1 homeobox B, adherens junctions-associated protein 1, and potassium voltage-gated channel subfamily J member 16) and endothelial activation genes (vascular cell adhesion molecule-1, matrix metalloproteinase-7, and matrix metalloproteinase-10) in coculture. Coculturing with HPTECs also promoted kidney-specific genotype expression in human umbilical vein ECs and human pluripotent stem cell-derived ECs. Compared with culture in HPTEC conditioned media, coculture of ECs with HPTECs showed increased upregulation of kidney-specific genes, suggesting potential bidirectional paracrine signaling. Importantly, our device is compatible with standard pipettes, incubators, and imaging readouts and could also be easily adapted to study cell signaling between other rare or sensitive cells.

A Novel Three-Dimensional Human Peritubular Microvascular System

Human kidney peritubular capillaries are particularly susceptible to injury, resulting in dysregulated angiogenesis, capillary rarefaction and regression, and progressive loss of kidney function. However, little is known about the structure and function of human kidney microvasculature. Here, we isolated, purified, and characterized human kidney peritubular microvascular endothelial cells (HKMECs) and reconstituted a three-dimensional human kidney microvasculature in a flow-directed microphysiologic system. By combining epithelial cell depletion and cell culture in media with high concentrations of vascular endothelial growth factor, we obtained HKMECs of high purity in large quantity. Unlike other endothelial cells, isolated HKMECs depended on high vascular endothelial growth factor concentration for survival and growth and exhibited high tubulogenic but low angiogenic potential. Furthermore, HKMECs had a different transcriptional profile. Under flow, HKMECs formed a thin fenestrated endothelium with a functional permeability barrier. In conclusion, this three-dimensional HKMEC-specific microphysiologic system recapitulates human kidney microvascular structure and function and shows phenotypic characteristics different from those of other microvascular endothelial cells.

Phlda3, a urine-detectable protein, causes p53 accumulation in renal tubular cells injured by cisplatin

Measurable indicators of renal injury are required for the assessment of kidney function after toxicant challenge. In our previous study, pleckstrin homology-like domain, family A, member 3 (Phlda3) was a most greatly up-regulated molecule downstream from p53, culminating with kidney tubular injury. This study investigated the positive feedforward effect of Phlda3 on p53 in an effort to explain the largest increase of Phlda3 in injured tubules and the potential of its urine excretion. qRT-PCR assays confirmed a rapid and substantial increase in Phlda3 messenger RNA (mRNA) in the kidney cortex of mice treated with a single dose of cisplatin. Cisplatin overexpression of Phlda3 was verified by gene set analyses of three different microarray databases. In the immunohistochemistry, Phlda3 staining intensities were augmented in the tubules as kidney injury worsened. Moreover, the urinary content of Phlda3 was increased after cisplatin treatment, as were those of other kidney injury markers (Kim-1 and Timp-1). By contrast, cisplatin failed to increase Phlda3 mRNA in the liver despite hepatocyte necrosis and ensuing increases in serum transaminase activities. In NRK52E tubular cells, siRNA knockdown of Phlda3 enhanced the ability of cisplatin to increase p-Mdm2 presumably via Akt, enforcing the interaction between Mdm2 and p53. Consistently, a deficiency in Phlda3 abrogated p53 increase by cisplatin, indicating that Phlda3 promotes p53 accumulation. Phlda3 overexpression had the opposite effect. In addition, treatment with cyclosporine A or CdCl2, other nephrotoxicants, increased Phlda3 mRNA and protein levels in NRK52E cells, as did cisplatin treatment. Overall, Phlda3 may cause p53 accumulation through a feedforward pathway, facilitating tubular injury and its urine excretion.

Micropuncture of the kidney: a primer on techniques

Techniques to evaluate renal function at the single nephron level have been instrumental and indispensible in furthering our understanding of the mammalian kidney. Techniques that were first introduce in the 1920s, and later refined in the 1950s and 1960s, permit sophisticated interrogation of glomerular filtration and hemodynamics, and tubular epithelial transport activity. Much of what we know about the physiology and pathophysiology of the kidney has been produced or, to some degree, confirmed by renal micropuncture. While micropuncture is perhaps not as widely employed as before, it remains an essential tool for comprehensive evaluation of kidney function, particularly in this age of genetically pliable experimental models. This review aims to provide a introduction to common methodologies and approaches used to conduct micropuncture experiments. Topics covered include instrumentation and equipment, pipet fabrication techniques, animal preparation, and experimental procedures for evaluating single nephron hemodynamics and tubular function.

Marinobufagenin, resibufogenin and preeclampsia

The bufodienolides are cardiac glycosides which have the ability to inhibit the enzyme, Na(+)/K(+) ATPase (sodium potassium adenosine triphosphatase). They are cardiac inotropes, cause vasoconstriction (and, potentially, hypertension) and are natriuretic. Evidence has accrued over time which supports the view that they are mechanistically involved in volume expansion-mediated hypertension. In this communication, the authors summarize data which support the view that the bufodienolides and, in particular, marinobufagenin (MBG) are involved in the pathogenesis of preeclampsia. In a rat model of the syndrome, MBG causes hypertension, proteinuria, intrauterine growth restriction and increased weight gain. All of these phenotypic characteristics are prevented by an antagonist to MBG, resibufogenin (RBG). The "preeclamptic" animals also develop a vascular leak syndrome, resulting in hemoconcentration. Abnormalities in the MAPK (mitogen-activated protein kinase) system play a role in the mechanism by which MBG produces the abnormalities in the pregnant rat. Studies to discover the relevance of these findings to human preeclampsia are currently underway in several laboratories and clinics.

Sources of Urinary Proteins and their Analysis by Urinary Proteomics for the Detection of Biomarkers of Disease

Renal disorders account for a substantial fraction of the budget for health care in many countries. Proteinuria is a frequent manifestation in afflicted patients, but the origin of the proteins varies based on the nature of the disorder. The emerging field of urinary proteomics has the potential to replace kidney biopsy as the diagnostic procedure of choice for patients with some glomerular forms of renal disease. To fully realize this potential, it is vital to understand the basis for the urinary excretion of protein in physiological and pathological conditions. In this review, we discuss the structure of the nephron, the functional unit of the kidney, and the process by which proteins/peptides enter the urine. We discuss several aspects of proteinuria that impact the proteomic analysis of urine of patients with renal diseases.

Modeling proximal tubule cell homeostasis: tracking changes in luminal flow

During normal kidney function, there are routinely wide swings in proximal tubule fluid flow and proportional changes in Na(+) reabsorption across tubule epithelial cells. This "glomerulotubular balance" occurs in the absence of any substantial change in cell volume, and is thus a challenge to coordinate luminal membrane solute entry with peritubular membrane solute exit. In this work, linear optimal control theory is applied to generate a configuration of regulated transporters that could achieve this result. A previously developed model of rat proximal tubule epithelium is linearized about a physiologic reference condition; the approximate linear system is recast as a dynamical system; and a Riccati equation is solved to yield the optimal linear feedback that stabilizes Na(+) flux, cell volume, and cell pH. The first observation is that optimal feedback control is largely consigned to three physiologic variables, cell volume, cell electrical potential, and lateral intercellular hydrostatic pressure. Parameter modulation by cell volume stabilizes cell volume; parameter modulation by electrical potential or interspace pressure act to stabilize Na(+) flux and cell pH. This feedback control is utilized in a tracking problem, in which reabsorptive Na(+) flux varies over a factor of two, in order to represent a substantial excursion of glomerulotubular balance. The resulting control parameters consist of two terms, an autonomous term and a feedback term, and both terms include transporters on both luminal and peritubular cell membranes. Overall, the increase in Na(+) flux is achieved with upregulation of luminal Na(+)/H(+) exchange and Na(+)-glucose cotransport, with increased peritubular Na(+)-3HCO(3)(-) and K(+)-Cl(-) cotransport, and with increased Na(+), K(+)-ATPase activity. The configuration of activated transporters emerges as a testable hypothesis of the molecular basis for glomerulotubular balance. It is suggested that the autonomous control component at each cell membrane could represent the cytoskeletal effects of luminal flow.

Micropuncturing the nephron

To achieve the role of the kidney in maintaining body homeostasis, the renal vasculature, the glomeruli, and the various segments of the nephron and the collecting duct system have to fulfill very diverse and specific functions. These functions are dependent on a complex renal architecture and are regulated by systemic hemodynamics, hormones, and nerves. As a consequence, to better understand the physiology of the kidney, methods are necessary that allow insights on the function of these diverse structures in the physiological context of the intact kidney. The renal micropuncture technique allows direct access to study superficial nephrons in vivo. In this review, the application of micropuncture techniques on the single nephron level is outlined as an approach to better understand aspects of glomerular filtration, tubular transport, and tubulo-glomerular communication. Studies from the author's lab, including experiments in gene-targeted mice, are briefly presented to illustrate some of the approaches and show how they can further advance our understanding of the molecular mechanisms involved in the regulation of kidney function.

Role of Cyclooxygenase-2-Derived Metabolites and NO in Renal Response to Bradykinin

-It has been reported that bradykinin (BK) can induce or activate both cyclooxygenase (COX) isoforms and that the renal effects of BK seem to be mediated by prostaglandins and NO. The first objective of this study was to evaluate the relative contribution of both COX isoforms in mediating the renal response to BK in anesthetized dogs. The second objective was to examine whether COX-2 inhibition potentiates the renal effects induced by NO reduction during BK administration. Intrarenal BK infusion (8 ng. kg(-1). min(-1), n=6) elicited a significant increment in renal blood flow, sodium excretion, urine volume, and the fractional excretion of lithium. COX-2 inhibition (nimesulide, 5 µg. kg(-1). min(-1), n=6) reduced the renal vasodilatation but did not significantly modify the natriuresis or diuresis secondary to BK. Administration of a nonspecific isozyme COX inhibitor (meclofenamate, 5 µg. kg(-1). min(-1); n=6) did not induce greater effects than those produced by nimesulide. NO synthesis reduction (N:(G)-nitro-L-arginine methyl ester [L-NAME], 3 µg. kg(-1). min(-1)) prevented the renal vasodilatation and the increment in the fractional excretion of lithium induced by BK but did not affect the natriuretic or diuretic response. Simultaneous nimesulide infusion did not modify the renal effects of L-NAME during BK infusion (n=6). Finally, inhibition of both COX isoforms with meclofenamate, in dogs treated with L-NAME (n=6), completely prevented the vasodilator and excretory actions of BK. The results of this study suggest that (1) NO and prostanoids dependent on COX-2 seem to be involved in the renal vasodilatation induced by BK, and (2) there is an interaction between NO and COX-1-derived metabolites in mediating the natriuretic and diuretic response to BK.

A hydrodynamic mechanosensory hypothesis for brush border microvilli

In the proximal tubule of the kidney, Na(+) and HCO(3)(-) reabsorption vary proportionally with changes in axial flow rate. This feature is a critical component of glomerulotubular balance, but the basic mechanism by which the tubule epithelial cells sense axial flow remains unexplained. We propose that the microvilli, which constitute the brush border, are physically suitable to act as a mechanosensor of fluid flow. To examine this hypothesis quantitatively, we have developed an elastohydrodynamic model to predict the forces and torques along each microvillus and its resulting elastic bending deformation. This model indicates that: 1) the spacing of the microvilli is so dense that there is virtually no axial velocity within the brush border and that drag forces on the microvilli are at least 200 times greater than the shear force on the cell's apical membrane at the base of the microvilli; 2) of the total drag on a 2.5-microm microvillus, 74% appears within 0.2 microm from the tip; and 3) assuming that the structural strength of the microvillus derives from its axial actin filaments, then a luminal fluid flow of 30 nl/min produces a deflection of the microvillus tip which varies from about 1 to 5% of its 90-nm diameter, depending on the microvilli length. The microvilli thus appear as a set of stiff bristles, in a configuration in which changes in drag will produce maximal torque.

A genetic model defines the importance of the atrial natriuretic peptide receptor (guanylyl cyclase-A) in the regulation of kidney function

Disruption of the atrial natriuretic peptide (ANP) receptor [guanylyl cyclase-A (GC-A)] gene yields mice with a salt-resistant form of hypertension, raising fundamental questions on the role of ANP in acute regulation of the kidney. Here, we show that water intake, food consumption, stool weight, urine volume, and sodium excretion are not significantly different between wild-type and GC-A null mice on standard rodent chow (0.7% NaCl) or a high-salt diet (8% NaCl). In conscious mice with an indwelling catheter, the infusion of a physiological saline solution containing 4% BSA resulted in a marked natriuresis/diuresis in wild-type mice but no response in GC-A null animals. When physiological saline was given by gavage, however, the kidney response of wild-type and null mice was equivalent, raising the possibility that the gastrointestinal tract can directly regulate kidney function. However, administration of 0.9% saline through an intraperitoneal route also resulted in equal kidney responses in wild-type and null mice. When 0.9% NaCl lacking protein was infused i.v., wild-type and null mice both responded at the kidney level. Thus, GC-A appears dispensable for regulation of sodium/water excretion in response to changes in dietary sodium concentration, but likely becomes critical in volume expansions where the isooncotic pressure remains constant, such as head-out immersion or the initial and correctable stages of congestive heart failure.

Renal haemodynamic and excretory responses to bradykinin in anaesthetized dogs

1. Effects of bradykinin (BK) on renal haemodynamics and urine formation were examined in anaesthetized dogs. 2. Renal arterial infusion of BK at doses of 5 or 50 ng/kg per min produced dose-dependent increases in renal blood flow (RBF), without affecting systemic arterial pressure or glomerular filtration rate. There were also significant and dose-dependent increases in urine flow (UF), urinary excretion of sodium (UNaV) and fractional excretion of sodium (FENa) and decreases in urine osmolality during BK infusion. 3. Renal haemodynamic and excretory responses to the BK infusion were completely abolished by the simultaneous administration of Hoe 140 (icatibant, 100 ng/kg per min intrarenally), a selective BK B2-receptor antagonist. 4. In the presence of NG-nitro-L-arginine (NOARG; 40 micrograms/kg per min intrarenally), a nitric oxide (NO) synthase inhibitor, BK-induced renal vasodilative and natriuretic effects were markedly attenuated, although responses of UF and urine osmolality to BK remained unchanged. The water diuretic effect of BK was abolished in dogs given both NOARG and ibuprofen (12.5 mg/kg bolus injection plus 12.5 mg/kg per h of sustained infusion intravenously), a cyclooxygenase inhibitor. 5. These results clearly indicate that renal haemodynamic and excretory responses to BK were mediated exclusively by the B2-receptor. Renal vasodilative and natriuretic responses are mainly linked to NO generation, while both NO and prostaglandin biosynthesis are involved in the BK-induced water diuresis.

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.

Alterations in glomerular dynamics in congenital, unilateral hydronephrosis

We have previously shown that rats with congenital, unilateral hydronephrosis exhibit a reduction in GFR that returns to normal when either the renin angiotensin system or thromboxane A2 (TxA2) is blocked. The current study defines the single nephron defect in congenital, unilateral hydronephrosis and evaluates the roles of angiotensin II (Ang II) and TxA2 in this renal derangement. Renal micropuncture experiments were performed on the right kidney of rats from an inbred colony with unilateral right-sided hydronephrosis (HYDRO), or non-affected litter mates (CONTROL). In addition, four separate groups of hydronephrotic animals were treated with either the TxA2 receptor antagonist SQ-29548 (SQ), one of two Ang II receptor antagonists [saralasin (SAR) or DuP-753 (DUP)]; or combined treatment with DuP-753 and SQ-29,548 (S&D). SNGFR was significantly reduced (P < 0.05) in HYDRO compared to CONTROL (17.6 +/- 2.0 vs. 35.9 +/- 3.7 nl/min, respectively). Treatment with SQ-29,548 normalized SNGFR (29.0 +/- 3.0 nl/min), while saralasin and DuP-753 resulted in only a partial recovery of function (25.6 +/- 1.6 and 27.8 +/- 1.4 nl/min, respectively). Combined SQ-29,548 and DuP-753 treatment resulted in full recovery of SNGFR to 32.9 +/- 4.4 nl/min. The glomerular ultrafiltration coefficient (Kf) was reduced (P < 0.05) approximately 45% in HYDRO compared to CONTROL (1.64 +/- .08 vs. 2.84 +/- .22 nl/min/mm Hg, respectively). Kf returned to control levels in SAR, DUP and SQ, and increased above control in S&D (5.58 +/- 1.6 nl/min/mm Hg). There were no differences (P > 0.05) in hydrostatic or oncotic pressures across the glomerular capillary between any of the groups studied. The observation that Kf increases above CONTROL with combined blockade of TxA2 and Ang II suggests that these regulatory hormones decrease Kf via independent mechanisms. These data indicate that the reduction in SNGFR in congenital, unilateral hydronephrosis is a result of a marked fall in Kf that is mediated by both Ang II and TxA2.

Glomerular filtration and tubular reabsorption of albumin in preproteinuric and proteinuric diabetic rats

Microalbuminuria (26-250 mg/d) is considered to be an indicator of incipient diabetic nephropathy in humans in insulin-dependent diabetes (IDD). However, before microalbuminuria is observed, glomerular alterations, such as glycosylation of the glomerular basement membrane and glomerular hyperfiltration, in IDD may result in increased filtration of albumin before any observed increase in albumin excretion. Glomerular and tubular albumin kinetics were examined in streptozotocin (65 mg/kg body wt, i.v.) diabetic, Munich-Wistar rats at 7-10 (untreated) and 50-70 d (poorly controlled with small doses of insulin) after the onset of diabetes and compared with nondiabetic controls. Additional rats in each condition received acute lysine treatment to prevent tubular protein reabsorption. Urinary albumin excretion and nonvascular albumin distribution volumes were measured in the renal cortex and compared with morphometric measurements of interstitial space and the proximal tubule to assess intracellular uptake of albumin in the proximal tubule. Urinary albumin excretion under anesthesia was not different in 7-10-d IDD versus controls (19 +/- 3 vs. 20 +/- 3 micrograms/min) but increased in the 50-70-d IDD (118 +/- 13 micrograms/min, P < 0.05). Lysine treatment resulted in increased albumin excretion compared with respective nontreatment in 7-10-d IDD (67 +/- 10 micrograms/min, P < 0.05) but not in controls (30 +/- 6 micrograms/min) or in 50-70-d IDD (126 +/- 11 micrograms/min). Glomerular filtration rate was increased both in 7-10-d IDD (2.7 +/- 0.1 ml/min, P < 0.05) and in 50-70-d IDD (2.6 +/- 0.1 ml/min, P < 0.05) compared with control (2.2 +/- 0.1 ml/min). Calculated urinary space albumin concentrations increased early in IDD with 2.5 +/- 0.4 mg% in 7-10-d IDD and 4.9 +/- 0.6 mg% in 50-70-d IDD compared with control (1.4 +/- 0.3 mg%). The increase in filtration of albumin is in excess of that attributable to hyperfiltration before increased albumin excretion early in diabetes. In 50-70-d IDD, absolute tubular reabsorption of albumin is decreased, correlating to the decrease in brush border height of the proximal tubule.

Glomerular hemodynamic alterations during acute hyperinsulinemia in normal and diabetic rats

Treatment of insulin dependent diabetes invariably requires exogenous insulin to control blood glucose. Insulin treatment, independent of other factors associated with insulin dependent diabetes, may induce changes that affect glomerular function. Due to exogenous delivery of insulin in insulin dependent diabetes entering systemic circulation prior to the portal vein, plasma levels of insulin are often in excess of that observed in non-diabetics. The specific effects of hyperinsulinemia on glomerular hemodynamics have not been previously examined. Micropuncture studies were performed in control (non-diabetic), untreated diabetic and insulin-treated diabetic rats 7 to 10 days after administration of 65 mg/kg body weight streptozotocin. After the first period micropuncture measurements were obtained, 5 U of regular insulin (Humulin-R) was infused i.v., and glucose clamped at euglycemic values (80 to 120 mg/dl). Blood glucose concentration in non-diabetic controls was 99 +/- 6 mg/dl. In control rats, insulin infusion and glucose clamp increased nephron filtration rate due to decreases in both afferent and efferent arteriolar resistance (afferent greater than efferent) resulting in increased plasma flow and increased glomerular hydrostatic pressure gradient. However, insulin infusion and glucose clamp produced the opposite effect in both untreated and insulin-treated diabetic rats with afferent arteriolar vasoconstriction resulting in decreases in plasma flow, glomerular hydrostatic pressure gradient and nephron filtration rate. Thromboxane A2 (TX) synthetase inhibition partially decreased the vasoconstrictive response due to acute insulin infusion in diabetic rats preventing the decrease in nephron filtration rate.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal nerve-mediated proximal tubule solute reabsorption contributes to hypertension in spontaneously hypertensive rats

Renal nerve activity increases (Na+, K+)-ATPase activity and contributes to the development of hypertension in young SHR. The present study was designed to examine the effect of sodium intake on blood pressure and proximal tubule solute reabsorption in sham-operated or renal denervated, 5-week old SHR and WKY. Three-week old SHR and WKY rats underwent sham surgery or renal denervation with 10% phenol and were maintained for 10 days on either a 0.6% or 2.2% NaCl diet. Blood pressure was obtained by indirect tail cuff measurements during this interval. Of the eight groups, only sham-operated SHR on a high sodium diet had hypertension, 122.0 +/- 4.2 mm Hg vs. 98.7 +/- 3.3 mm Hg (mean for remaining groups). Renal plasma flow (RPF), glomerular filtration rate (GFR), and the fractional excretion of lithium (FELi) were determined in rats maintained on a 2.2% sodium diet at 5 weeks of age. FELi was less in sham-operated SHR, 5.3 +/- 0.7%, compared to WKY, 9.4 +/- 2.8% (P less than 0.02). Furthermore, denervation ameliorated the reduced FELi in SHR, 10.2 +/- 1.2%, without affecting FELi in WKY. RPF and GFR were similar between sham-operated and renal denervated SHR and WKY. No significant difference could be detected in net sodium balance between WKY and SHR during this period. These findings demonstrate 1) from the basis of FELi, young SHR, of this strain, exhibit enhanced proximal tubule solute reabsorption and hypertension while on a high sodium diet and, 2) renal denervation ameliorates both the enhanced proximal tubule solute reabsorption and the early development of hypertension. These data support the concept that renal nerve activity of young SHR is augmented and contributes to the development of hypertension by enhancing salt retention.

Renal Effects of α-Adrenoceptor Blockade During Furosemide Diuresis in Conscious Rats

Clearance experiments were performed in conscious rats in order to investigate whether intravenous infusion of the non-selective alpha-adrenoceptor antagonist phentolamine could block compensatory sodium reabsorption during furosemide-induced volume contraction. By measuring inulin clearance, urinary excretion rates of sodium and water, and lithium clearance, the effects on proximal and distal nephron segments were dissociated. The renal effect of intravenous infusion of 0.3 mg/kg/hr phentolamine (n = 6) was compared with time control animals (n = 9). Furosemide was administered as constant intravenous infusion (7.5 mg/kg/hr) with simultaneous phentolamine infusion at four dose levels: 0 (n = 9), 0.3 (n = 6), 1.0 (n = 7) and 3.0 mg/kg/hr (n = 6). Phentolamine infusion reduced norepinephrine-induced increase in blood pressure at all three dose levels (n = 5). Phentolamine infusion induced transient antidiuresis and a prolonged antinatriuretic response. Compared with rats given furosemide only, phentolamine attenuated dose-dependently the diuretic and natriuretic peak response to furosemide. This effect was associated with dose-dependent reductions in mean arterial pressure. The reduced natriuretic response was due to a reduced fractional sodium excretion in the distal nephron segment (at all doses of phentolamine) and a reduction of the glomerular filtration rate (1.0 and 3.0 mg/kg/hr phentolamine). The fractional lithium excretion (FELi) increased to 65 +/- 3% at 0.3 mg/kg/hr phentolamine during the natriuretic peak response of furosemide, while it only increased to 52 +/- 3% during furosemide alone. At steady-state conditions (120-180 min. after start of furosemide infusion) after infusion with furosemide plus 0.3 mg/kg/hr phentolamine the animals were still volume-depleted, but the compensatory tubular Na reabsorption in the proximal tubules was inhibited (FELi = 48 +/- 2% versus 39 +/- 1% in rats given furosemide alone). During furosemide infusion plasma epinephrine increased 700% and plasma norepinephrine increased 50%. These results are compatible with increased systemic sympathetic nervous activity and a contributory role of proximal tubular alpha-adrenoceptors in mediating compensatory sodium reabsorption during acute furosemide-induced volume contraction.

Structural changes induced by osmotic water flow in rabbit proximal tubule

When a transepithelial osmotic difference was imposed in perfused proximal straight tubules (270 mOsm/kg H2O in the lumen and 290 in the bath) in the absence of bath colloid, a severe vacuolation (appearance of lucent spaces) developed within the epithelium such that view of the lumen border was obscured within 5 +/- 1 min (N = 13 tubules at 23 degrees C). This vacuolation was less severe if the bath was hypotonic to the lumen or if the magnitude of the osmotic difference was reduced. If colloid (6% wt/vol of either bovine serum albumin or 70,000 molecular wt dextran) was included in the bathing medium, vacuolation was either not observed or was minimal, but became severe upon removal of the colloid and obscured the lumen within 6 +/- 1 min (N = 8 for albumin and N = 4 for dextran at 23 degrees C). At 38 degrees C, vacuolation obscured the lumen within 4 +/- 1 min following the removal of albumin (N = 5). ANOVA suggests that none of the times for vacuolation to occur differed. The rate of passive volume flow due to the osmotic difference was unaffected by vacuolation (0.9 +/- 0.1 nl.min-1.mm-1 with albumin to 0.8 +/- 0.1 without albumin and vacuolated, N = 8 at 23 degrees C, P greater than 0.2 using a paired t-test). Electron microscopic examination of tubules fixed after vacuolation showed lucent spaces within the cytoplasm. These results suggest that the presence of serosal colloid protected the epithelial cells from injury during rapid transepithelial water flow. The mechanism for this protective effect is not apparent, but may be related to effects of colloid in maintaining normal volume absorption in the proximal nephron.

Effect of extracellular volume expansion on erythrocyte sodium transport in rats

The effects of extracellular volume expansion (EVE) on the major sodium transport systems and sodium and potassium contents in rat erythrocytes have been examined in the present study. Study has been performed in anesthetized Wistar rat weighing about 300 g. Acute extracellular volume expansion (EVE) was induced by a constant intravenous saline infusion (3% body wt, 3 hours). Rats anaesthetized and catheterized but not expanded were used as controls. Arterial blood samples from control and expanded rats were obtained at the same time, and assayed immediately. Intracellular sodium and potassium concentration and ouabain sensitive (Na(+)-K(+)-pump) and bumetanide sensitive (Na(+)-K(+)-cotransport system) outward Na+ fluxes in erythrocytes were measured. The effect of plasma on erythrocyte transport was also analyzed by measuring 86Rb uptake. Neither of two plasma cations (Na+ and K+) were modified by the EVE. Also intracellular Na+ and K+ levels remained unvariable. Total Na+ efflux was not modified by EVE, but pump-mediated Na+ efflux was smaller after than before EVE. The ouabain-inhibible Na+ efflux rate constant decreased after EVE (from 687 +/- 81 to 525 +/- 29 h-1 x 10(-3); P less than 0.05). Both Na(+)-K(+)cotransport-mediated Na+ efflux and passive permeability increased significantly after EVE. The incubation with plasma from saline-infused animals induced a significant decrease in Rb uptake rate constant, that was not observed after incubation with plasma from non-expanded rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Renal responses to magnesium lithospermate B

Renal responses to magnesium lithospermate B isolated from Salviae miltiorrhizae radix were examined in normal rats. Urinary sodium, potassium, prostaglandin E2 and kallikrein excretion was significantly increased after magnesium lithospermate B administration, whereas excretion of urinary 6-keto-prostaglandin F1 alpha and thromboxane B2 was unchanged. Rats administered with the drug also revealed a slight elevation of plasma renin activity and the levels of angiotensins I and II. Plasma aldosterone was decreased slightly. No significant changes were observed in angiotensin-converting enzyme or blood pressure.

Acute cyclosporine renal dysfunction reversed by dopamine infusion in healthy subjects

Up to now, no studies have been performed in normal humans to investigate the role of renal hemodynamic abnormalities in relation to acute-cyclosporin A (CsA) renal dysfunction and to verify whether the specific renal vasodilator, dopamine, can counteract these abnormalities. Eight normal subjects were examined both (A) after oral CsA (12 mg/kg body wt) and (B) after oral CsA + dopamine infusion (2 mg/kg body wt/min), under water diuresis. Both in protocols A and in B, four basal renal clearances were performed before CsA and every twenty minutes for four hours after CsA administration. In protocol A, after CsA, inulin (GFR) and PAH clearance (RPF) fell by up to 27% and to 41%, respectively, so that filtration fraction (FF) increased (P less than 0.01). A slight (not significant) hypertension occurred while renal resistances were markedly raised (P less than 0.001). Fractional urine and Na+ excretion as well as CH2O decreased, while UOsm increased (P less than 0.01). In protocol B, dopamine was infused from 120 to 180 minutes after CsA (that is, when the maximal adverse effects of CsA on renal hemodynamics had been observed in A). Dopamine infusion could reverse completely the effects of CsA on RPF, GFR, fractional urine output and CH2O; only UOsm remained higher than normal in conclusion with an increased fractional excretion of sodium (P less than 0.01). No changes were observed in plasma renin activity, aldosterone and in urinary epinephrine and norepinephrine excretion both in protocols.(ABSTRACT TRUNCATED AT 250 WORDS)

Development of acute tolerance to bumetanide: constant-rate infusion studies

Bumetanide was administered intravenously to four mongrel dogs as a bolus of 8.7 micrograms/kg, immediately followed by a constant-rate infusion of 0.35 microgram/min/kg at 0.036 ml/min. Treatment A consisted of a 90-min equilibration period and first hour (Phase I) of study in which animals were maintained under euvolemic conditions. During the subsequent 3 hr of Treatment A (Phase II), animals were maintained under hydropenic conditions. These experiments were then repeated 1 week later (Treatment B) with the temporal aspects of hydration reversed (Phase III, hydropenia; Phase IV, euvolemia). Serial plasma and urine samples were assayed for bumetanide by high-performance liquid chromatography (HPLC) and for sodium by flame photometry. The bumetanide excretion rate was not significantly different during the 4 hr of Treatment A, although minor differences were observed between Phase III and Phase IV of Treatment B. The sodium excretion rate showed significant differences between euvolemic and hydropenic conditions of both treatments. A two- to threefold difference in the sodium excretion rate persisted even when slight differences (less than 20%) in bumetanide excretion rates were taken into account. These results demonstrate that an acute tolerance does develop to constant-rate infusions of bumetanide when inadequate fluid and electrolyte replacement occurs and that this tolerance can be reversed by rehydration.

Group B streptococcal sepsis in the piglet: effects of fluid therapy on venous return, organ edema, and organ blood flow

We investigated the physiologic effects of normal saline versus 5% albuminated saline fluid resuscitation on 10-12-day-old piglets infected with group B streptococci for four hours. After intravenously receiving 1 X 10(10) bacteria/kg over 45 minutes, one group was untreated while the two fluid-treated groups received enough intravenous fluid to maintain the baseline cardiac output. An increase in the resistance to venous blood return was the major limitation to cardiac output. The resistance nearly quadrupled in the untreated piglets as shown by a 50% decrease in cardiac output with a nearly doubling of the driving pressure for venous return (mean circulatory pressure was normal and atrial pressures decreased by 70%). In both fluid-treated groups, resistance doubled as shown by an unchanged cardiac output with a doubling of the driving pressure (mean circulatory pressure increased by 50%) and atrial pressures remained at baseline). Blood volume was 9% below control in the untreated group and 13% above control in both fluid-treated groups. Much more crystalloid (155 ml/kg) than colloid (58 ml/kg) was necessary to maintain baseline cardiac output; this resulted in a 36% decrease in the plasma protein oncotic pressure of the former group and a 15% increase in the oncotic pressure of the latter group. Organ edema formation (ileum, pancreas, kidney, adrenal gland, lung) occurred only in the saline-treated animals. We conclude that increased resistance to venous return was the primary cause of shock in our model and that this can be effectively treated by giving enough intravenous fluid to elevate the mean circulatory pressure. However, if the plasma protein oncotic pressure is also lowered (saline group), organ edema results.

Renal haemodynamics and sodium handling after hyperoncotic albumin infusion in sodium-restricted normal man

The effect of plasma volume expansion with hyperoncotic albumin (HA) on renal haemodynamics and segmental tubular sodium (Na) handling was studied in eight water-loaded normal men. Clearance studies were performed before, during and after a 60-min infusion of 300 ml 20% HA. Sodium intake was restricted (20 mmol day-1) to mimic clinical conditions of relative hypovolaemia in which HA is often applied. Plasma volume rose by 740 +/- 160 ml after infusion and colloid oncotic pressure (COP) by 3.6 +/- 1.3 mm Hg. No natriuresis was induced. In fact, Na output fell from 43 +/- 29 to 28 +/- 25 mumol min-1 during infusion, returning to 41 +/- 36 mumol min-1 afterwards. Corresponding clearances of inulin were 121 +/- 19, 110 +/- 19 and 117 +/- 21 ml min-1 and of p-aminohippurate (CPAH) 602 +/- 87, 637 +/- 100 and 751 +/- 148 ml min-1. Fractional reabsorption of sodium in the proximal tubules (FPRNa), assessed from maximal free-water and lithium clearance, rose consistently during infusion but diverging patterns (further rise, no change or fall) were seen afterwards. Fractional distal reabsorption remained unchanged both during and after HA infusion. Changes in plasma volume and CPAH in the post-infusion period were correlated. These results indicate that, despite considerable plasma volume expansion, HA infusion does not enhance Na excretion in Na-restricted subjects. This is mainly due to elevation of plasma COP, which reduces glomerular filtration and enhances proximal reabsorption.(ABSTRACT TRUNCATED AT 250 WORDS)

Role of peritubular capillary forces in the renal action of carbonic anhydrase inhibitor

Micropuncture study was performed in Munich-Wistar rats to assess peritubular capillary Starling forces in renal superficial cortex during suppression of proximal fluid reabsorption by carbonic anhydrase inhibitor. Administration of benzolamide (2 mg/kg/hr, i.v., Group 1, N = 7 rats) caused not only reduction in absolute rate of proximal fluid reabsorption (APR, from 26.7 +/- 4.0 nl/min to 17.7 +/- 3.6, P less than 0.001), but also an increase in peritubular transcapillary hydraulic-pressure difference (from 10.0 +/- 0.5 mm Hg to 15.2 +/- 0.5, P less than 0.001). In a separate group of seven rats (Group 2), these parameters did not change significantly without benzolamide treatment. In Group 1 rats, an attempt was made to nullify the benzolamide-induced reduction in the peritubular capillary net reabsorptive forces by infusing hyperoncotic high-hematocrit blood. Following this treatment, while benzolamide administration was continued, values for APR returned to levels (25.6 +/- 4.8 nl/min) nearly identical to those measured prior to benzolamide administration, in association with a rise in peritubular transcapillary oncotic pressure difference. A separate group of six rats treated in a fashion identical to that of Group 1 showed continued suppression of carbonic anhydrase activity following blood infusion as indicated by low levels of whole kidney bicarbonate reabsorption rate. Peritubular capillary reabsorption coefficient was calculated based on the measured values for Starling forces in Group 1 and were unaffected throughout the study. Continued benzolamide administration alone without the treatment of hyperoncotic blood did not change APR significantly (Group 3, N = 7 rats).(ABSTRACT TRUNCATED AT 250 WORDS)

Changes in glomerular hemodynamic response to angiotensin II after subacute renal denervation in rats

We examined the changes in glomerular hemodynamics produced by angiotensin II (AII) in both normal Munich-Wistar rats and rats which were unilaterally renal denervated (measured kidney) 4-6 d prior to the measurement periods. Measurements of glomerular dynamics were performed in a control period after plasma volume expansion and during infusion of 11 ng X 100 g body wt-1 X min-1 of AII. The glomerular hydrostatic pressure gradient increased from 38 +/- 1 to 49 +/- 1 mmHg in denervated rats compared with a lesser response in controls (from 39 +/- 1 to 45 +/- 1 mmHg, P less than 0.05). Single nephron plasma flow decreased from 213 +/- 17 to 87 +/- 4 nl X min-1 X g kidney wt (KW)-1 in denervated kidneys versus a more modest decrease in control kidneys (from 161 +/- 9 to 102 +/- 5 nl X min X gKW-1). These changes were due to a greater increase in both afferent and efferent arteriolar resistance after AII infusion in denervated compared with control kidneys. Glomerular AII receptor maximum binding was 1,196 +/- 267 fmol/mg protein in denervated kidneys compared with 612 +/- 89 fmol/mg protein (P less than 0.01) in controls with no change in receptor affinity. We conclude the subacute unilateral renal denervation results in renal vasodilation, denervation magnifies the vasoconstrictive effect of AII infusion on glomerular hemodynamics, and the observed increased response to AII after denervation is associated with increases in glomerular AII receptors.

Renal interstitial pressure measured in the subcapsular space using an in vivo oncometer

Continuous measurements of renal interstital pressure are of importance for several reasons. The present paper describes an in vivo oncometer developed for this purpose. A piece of dialysis tubing was filled with a 0.15 M NaCl solution containing 5 g albumin 100 ml-1. For detecting the hydrostatic pressure inside the tubing, a thin catheter and a silver wire were inserted into it and both ends of the tubing were sealed with glue. The catheter and the silver wire were connected to a servo-nulling pressure device. The oncometer was then placed under the renal capsule. The pressure inside the dialysis tubing was pi onc+Psc-pi sc, and since pi onc was known, the net interstitial pressure (Pnet, i.e. Psc-pi sc) could be measured continuously in the subcapsular space. Measurements were made during (I) intravenous bolus injection of 2 ml of 0.9% NaCl, (2) saline expansion of 5% of body weight, and (3) elevation of renal venous pressure to 20 mmHg by clamping the renal vein. In the control situation, Pnet averaged-3.3 mmHg, a value in good accordance with findings in earlier studies in which the hydrostatic and oncotic pressure components have been measured separately. Following bolus injection of fluid, Pnet increased transiently by 2.6 mmHg, whereas volume expansion produced a permanent increase in Pnet of almost the same magnitude. During elevated renal venous pressure Pnet was unaffected, except for a minor increase on clamping and a minor decrease on release of the clamp. The results show that reproducible and accurate measurements of Pnet in the renal subcapsular space can be made with an in vivo oncometer.

Effect of leukocyte depletion on glomerular dynamics during acute glomerular immune injury

Large doses of anti-glomerular basement membrane antibody (AGBM-Ab) have been shown consistently to decrease both single nephron filtration rate (SNGFR) and the glomerular ultrafiltration coefficient (LpA) within 60 min of administration of the antibody. Both the decrease in SNGFR and LpA may be the result of infiltration of leukocytes blocking capillary loops and/or endothelial cell separation from the glomerular basement membrane through leukocyte dependent activated cytotoxic products or by mechanisms associated with leukocyte activation and infiltration. Administration of 2.5 micrograms/g body wt AGBM-Ab was performed in 10 control Munich-Wistar rats and in six Munich-Wistar rats in which 3 to 5 days prior to micropuncture experiments the rats were splenectomized and then irradiated to produce leukocyte depletion. Micropuncture measurements were performed in a condition of plasma volume expansion both prior to and after AGBM-Ab administration. In the control group, SNGFR decreased from 64 +/- 3 to 48 +/- 2 nl/min X g kidney wt after AGBM-Ab administration due to a decrease in LpA from 0.13 to 0.06 nl X sec-1 X mm Hg-1 X g kidney wt-1. This decrease in either SNGFR or LpA did not occur in the leukocyte depleted group. Linear deposits of IgG and C3 were similar in both groups. Polymorphonuclear leukocytes were significantly decreased in glomerulus from 7.4 +/- 0.7 in control vs. 0.7 +/- 0.3 in leukocyte depletion (P less than 0.01). There was no difference in glomerular dynamics between controls and leukocyte depleted rats prior to AGBM-Ab administration.(ABSTRACT TRUNCATED AT 250 WORDS)

Electron microprobe analysis of proximal tubule cellular Na, Cl and K element concentrations during acute mannitol-saline volume expansion in rats: evidence for inhibition of the Na pump

It has previously been shown that during mannitol-saline volume expansion (VE) Na transport was inhibited 50% by harvested proximal tubular fluid without a change in paracellular shunt pathway permeability to Na. To determine whether this inhibition was due to changes in cellular entry step or an effect on the pump itself, intracellular element concentrations were measured by electron microprobe X-ray ranalysis in proximal tubular cells of control (non-expanded, NE) and VE rats. Nai, Cli and phosphorusi were increased (mean +/- S.E.) from 19.3 +/- 0.8 to 23.4 +/- 0.6, 15.8 +/- 0.4 to 21.3 +/- 0.4 and 124.3 +/- 2.6 to 138.0 +/- 1.8 mmol . kg-1 wet weight (P less than 0.001) respectively while Ki remained unchanged: 122.9 +/- 2.2 and 124.2 +/- 1.3 mmol . kg-1 wet weight. The increases in Nai and Cli were in excess of cell shrinkage produced by the hyperosmolal peritubular environment while the unchanged Ki in the face of cell shrinkage indicates and actual loss. It is concluded that mannitol-saline VE inhibits the Na pump producing a rise in Nai and a fall in Ki.

Inhibitory effects of harvested proximal tubular fluid on Jv and delta cNa during acute saline volume expansion in the rat

The present micropuncture experiments were carried out in male Wistar rats during isotonic saline volume expansion (VE) to explore the relative importance of peritubular physical forces and tubular factors on proximal tubular Na transport. Isotonic volume flux, measured by the shrinking drop technique was reduced from 3.53 +/- 0.09 X 10(-4) . mm3 . mm-2 . s-1 with the artificial fluid to 1.79 +/- 0.1 with harvested autologous proximal tubular fluid (HTF) (49%), but only to 2.77 +/- 0.1 (78% of control) with artificial tubular solution (AS), both during volume expansion. delta cNa was reduced from a control of 18.0 +/- 2.2 mmol . kg-1 -14.5 +/- 2.0 with AS (81%) and 10.0 +/- 2.4 with HTF (56%) during VE. Thus both isotonic volume flux as well as delta cNa were reduced to the same degree by saline VE. These results and those obtained previously with mannitol-saline VE, indicate the presence of a factor in harvested proximal tubular fluid of volume expanded rats which inhibits sodium and water transport independent of peritubular osmolarity.

Arterial hypertension--a disease of the juxtaglomerular apparatus?

From a special strain of genetically hypertensive rats, the Milan hypertensive strain (MHS), arterial hypertension can be transplanted with the kidney to the Milan normotensive strain (MNS). During development of hypertension in MHS rats there was an activation of the tubuloglomerular feedback control that reduced glomerular filtration rate, leading to retention of electrolytes and fluid. This increased extracellular fluid volume reduces feedback sensitivity, but in a fashion that gives rise to chronic extracellular fluid expansion and can thereby raise the blood pressure. In a limited sense, arterial hypertension in these animals exists to prevent the kidney from retaining more extracellular fluid volume. The altered function in the juxtaglomerular apparatus of the MHS rats thus may explain the rise in arterial blood pressure.

Renal sodium handling in minimal change nephrotic syndrome

Renal sodium handling was studied in 23 children at three different stages of the minimal change nephrotic syndrome--the oedema forming state, proteinuric steady state, and remission. Clearances of inulin and para-aminohippuric acid and urinary sodium excretion were determined basally, after intravenous infusion of isotonic saline and hyperoncotic albumin, and after furosemide injection. Absolute and fractional basal sodium excretion were significantly lower in oedema forming patients than in proteinuric patients in steady state, and non-proteinuric patients. In contrast to proteinuric patients in steady state and non-proteinuric patients, the oedema forming patients failed to respond to isotonic saline infusion with increased sodium excretion. After diuretic blockade with furosemide, the fractional sodium excretion of the oedema forming patients increased to values no different from those of the non-proteinuric patients, whereas the fractional sodium excretion of the steady state patients increased to significantly higher values. The plasma aldosterone concentration was within normal limits in 11 of 14 proteinuric patients, and did not correlate with the basal sodium excretion. Thus, sodium retention in the minimal change nephrotic syndrome was found only in oedema forming patients, and since this is not related to the plasma aldosterone concentration it may be caused by an intrarenal mechanism, probably sited in distal parts of the nephron.

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 furosemide administration on glomerular and tubular dynamics in the rat

Furosemide, a potent diuretic, has also been shown (1) to inhibit or reduce tubuloglomerular feedback activity, (2) act as a vasodilatory agent, and (3) exhibit a modest carbonic anhydrase inhibitory effect, which could potentially reduce proximal tubule reabsorption. If furosemide can inhibit tubuloglomerular feedback as well as cause vasodilation, then glomerular filtration rate (GFR) should increase through alterations in the dynamics of glomerular ultrafiltration. The effect of acute furosemide infusion (4 mg/kg of body wt per hour) on glomerular and tubular dynamics was examined in Munich-Wistar rats by two protocols: The first allowed a 3% volume depletion (based on body wt) to occur as a result of furosemide administration (group 1); the second allowed a complete replacement of volume after furosemide administration (group 2). The results demonstrated that when volume status was maintained after furosemide administration, the nephron filtration rate remained constant (35 +/- 3 vs. 33 +/- 2 nl/min, NS) despite a twofold increase in distal flow rate (5 +/- 1 vs. 10 +/- 1 nl/min, P less than 0.01), indicating an inhibition or suppression of the tubuloglomerular feedback system. With either protocol, furosemide administration did not alter total nephron vascular resistance and nephron blood flow (190 +/- 17 vs. 200 +/- 15 ml/min); however, the afferent arteriolar resistance did decrease in rats in which volume status was maintained. Finally, with volume status maintained, we were not able to demonstrate a reduction in absolute proximal fluid reabsorption despite a 7 mm Hg increase in interstitial hydrostatic pressure (4 +/- 1 to 11 +/- 1 mm Hg, P less than 0.01) and no compensatory increase in interstitial oncotic pressure. These data indicate that tubuloglomerular feedback was inhibited but that GFR was not increased. Major changes occurred in interstitial pressures and interstitial volume after furosemide administration, but absolute proximal reabsorption remained constant.

Physiologic basis for the maintenance of glomerulotubular balance in young growing rats

To examine the physiologic basis of preservation of glomerulotubular balance in young growing animals, we measured the various determinants for fluid transfer across the glomerular and postglomerular capillaries in young (approximately 40 days, N = 8) and adult (N = 8) male Munich-Wistar rats under mild volume expansion. The single nephron (SN) GFR increased by approximately 2.5-fold from young to adult animals. The increase in SNGFR was due to marked rises in both glomerular plasma flow rate (QA) and ultrafiltration coefficient (Kf). The increase in QA was associated with a nearly 60% reduction in afferent and efferent arteriolar resistances. As with SNGFR, the absolute proximal reabsorption rate (APR) increased by some 2.5-fold, indicating preservation of perfect glomerulotubular balance. Of the factors determining peritubular capillary uptake of APR, the mean oncotic pressure difference across the peritubular capillary was similar in young and adult animals. The mean hydraulic pressure difference was also comparable in the two groups. By contrast, the peritubular capillary reabsorption coefficient (Kr) rose markedly and accounted entirely for the increase in peritubular capillary uptake of APR during growth. These results obtained under mild volume expansion indicate that the maintenance of glomerulotubular balance in the growing rat requires harmonious growth of renal microcirculation, that is, glomerular capillary (Kf) and arteriolar (QA) maturation balances the development of peritubular capillary (Kr).

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.

Prevention of interstitial pressure change at unilateral nephrectomy by prostaglandin synthesis inhibition

The mechanisms underlying the adaptive process in the remaining kidney after unilateral nephrectomy are not well known. In the present study adaptive changes in interstitial pressure conditions following uninephrectomy were investigated in male Sprague-Dawley rats. Direct subcapsular hydrostatic pressure recordings were made via microcatheters , renal lymph was collected for lymph flow rate estimations and determinations of lymph protein content and the urine flow rate and urinary excretion of sodium and potassium were measured, before and after contralateral nephrectomy. There was a significant rise in subcapsular hydrostatic pressure by about 50%, and in the lymph flow rate, by more than 100%, within 1 hr after nephrectomy. The protein concentration in collected renal lymph was significantly decreased (from 2.30 +/- 0.25 to 1.45 +/- 0.26 g/dl), compared with control collections in sham-operated animals (from 2.22 +/- 0.23 to 1.78 +/- 0.19 g/dl). These findings indicate an increased hydrostatic and decreased intersititial pressure in response to contralateral nephrectomy. Urine flow rate and electrolyte excretion were significantly elevated (urine flow rate by 92%, sodium excretion from 0.210 +/- 0.035 to 0.352 +/- 0.067 mumoles/min and potassium excretion from 0.306 +/- 0.074 to 1.617 +/- 0.228 mumoles/min). Inhibition of prostaglandin synthesis prior to nephrectomy abolished the lymph flow increase and oncotic pressure decrease and also the diuretic and natriuretic responses. The adaptively increased potassium excretion was, however, only blocked by diclofenac sodium and not by indomethacin. These results demonstrate the important role of the renal interstitium and the prostaglandin system in the renal adaptation to nephron loss.

Blood flow dependence of postglomerular fluid transfer and glomerulotubular balance

The rate of blood flow entering a capillary network can, in some vascular systems, regulate capillary surface area and the rate of fluid and solute transfer. To determine whether such a mechanism exists in the renal peritubular capillary, we performed micropuncture studies in 28 rats during relatively low and high efferent arteriolar blood flow (EABF). High EABF was achieved by intravenous infusion of isoncotic plasma (group 1: from 120 +/- 11 to 301 +/- 49 nl/min [+/- SE]); whole blood with high hematocrit (approximately 75 vol %) (group 2: from 141 +/- 14 to 252 +/- 31 nl/min); or acetylcholine (group 3: from 193 +/- 20 to 266 +/- 26 nl/min). In group 1 rats, plasma infusion caused an increase in single nephron glomerular filtration rate (SNGFR), on average, from 23.2 +/- 2.4 to 45.2 +/- 3.9 nl/min, owing primarily to increased glomerular plasma flow rate (from 63 +/- 5 to 210 +/- 21 nl/min). The rate of fluid uptake by the peritubular capillary, assessed by the absolute rate of proximal fluid reabsorption (APR), also rose significantly, on average from 10.5 +/- 1.2 to 17.5 +/- 2.4 nl/min. This rise in APR was associated with near constancy in mean transcapillary hydraulic (delta Pc) and oncotic (delta IIc) pressure differences, and was therefore attributed to a significant increase in peritubular capillary reabsorption coefficient (Kr), with the mean from 0.017 +/- 0.003 to 0.030 +/- 0.005 nl/(s . mmHg). In group 2 rats, high hematocrit blood infusion led to a significant rise in APR; on average, from 10.7 +/- 0.7 to 15.0 +/- 1.2 nl/min, without changing SNGFR. This rise in APR occurred despite unfavorable changes in the physical forces, namely a significant increase in delta Pc and constancy in delta IIc. Instead, an increase in EABF was again associated with a significant rise in Kr (on average, from 0.016 +/- 0.002 to 0.030 +/- 0.06 nl/[s . mmHg]), which accounted entirely for the rise in APR, independently of SNGFR. In group 3 rats, in which an increase of EABF was induced pharmacologically with acetylcholine, a rise in EABF was also accompanied by a significant increase in Kr, on average, from 0.019 +/- 0.002 to 0.026 +/- 0.004 nl/(s . mmHg). The results indicate that: (a) Kr is modulated by EABF. (b) In view of plasma flow dependence of GFR, blood flow dependence of Kr and APR provides an important basis for glomerulotubular balance.

Rabbit kidney function in vitro: the effect of colloids, energy substrate, a vasodilator, perfusion pressure, and bovine serum albumin

An in vitro perfusion system at 37 degrees C for the assessment of rabbit kidney function is described. The purpose of this assay system is to evaluate the effects of cryobiological manipulation on kidney function. The effect of the colloids dextran (MW = 70,000, 80,000, and 180,000) in the perfusate at 110 mm Hg were compared to a reduced perfusion pressure, colloid-free perfusate. Better function was obtained at lower perfusion pressure with the colloid-free perfusate. Less damage was noted histologically on light and electron microscopy. Investigation of energy substrates on rabbit kidney function demonstrated that butyrate, or lactate, in addition to glucose resulted in increased sodium and glucose reabsorption over glucose alone. Substrate-free perfused kidneys exhibited depressed Na transport. Lactate, and to some extent butyrate, decreased net glucose utilization. An alpha-adrenergic blocking agent, isoxsuprine, in the initial flush solution did not appear to be beneficial. An increase of perfusion pressure from 50 to 75 mm Hg resulted in an increase in GFR. Tubular function was enhanced by inclusion of small amounts of BSA in the perfusate.