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PubMed1982

[Bumetanide in renal insufficiency].

Intravenous bumetanide was tested in patients with cardiac and renal failure with creatinine clearance below 12 ml/min. Water diuresis and natriuresis occur 2 or 3 hours after the injection, this delayed activity of the drug being due to renal insufficiency. The loss of potassium caused by the diuretic is slight. Bumetanide is effective at the level of the Henle loop. The rise in filtered sodium excretion suggests that the drug may have an action on the distal tubule. One patient with pericarditis and terminal renal failure (creatinine clearance 2 ml/min) did not respond to bumetanide.

Aged↗
PubMed1997

Morphology of cystic renal lesions. Lectin and immuno-histochemical study.

Renal cystic disease include heritable, developmental and acquired disorders. Morphological features were extensively studied mainly in cases of autosomal dominant polycystic and experimentally induced cystic disorders. We report the immunohistochemical (cytokeratin, epithelial membrane antigen, vimentin, Tamm-Horsfall protein, proliferating cell nuclear antigen) and lectin-binding (soybean agglutinin, Dolichos biflorus agglutinin) profile of cystic kidneys from 9 surgically removed and 21 autopsy cases. The primary renal diseases displayed great diversity. Beside polycystic kidney diseases we studied cysts associated to renal neoplasm, hemodialysis, nephrosis syndrome and chronic transplant rejection. Cystic epithelium demonstrated positive reactions with distal tubular markers (epithelial membrane antigen, cytokeratin) or collecting duct (soybean agglutinin, Dolichos biflorus agglutinin) and Henle loop markers (Tamm-Horsfall protein) but the latter in lesser extent. The large number of the vimentin positive cases are suggestive to dedifferentiation or cellular regeneration. The former might be underlined by the diffuse cytoplasmic or basolateral membrane staining of the epithelial membrane antigen in some cystic epithelial cells. Not the cystic epithelium but rather the neighbouring non-dilated tubular cells and interstitial cells presented proliferative activity which was most intense in areas where vimentin and variable nephron segment markers in the same tissue were expressed. Positive reaction of the type IV basement membrane collagen and the rate of the inflammation failed to show similar connection. This finding suggests the importance of the inflammatory cells in the development and/or expansion of the cysts.

Cell Differentiation↗
PubMed1997

[Nocturnal enuresis as a manifestation of autocoidosis].

The study entered 30 children with nocturnal enuresis and 20 healthy controls aged 6-15 years. The enuretic children had a higher night diuresis and free water reabsorption; there was an increase in nocturnal excretion of sodium, calcium and magnesium ions. Before going to bed the patients received diclofenac-sodium. Inhibition of cyclooxygenase and decrease of prostaglandin production led to normalization of diuresis and natriuresis, elimination of nocturnal enuresis episodes. The evidence has been obtained that nocturnal enuresis is accompanied by an increased production of autocoids in the thick ascending Henle loop and, as a result, of an increase in saluresis and diuresis. It is suggested that there is a form of nocturnal diuresis which depends on a local hyperproduction of autocoids. The problem of autocoids role in the internal medicine is discussed.

Adolescent↗
PubMed1975

Urea handling by the renal countercurrent system: insights from computer simulation.

The renal handling of urea has been investigated with the aid of a computer model of the countercurrent system in which active electrolyte reabsorption occurs along the entire ascending limb of Henle's loop. In this model, summarized in Fig.9, the buildup of a corticopapillary gradient for urea is optimized if there is net addition of urea to loops of Henle only in the outer medulla. This added urea remains within the tubular system until it is reabsorbed from collecting ducts in the inner medulla. Thus, a net transfer of urea from outer to inner medulla is accomplished (via distal tubule and cortical collecting duct). There is no net addition of urea to loops of Henle within the inner medulla; in this region, the loops act simply as countercurrent exchangers for urea. Computer simulation of systematic variation in the urea permeabilities of each nephron segment shows that interference with any element of the above schema results in impairment of the medullary accumulation of urea relative to plasma. Simulation of varying rates of urinary urea excretion demonstrates that this model can account for the ability of the kidney to excrete substantial amounts of urea without an accompanying osmotic loss of water. The major insight gained from this study is that net addition of urea to loops of Henle in the outer medulla greatly enhances the medullary accumulation of urea, whereas, net addition of urea to loops within the inner medulla tends to defeat such accumulation and hence the urinary concentrating process. This general principle applies also to an alternate model of the countercurrent system, in which electrolyte reabsorption from thin ascending limbs of Henle is passive.

Computers↗
PubMed2004

Two modes for concentrating urine in rat inner medulla.

We used a mathematical model of the urine concentrating mechanism of rat inner medulla (IM) to investigate the implications of experimental studies in which immunohistochemical methods were combined with three-dimensional computerized reconstruction of renal tubules. The mathematical model represents a distribution of loops of Henle with loop bends at all levels of the IM, and the vasculature is represented by means of the central core assumption. Based on immunohistochemical evidence, descending limb portions that reach into the papilla are assumed to be only moderately water permeable or to be water impermeable, and only prebend segments and ascending thin limbs are assumed to be NaCl permeable. Model studies indicate that this configuration favors the targeted delivery of NaCl to loop bends, where a favorable gradient, sustained by urea absorption from collecting ducts, promotes NaCl absorption. We identified two model modes that produce a significant axial osmolality gradient. One mode, suggested by preliminary immunohistochemical findings, assumes that aquaporin-1-null portions of loops of Henle that reach into the papilla have very low urea permeability. The other mode, suggested by perfused tubule experiments from the literature, assumes that these same portions of loops of Henle have very high urea permeabilities. Model studies were conducted to determine the sensitivity of these modes to parameter choices. Model results are compared with extant tissue-slice and micropuncture studies.

Animals↗
PubMed1981

Effect of furosemide on calcium and magnesium transport in the rat nephron.

Superficial tubules were perfused in vivo to determine the effect of intraluminal furosemide on electrolyte transport in the loop of Henle and distal tubule of the rat with special reference to calcium and magnesium reabsorption. in vivo perfusion of single tubules allowed us the opportunity to investigate separate electrolyte transfers with altering the corticomedullary concentration gradient within the kidney. Intraluminal furosemide (3 X 10(-6) and 3 X 10(-5) M) resulted in proportionately greater calcium and magnesium inhibition relative to sodium and chloride in Henle's loop. Furosemide had little effect on transport function within the perfused superficial distal tubule. Distal calcium and magnesium reabsorption was dependent on their respective deliveries to this segment. Parathyroid hormone increased fractional calcium and magnesium reabsorption in Henle's loop and the distal tubule in the presence of intraluminal furosemide. These results are consistent with a luminal effect of furosemide in the loop of Henle that inhibits calcium and magnesium transport to a greater degree than sodium chloride. Intraluminal ethacrynic acid (10(-4) M) or its cysteine complex had no effect on electrolyte transport in the perfused rat nephron.

Animals↗
PubMed1975

Tubular organization and vascular-tubular relations in the dog kidney.

Tubular organization and vascular-tubular relations were studied by double injection in canine kidneys. Blood vessels were injected via the artery after perfusion fixation. Tubules were injected by micropipettes inserted into the urinary spaces of selected glomeruli in cleared slices. One hundred proximal convoluted tubules, 16 Henle loops, and 5 distal convoluted tubules were defined. Only subcapsular proximal convolutions were perfused by efferent vessels arising from the same glomerulus (43 of 55). In midcortex, proximal convolutions were generally perfused over less than half their length by the parent efferent (21 of 31). Here tubules entirely perfused by the parent efferent were rare (2 of 31). No inner cortical proximal convolutions were perfused by the efferent from the same glomerulus (0 of 14). Henle's loops were found to be perfused by the efferents of many glomeruli regardless of the cortical position of the parent glomerulus. Distal convolutions shared the perfusion of proximal convolutions of the same glomerulus. Thus, each nephron is apparently functionally dependent on efferent blood from glomeruli of many other nephrons. New synoptic diagrams of canine renal organization are presented.

Animals↗
PubMed1982

Effect of hypercalcemia on renal tubular handling of calcium and magnesium.

Tubular calcium and magnesium transport was investigated in thyroparathyroidectomized rats following acute elevation of extracellular calcium concentration. Fractional urinary excretion of calcium increased from 0.2 to 8.3% and magnesium increased from 15 to 39%, while sodium increased modestly from 0.1 to 1.1%. Superficial proximal tubules, Henle's loop, and distal tubules were perfused in vivo to determine the segmental effects of hypercalcemia. Fractional calcium absorption within the loop of Henle was significantly less in the hypercalcemic rats (58%) compared with normal animals (86%). Magnesium transport was inhibited to a greater extent compared with calcium in the loop as the fractional reabsorption decreased from 78% in the normal rats to 35% in the hypercalcemic animals. Sodium absorption was inhibited by 8%. Absolute calcium and magnesium absorption within the superficial distal convoluted tubule increased about three- to four-fold with increased delivery to this segment. These data indicate that hypercalcemia inhibits calcium and magnesium transport relatively more than sodium absorption in the loop of Henle and that this action principally accounts for the increase in urinary excretion of these electrolytes.

Animals↗
PubMed1980

Magnesium transport in the nephron.

Magnesium is filtered at the glomerulus to the extent of 70-80%, of which about 80-95% is reabsorbed by the various nephron segments. Recent evidence from micropuncture and microperfusion experiments has characterized the tubular handling of magnesium. The proximal convoluted tubule reclaims 20-30% of the filtered magnesium, considerably less than the fractional reabsorption of sodium and calcium. The proximal tubule is poorly permeable to magnesium but overall reabsorption is dependent on the filtered load and net water reabsorption. Specific knowledge of magnesium handling in the straight portion of the proximal tubule is lacking. Definitive evidence has been presented to indicate the important role of the thick ascending limb of the loop of Henle. The loop reabsorbs approximately 50-60% of the filtered magnesium or about 80% of that delivered to this segment. In vivo microperfusion studies have shown that elevation of luminal magnesium results in enhanced reabsorption proportional to delivery, whereas elevation of contraluminal magnesium leads to a fall in magnesium transport dependent on the absolute plasma concentration. This suggests a unique magnesium transport interaction on the contraluminal side of the ascending limb membrane that may also involve calcium. Parathyroid hormone increases magnesium reabsorption in the loop; however, its physiological role remains undefined. The distal convoluted tubule reabsorbs only 1-5% of filtered magnesium. Although it is now clear that successive segments of the nephron transport magnesium in different ways, the nature of the cellular mechanisms are unknown. The search for a specific physiological regulator of renal magnesium reabsorption remains unsuccessful. However, recent evidence suggests that overall renal magnesium homeostasis is determined to a large extent by transport in the ascending limb of Henle's loop.

Animals↗
PubMed1978

Mechanism of exaggerated diuresis in spontaneously hypertensive rats.

The mechanism of exaggerated diuresis and natriuresis was studied in spontaneously hypertensive rats (SHR) by renal clearance and micropuncture techniques. Control normotensive rats of the same age and sex [Wistar-Kyoto rats (WKY)] were also studied. During the hydropenic control and the volume-expansion experimental periods absolute and fractional water and sodium excretion were greater in SHR than in WKY. Although fractional and absolute water and sodium reabsorption were similar along the proximal convolution in SHR and WKY, fractional and absolute water reabsorption in Henle's loop was less in SHR than in WKY. Hydrostatic and colloid osmotic pressures in the cortical peritubular microvasculature were similar in WKY and SHR. Acute normalization of renal perfusion pressure by aortic constriction reversed the exaggerated diuresis and natriuresis in SHR by halving the filtered load of water and sodium; whole kidney and single nephron glomerular filtration rates and blood flows decreased by 50%. It is concluded that the exaggerated diuresis and natriuresis of the spontaneously hypertensive rat is caused by a decreased reabsorption in the loop of Henle. The mechanism of this decreased reabsorption in the loop of Henle cannot be explained by alterations in the measured physical forces in the renal cortical microvasculature.

Animals↗
PubMed1997

Segmental localization of urea transporter mRNAs in rat kidney.

Renal epithelia express at least two distinct urea transporter mRNAs, termed UT1 and UT2, that are derived from a single UT gene by alternative splicing. Previous immunolocalization studies using a polyclonal antibody that does not distinguish between the protein products of these two transcripts revealed that expression of urea transporter protein is restricted to inner medullary collecting ducts and descending thin limbs of Henle's loop. To identify which transcripts account for protein expression in these two structures, we carried out reverse transcription-polymerase chain reaction studies in microdissected structures using UT1- and UT2-specific primers. UT1 mRNA was detected only in the inner medullary collecting duct, consistent with its identification as the vasopressin-regulated urea transporter. In contrast, UT2-mRNA was detected in the late part of descending thin limbs of short loops of Henle and in the inner medullary part of descending thin limbs of long loops of Henle. This localization is consistent with the predicted role of UT2 in medullary urea recycling. Thus, in conjunction with foregoing physiological studies, our data indicate that these transporters play central roles in the urinary concentrating mechanism.

Alternative Splicing↗
PubMed1976

Nephron function of the isolated perfused rat kidney.

Nephron functions of an improved isolated perfused rat kidney preparation were studied by micropuncture techniques. Single-nephron glomerular filtration rate (SNGFR), intratubular pydrostatic pressures (IP), transit time (TT), and the reabsorption (R) of H2O, Na, Cl, and K were measured in superficial proximal (PT) and distal tubules (DT) of the preparation. Mean SNGFR was 27.2 nl/min and 25.2 nl/min when measured in PT and DT, respectively. The PT transport functions were well maintained throughout the perfusion (mean values were: IP, 14.3 mmHg; TT, 17.7 s; fractional (F) RH2O, 64%; absolute RH2O, 15.4 nl/min; FRNA, 66.5%; FRK, 71%, and tubular fluid-to-perfusate tf/p) ratio of Cl, 1.37). The short loops of Henle reabsorbed less than 10% of the load of H2O and Na delivered to them and the TF/P ratio of electrolytes in the earliest DT segments were high (TF/P)Na = 0.88, (TF/P)Cl = 1.27, and (TF/P)K = 1.11). This deficiency in function of Henle's loop explains, at least in part, the degree of natriuresis of the preparation (overall FRNa = 97.5%). Transit time to end DT was prolonged (82.3 S) and IP in DT elevated (14.9 mmHg). The DT was able to compensate, in part, for the overload from Henle's loop by reabsorbing 36% of the fluid load and 54% of the Na load delivery to it. We concluded that the improved isolated perfused rat kidney is a suitable preparation with which to study several aspects of renal function, particularly proximal tubules transport functions.

Animals↗
PubMed1986

Effects of human calcitonin on water and electrolyte movements in rat juxtamedullary nephrons: inhibition of medullary K recycling.

The effects of synthetic human calcitonin (HCT) on water and electrolyte deliveries to the thin limbs of Henle's loop of juxtamedullary nephrons were investigated by micropuncture in the rat. To avoid undesirable interference with exogenous calcitonin, experiments were performed in hormone-deprived rats with reduced circulating calcitonin, antidiuretic hormone, parathyroid hormone and glucagon, all four of which stimulate the adenylate-cyclase activity in the thick ascending limb and the distal tubule. Administration of HCT (1.0 mU/min X 100 g body wt) to such rats significantly reduced the urinary fractional excretion rate of water, Mg, Ca and K. At the tip of the longlooped nephrons, the fractional delivery of water diminished in the presence of HCT, although the glomerular filtration rate of these nephrons was unaltered. Simultaneously, the loop fluid osmolality rose significantly. HCT, however, did not alter the fraction of total filtered solutes remaining in the thin limbs, nor the NaCl fractional delivery. As previously observed in this laboratory with dDAVP, the reduced fractional delivery of water at the hairpin turn was accompanied by a decrease in Mg and Ca deliveries in rats given HCT, indicating that the handling of these two ions along the descending limb may be linked in part to the water movements in this nephron segment. The fractional deliveries of K at the hairpin turn and in urine were significantly correlated, and both decreased in the presence of HCT. Since, as shown previously, HCT reduces the net addition of K along the superficial distal tubule, it is concluded that calcitonin inhibits the medullary recycling of K between the nephron terminal segments and the loop of Henle of juxtamedullary nephrons.

Animals↗
PubMed1986

Effect of dietary sodium content on renal handling of lithium. Experiments in conscious diabetes insipidus rats.

Previous studies have shown that the clearance of lithium (CLi) is a quantitative measure of the delivery of tubular fluid to Henle's loop in rats given food with an ordinary or high sodium content but not in rats given food with a low sodium content, because under these circumstances lithium is also reabsorbed to some extent in the distal nephron segment. The present study examines CLi, CNa and urine flow in diabetes insipidus rats at various dietary sodium contents. The results showed that CLi was 120 microliter/min/100 g b.w. when no distal reabsorption took place at a dietary sodium content of 300 mmol/kg. At a dietary sodium content of 5 mmol/kg the calculated distal lithium reabsorption reduced CLi by 55 microliter/min/100 g b.w.; at 25 mmol/kg distal reabsorption was reduced to half this value; at 50 mmol/kg distal reabsorption was slight and barely significant, and at 75-300 mmol/kg there was no distal reabsorption of lithium. It is concluded that CLi can be used as a quantitative measure of the delivery of tubular fluid to the loop of Henle at dietary sodium contents higher than 50-75 mmol/kg in the rat.

Animals↗
PubMed1980

Studies with the optically active isomers of the new diuretic drug ozolinone. II. Inhibition by d-ozolinone of furosemide-induced diuresis.

The effect of the non-diuretic dextrorotatory isomer of ozolinone on furosemide-induced diuresis was studied by means of clearance and micropuncture techniques in rats. After intravenous injection, d-ozolinone antagonized the furosemide-induced increase in renal fluid and electrolyte excretion in a dose-related manner. Microperfusion experiments of Henle's loop in vivo revealed that d-ozolinone did not interfere with the action of furosemide at this tubular site. However, d-ozolinone markedly decreased the furosemide to inulin clearance ratio, presumably as a consequence of inhibition of furosemide secretion into the proximal tubules. It is assumed that, in consequence of a high affinity for the proximal organic acid transport system, d-ozolinone depresses proximal tubular furosemide secretion and prevents transfer of this diuretic to the tubular fluid. Thus, under the influence of d-ozolinone, furosemide cannot reach the loop of Henle in sufficient amounts and its diuretic effect is blocked.

Animals↗
PubMed1980

Effect of parathyroid hormone on renal calcium and magnesium reabsorption in magnesium deficient rats.

Tubular magnesium reabsorption was investigated by recollection micropuncture and in vivo microperfusion techniques in acutely thyroparathyroidectomized rats made magnesium deficient by dietary deprivation. Henle's loop which normally reclaims the major portion of filtered magnesium was examined by elevation of intraluminal magnesium concentration. The transport capacity in these conditions was significantly lower in magnesium deficient rats (41%) compared to normal animals (71%) at comparable magnesium delivery rates. Acute infusion of MgCl2 further depressed loop magnesium reabsorption independent of intraluminal magnesium delivery. Parathyroid hormone did not alter magnesium transport capacity in magnesium deficient rats but resulted in enhanced transport in acutely hypermagnesemic deficient rats. Calcium reabsorption followed a similar qualitative pattern as magnesium with respect to loop function and urinary excretion. These results are consistent with a depressed transport capacity for magnesium in the loop of Henle of magnesium deficient rats which is independent of intraluminal magnesium delivery and circulating parathyroid hormone level.

Absorption↗
PubMed2006

Maxi-K channels contribute to urinary potassium excretion in the ROMK-deficient mouse model of Type II Bartter's syndrome and in adaptation to a high-K diet.

Type II Bartter's syndrome is a hereditary hypokalemic renal salt-wasting disorder caused by mutations in the ROMK channel (Kir1.1; Kcnj1), mediating potassium recycling in the thick ascending limb of Henle's loop (TAL) and potassium secretion in the distal tubule and cortical collecting duct (CCT). Newborns with Type II Bartter are transiently hyperkalemic, consistent with loss of ROMK channel function in potassium secretion in distal convoluted tubule and CCT. Yet, these infants rapidly develop persistent hypokalemia owing to increased renal potassium excretion mediated by unknown mechanisms. Here, we used free-flow micropuncture and stationary microperfusion of the late distal tubule to explore the mechanism of renal potassium wasting in the Romk-deficient, Type II Bartter's mouse. We show that potassium absorption in the loop of Henle is reduced in Romk-deficient mice and can account for a significant fraction of renal potassium loss. In addition, we show that iberiotoxin (IBTX)-sensitive, flow-stimulated maxi-K channels account for sustained potassium secretion in the late distal tubule, despite loss of ROMK function. IBTX-sensitive potassium secretion is also increased in high-potassium-adapted wild-type mice. Thus, renal potassium wasting in Type II Bartter is due to both reduced reabsorption in the TAL and K secretion by max-K channels in the late distal tubule.

Adaptation, Physiological↗
PubMed1977

Effects of acute bilateral ureteral obstruction on deep nephron and terminal collecting duct function in the young rat.

The effects of acute bilateral ureteral obstruction (BUO) of 18-h duration on deep nephron and collecting duct function were studied by micropuncture in 11 weanling rats. After release of BUO glomerular filtration rate was reduced (178+/-15 vs. 1,343+/-119 mul/min per g kidney weight in shams), while urine flow was increased averaging 17.5+/-1.3 vs. 6.8+/-0.72 mul/min per g kidney weight in controls. There was a marked increase in the absolute and fractional excretion of Na. Single nephron glomerular filtration rate of deep nephrons was reduced in the BUO group, mean 19.4+/-3.5 vs. 77.0+/-7.7 nl/min per g kidney weight in shams. Single nephron glomerular filtration rate of superficial nephrons fell to the same extent after relief of BUO. Mean tubular fluid to plasma inulin ratio of fluid from Henle's loop was 2.46+/-0.20 after relief of BUO vs. 8.23+/-0.85 in shams. This suggested a reduction in the reabsorption of Na and water before the bend of the loop of Henle, most likely in both the proximal tubule and descending limb. Fluid osmolality was depressed due to a decline in both Na and nonelectrolyte solute content. After release of BUO the percentage of filtered water remaining in the collecting duct (CD) at the base of the papilla was greater than in controls (13.3+/-2.0 and 1.72+/-0.01%, respectively) but fell significantly by the tip of the papilla to 7.92+/-1.12 vs. 1.17+/-0.02% in controls. These results indicate that water was reabsorbed along the terminal CD after relief of ureteral obstruction. In fact, a greater fraction was reabsorbed in this segment after release of BUO (5.37+/-1.58%) than after sham operation (0.55+/-0.15%). Similar changes were seen in Na excretion. Thus alterations in deep nephron function appear to contribute to the natriuresis and diuresis which follow release of BUO while terminal CD function in this model appears intact.

Animals↗