bluuebunny/crossref_metadata_2025 huggingface dataset:
Autoradiographic localization of beta-adrenergic receptors in rat kidney slices using [125I]iodocyanopindolol
Authors: Munzel P. A. , Healy D. P. , Insel P. A.
Published: December 2017

We have used autoradiography of [125I]iodocyanopindolol [( 125I]-ICYP) to define the distribution and localization of beta-adrenergic receptors in the rat kidney. [125I]ICYP, a radiolabeled beta-adrenergic antagonist, proved to be an excellent probe to identify these receptors in kidney slices in that specific [125I]ICYP binding was 1) saturable, 2) competed stereoselectively by the agonist isoproterenol and the antagonist propranolol, and 3) competed by agonists in a classical rank order of potency for beta 1-adrenergic receptors (isoproterenol greater than epinephrine congruent to norepinephrine). Autoradiographic studies demonstrated that specific [125I]ICYP sites were present exclusively in the cortex and outer medulla and were localized in glomeruli, ascending limb, and distal tubule-cortical collecting duct. Autoradiography of probes like [125I]ICYP appears to offer a simple and rapid method to assess distribution of adrenergic receptors in the kidney and presumably in other tissues as well.
Blood pressure effects of renin inhibition by human renin antiserum in normotensive marmosets
Authors: Michel J. B. , Wood J. , Hofbauer K. , Corvol P. , Menard J.
Published: December 2017

The effects on blood pressure of an antiserum against pure human kidney renin were studied in conscious and anesthetized (pentobarbital, 24 mg X kg-1 i.p.) small new world monkeys (common marmosets). The antiserum inhibited the enzymatic activity of renin by 50% in a dilution of 1:45,000 in marmoset and 1:50,000 in human plasma. The antiserum (0.2 ml i.v.) decreased blood pressure in conscious marmosets on normal sodium intake by 15 +/- 5 (SD) mmHg and after salt depletion by 31 +/- 13 mmHg. A converting enzyme inhibitor (teprotide, 2 mg X kg-1 i.v.) induced a comparable fall in blood pressure: -16 +/- 10 and -30 +/- 10 mmHg, respectively. Similar effects were observed on blood pressure of anesthetized marmosets. The correlation between pretreatment plasma renin concentration and the maximum fall in blood pressure was significant and identical for the experiments with antiserum and teprotide. These results demonstrate that antisera against human renin can be used for the specific blockade of the renin-angiotensin system in primates. In normotensive marmosets the renin-angiotensin system participates in the maintenance of blood pressure, to a degree depending on the state of sodium balance.
In vitro perfusion of juxtamedullary nephrons in rats
Authors: Casellas D. , Navar L. G.
Published: December 2017

Anatomical studies of rat kidneys revealed the presence of a unique population of juxtamedullary glomeruli (JMG) located at the inside cortical surface apposed to the pelvic lining and arcuate veins. These "superficial" JMG were exposed by longitudinally bisecting the kidney, reflecting the papilla, removing the pelvic mucosa, and transecting the venous walls. A microperfusion system was developed to allow blood perfusion of these nephrons via arcuate arteries. At a perfusion pressure of 100 mmHg, with most of the preglomerular pressure drop being localized to the terminal afferent arteriolar segment. In subsequent studies, blood hematocrit was reduced to approximately 30% with physiological solutions devoid of or containing albumin, and rats were treated with a converting enzyme inhibitor. In these conditions, single nephron glomerular filtration rate averaged 34 +/- 4 nl/min (low plasma colloid osmotic pressure, PCOP) and 23.3 nl/min (maintained PCOP). Proximal tubule reabsorption ranged from 17 to 29%. In conclusion, the integrity of nephron function is maintained in this model, which may provide further insights into the dynamics of filtration and reabsorption processes of juxtamedullary nephrons.
Parathyroid hormone-induced phosphate excretion following preequilibration with 32P
Authors: Wideman R. F.
Published: December 2017

Parathyroid hormone (PTH) stimulates a secretory component of avian renal inorganic phosphate (Pi) transport, but the secreted Pi does not appear to be derived directly from peritubular (plasma) Pi. In the present study, experiments were conducted to determine whether differences in parathyroid status during 32P infusion influenced entry of the isotope into the Pi secretory pool. Fractional excretion values for Pi (FEPi) and 32P (FE32P) were compared in normal and parathyroidectomized (PTX) anesthetized birds that had been preinfused with 32P for 0, 90, and 240 min before PTH infusion. The results demonstrate that in the absence of exogenous PTH, FEPi is identical to FE32P in normal and PTX birds, reflecting full equilibration of 32P with excreted Pi under these conditions; and, regardless of the duration of 32P preequilibration or the parathyroid status of the experimental animals, exogenous PTH always causes FEPi to exceed FE32P. It is concluded that the Pi secretory pool is inaccessible to 32P under conditions that should markedly alter cellular Pi influx and efflux.
Ion and water transport by the flounder urinary bladder: salinity dependence
Authors: Demarest J. R.
Published: December 2017

Urinary bladders from seawater-acclimated (SW) flounder had a transepithelial resistance (Rt) of congruent to 2,000 omega X cm2 and absorbed Na and Cl at equal rates of about 3 mueq X cm-2 X h-1 in an electrically silent manner; the short-circuit current (Isc) was 0.03 +/- 0.01 mueq X cm-2 X h-1. The transport of Na and Cl was only partially coupled. Removal of Na (or Cl) from the bathing solutions reduced net Cl (or Na) absorption by only 60%, yet there was neither a change in transepithelial potential nor the appearance of a short-circuit current that could be associated with the net Cl (or Na) transport that remained. Bladders from freshwater-acclimated (FW) flounder had a fivefold lower Rt and exhibited the same partially coupled and equal Na and Cl transport, but the ion transport rates were twice as large as those of SW bladders and the bladders exhibited a significant Isc of 0.51 +/- 0.08 mueq X cm-2 X h-1. The rate of fluid transport was much lower in FW than in SW bladders, reflecting a sixfold decrease in hydraulic conductivity (Lp). In both SW and FW bladders a large portion of the serosal-to-mucosal ion movement appears to be through nonconductive pathways.
Heterogeneity of uridine incorporation along the rabbit nephron. I. Autoradiographic study
Authors: Vandewalle A. , Farman N. , Cluzeaud F. , Bonvalet J. P.
Published: December 2017

We present here an autoradiographic study of uridine labeling in tubular segments micro-dissected from the rabbit kidney. Kidney pyramids were incubated for 60 min with low (66 nM) and high (66 microM) [3H]-uridine concentration. At the two concentrations studied the labeling was almost exclusively nuclear in all segments studied. At the low concentration, labeling predominated in the macula densa (MD = 63.88 +/- 6.15 silver grains/100 micron2, n = 11), cortical ascending limb (CAL = 19.65 +/- 1.65, n = 15), and initial distal tubule (DCTa = 24.31 +/- 2.70, n = 6). It was minimal in the proximal tubule (PCT2 = 9.14 +/- 1.61, n = 16) and in the cortical (CCT = 5.23 +/- 0.75, n = 18) and medullary (MCT = 5.52 +/- 1.10, n = 12) collecting ducts. At a high concentration, the profile of labeling was roughly similar except for a relative increase in labeling much more pronounced in collecting ducts (CCT = +373, MCT = +323%) than in the other structures (MD = -14, CAL = +66, DCTa = +49, PCT = +9%). Pulse-chase experiments do not show evidence for differences in turnover or degradation rates of RNA between segments, at least in the PCT and the connecting part of the CCT. Analysis of the results at low and high concentration suggests that the observed heterogeneity in uridine labeling depends on both variable endogenous nucleoside pools and different rates of uridine incorporation into RNA from one segment to another.
Ca-dependent hemodynamic and natriuretic effects of atrial extract in isolated rat kidney
Authors: Camargo M. J. , Kleinert H. D. , Atlas S. A. , Sealey J. E. , Laragh J. H. , Maack T.
Published: December 2017

The effects of rat atrial tissue extract on renal hemodynamics and fluid and electrolyte excretion were investigated in the isolated perfused rat kidney (IK). IK were perfused at a constant effective perfusion pressure of about 90 mmHg. After control clearance periods (C), extracts of rat atria (AE) or ventricles (VE) were added to the perfusate and three 10-min experimental periods followed. AE, but not VE, significantly increased (P less than 0.001) renal vascular resistance (RVR) to 133 +/- 8% of C, GFR to 201 +/- 34%, filtration fraction to 245 +/- 41%, urine flow (V) to 675 +/- 131%, fractional excretion (FE) of H2O to 336 +/- 29%, absolute Na excretion (UNaV) to 1,259 +/- 290%, FENa to 642 +/- 129%, UKV to 2,226 +/- 1,237%, and FEK to 542 +/- 119%. Despite the marked natriuresis, since GFR doubled, Na reabsorption rose from 78.3 +/- 36.3 in C to 132 +/- 36.3 mueq/min after AE. The effects of AE were immediate and lasted to the end of the perfusion. The lower the initial control GFR, the larger was the AE-induced increase in GFR. Perfusion with low [Ca] (0.2 mM) or verapamil (10(-5) M) severely blunted the hemodynamic, diuretic, kaliuretic, and natriuretic effects of AE. AE decreased rather than increased the RVR when IK were perfused with vasoconstrictors such as angiotensin II, norepinephrine, or vasopressin. The results demonstrate that AE acts directly on the kidney, eliciting powerful Ca-dependent hemodynamic and natriuretic responses. The natriuresis induced by AE can be accounted for, at least in part, by its renal hemodynamic effects rather than by the presence of a putative tubular natriuretic factor. The hypothesis is advanced that AE contains a substance(s) which behaves as a functional agonist/antagonist of endogenous vasoconstrictors with a preferential site of action on the efferent arterioles of the renal vasculature.
Actions of angiotensin II on the brain: mechanisms and physiologic role
Authors: Reid I. A.
Published: December 2017

Angiotensin II acts on the brain to produce a variety of effects including elevation of arterial blood pressure, increased release of vasopressin and ACTH, stimulation of drinking and sodium appetite, and natriuresis. Many, and possibly all, of these effects can be produced by centrally administered angiotensin II or by circulating angiotensin II, which appear to act at common receptor sites located in the circumventricular organs. Whether these effects are normally produced by blood-borne angiotensin II formed by the renal renin-angiotensin system, by angiotensin II formed centrally by the putative brain renin-angiotensin system, or by both, remains to be determined. A large body of information concerning the site and mechanism of these different central actions of angiotensin II is available, and the physiologic significance of these actions is beginning to be understood. Nevertheless, much additional research will be required before the actions of angiotensin II on the brain are completely understood.
Glomerular capillary wall function in human lupus nephritis
Authors: Friedman S. , Strober S. , Field E. H. , Silverman E. , Myers B. D.
Published: December 2017

Eighteen patients with nephrotic-range proteinuria due to lupus nephritis were evaluated with a differential solute clearance technique. Renal plasma flow was similar to that in 17 healthy volunteer controls (506 +/- 75 vs. 503 +/- 32 ml/min, P = NS), while oncotic pressure in pre- and postglomerular plasma was depressed by 9.2 and 17.3 mmHg, respectively. These findings are consistent with elevation of net ultrafiltration pressure and suggest that glomerular hypofiltration (51 +/- 9 vs. 103 +/- 8 ml/min, P less than 0.001) was due to a lowered glomerular ultrafiltration coefficient (Kf). In lupus nephritis the fractional clearance of smaller dextrans (radii less than 50 A) was depressed, while that of larger dextrans (radii greater than 50 A) was elevated. A pore model of solute transport, when applied to the dextran filtration data, revealed a subpopulation of large protein-permeable pores in lupus nephritis not present in controls. Moreover, the fraction of glomerular filtrate permeating these enlarged pores correlated directly with the respective fractional clearances of albumin (r = 0.71) and immunoglobulin G (r = 0.75) in individual patients. Immunosuppression in nine patients was associated with an increase of the filtration rate and filtration fraction. Conversely, fractional protein clearances and the area fraction of the glomerular membrane occupied by large pores decreased. We conclude that human immune glomerular inflammation is manifested by a reduction of Kf and increased glomerular porosity and that these membrane alterations are partially reversible.
Intracellular pH of hepatocytes in primary monolayer culture
Authors: Pollock A. S.
Published: December 2017

Nonproliferating rat hepatocytes in primary monolayer culture were used for determining liver cell intracellular pH and the degree of intracellular pH homeostasis. The dimethyloxazolidinedione weak acid distribution method was adapted for use in monolayer culture. Intracellular pH of cultured hepatocytes in bicarbonate:CO2 medium was relatively constant at 6.85-7.05 over the external pH range of 7.0-8.0. Below an external pH of 7.0, intracellular pH fell below 6.8. Varying PCO2 between 15 and 40 mmHg did not alter the extracellular versus intracellular pH curve. In N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid medium, in the absence of bicarbonate, intracellular pH homeostasis was less well defended. In this setting, the intracellular versus extracellular pH relationship curve could be described by a straight line with slope of 0.59 +/- 0.04. The system responded to the addition of the protonophore carbonyl cyanide p-trifluoromethoxyphenyl hydrazone with an increase in the transmembrane pH gradient. Addition of nigericin in 5 mM K+ medium resulted in intracellular acidification to pH 5.5 +/- 0.2. Metabolism of 20 mM added fructose resulted in intracellular acidification. Incubation in sodium-free media at extracellular pH of 7.6 reduced intracellular pH to 6.67 +/- 0.02 compared with an intracellular pH of 6.99 +/- 0.04 in cultures exposed to medium sodium concentrations of 20-80 meq/liter.
Pressure natriuresis during saline expansion in newborn and adult dogs
Authors: Kleinman L. I. , Banks R. O.
Published: December 2017

Pressure natriuresis was studied in anesthetized saline-expanded adult (n = 10) and neonatal (n = 23) dogs. One group (protocol B) received ethacrynic acid and amiloride to block distal nephron function. Studies in the other group (protocol A) were done without diuretics. Renal arterial blood pressure was raised by bilateral carotid artery occlusion. Renal perfusion pressure was then lowered in steps by partially occluding the aorta proximal to the renal arteries. In protocol B carotid occlusion was associated with an increase in both absolute and fractional sodium excretion by adult and newborn dogs. Moreover, there was significant negative correlation (P less than 0.01) between absolute change in renal arterial pressure and change in tubular reabsorption of sodium per milliliter glomerular filtrate for both age groups. For each mmHg increase in blood pressure there was greater inhibition of sodium reabsorption in the puppy (0.55 mueq/ml glomerular filtrate) than in the adult (0.18 mueq/ml, P less than 0.05). In protocol A puppies, the inhibition of sodium reabsorption due to increases in renal perfusion pressure was less than that occurring in protocol B, indicating that some of the sodium escaping proximal nephron reabsorption was reabsorbed distally. Results of these studies indicate that during saline expansion pressure natriuresis is primarily a proximal tubular event, and the sensitivity of the proximal tubule to changes in renal arterial blood pressure is greater in the newborn than the adult kidney.
Handling of phosphate by a parotid gland (ovine)
Authors: Wright R. D. , Blair-West J. R. , Nelson J. F. , Tregear G. W.
Published: December 2017

The handling of phosphate by the sheep's parotid gland was investigated by examining the effects on the composition of saliva of phosphate depletion, secretomotor nerve stimulation, enrichment of phosphate in the blood supply, and parotid arterial infusion of parathyroid hormone (PTH) and calcitonin. Experiments were performed in anesthetized sheep after vascular isolation of the parotid gland. In phosphate depletion arterial plasma phosphate fell from 1.50 +/- 0.12 to 0.73 +/- 0.08 mM. In phosphate repletion salivary phosphate ion was concentrated 8- and 16-fold compared with parotid arterial and venous plasma, respectively. In depletion salivary phosphate concentration was unchanged at slow salivary flow rate but was significantly lower at high flow rate. Enrichment of phosphate in the arterial blood increased salivary phosphate concentration in both situations. Synthetic bPTH (1-34), highly purified bPTH (1-84), and bovine parathyroid extract were equipotent in increasing salivary phosphate concentration in phosphate repletion and had no effect in phosphate depletion. They also increased parotid blood flow. The rise in phosphate with PTH was conditional on the rise in blood flow, but the same rise in blood flow alone did not reproduce the effect of PTH on salivary phosphate. PTH increased work done and oxygen consumption by the gland but arterial phosphate enrichment did not. Increases in salivary phosphate were associated with decreases in salivary bicarbonate, and the sum [HCO-3] + [Cl-] + (HPO2-4] remained almost constant. Micropuncture studies have shown that ovine parotid ducts do not normally reabsorb phosphate and therefore PTH probably increases phosphate secretion in the endpieces.
Proximal tubular Na, Cl, and HCO3 reabsorption and renal oxygen consumption
Authors: Weinstein S. W. , Klose R. , Szyjewicz J.
Published: December 2017

The majority of the oxygen consumed by the rat kidney appears to occur in the proximal tubule. Therefore changes in metabolically linked ion transport in this segment of the nephron should result in changes in renal oxygen consumption. To study the role of bicarbonate reabsorption in metabolically linked proximal tubular ion transport a series of micropuncture-clearance-extraction experiments were performed comparing the effects of the carbonic anhydrase inhibitor benzolamide and of hypertonic sodium bicarbonate infusion with control conditions in the rat. End-proximal tubular fluid and chloride reabsorption were measured. From these, the rates of sodium and bicarbonate reabsorption were estimated. Simultaneously with the tubular fluids, extraction collections were obtained for determination of renal oxygen consumption. Both benzolamide and hypertonic bicarbonate reduced proximal tubular fluid reabsorption while concomitantly reducing the transepithelial gradient for chloride. The mean rate of renal oxygen consumption did not differ from the control rate in either experimental group and could be dissociated from the calculated net rates of proximal tubular sodium, chloride, and bicarbonate reabsorption. We interpret these data as evidence that proximal tubular hydrogen ion secretion supporting bicarbonate reabsorption requires at most small amounts of oxidative energy, less than detectable by these techniques. The data, in contrast, support the conclusion that the chloride-bicarbonate transepithelial gradient appears to be an important passive driving force in vivo for proximal tubular fluid reabsorption.
Effects of 1,25-dihydroxycholecalciferol on phosphate transport in vitamin D-deprived rats
Authors: Kurnik B. R. , Hruska K. A.
Published: December 2017

To clarify the role of vitamin D in renal phosphate transport, weanling rats were fed a vitamin D-deficient diet containing 1.8% calcium and 1.2% phosphorus. After 5-6 wk, the rats were normocalcemic, normophosphatemic, and had normal levels of PTH. Assays of vitamin D metabolites revealed undetectable plasma levels of 25(OH)D, and 1,25(OH)2D levels of 92 +/- 16 pg/ml in partially vitamin D-depleted (PVDD) rats and 169 +/- 58 pg/ml in normal rats. PVDD rats had increased phosphate excretion, both absolute and fractional, and a decrease in Na+ gradient-dependent Pi transport in proximal tubular brush border membrane vesicles (BBMV) prepared from their kidneys. Vitamin D repletion of PVDD rats with 1,25(OH)2D3, 15 pmol/100 g body wt, decreased fractional excretion of Pi from 22.6 +/- 1.9 to 13.5 +/- 1.3%; the latter values were similar to normal rats. Repletion with 1,25(OH)2D3 also increased Na+-dependent phosphate transport in BBMV from 322 +/- 24 pmol X mg protein-1 X 15 s-1 in BBMV from PVDD rats to 698 +/- 70 pmol X mg protein-1 X 15 s-1. Repletion with larger doses of 1,25(OH)2D3 produced hypercalcemia and hyperphosphatemia from intestinal absorption, an increase in phosphate excretion, and a blunted response of Pi transport to 1,25(OH)2D3. Prevention of hyperphosphatemia by dietary adjustments allowed full expression of the stimulatory effects of 1,25(OH)2D3 on Pi transport. These later data may partially explain the inhibitory effects reported in prior studies in which plasma Pi was not controlled and the larger doses of 1,25(OH)2D3 administered.(ABSTRACT TRUNCATED AT 250 WORDS)
Proximal HCO3- reabsorption and the determinants of tubular and capillary PCO2 in the rat
Authors: Maddox D. A. , Atherton L. J. , Deen W. M. , Gennari F. J.
Published: December 2017

Studies were carried out in Munich-Wistar rats to define the CO2 partial pressure (PCO2) profile in the surface tubules and capillaries of the kidney and to relate these measurements to proximal tubular HCO3- reabsorption, renal blood flow, and O2 consumption. In euvolemic rats, PCO2 in Bowman's space (BS) was 12.5 mmHg higher than in arterial blood, indicating CO2 addition to the arterial tree as it traverses the cortex. PCO2 further rose by 3.9 mmHg between the efferent arteriole (EA) and the peritubular capillaries (PC) (P less than 0.01) and by 4.9 mmHg between BS and the early proximal tubule (EP) (P less than 0.01). In studies with paired measurements, PCO2 in EP was 1.8 mmHg higher than in the adjacent PC (P less than 0.05). HCO3- reabsorption in EP (first 0.4-1.25 mm) was 579 pmol X min-1 X mm-1 (34.3 +/- 4.6% of the filtered load). By use of a model of facilitated diffusion of CO2 across the cell, the trans-epithelial PCO2 gradient in EP can be accounted for by the CO2 generated from HCO3- reabsorption, assuming an intracellular pH of 7.3. In the vascular compartment, roughly half the rise in PCO2 between the afferent arteriole (estimated to equal BS PCO2) and PC can be accounted for by metabolic CO2 production and half by titration of blood buffers by reabsorbed HCO3-.
Effects of bradykinin on renal interstitial pressures and proximal tubule reabsorption
Authors: Mertz J. I. , Haas J. A. , Berndt T. J. , Burnett J. C. , Knox F. G.
Published: December 2017

Renal interstitial Starling forces have been postulated as the link between the peritubular microcirculation and fluid reabsorption by the proximal tubule. The renal vasodilator bradykinin was used as a tool to test this relationship in micropuncture studies in the rat. Bradykinin increased peritubular capillary and interstitial hydrostatic pressures and decreased peritubular and interstitial oncotic pressures. The balance of Starling forces in the interstitium (interstitial oncotic pressure minus interstitial hydrostatic pressure) was significantly decreased from 6.5 +/- 2.3 to -4.0 +/- 1.3 mmHg without a change in fluid reabsorption by the proximal tubule. We conclude that renal interstitial Starling forces do not regulate reabsorption by the superficial proximal tubule in the rat in response to bradykinin.
Luminal and peritubular ionic substitutions and intracellular potential of the rabbit proximal convoluted tubule
Authors: Cardinal J. , Lapointe J. Y. , Laprade R.
Published: December 2017

Transepithelial (psi T) and basolateral (psi BL) potential difference was measured in rabbit proximal convoluted tubules perfused in vitro. In control solution without protein, the mean psi BL was -54 +/- 2.2 mV (n = 57). Luminal substitution of K by Na had no effect. Complete luminal substitution of glucose and alanine, 110 mM substitution of Na or NaCl produced transient hyperpolarizations of psi BL of 14, 10, and 13 mV, respectively, with a return close to the control value within 4-8 min in all cases. Returning to control solution produced similar time-course transient depolarizations of psi BL of 17, 11, and 16 mV, respectively, again with a return to the control value in 4-10 min. Omission of glucose and alanine in the perfusate produced a decrease in cell volume of 14% that was maximal in 4 min with a complete recovery in the post-control period. A 110 mM luminal or peritubular substitution of Cl by cyclamate produced no significant effect on psi BL after taking into account the large psi T generated by the diffusion of Cl across the paracellular pathway. On the other hand, complete peritubular substitution of K by Na and 110 mM substitution of Na or NaCl produced sustained but reversible depolarizations of psi BL of 37.5, 10.2, and 20.4 mV, respectively. The transient nature of the hyperpolarization following luminal substitution of glucose, alanine, or Na can be interpreted in terms of changes in the intracellular sodium activity that would affect the Na-K-ATPase pump. Similarly, the sustained depolarization seen after a peritubular substitution of K and Na would also be compatible with a decrease in the basolateral ionic pump activity.
Adenosine-induced decrease in renin release: dissociation from hemodynamic effects
Authors: Arend L. J. , Haramati A. , Thompson C. I. , Spielman W. S.
Published: December 2017

Adenosine has been reported to produce a biphasic renal blood flow (RBF) response (vasoconstriction followed by a return of flow to control level) and a decrease in glomerular filtration rate (GFR) when infused into the kidney. Intrarenal adenosine infusion also leads to a decrease in renin release. By altering the hemodynamic response to adenosine, we sought to determine whether the decrease in renin release depends on vascular or filtration-induced events. In nine dogs with nonfiltering kidneys, adenosine infusion (3 X 10(-7) mol/min) resulted in a biphasic RBF response and an inhibition of renin release (309 +/- 53 vs. 71 +/- 26 ng ANG I/min). In 11 dogs treated with verapamil (10 micrograms X kg-1 X min-1) no vasoconstriction or decrease in GFR occurred; however, renin release was inhibited by adenosine (1,300 +/- 159 vs. 534 +/- 225 ng ANG I/min). In a third group of nine dogs whose ureteral pressure was raised to 80 cmH2O, adenosine infusion produced a sustained vasoconstriction and an inhibition of renin release (3,086 +/- 1,144 vs. 328 +/- 130 ng ANG I/min). These experiments, in which the renin release effects of adenosine are dissociated from the hemodynamic effects, lead us to conclude that the inhibition of renin release produced by adenosine does not depend either on the vascular or filtration-induced effects of adenosine.
Mechanisms of Na+ uptake into renal brush border membrane vesicles
Authors: Nord E. P. , Hafezi A. , Wright E. M. , Fine L. G.
Published: December 2017

Brush border membrane vesicles were used to investigate the pathways for Na+ uptake across the apical membrane of the renal proximal tubular cell. The kinetics of uptake in the absence of organic solutes were consistent with parallel saturable and nonsaturable pathways. At pH equilibrium (pHin = pHout = 7.5), the Jmax and Kt for saturable uptake were 41 +/- 15 (+/- SE) nmol X mg-1 X min-1 and 33 +/- 9, respectively, and the apparent permeability coefficient, P'Na, was 0.27 +/- 0.02 microliters X mg-1 X min-1. As the equilibrium pH was varied between 6.0 and 8.0, no consistent trend for Kt or P'Na was observed; Jmax varied up to twofold. In contrast, in the presence of an outward H+ gradient (pHin = 6.0 vs. pHout = 7.5), the Kt decreased by an order of magnitude, with little change in Jmax. At low sodium concentrations (1 mM) external Li+ and NH+4, and to a lesser extent K+, Rb+, and Cs+, inhibited Na+ uptake. Amiloride (10(-3) M) inhibited 1 mM Na+ uptake by 80% even in the absence of a H+ gradient. Uptake also varied with the anion composition at high sodium concentrations (100 mM), as predicted from the anion permeabilities. Sodium uptake was more sensitive to variations in membrane potential at high sodium concentrations than at low concentrations. On the basis of these experiments we suggest that the saturable Na+ uptake occurs via an electroneutral Na+-H+ antiporter and that the diffusive flux occurs through a conductive pathway.
Mechanism of furosemide-induced natriuresis by direct stimulation of renal prostaglandin E2
Authors: Katayama S. , Attallah A. A. , Stahl R. A. , Bloch D. L. , Lee J. B.
Published: December 2017

Studies were conducted to investigate the interaction of renal prostaglandin E2 (PGE2) production and the renin-angiotensin system in the mechanism of furosemide-induced natriuresis. In conscious rabbits with permanent urinary bladder cannulation, furosemide in vivo (10 mg/kg) increased urinary water, sodium, and PGE2 excretion and plasma renin activity (PRA) over 50 min. Furosemide administered in vivo enhanced renal papillary but not cortical in vitro PGE2 biosynthesis. Prior administration of indomethacin at 2 mg/kg augmented the saluretic effect of furosemide, decreased its effect on UPGE2 V, abolished the rise in PRA, and reduced cortical but not papillary PGE2 biosynthesis. However, at 10 mg/kg, indomethacin reduced the saluretic effect of furosemide and eliminated the increase in UPGE2 V with continued suppression of PRA. Direct addition of furosemide in vitro to the incubation medium (10(-5) and 10(-3) M) markedly augmented papillary PGE2 synthesis. It is concluded that furosemide stimulates renal papillary PGE2 biosynthesis directly without mediation by angiotensin II, resulting in an increase in UPGE2 V, and the enhanced or inhibitory effect of indomethacin on furosemide-induced natriuresis is dose related and dependent on the degree of PGE2 synthesis inhibition in the presence of suppressed PRA, which occurred at all doses studied.
Substrate support for renal functions during hypoxia in the perfused rat kidney
Authors: Gronow G. H. , Cohen J. J.
Published: December 2017

Do the substrates that can be utilized for anaerobic ATP production by cytosolic (G, glycolytic) and/or mitochondrial (M) metabolic pathways support renal function during marked hypoxia? The isolated rat kidney was perfused at 38 degrees C, pH 7.4, at a mean pressure of 120 mmHg for 110 min with a Krebs-Ringer bicarbonate solution containing 6 g/100 ml substrate-free albumin (SFA0). After substrate-free aerobic (PO2 = approximately 646 mmHg) internal control observations were made, the perfusate was gassed with 95% N2/5% CO2 (n = 15) and substrates (each 5 mM) were added (G, glucose, K, alpha-ketoglutarate, A, aspartate), or SFA0 perfusion was continued. Perfusion flow rate (PFR) increased 20-43% during hypoxia; thus there was no limitation in substrate delivery to the kidney. Although GFR decreased during all hypoxic perfusions, due to the variations in GFR, the reductions in GFR were not significant. Fractional Na+ reabsorption (%TNa+) was reduced in the hypoxic kidney but the decreases in %TNa+ in the presence of G or M substrates were significantly smaller (-26 to -36%) than the decreases observed during hypoxic SFA0 perfusion (-44%). Free water clearance decreased markedly during substrate-free hypoxic perfusion; by contrast, addition of G or M substrates either increased or maintained CH2O. G increased hypoxic CH2O (+194% to +440% of internal control) more than did M substrates. It is postulated that the increases in %TNa+ in the presence of substrates during hypoxia results in the increases in GFR. By making substrates available that can be oxidized anaerobically in cytosol or in mitochondria, the kidney can better maintain a portion of its tubular functions during severe hypoxia.
Alpha 2-adrenoceptors and sodium reabsorption in the isolated perfused rat kidney
Authors: Smyth D. D. , Umemura S. , Pettinger W. A.
Published: December 2017

Alpha 2-Adrenoceptors are known to inhibit adenylate cyclase in a number of tissues, but their function in the kidney is unknown. Adenylate cyclase and sodium excretion were stimulated with furosemide (30 microM) in the rat kidney perfused with Krebs-Henseleit solution (albumin 6.5 g/100 ml, 36 degrees C). beta-Adrenoceptors and alpha 1-adrenoceptors were blocked by propranolol (100 nM) and prazosin (30 nM) in the perfusate. Urinary cAMP and sodium excretion increased with furosemide. Activation of alpha 2-adrenoceptors with epinephrine (28 nM) caused no change in perfusion pressure or flow but decreased urinary cAMP and sodium excretion. These effects of epinephrine were reversed by the alpha 2-selective adrenoceptor blocking agent yohimbine (300 nM). Thus, in the setting of furosemide-stimulated sodium excretion and an associated elevation of adenylate cyclase, alpha 2-adrenoceptor stimulation resulted in sodium retention and inhibition of adenylate cyclase. By this receptor mechanism the sympathoadrenal system may contribute to retention of sodium.
Axial heterogeneity in the rat proximal convoluted tubule. I. Bicarbonate, chloride, and water transport
Authors: Liu F. Y. , Cogan M. G.
Published: December 2017

To measure simultaneously the concentration profiles of bicarbonate, chloride and inulin along the length of the superficial proximal convoluted tubule, free-flow micropuncture measurements were made sequentially from the end-proximal tubule to Bowman's space in 10 tubules of hydropenic Munich-Wistar rats. Bicarbonate and volume reabsorption were 354 +/- 21 pmol X mm-1 X min-1 and 5.9 +/- 0.4 nl X mm-1 X min-1 in the first millimeter and fell progressively in the remaining 3.8 mm of tubule, averaging 83 +/- 4 pmol X mm-1 X min-1 and 2.3 +/- 0.5 nl X mm-1 X min-1, respectively. The values in the initial millimeter represents a high transport capacity since they exceed rates that have been observed when comparable or even higher mean luminal substrate concentrations were presented to the late proximal tubule. In contrast, chloride reabsorption was only 206 +/- 55 peq X mm-1 X min-1 in the first millimeter compared with a mean of 306 +/- 22 peq X mm-1 X min-1 in the rest of the tubule. In conclusion, there is substantial axial transport heterogeneity, with bicarbonate and water reabsorption higher but chloride reabsorption lower in the early compared with the late superficial proximal convoluted tubule.
Transport by epithelia with compliant lateral intercellular spaces: asymmetric oncotic effects across the rat proximal tubule
Authors: Weinstein A. M.
Published: December 2017

Mathematical models of the proximal tubule are considered in which the lateral intercellular spaces distend in response to increased interstitial pressures and basal outlet permeabilities increase as a result of interspace widening. An approximate analytical model of the interspace reveals the possibility that such compliance may introduce an asymmetry to the effect of protein oncotic forces on transepithelial volume flow. Peritubular oncotic forces close the interspace, enhance interspace hypertonicity, and thus substantially increase volume reabsorption (enhanced intraepithelial solute-solvent coupling). The model also predicts a decline in epithelial water permeability (Lp), salt reflection coefficient, and salt permeability, with the application of peritubular protein. When parameters are chosen so as to represent the rat proximal tubule, the predicted effect on solute permeability is comparable to the observed changes in electrical resistance of the epithelium. However, when the luminal solution is slightly hypotonic to blood and proximal reabsorption has become isosmotic, the models show relatively small protein effects, which are dependent upon cell and tight junction permeabilities and are little influenced by interspace compliance. The capability of such models to represent the peritubular protein enhancement of isosmotic salt and water reabsorption by the proximal tubule in vivo is questioned.
Opposing effects of captopril and aprotinin on tubuloglomerular feedback responses
Authors: Schnermann J. , Briggs J. P. , Schubert G. , Marin-Grez M.
Published: December 2017

We investigated the effect of two protease inhibitors, captopril and aprotinin, on tubuloglomerular feedback. In anesthetized rats, 15 or 25 mg/kg captopril significantly reduced the change of early proximal flow rate achieved by raising loop of Henle perfusion rate from 0 to 40 nl/min. Consistent with this reduction of maximum responses, there was a rise of single nephron glomerular filtration rate from 30.7 +/- 1.15 to 35.0 +/- 0.93 nl/min (P less than 0.01) following 25 mg/kg captopril. Infusion of aprotinin at 40,000 KIU/h produced an increase in maximum feedback responses from 38.2 +/- 1.66 to 56.8 +/- 2.35% (P less than 0.05). Infusion of aprotinin in two different doses (20,000 or 40,000 KIU/h) diminished or prevented the effect of 25 mg/kg captopril on maximum feedback responses. Since the main action of aprotinin is believed to be kallikrein inhibition, our data suggest that the magnitude of feedback responses may be affected by the kallikrein-kinin system and that the action of captopril may be in part mediated by its interference with kinin metabolism.
Suspension of medullary thick ascending limb tubules from the rabbit kidney
Authors: Chamberlin M. E. , LeFurgey A. , Mandel L. J.
Published: December 2017

A procedure for isolating a suspension of tubules derived from the rabbit medullary thick ascending limb is described. The purity of the preparation was assessed by microscopy and enzyme assays and the viability of the preparation was assessed by measuring oxygen consumption. Microscopy revealed that the suspension contains 95% thick ascending limbs and that the isolation procedure preserves the structure of the epithelium except for the loss of the basement membrane. The preparation had a high activity of calcitonin-sensitive adenylate cyclase, a marker enzyme for the medullary thick ascending limb. Control oxygen consumption was considerably higher than that reported for proximal tubules in the literature, and nystatin or carbonyl cyanide p-trifluoromethoxyphenylhydrazone addition produced a more than 100% increase in oxygen consumption. Furosemide inhibited the oxygen consumption by 43% and ouabain inhibited it by 42%. Furosemide inhibited sodium chloride entry without directly affecting the Na-K-ATPase or cellular metabolism. Chloride removal depressed oxygen consumption to the same extent as furosemide, but some of this action was through direct inhibition of cellular metabolism.
Effect of magnesium loading on magnesium delivery to the juxtamedullary end-descending limb
Authors: Roy D. R.
Published: December 2017

Previous micropuncture and microperfusion studies in acutely hypermagnesemic rats have yielded conflicting results with respect to magnesium transport in Henle's loop. The following experiments were performed to reexamine, by micropuncture of papillary end-descending limb, whether magnesium undergoes intratubular secretion in magnesium-loaded rats. Group 1 animals served as normal controls; group 2 animals received an acute intravenous magnesium load; group 3 animals were orally magnesium loaded for 3 wk before receiving an acute intravenous magnesium load during micropuncture; group 4 animals were acutely thyroparathyroidectomized and water loaded before receiving an acute magnesium load. Fractional magnesium delivery to the end-descending limb did not differ from the corresponding value observed in the superficial proximal tubule in normal animals (67 +/- 5.3 vs. 76 +/- 7.6%). Acute magnesium loading raised plasma magnesium concentration and fractional magnesium excretion more than twofold but did not change fractional magnesium delivery to the end-descending limb or superficial nephron significantly from control values (75 and 73%). Chronic oral magnesium loading raised daily urinary magnesium excretion threefold (183 vs. 53 mumol X day-1 X 100 g body wt-1, P less than 0.05), but acute magnesium loading in this group did not significantly alter fractional delivery to the end-descending limb (85 +/- 10%, NS). Increasing intratubular flow rate while acutely raising plasma magnesium concentration (group 4) also did not induce intratubular magnesium secretion. The absence of significant changes in fractional magnesium delivery to the end-descending limb during magnesium loading suggests that intratubular magnesium secretion, if at all present, is very small and of questionable significance.
Glucocorticoid effects on Na-K-ATPase in rabbit nephron segments
Authors: Garg L. C. , Narang N. , Wingo C. S.
Published: December 2017

We determined the effect of dexamethasone on Na-K-ATPase activity in six nephron segments of the adrenalectomized rabbit. Treatment consisted of 1.4 micrograms dexamethasone X 100 g body wt-1 X day-1 for 7 days prior to the study of the nephron segments. Enzyme activity was determined in individual nephron segments by a microfluorometric assay. There was 40-50% less activity of Na-K-ATPase in the S1 portion of the proximal convoluted tubule (PCT, S1), the medullary thick ascending limb (MTAL), and the distal convoluted tubule (DCT) of adrenalectomized rabbits compared with that of control (sham-operated) animals. There was no significant difference in the enzyme activity in proximal straight tubules (PST, S2 and S3) and cortical thick ascending limb (CTAL) of adrenalectomized and control animals. Dexamethasone treatment produced a dexamethasone concentration of 5 +/- 0.8 nM in the plasma and increased Na-K-ATPase activity in PCT (S1), MTAL, and DCT of the adrenalectomized animals to the control levels without significantly affecting the enzyme activity in the PST (S2, S3) or CTAL. The concentration of dexamethasone in the plasma was such that the hormone should bind mainly to dexamethasone receptors (Kd = 5 nM) and very little to aldosterone receptors (Kd greater than 60 nM). Thus, glucocorticoids probably stimulate Na-K-ATPase in PCT, MTAL, and DCT through glucocorticoid (Type II) receptors and not through mineralocorticoid (Type I) receptors.
Regulation of the maximum rate of renal ammoniagenesis in the acidotic dog
Authors: Halperin M. L. , Vinay P. , Gougoux A. , Pichette C. , Jungas R. L.
Published: December 2017

Metabolism of glutamine results in the net production of ATP; however, cells cannot sustain an ATP production rate greater than their rate of ATP utilization. The purpose of these studies was to determine whether the rate of ATP turnover in the kidney could set an upper limit on renal glutamine metabolism and thereby renal ammoniagenesis. The acidotic dog kidneys extracted glutamine, lactate, citrate, and oxygen from the arterial blood and added ammonium and alanine to the venous blood. Renal glutamine metabolism was responsible for almost all the ammonium production. Renal ATP production was estimated from the rate of oxygen consumption and appeared to be derived roughly equally from the oxidation of glutamine and lactate. There was no apparent renal glucose production from ATP balance calculations and this impression was supported when the inhibitor of gluconeogenesis, 3-mercaptopicolinate, did not inhibit ammoniagenesis. Approximately 90% of the ATP synthesized was utilized to reabsorb sodium. When the amount of ATP utilized for sodium reabsorption in the proximal convoluted tubule (assumed to be 60% of filtered sodium) was compared with the amount of ATP produced from glutamine metabolism, the values were similar despite the fact that the glomerular filtration rate in individual dogs varied more than fourfold. When the quantity of ATP expended for sodium reabsorption was decreased by the infusion of ouabain or by the constriction of one renal artery without reducing glutamine delivery, the kidney lowered its rate of ammoniagenesis to a quantitatively predictable amount.(ABSTRACT TRUNCATED AT 250 WORDS)
Lack of potassium effect on Na-Cl cotransport in the medullary thick ascending limb
Authors: Alvo M. , Calamia J. , Eveloff J.
Published: December 2017

The effect of potassium on sodium chloride uptake into rabbit renal medullary thick ascending limb of Henle's loop (mTALH) cells was studied to assess whether K participates in the Na-Cl cotransport system. Na uptake into the mTALH cells was inhibited 70% at 3 min by 1 mM furosemide. The total and furosemide-sensitive Na uptake was stimulated by Cl. Additionally, Cl uptake into the mTALH cells was stimulated by Na gradients and inhibited 42% at 3 min by 1 mM furosemide. Na uptake was studied in the presence of 0,5, or 140 mM external K gradients. Na uptake was similar in the absence and presence of K. Additionally, furosemide inhibited Na uptake as effectively in the absence or presence of K. Similar studies were conducted to study the effects of Na on 86Rb uptake. Na did not stimulate 86Rb uptake. The uptake of 86Rb was similar in the presence of 0,5, or 140 mM Na gradients. Furosemide had no significant inhibitory effect on 86Rb uptake. Barium (5 mM), an inhibitor of K conductance pathways, inhibited total 86Rb uptake by 19%. In the presence of 5 mM BaCl2, Na still did not have a stimulatory effect on 86Rb uptake. The results confirm the existence of a Na-Cl cotransport system in mTALH cells, but a direct effect of K on the NaCl cotransport system could not be demonstrated under the experimental conditions we used.
Developmental changes in the phosphaturic response to parathyroid hormone in the rat
Authors: Webster S. K. , Haramati A.
Published: December 2017

The need for young, immature rats to maintain positive phosphate balance for growth is well recognized. However, whether this process is associated with a resistance to the phosphaturic effect of parathyroid hormone (PTH) is not clear. In these experiments we examined the effect of PTH on urinary phosphate and cAMP excretion in rats at 3, 6, 12, and 20 wk of age. Clearance experiments were performed in acutely thyroparathyroidectomized (TPTX) rats fed a normal phosphate diet (0.86%). Basal fractional excretion of phosphate (FEPi) was low in all TPTX rats (less than 1%). The phosphaturic response to a high dose of PTH (1 U X kg-1 X min-1) increased with development (from 4 to 29%). The responses to increasing doses of PTH demonstrated a decrease in sensitivity to PTH in 6- compared with 20-wk-old rats. Urinary cAMP excretion (either per milliliter glomerular filtrate or per gram kidney weight) following PTH was not different among 6-, 12-, and 20-wk-old rats, thus demonstrating a dissociation between the increase in phosphate excretion and cAMP excretion. These results indicate that the phosphaturic response to PTH is blunted in immature, acutely TPTX rats and that the phosphaturia increases progressively with development.