bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonia transport in the mammalian kidney
Authors: Good D. W. , Knepper M. A.
Published: December 2017

Ammonia, an important urinary buffer in mammals, is synthesized primarily in the proximal tubules and is transferred to the final urine by a sequence of specialized transport processes. The pathway of ammonia transfer to the urine involves secretion into the proximal tubules, absorption from the loops of Henle, accumulation in the renal medullary interstitium, and secretion into the collecting ducts. Ammonia is transported as NH3 at some nephron sites and as NH+4 at others. In this paper, we discuss the physical basis of NH3 and NH+4 transport in epithelia and then describe ammonia transport mechanisms in individual nephron segments. Information about ammonia transport in individual nephron segments from isolated perfused tubule studies is integrated with data from in vivo studies to obtain an expanded overall model of renal ammonia handling.
Biochemical changes in the pancreas of rats with chronic renal failure
Authors: Kaysen G. A. , Majumdar A. P. , Dubick M. A. , Vesenka G. D. , Mar G. , Geokas M. C.
Published: December 2017

Chronic renal failure (CRF) was produced in female Sprague-Dawley rats by 7/8 nephrectomy. Creatinine clearance was depressed significantly (P less than 0.005) and blood urea nitrogen (BUN) increased in CRF rats when compared with the sham-operated (S) controls. CRF caused no apparent change in body weight but significantly increased pancreatic weight as well as increased DNA, RNA, and protein content. Pancreatic protein-to-DNA and RNA-to-DNA ratios were also found to be significantly higher in CRF rats than in the S controls. Trypsin-like activity and immunoreactive cationic trypsinogen levels were both increased in the pancreas of CRF rats, but not in their serum. On the other hand, protease inhibitory activity in the pancreas and serum was significantly decreased by CRF. The ability of the dispersed pancreatic acini isolated from CRF rats to incorporate [3H]-leucine into protein, in the absence and presence of 0.25 nM cholecystokinin octapeptide (CCK-8), was found to be lower than in the controls. Furthermore, discharge of both trypsinogen and chymotrypsinogen induced by CCK-8 was markedly reduced from acini of CRF rats as compared with the S controls. In contrast, lactate dehydrogenase (LDH) was released more readily from pancreatic acini of CRF. It is concluded that mild CRF produces hyperplasia and hypertrophy of the pancreas and lowers the responsiveness of acini to CCK-8 with respect to synthesis and secretion of proteins.
Alpha and beta types of carbonic anhydrase-rich cells in turtle bladder
Authors: Stetson D. L. , Steinmetz P. R.
Published: December 2017

The carbonic anhydrase-rich (CA) cell population of the turtle urinary bladder, which is responsible for the secretion of H+ and probably of HCO-3, was studied by freeze-fracture and thin-section electron microscopy. The apical membrane of the major CA cell type (alpha type) was characterized by microplicae and by a coat of studs on its cytoplasmic side; on freeze-fracture, it contained a dense population of rod-shaped intra-membrane particles. When fixed at low CO2 tension, the apical membrane area of the alpha cell was reduced; its surface displayed microplicae as well as microvilli, and the apical cytoplasm contained many vesicles with rod-shaped particles and studs. The apical membrane of the other (beta type) CA cell was characterized by numerous individual microvilli without microplicae and by a relative absence of rod-shaped particles and studs. Instead, the beta cell contained studs and rod-shaped particles in its basolateral membrane. The ultrastructure and frequency of the beta CA cell were not affected by changes in CO2 tension. We suggest that the alpha cell is responsible for H+ secretion. The reversal of the polarity of the membrane elements in the beta cell and failure to respond to CO2 with amplification of its apical membrane are consistent with a role in HCO-3 secretion.
Urate and p-aminohippurate transport in rat renal basolateral vesicles
Authors: Kahn A. M. , Shelat H. , Weinman E. J.
Published: December 2017

We examined the transport of urate in basolateral membrane vesicles from the rat kidney and determined the relationship between the transport of urate and p-aminohippurate (PAH). Urate was not converted to allantoin, and the uptake of urate represented transport into an osmotically active intravesicular space. The 10-s uptake of 53 microM [14C]urate in basolateral vesicles was inhibited 39 +/- 6, 49 +/- 10, and 35 +/- 3% by (in mM) external 2.4 probenecid, 2.4 DIDS, and 1.4 unlabeled urate, respectively. The 10-s uptake of 353 microM [14C]urate was trans-stimulated 82 +/- 8% by preloading basolateral vesicles with 1.5 mM unlabeled urate. The uptake of urate was stimulated by an outwardly directed gradient for Cl- (Cl-in = 25 mM, Cl-out = 5 mM). This effect was not consequent to a more electropositive intravesicular space, as monitored by the voltage-sensitive sodium-L-malate cotransport system. The Cl- gradient-stimulated component of urate uptake in basolateral vesicles was not cis-inhibited by 4.8 mM PAH, whereas Cl gradient-stimulated urate uptake in brush border vesicles was cis-inhibited 43 +/- 5% by PAH. In the absence of Cl-, 4.8 mM PAH did not cis-inhibit, and 5.4 mM PAH or 6.4 mM lactate did not trans-stimulate the uptake of urate in basolateral vesicles, contrasting with results obtained with brush border vesicles. The uptake of urate in basolateral vesicles was not stimulated by external Na+ relative to K+, Li+, or Cs+. In contrast, PAH uptake in basolateral vesicles was stimulated 87 +/- 9% by external Na+.(ABSTRACT TRUNCATED AT 250 WORDS)
N1-methylnicotinamide transport by isolated perfused snake proximal renal tubules
Authors: Dantzler W. H. , Brokl O. H.
Published: December 2017

N1-methylnicotinamide (NMN) transport was studied in isolated perfused snake (Thamnophis spp.) proximal renal tubules. Unidirectional lumen-to-bath (Jl----bNMN) and bath-to-lumen (Jb----lNMN) fluxes saturated. Although Jl----bNMN and Jb----lNMN were similar, mean Jl----bNMN tended to exceed mean Jb----lNMN at all concentrations studied. Direct measurements confirmed a net reabsorptive flux equal to the difference between the unidirectional fluxes. This transport, opposite in direction to tetraethylammonium (TEA) transport, was not inhibited by TEA. Transport into the cells across both the luminal and peritubular membranes during flux measurements was apparently down an electrochemical gradient by a mediated process that was sodium dependent. Inhibition with NMN analogues suggested that transport into the cells across the luminal membrane during Jl----bNMN was more specific than transport into the cells across the peritubular membrane during Jb----lNMN. Transport out of the cells across both the luminal and peritubular membranes during flux measurements was apparently against an electrochemical gradient.
Dissociation of urinary kallikrein activity and salt and water excretion in the rat
Authors: Pollock D. M. , Butterfield M. I. , Ader J. L. , Arendshorst W. J.
Published: December 2017

Experiments were designed to examine the relationship, if any, between urinary kallikrein activity (amidolytic assay) and sodium and water excretion in 12-wk-old Munich-Wistar rats. Five groups of animals were studied: euvolemic, saline-expanded and water-loaded anesthetized rats, and euvolemic and saline-expanded conscious restrained rats. Following surgery, animals were allowed to stabilize (60-180 min) and reach a steady-state urine flow. By design, basal sodium and/or water excretion varied markedly among groups as a function of hydration state. Group means for sodium excretion and urine flow ranged from 0.8 to 12.4 mu eq/min and 6 to 112 microliter/min, respectively. In contrast, neither active nor total urinary kallikrein activity differed significantly among the five groups. In anesthetized euvolemic rats, intravenous administration of aprotinin produced a dose-dependent decrease in urinary kallikrein activity. The greatest inhibition of 93 +/- 3% (active) and 72 +/- 10% (total) was observed with a dose of 5,000 kallikrein inhibiting units (KIU)/kg and 1,000 KIU X kg-1 X min-1. This dose produced a significant decrease in active and total kallikrein activity in each group (P less than 0.001). However, sodium and water excretion were unchanged in aprotinin-treated rats and similar to values in vehicle-treated time-control groups. Linear regression analysis revealed no significant correlations between urinary kallikrein activity and sodium excretion or urine flow either among or within groups. These results indicate that urinary kallikrein activity is not related to acute sodium and water homeostasis in anesthetized or conscious rats.
Influence of oxytocin on renal hemodynamics and electrolyte and water excretion
Authors: Conrad K. P. , Gellai M. , North W. G. , Valtin H.
Published: December 2017

We examined the renal effects of synthetic oxytocin (OT) in the presence and absence of vasopressin in conscious euvolemic rats. Both sexes of the Long-Evans (LE) and Brattleboro homozygous (DI) strains were used. OT infused intravenously at 0.25 and 2.5 ng X min-1 X 100 g body wt (BW)-1 resulted, respectively, in plasma concentrations of 30 +/- 6 and 265 +/- 88 pg/ml in LE rats and 46 +/- 5 and 327 +/- 29 pg/ml in DI rats. Glomerular filtration rate (GFR) was augmented most consistently by the larger dose of hormone in LE rats (P less than 0.05), whereas the low infusion rate of OT enhanced GFR in DI rats (P less than 0.01). Effective renal plasma flow was not changed significantly. OT (both doses) increased the fractional excretion of sodium two- to threefold in each strain of animal (all at least P less than 0.05 from control), whereas the fractional excretion of potassium was largely unaffected. In LE rats, a diuresis was observed with either infusion rate of hormone, accompanied by a rise in osmolar clearance (COsm). In contrast, there was no change of urine flow with the low dose of OT in DI rats, because COsm increased and the clearance of free water (CH2O) decreased proportionately. The higher infusion rate of OT promoted antidiuresis in DI rats, with negative CH2O and little change in COsm. We conclude that oxytocin enhances GFR and is natriuretic regardless of the presence or absence of endogenous vasopressin.(ABSTRACT TRUNCATED AT 250 WORDS)
Intracellular pH regulation in frog skin: a 31P-nuclear magnetic resonance study
Authors: Civan M. M. , Peterson-Yantorno K.
Published: December 2017

The 31P-nuclear magnetic resonance spectra of single frog skins were monitored during perfusion with reference and experimental solutions, permitting each tissue to serve as its own series control. Over an external pH (pHo) range of approximately 7.25-7.64 U, the intracellular pH (pHc) displayed both homeostasis and response. External alkalinization produced a transient intracellular regulation, but pHc returned to its base-line value even in the absence of a further change in pHo. Below this range, pHc was linearly and strongly dependent on pHo with a slope close to 1, when the external pH was varied by addition of nonvolatile base. Measurements were generally performed with tissues bathed in Ringer solutions containing 2.5 mM HCO3- and bubbled with 99% O2-1% CO2. Replacement of external Cl- by gluconate reversibly increased pHc by 0.34 +/- 0.05 U. Substitution of SO4(2-) for Cl- also alkalinized the cells; pHc was increased by 0.16 +/- 0.01 U in the presence of the standard concentration of external HCO3-, but an alkaline shift was only just detectable (0.05 +/- 0.02 U) in its nominal absence. The application of 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid blocked the sustained intracellular alkalinization characteristically produced by external Cl- replacement but did not alter the reduction in short-circuit current and increase in transepithelial resistance caused by gluconate substitution.(ABSTRACT TRUNCATED AT 250 WORDS)
Renal failure in dogs with experimental acute pancreatitis: role of hypovolemia
Authors: Levy M. , Geller R. , Hymovitch S.
Published: December 2017

The factors causing a decline in renal perfusion were studied in anaesthetized dogs with acute pancreatitis 4 h after the forceful injection of bile into the pancreatic duct. In 11 such dogs, glomerular filtration rate (GFR) decreased by 40.4% from the control state (P less than 0.05), whereas the clearance of para-aminohippurate (CPAH) declined by 50.2%. These changes were associated with a 15.3% decline in cardiac output (P less than 0.05) and a 26.2% fall in plasma volume. Glomerular morphology was entirely normal. When hypovolemia was prevented by infusing homologous plasma over the 4-h period of observation, the normally observed decline in GFR, CPAH, and cardiac output was prevented. The decline in plasma volume, associated with a rising hematocrit and declining plasma protein concentration, and the associated decrement in renal perfusion, could be entirely duplicated by the infusion of trypsin, chymotrypsin, elastase, and phospholipase A2 (but not lipase or amylase) into normal dogs. These perturbations also were prevented by the concurrent infusion of 4% albumin in saline. At 24 h, however, the renal failure became unresponsive to volume replenishment. We conclude that the decline in renal perfusion in dogs at 4 h with acute pancreatitis is entirely due to hypovolemia, induced by the release of specific enzymes from the inflamed gland, which causes the loss of protein-rich plasma from the vascular space.
Mechanism of bicarbonate exit across basolateral membrane of rabbit proximal straight tubule
Authors: Sasaki S. , Shiigai T. , Yoshiyama N. , Takeuchi J.
Published: December 2017

To clarify the mechanism(s) of HCO3- (or related base) transport across the basolateral membrane, rabbit proximal straight tubules were perfused in vitro, and intracellular pH (pHi) and Na+ activity (aiNa) were measured by double-barreled ion-selective microelectrodes. Lowering bath HCO3- from 25 to 5 mM at constant PCO2 depolarized basolateral membrane potential (Vbl), and reduced pHi. Most of these changes were inhibited by adding 1 mM 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS) to the bath. Total replacement of bath Na+ with choline also depolarized Vbl and reduced pHi, and these changes were also inhibited by SITS. Reduction in aiNa was observed when bath HCO3- was lowered. Taken together, these findings suggest that HCO3- exists the basolateral membrane with Na+ and negative charge. Calculation of the electrochemical driving forces suggests that the stoichiometry of HCO3-/Na+ must be larger than two for maintaining HCO3- efflux. Total replacement of bath Cl- with isethionate depolarized Vbl gradually and increased pHi slightly, implying the existence of a Cl(-)-related HCO3- exit mechanism. The rate of decrease in pHi induced by lowering bath HCO3- was slightly reduced (20%) by the absence of bath Cl-. Therefore, the importance of Cl(-)-related HCO3- transport is small relative to total basolateral HCO3- exit. Accordingly, these data suggest that most of HCO3- exits the basolateral membrane through the rheogenic Na+/HCO3- cotransport mechanism with a stoichiometry of HCO3-/Na+ of more than two.
Atrial natriuretic peptide stimulates salt secretion by shark rectal gland by releasing VIP
Authors: Silva P. , Stoff J. S. , Solomon R. J. , Lear S. , Kniaz D. , Greger R. , Epstein F. H.
Published: December 2017

Salt secretion by the isolated perfused rectal gland of the spiny dogfish shark, Squalus acanthias, is stimulated by synthetic rat atrial natriuretic peptide (ANP II) as well as extracts of shark heart, but not by 8-bromo-cyclic guanosine 5'-monophosphate. Cardiac peptides have no effect on isolated rectal gland cells or perfused tubules, suggesting that stimulation requires an intact gland. The stimulation of secretion by ANP II is eliminated by maneuvers that block neurotransmitter release. These include: perfusion with procaine (10(-2) M), perfusion with high Mg2+ (9.5 mM) and low Ca2+ (0.5 mM) concentrations, and addition to the perfusate of the calcium channel blockers nifedipine (10(-6)M), diltiazem (5 X 10(-5)M), or verapamil (10(-4)M). Cardiac peptides stimulate the release of vasoactive intestinal peptide (VIP), known to be present in rectal gland nerves, into the venous effluent or perfused glands in parallel with their stimulation of salt secretion, but the release of VIP induced by ANP II is prevented by perfusion with procaine. Cardiac peptides thus appear to regulate rectal gland secretion by releasing VIP from neural stores within the gland. It is possible that other physiological effects of these hormones might be explained by an action to enhance local release of neurotransmitters.
Influence of transmembrane potential differences of renal tubular epithelial cell on ANG II binding
Authors: Brown G. P. , Douglas J. G.
Published: December 2017

Previous studies from this laboratory demonstrated specific high-affinity binding sites of rat renal brush-border membrane vesicles (BBMV). The time course of angiotensin II (ANG II) binding in the presence of a NaCl gradient (medium greater than intravesicular) demonstrated an "overshoot" characteristic of electrogenic sodium-dependent D-glucose uptake. The time course of ANG II binding to membrane vesicles equilibrated with NaCl did not exhibit such "overshoot" and was lower in magnitude. Therefore, studies were designed to test the hypothesis that ANG II binding to BBMV was enhanced by a transmembrane potential difference in a manner similar to sodium-dependent D-glucose uptake. The effects of sodium salts with differing rates of anion equilibration were compared on ANG II binding. Peak binding was achieved most rapidly with NaSCN followed by NaCl and Na2SO4. By contrast, sodium acetate, which is translocated electroneutrally, exhibited no overshoot. ANG II binding in the presence of a KCl gradient was similar to NaCl. The overshoot was abolished in the presence of an inwardly directed KCl gradient plus valinomycin. Magnesium salts with differing rates of anion permeabilities had similar effects on binding, as did sodium salts. Scatchard analysis revealed that the receptor density was fourfold higher in the presence of an electrochemical gradient compared with nongradient conditions. These data are consistent with the conclusion that ANG II binding to BBMV is enhanced by a transmembrane potential difference, and suggest that this may be an important modulator of tubular epithelial responses to ANG II in vivo.
Centrally administered atrial natriuretic factor increases renal water excretion
Authors: Lee J. , Feng J. Q. , Malvin R. L. , Huang B. S. , Grekin R. J.
Published: December 2017

The effects of intracerebroventricular (ICV) infusion of atrial natriuretic factor (ANF; atriopeptin III) on renal function, plasma concentrations of antidiurectic hormone, aldosterone, and plasma renin activity (PRA) were examined in anesthetized rats and sodium-depleted conscious sheep. The results were compared with those obtained by intravenous infusion of the same dose of ANF. In both rats and sheep, urine volume was increased four- to sixfold over basal values by ICV infusion of ANF. The response was not associated with increased excretion of sodium or potassium. However, urine osmolality was decreased, and free water clearance increased. Intravenous infusion of the same dose of ANF was without effect. Neither mean arterial blood pressure nor heart rate was changed by the ICV infusion of ANF. In the sheep, renal plasma flow showed no significant changes and glomerular filtration rate was unaltered with the exception of a single experimental period out of four periods of ICV ANF infusion. Plasma concentration of ADH was decreased and PRA increased, whereas aldosterone levels remained unchanged as a function of ICV ANF. In the rat, the diuretic response to ANF was prevented by continuous intravenous infusion of a subpressor dose of ADH. These results suggest that ANF within the central nervous system inhibits secretion of ADH.
De novo intrarenal formation of angiotensin II during control and enhanced renin secretion
Authors: Rosivall L. , Narkates A. J. , Oparil S. , Navar L. G.
Published: December 2017

In previous studies it has not been possible to determine net intrarenal formation of angiotensin II (ANG II) from arteriovenous ANG II concentrations because of the high intrarenal ANG II degradation rates (DR). This study was designed to determine ANG II-DR and to estimate net intrarenal ANG II formation during normal and enhanced renin secretion rate (RSR). In anesthetized dogs, plasma renin activity and ANG II were measured in arterial and renal venous blood by radioimmunoassay during four periods: control, renal arterial constriction (RAC), angiotensin converting enzyme (ACE) inhibition (MK 422), and MK 422 plus systemic arterial ANG II infusion. ANG II-DR was determined in each dog from the arterial-renal venous ANG II concentration difference during the period of ANG II infusion in the presence of ACE inhibition; this value was used to estimate net ANG II formation by predicting the amount of arterially delivered ANG II that escaped degradation. The average percent ANG II-DR calculated during ANG II infusion (range of 0.05 to 0.20 microgram/min) was 89 +/- 2%. In response to RAC, RSR increased from 11 +/- 3 to 24 +/- 5 ng ANG I X h-1 X min-1 X g-1. Arterial ANG II (67 +/- 11 pg/ml) and renal venous ANG II (29 +/- 6 pg/ml) increased to 133 +/- 18 and 61 +/- 10 pg/ml, respectively. Net intrarenal ANG II formation increased from 44 +/- 11 to 83 +/- 13 pg X min-1 X g-1 after renal arterial constriction. There was a significant relationship between the change in RSR and the change in ANG II formation rate.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of atrial natriuretic factor on renal function in rats with papillary necrosis
Authors: Hildebrandt D. A. , Banks R. O.
Published: December 2017

The current study was designed to evaluate whether the renal papilla participates in the natriuretic and diuretic response to atrial natriuretic factor (ANF). Papillary necrosis was induced in female rats by intravenous infusion of 2-bromoethylamine hydrobromide (BEA) 48 h prior to clearance experiments; untreated (UNT) animals served as controls. Rats were anesthetized with pentobarbital sodium, tracheotomized, and catheters placed in a femoral artery and vein and in the bladder. At the time of surgery, the bladder urine was collected and its osmolality used as an indication of papillary destruction. Mean urine osmolalities (+/- SE) of BEA rats were significantly lower than those of UNT rats (443 +/- 10 vs. 1,229 +/- 57 mosmol/kg, respectively), indicating that BEA caused papillary necrosis. Synthetic ANF (rat 8-33) was given as a bolus intravenously (1.25, 2.5, 5.0 micrograms/kg). The ANF-induced increases in sodium excretion were not significantly different between UNT and BEA rats at any ANF dose. These results demonstrate that a functional papilla is not required for the action of ANF in the rat.
Ionic dependence of active Na-K transport: "clamping" of cellular Na+ with monensin
Authors: Haber R. S. , Pressley T. A. , Loeb J. N. , Ismail-Beigi F.
Published: December 2017

The Na+ ionophore monensin was used to study the Na+- and K+-dependence of ouabain-inhibitable 86Rb+ uptake in ARL 15 cells, a rat liver cell line. Graded concentrations of monensin rapidly induced incremental elevations of cellular Na+ that were stable for up to 2 h. In experiments in which cellular Na+ was thus “clamped” at various levels, the activation curve for ouabain-inhibitable 86Rb+ uptake as a function of intracellular Na+ was found to be steepest near basal Na+ levels (Hill coefficient approximately equal to 2.4), indicating that these cells can respond to relatively large changes in passive Na+ entry by increasing the race of Na-K pump function with only minimal increases in cellular Na+. Exposure of cells to monensin also permitted examination of the extracellular-K+ dependence of ouabain-inhibitable 86Rb+ uptake in the presence of saturating intracellular Na+ and yielded a Hill coefficient of approximately 1.5. The rate of ATP hydrolysis calculated from measurements of the maximal rate of ouabain-inhibitable 86Rb+ uptake in intact cells was similar to the enzymatic Vmax of the Na+-K+-ATPase in cell lysates, suggesting that the Na+-K+-ATPase activity in these broken-cell preparations closely reflects the functional transport capacity of the Na-K pump.
Effects of leukotriene D4 on glomerular dynamics in the rat
Authors: Badr K. F. , Brenner B. M. , Ichikawa I.
Published: December 2017

Glomerular micropuncture studies were performed in euvolemic, anesthetized, adult, male Munich-Wistar rats to evaluate the glomerular microcirculatory actions of leukotriene D4 (LTD4). In preliminary experiments, intrarenal arterial administration of LTD4 (1 microgram X kg-1 X min-1) was found to cause a rise in mean systemic arterial pressure, a loss of plasma volume, and a fall in renal blood flow, effects identical to those previously reported for LTC4. To assess the local glomerular actions of LTD4 independently of these systemic effects, glomerular microcirculatory dynamics were assessed during LTD4 infusion while constancy of renal perfusion pressure and plasma volume were maintained by partial aortic constriction and isoncotic plasma infusion, respectively. To ascertain the LTD4 actions that are independent of angiotensin II, saralasin (5 micrograms X kg-1 X min-1 iv) was also given throughout the study. LTD4 caused a significant increase in efferent arteriolar resistance in association with a fall in glomerular plasma flow rate (QA) and a rise in glomerular capillary hydraulic pressure. Despite the latter, single-nephron filtration rate fell due to combined reductions in QA and the glomerular ultrafiltration coefficient. These local glomerular constrictor actions of LTD4 support the possibility that this eicosanoid might play an important intermediary role in the functional impairment accompanying some forms of inflammatory injury.
Control of steady-state pH in rabbit proximal straight tubules
Authors: Atkins J. L. , Burg M. B.
Published: December 2017

Steady-state pH (defined as the limiting pH reached at slow flow rates) was measured in isolated perfused rabbit proximal straight tubules (S2). With normal bath conditions (pH 7.4, bicarbonate 25 mM) the luminal steady-state pH was 6.85. Steady-state pH was directly related to bath pH and bicarbonate, but not to bath PCO2. Lowering of bath pH or bicarbonate consistently decreased luminal steady-state pH, and raising either caused steady-state pH to increase. When bath PCO2 was increased, on the other hand, steady-state pH either increased or decreased, depending on the concomitant changes in bicarbonate and pH. The changes in steady-state pH observed in the present studies following alterations in bath pH and bicarbonate concentration should, when extrapolated to the in vivo kidney, result in decreased delivery of bicarbonate from the proximal tubule in acidosis and increased delivery in alkalosis. The effects of potassium and chloride were also determined. Removal of potassium from the bath increased the steady-state pH, but removal of chloride from both the perfusate and bath had no significant effect.
Temperature sensitivity of renin-angiotensin system in the ground squirrel
Authors: Harker C. T. , Kluger M. J. , Malvin R. L.
Published: December 2017

The alteration of renin release by alpha- and beta-adrenoceptors located on the juxtaglomerular cells has been shown to be temperature sensitive in nonhibernating mammals. These experiments investigate the effects of temperature on renin secretion by cortical slices of kidneys from the thirteen-lined ground squirrel Spermophilus tridecemlineatus. At 37 degrees C, beta-stimulation (isoproterenol 10(-7) M) increased the release of renin by slices taken from nonhibernating ground squirrels but had no effect on those taken from hibernating squirrels. The alpha-agonist phenylephrine (10(-5) M) had no effect on slices from nonhibernating squirrels but enhanced the release rate in those from hibernating ground squirrels, providing the first evidence of in vitro stimulation of renin release by an alpha-agonist. When incubated at 11 degrees C, kidney slices from both hibernating and nonhibernating animals were unresponsive to both alpha- and beta-agonists until incubation times were doubled. Under these prolonged conditions, phenylephrine again stimulated renin release. These results indicate that both in vitro and in vivo cooling alter the responses of alpha- and beta-adrenoceptors to renin-releasing stimuli.
Hypocalcemia-associated modulation of renal response to acute volume expansion in rats
Authors: Wesson D. E.
Published: December 2017

The present study used free-flow micropuncture and whole-kidney clearance studies to determine the renal response to normocalcemic vs. hypocalcemic acute volume expansion (AVE) in anesthetized Munich-Wistar rats. Animals received AVE with Ringer bicarbonate to 10% body weight; half of these animals were supplemented with calcium to maintain normocalcemia (VE + Ca2+) and half were allowed to become hypocalcemic (VE). Filtered load of chloride and total CO2 (TCO2) to the superficial proximal tubule and delivered load to the superficial loop segment were not different between groups. Superficial proximal tubule absolute Cl reabsorption was not different, but superficial loop segment absolute Cl reabsorption was less in the VE + Ca2+ animals (2,221+/- 106 vs. 2,651+/- 125 pmol/min, P less than 0.05) and whole-kidney fractional chloride excretion was greater (10.5+/- 1.6 vs. 4.3+/- 0.5%, P less than 0.05). When indomethacin (I) was administered to hypocalcemic (VE + I) and normocalcemic (VE + Ca2+ + I) AVE animals, both groups of animals had tubular and whole-kidney chloride reabsorption similar to VE animals. TCO2 reabsorption was not influenced by Ca2+ or I. The data indicate that normocalcemic vs. hypocalcemic AVE results in reduced superficial loop segment chloride reabsorption and greater whole-kidney fractional chloride excretion in the absence but not in the presence of prostaglandin inhibition. The data are compatible with an effect of hypocalcemia during AVE to limit superficial loop segment and whole-kidney chloride excretion by inhibiting renal prostaglandin synthesis.
Ammonia entry along rat proximal tubule in vivo: effects of luminal pH and flow rate
Authors: Simon E. E. , Hamm L. L.
Published: December 2017

The roles of luminal pH and flow rate in determining ammonia entry along the rat proximal tubule were examined using in vivo microperfusion. With perfusion rate constant at 15 nl/min, perfusate bicarbonate concentration was varied. Collected fluid ammonia concentration correlated with collected fluid bicarbonate concentration, consistent with nonionic diffusion (r = 0.726; P less than 0.001). Hence ammonia entry was dependent on luminal pH. With perfusate bicarbonate constant at 5 or 25 mM, perfusion rate was varied. In all groups, there was little change in collected fluid ammonia concentration with flow rate. Thus ammonia entry was also highly dependent on flow rate. With paired collections using a 25 mM bicarbonate perfusate, collected fluid bicarbonate was higher at a 30 nl/min perfusion rate than at 15 nl/min (16.8+/- 1.1 vs. 10.3+/- 1.1 mM), whereas total ammonia concentrations were similar (0.54+/- 0.1 and 0.55+/- 0.1). Thus the NH3 concentration was higher at 30 than at 15 nl/min (6.1+/- 1.2 vs. 3.4+/- 0.5 microM; P less than 0.025), a result not predicted by simple nonionic diffusion. Thus these studies demonstrate the importance of nonionic diffusion in determining ammonia entry along the proximal tubule. However, the results also demonstrate that flow rate importantly determines ammonia entry in vivo in a manner not predicted by simple nonionic diffusion of NH3. This augmentation of ammonia entry with increasing flow rate may involve flow-dependent alterations in ammonia synthesis or transport of NH+4.
Hormonal regulation of gluconeogenesis in cultured proximal tubular cells: role of cytosolic calcium
Authors: Goligorsky M. S. , Osborne D. , Howard T. , Hruska K. A. , Karl I. E.
Published: December 2017

Gluconeogenic competence of primary cultures of canine renal proximal tubular cells has been examined. Cells grown in 5 mM glucose media or in glucose-free media exhibited pyruvate-stimulated glucose production, as opposed to cells grown in 20 mM glucose media. By 72 h after the last media change, confluent cells grown in 5 mM glucose medium turn from a predominantly glycolytic to an oxidative type of metabolism. By this time, glucose production exhibited pH, 3-mercaptopicolinate, and insulin sensitivity. Parathyroid hormone, angiotensin II, and phenylephrine stimulated glucose production in a nonadditive fashion. Single-cell cystolic Ca2+ measurements using microspectrofluorometric techniques revealed that all three hormones elicited Ca2+ transients in proximal tubular cells. Ionomycin stimulated glucose production by proximal tubular cells, suggesting that Ca2+ transients could represent a sufficient stimulus for glucose production. When hormone-induced Ca2+ transients were curtailed by a pretreatment with the membrane-permeant Ca2+ chelator, Maptam, hormonal stimulation of glucose production was abolished, suggesting that Ca2+ transients represent not only a sufficient, but a necessary event in the stimulation of glucose production by these hormones.
Renal synthesis and urinary excretion of eicosanoids during pregnancy in rats
Authors: Conrad K. P. , Dunn M. J.
Published: December 2017

We tested whether vasodilatory prostaglandins (PGs) mediate the adaptation of the maternal renal circulation to pregnancy by assessing production of PGs by kidney tissues in vitro. We reasoned that if PGs are crucial, then local synthetic rates of these hormones would most likely be increased. Glomeruli harvested from gravid rats of gestational days 6, 12, and 20 did not demonstrate greater basal or stimulated syntheses of PGF2 alpha, PGE2, or 6-keto-PGF1 alpha than those from virgin controls. Production of PGE2 and 6-keto-PGF1 alpha by renal cortical slices obtained from pregnant rats was not greater than that of virgins either. Urine 24-h excretory rates of PGE2 and 6-keto-PGF1 alpha, but not PGF2 alpha, were significantly increased during pregnancy (all P less than 0.05 from prepregnant levels). During midgestation, when urinary excretion of PGE2 and 6-keto-PGF1 alpha was greatest, medullary syntheses of these PGs were found to be comparable between virgin and gravid animals. The present study, which fails to show augmented synthesis of PGs by renal tissues derived from gravid rats, is consistent with our previous investigation in which cyclooxygenase inhibition did not reduce the gestational increase of renal hemodynamics or restore the attenuated renal pressor responsiveness to exogenous angiotensin II. Taken together, we conclude that in rats, PGs most likely do not mediate the alterations in the renal circulation observed during pregnancy.
Kinetic model for phosphate transport in renal brush-border membranes
Authors: Beliveau R. , Strevey J.
Published: December 2017

Phosphate transport was studied in brush-border membrane vesicles purified from rat kidney cortex. Influx and efflux were strongly dependent on the presence of cis sodium; the rate of efflux, calculated by linear regression performed on the first time points, was much lower than the rate of influx (0.044 vs. 0.198 pmol.microgram protein-1.s-1). Trans phosphate had a stimulatory effect on phosphate influx (145% stimulation at 10 mM phosphate trans, with 0.2 mM phosphate cis). Trans phosphate was, however, inhibitory for phosphate efflux (89% inhibition at 10 mM phosphate trans). Trans effects of sodium were also studied. With 200 mM trans sodium, we observed 73% inhibition of phosphate influx and 60% inhibition of phosphate efflux. Studies involving sodium and phosphate present at the same time as trans substrates showed that the trans inhibition of phosphate influx by sodium could be completely reversed by trans phosphate. Trans inhibition of phosphate efflux by phosphate was not additive to the inhibition caused by sodium. Addition of trans phosphate had a stimulatory effect on sodium-independent influx, indicating that the binary complex (C-P) could translocate in efflux. These results indicate that the renal phosphate carrier presents a random binding scheme for the intra- and extravesicular sides of the membrane.
An acute increase of peritubular K stimulates K transport through cell pathways of CCT
Authors: Muto S. , Giebisch G. , Sansom S.
Published: December 2017

In this study, we have investigated net transport and electrical properties of isolated perfused cortical collecting ducts of control and DOCA-treated rabbits to clarify the cell mechanism for secreting K on an acute increase of peritubular K concentration. Raising bath K in control experiments caused an increase in net K secretion (-JK) and net Na absorption (JNa). Barium (5 mM), a known blocker of basolateral K conductance, added to the bath had no effect on this transport stimulation. In the presence of luminal Ba (5 mM) -JK was reduced to zero, but JNa was unaltered. When bath K was increased -JK increased to a value slightly greater than zero, but not different from the predicted passive flux through the paracellular pathway. In tubules of DOCA-treated rabbits, raising K in the bath increased -JK and JNa. The observed stimulation of -JK was blunted in the presence of Ba in the bath, whereas the increase in JNa remained the same. Thus, in DOCA-treated tubules, Ba in the bath significantly attenuated the increase in K secretion without affecting the transport stimulation of JNa. When Ba was added to the perfusate and bath K increased, -JK, which was initially 22.1, increased to 36.4 pmol.mm-1.min-1. Thus a "Ba-insensitive" pathway became more evident in CCTs from DOCA-treated rabbits.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of cAMP analogue infusion on phosphate reabsorption in phosphate-deprived rats
Authors: Berndt T. J. , Onsgard M. J. , Knox F. G.
Published: December 2017

The present study was performed to compare the effects of 8-(4-chlorophenylthio)-adenosine 3',5'-cyclic monophosphate (cAMP analogue) and parathyroid hormone (PTH) infusion on segmental phosphate reabsorption in phosphate-deprived rats. Micropunctures of the late proximal and the early distal tubules were performed in acutely thyroparathyroidectomized (TPTX) rats fed either a normal (NPD) or low phosphate diet (LPD), and the phosphaturic response to infusion of PTH and cAMP analogue was evaluated. In NPD rats, PTH (n = 10) and the cAMP analogues (n = 11) markedly increased urinary phosphate excretion, due to inhibition of phosphate reabsorption along the proximal convoluted tubule and pars recta. In phosphate-deprived rats, PTH (n = 10) or the cAMP analogue (n = 11) did not increase urinary phosphate excretion. However, PTH and the cAMP analogue inhibited phosphate reabsorption along the proximal convoluted tubule but not in the pars recta in phosphate-deprived rats. We conclude that cAMP analogue infusion mimics the effect of PTH infusion on phosphate reabsorption along the proximal convoluted and proximal straight tubule in normal and phosphate-deprived rats. The resistance to the phosphaturic effect of PTH and cAMP infusions is a result of a blunted inhibition of phosphate reabsorption by the proximal convoluted tubule and also an increased phosphate reabsorption by the proximal straight tubule.
Course and pathogenesis of postischemic acute renal failure in the rat
Authors: Yagil Y. , Myers B. D. , Jamison R. L.
Published: December 2017

The effect of 45-min clamping of the renal artery was studied in the conscious uninephrectomized rat to reproduce the syndrome of hemodynamically mediated acute renal failure in humans after a single ischemic insult. Twenty-four hours after ischemia, creatinine clearance was reduced by 90%, whereas fractional excretion of sodium was markedly increased; over the subsequent 5 days, both values returned to normal. The animals were nonoliguric. Fractional clearances of graded sizes of neutral dextrans (radii 20–44 A), employed to detect transtubular backleak of inulin, were not significantly different 24 or 48 h postischemia from those in normal animals. The implication that the normal fractional dextran clearances excluded tubular backleak was tested directly by microinjecting [methoxy-3H]inulin into the proximal tubule. In most tubules injected, the recovery of radioactivity in the urine was markedly lower 24 and 48 h postischemia than that in normal rats; in a few injected tubules of postischemic kidneys, recovery was not different from that in normal animals. The low recovery of radioactive inulin was accounted for, at least in part, by transtubular backleak, as shown in experiments in which rats subjected to renal ischemia were cross-transfused with normal animals. These studies indicate that, despite the normal fractional dextran clearances, most tubules were severely injured as shown by tubule backleak of inulin.
Renal ornithine decarboxylase activity, polyamines, and compensatory renal hypertrophy in the rat
Authors: Humphreys M. H. , Etheredge S. B. , Lin S. Y. , Ribstein J. , Marton L. J.
Published: December 2017

We determined the role of ornithine decarboxylase (ODC) in compensatory renal hypertrophy (CRH) by relating renal ODC activity and polyamine content to kidney size, expressed as a percent of body weight, 1 wk after unilateral nephrectomy (UN). In normal rats, renal ODC activity increased from 11.0 +/- 7.4 (SD) to 36.7 +/- 15.4 pmol 14CO2.min-1.g wet wt-1 3 h after UN (P less than 0.002); 1 wk later the remaining kidney weight had increased from 0.38 to 0.46% body weight (P less than 0.001). Renal concentration of putrescine, the product of ODC's decarboxylation of ornithine, was increased 3, 8, and 48 h after UN, but concentrations of polyamines synthesized later in the pathway, spermidine and spermine, were not appreciably affected. Pretreatment with difluoromethylornithine (DFMO), an irreversible inhibitor of ODC, as a 1% drinking water solution inhibited both base-line renal ODC activity and putrescine concentration as well as increases stimulated by UN, although concentrations of spermidine and spermine were not decreased. In these rats, CRH still occurred, since kidney weight increased from 0.36 to 0.46% (P less than 0.001). A 2% DFMO solution caused depletion of all three polyamines, but CRH took place nevertheless. In hypophysectomized rats, both increased renal ODC activity and CRH occurred as well, indicating that these two consequences of UN do not require intact pituitary function. Although increased renal ODC activity and CRH after UN are correlated in normal and hypophysectomized rats, CRH takes place in rats treated with DFMO despite inhibition of ODC activity and depletion of polyamines.(ABSTRACT TRUNCATED AT 250 WORDS)
Analysis of PCO2 variations in the renal cortex. I. Single nephron
Authors: Atherton L. J. , Maddox D. A. , Gennari F. J. , Deen W. M.
Published: December 2017

A mathematical model was developed to predict differences in CO2 partial pressure between afferent arterioles and peritubular capillaries, based on the flow rate and composition of afferent arteriolar blood. Buffering reactions in blood were described by use of conditions of chemical equilibrium and electroneutrality in separate plasma and red cell compartments, with inclusion of such factors as the effect of hemoglobin oxygenation (alkaline Bohr effect) and formation of carbamino compounds. Steady-state mass balance equations allowed the prediction of peritubular capillary blood composition based on the inputs of blood from the efferent arteriole and the addition of water, CO2, NaHCO3, and NaCl derived from tubule reabsorbate. Models developed previously to describe the rates of glomerular filtration, and of proximal tubule reabsorption of HCO3- and CO2, were combined with the peritubular capillary model to allow realistic simulations for a single superficial nephron. The predicted difference of 5.5 mmHg between the CO2 partial pressures in peritubular capillaries and afferent arterioles (delta PCO2) was in good agreement with values reported for normal Munich-Wistar rats. For a given afferent arteriolar blood composition, the calculated delta PCO2 generally decreased with increasing blood flow rate. At a given blood flow rate and afferent PCO2, delta PCO2 decreased as afferent plasma HCO3- concentration was increased. When afferent PCO2 was varied at constant blood flow rate and HCO3- concentration, delta PCO2 changed in parallel with afferent PCO2.
Enhanced tubuloglomerular feedback during peritubular infusions of angiotensins I and II
Authors: Mitchell K. D. , Navar L. G.
Published: December 2017

Experiments were performed in pentobarbital sodium-anesthetized rats to determine whether increases in intrarenal generation of angiotensin II (ANG II) can enhance the sensitivity of the tubuloglomerular feedback mechanism. Stop-flow pressure (SFP) feedback responses to step increases in late proximal perfusion rate were obtained during control conditions and during simultaneous peritubular capillary infusion of either angiotensin I (ANG I) or ANG II. Infusion of either 10(-7) M ANG II or 10(-5) M ANG I, at rates (18.3 +/- 0.9 and 14.8 +/- 1.5 nl/min, respectively) that did not affect resting SFP, enhanced the magnitude of SFP feedback responses both at a low proximal perfusion rate of 10 nl/min (2.9 +/- 0.9 vs. 0.3 +/- 0.2 and 4.5 +/- 1.0 vs. 0.1 +/- 0.1 mmHg, respectively) and at proximal perfusion rates (greater than 30 nl/min) that elicited a maximal feedback response (13.1 +/- 1.0 vs. 10.1 +/- 0.7 and 13.5 +/- 1.6 vs. 9.8 +/- 0.8 mmHg, respectively). With a higher ANG I infusion rate (20 nl/min), control SFP measured in the absence of distal volume delivery decreased from 39.2 +/- 0.6 to 12.0 +/- 2.8 mmHg (n = 18). These effects were blocked when the ANG II receptor antagonist, saralasin (10(-5) M, Sar), was added to the infusate. In addition, the magnitude of the maximal SFP feedback response was not altered during infusion of Sar alone or ANG I + Sar. These findings indicate that ANG II, either added or formed de novo beyond the glomerular circulation, can enhance the sensitivity of the tubuloglomerular feedback mechanism.
Renal hemodynamics in response to a kinin analogue antagonist
Authors: Beierwaltes W. H. , Carretero O. A. , Scicli A. G.
Published: December 2017

The influence of endogenous kinins on renal hemodynamics was studied using a kinin analogue antagonist ([DArg0-Hyp3-Thi5-DPhe7-Thi8]bradykinin) in eight sodium-restricted anesthetized dogs. Clearance periods were run during intrarenal infusion of vehicle or 50 micrograms/min of analogue during normal and reduced renal perfusion pressure within (95 mmHg) and below (65 mmHg) the range of renal autoregulation. During normal renal perfusion, the analogue did not affect arterial pressure, glomerular filtration rate (GFR), or sodium excretion but decreased renal blood flow (RBF) by 20% (6.41 +/- 0.35 vs. 5.61 +/- 0.38 ml.min-1.g kidney wt-1, P less than 0.05) due to increased renal vascular resistance (RVR, 0.44 +/- 0.03 vs. 0.54 +/- 0.04 U, P less than 0.01). The analogue increased renin secretion rate (RSR, 311 +/- 190 vs. 654 +/- 202 ng angiotensin I/min, P less than 0.001). With reduced renal perfusion (95 mmHg), RBF was unchanged, and sodium excretion and RVR decreased. Vehicle did not change GFR, but the analogue abolished autoregulation of GFR (-37%, P less than 0.02) and decreased filtration fraction (24 +/- 4 vs. 34 +/- 4%, P less than 0.05). Renal perfusion pressure of 65 mmHg decreased RBF, GFR, and sodium excretion similarly with vehicle or analogue. Converting-enzyme inhibition eliminated the changes in RVR. Thus kinin antagonism increased RSR and consequently RVR at normal renal perfusion. As renal perfusion pressure decreased, kinin antagonism diminished autoregulation of GFR but not of RBF. These results suggest that kinin antagonism may either modify the arteriolar resistance or alter the coefficient of filtration, resulting in decreased GFR at reduced renal perfusion pressure.