bluuebunny/crossref_metadata_2025 huggingface dataset:
Hypertension transmitted by kidneys from stroke-prone spontaneously hypertensive rats
Authors: Rettig R. , Stauss H. , Folberth C. , Ganten D. , Waldherr B. , Unger T.
Published: December 2017

We determined whether transplantations of kidneys from stroke-prone spontaneously hypertensive rats (SPSHR) and from normotensive Wistar-Kyoto rats (WKY) alter blood pressure in renal graft recipients. Kidneys taken from seven male SPSHR and seven male WKY rats (blood pressure 186 +/- 4.8 and 111 +/- 3.7 mmHg, respectively) at the age of 20 wk were transplanted, using microsurgical techniques, to bilaterally nephrectomized age-matched male F1 hybrids (blood pressure 136 +/- 2.6 and 138 +/- 6.3 mmHg, respectively) bred from SPSHR and WKY parents. After renal transplantation, blood pressure in recipients of SPSHR kidneys rose to 146 +/- 11.8 (week 2), 163 +/- 16.4 (week 3), 192 +/- 17.1 (week 4), 222 +/- 17.7 (week 5), 221 +/- 12.6 (week 6), 218 +/- 20.3 (week 7), and 239 +/- 9.2 mmHg (week 8). There was no significant change in blood pressure in recipients of WKY kidneys. All rats recovered rapidly from surgery. After renal transplantation, there was a significant increase in daily water intake, a decrease in plasma renin activity, and a slight rise in plasma urea concentration. Our data show that transplantation of kidneys from adult SPSHR causes hypertension in normotensive recipients, indicating a major function for the kidney in SPSHR hypertension.
Effect of adenosine A1 analogue on tubuloglomerular feedback mechanism
Authors: Franco M. , Bell P. D. , Navar L. G.
Published: December 2017

To evaluate further the role of adenosine in the transmission of tubuloglomerular feedback signals, we studied the effects of an adenosine receptor antagonist and an adenosine A1-receptor agonist on feedback-mediated changes in stop-flow pressure (SFP). In orthograde perfusion experiments conducted in anesthetized rats, systemic administration of the adenosine receptor blocker 1,3-dipropyl-8-sulfophenylxanthine (PSPX) did not inhibit feedback responses. Control SFP feedback responses averaged 9.7 +/- 0.65 before and 8.6 +/- 0.55 mmHg during systemic infusion of the receptor blocker. In retrograde perfusion experiments, intratubular administration of the A1 agonist (360 nM) N6-cyclopentyladenosine (CPA), added to a hypotonic solution, markedly enhanced feedback responses. This effect was completely prevented by coinfusion of PSPX. Addition of 10 mM of the antagonist to the CPA-containing solution attenuated SFP feedback responses to less than 1 mmHg (delta = 0.44 +/- 0.50). Furthermore, PSPX also inhibited feedback responses obtained with an isotonic solution alone. Furosemide, which has been shown to block normal SFP responses obtained with isotonic solutions, failed to block CPA-induced decreases in SFP. These data demonstrate that intraluminal administration of an adenosine A1 analogue causes feedback-mediated decreases in SFP and therefore support a role for adenosine receptors in the signal transmission pathway.
The dopamine receptor in adult and maturing kidney
Authors: Felder R. A. , Felder C. C. , Eisner G. M. , Jose P. A.
Published: December 2017

Dopamine, like other neurotransmitters, exerts its biological effects by occupation of specific receptor subtypes. The dopamine receptors in the central nervous system and certain endocrine organs are classified into the D1/D2 subtypes. Outside the central nervous system, the dopamine receptors are classified into the DA1/DA2 subtypes. The D1/D2 and DA1/DA2 receptor have marked similarities and some differences, the most notable of which is the lower affinity of the DA dopamine compared with the D dopamine receptor. DA1 receptor activation increases renal blood flow (RBF); stimulation of DA1 and DA2 receptors may also increase glomerular filtration rate (GFR). DA1 agonists inhibit fluid and electrolyte transport indirectly via hemodynamic mechanisms and directly by occupation of DA1 receptors in specific nephron segments. In the proximal tubule, DA1 agonists simulate adenylate cyclase and inhibit Na+-H+ antiport activity. They also increase phospholipase C and inhibit Na+-K+-ATPase activity (presumably as a consequence of protein kinase C activation). The latter effects may be facilitated by DA2 agonists. In cortical collecting ducts, dopamine antagonizes the effects of mineralocorticoids and the hydrosomotic effect of antidiuretic hormone. It has also been suggested that DA1 may also decrease sodium transport by influencing other hormones, such as atrial natriuretic peptide. Studies of dopamine in the young are complicated because of the propensity for dopamine to stimulate alpha-adrenoceptors. Dopamine alone may actually decrease RBF in the perinatal period. In some animals, the renal vasodilatory and natriuretic effects of dopamine increase with age. Renal tubular DA1-stimulated adenylate cyclase activity increases, whereas renal tubular DA1 receptors decrease with age. Renal DA2 receptor density is greater in the fetus; after birth renal DA2 receptors do not change. Endogenous dopamine may regulate sodium excretion in the young differently than in the adult. In the adult, sodium surfeit is associated with an increase in urinary dopamine; the opposite occurs in the young. A decrease in dopamine production or blockade of dopamine receptors results in an antinatriuresis in the adult; dopamine blockade in the young results in a natriuresis. It remains to be determined whether these age-related differences in dopamine effects are due to changes in receptor DA subtype density, second messengers, and/or interaction with other receptors.
Effects of atrial natriuretic peptide on renal medullary prostaglandin E2 production
Authors: Bolterman R. J. , Bentley M. D. , Sandberg S. M. , Fiksen-Olsen M. J. , Romero J. C.
Published: December 2017

Like arachidonic acid (AA) and bradykinin (BK), the intrarenal administration of atrial natriuretic peptide (ANP) has been shown to increase the urinary excretion of prostaglandin E2 (PGE2). In the present study, the direct in vitro effects of ANP on PGE2 production were compared with those of AA and BK. Canine renal inner medullary slices were preincubated for 30 min and washed in aerated Krebs-Ringer buffer (37 degrees C). During the final incubation period, with the use of varied concentrations of AA, BK, or ANP in Krebs-Ringer buffer, samples were obtained at 0 and 30 min to be used for radioimmunoassay of PGE2. Although the rate of PGE2 production was significantly increased 11-fold with AA and threefold with BK, it was unaffected by four different doses of ANP (10(-5) to 10(-11) M). Furthermore, the production of PGE2 during basal and stimulated (BK or AA) conditions was significantly blocked by indomethacin but not by ANP. These results indicate that ANP had no direct stimulatory or inhibitory effect on the medullary production of PGE2.
Phosphatidates inhibit vasopressin-induced water transport via protein kinase C activation
Authors: Ando Y. , Jacobson H. R. , Breyer M. D.
Published: December 2017

Phosphatidic acid (PA), best known as an intermediate of phosphatidylinositol bisphosphate (PIP2) turnover, inhibits vasopressin (AVP)-induced increase in hydraulic conductivity (Lp) in rabbit cortical collecting ducts (CCD) perfused in vitro (Ando, Y., H. R. Jacobson, and M. D. Breyer, J. Clin. Invest. 80: 590, 1987). The present study addresses the mechanism(s) responsible for this action of PA. In control experiments, 10 microU/ml AVP (23 pM) increased Lp of CCDs from a basal of 4.9 +/- 0.4 X 10(-7) cm.atm-1.s-1 to a peak of 171.2 +/- 4.6 X 10(-7) cm.atm-1.s-1. Basolateral pretreatment of the tubule with PA (25 micrograms/ml) suppressed AVP-induced increase in peak Lp by 45.0%. This suppression was not attenuated by 5 microM indomethacin pretreatment. L-alpha-dipalmitoyl(C16) PA (DPPA, 25 micrograms/ml), an arachidonate-free synthetic PA, inhibited peak Lp by 79.0%, whereas another synthetic PA with shorter fatty acid (C12), L-alpha-dilauroyl PA (DLPA, 25 micrograms/ml), had no significant effect on AVP-induced peak Lp. In the presence of 100 nM staurosporine, a protein kinase C (PKC) inhibitor, the inhibition by PA and DPPA on AVP-induced peak Lp were abolished. Furthermore, another PKC inhibitor, 100 microM 1-(5-isoquiniline-sulfonyl)-2-methylpiperzine, also reversed the DPPA-induced inhibition of AVP action. In separate experiments using fura-2-loaded isolated perfused CCDs, however, neither PA nor DPPA caused a significant increase in intracellular free Ca2+ concentration [( Ca2+]i). Taken together, in CCD, PA-induced inhibition of AVP action is primarily mediated by PKC but not by an increased [Ca2+]i or the production of arachidonate metabolites, such as prostaglandins. Thus the PA-induced activation of PKC does not seem to involve the classic pathway for PKC activation, breakdown of PIP2.
Divergent effects of KCl-induced depolarization on afferent and efferent arterioles
Authors: Loutzenhiser R. , Hayashi K. , Epstein M.
Published: December 2017

We have previously proposed that renal microvessels exhibit a unique regional heterogeneity. Studies with calcium channel agonists and antagonists suggest that potential-dependent calcium channels may play a more prominent role in the activation of the afferent arteriole than the efferent arteriole. Because KCl-induced depolarization elicits vasoconstriction exclusively by the activation of potential-dependent calcium channels, we tested this postulate directly by ascertaining the vasoconstrictor effects of KCl and countervailing effects of a calcium channel blocker on the afferent and efferent arteriole of isolated perfused hydronephrotic kidneys. Increasing media potassium concentration from 5 to 30 mM resulted in a marked renal vasoconstriction decreasing renal perfusate flow by 61 +/- 4%. An examination of the microvascular response to KCl revealed a predominant response of the afferent arteriole. Thus afferent arteriolar diameter decreased by 38 +/- 6% (i.e., from 20.7 +/- 1.5 to 13.0 +/- 1.8 microns, P less than 0.005), whereas efferent arteriolar diameter decreased by only 12 +/- 4% (i.e., from 15.8 +/- 1.6 to 13.8 +/- 1.4 microns, P = 0.05). Nifedipine completely returned afferent arteriolar diameter to control levels with a mean effective dose of 41 +/- 2 nM. These findings indicate that the afferent arteriole is more responsive to depolarization-induced vasoconstrictor stimuli than is the efferent arteriole and suggest a greater prevalence of potential-dependent calcium channels in this vessel.
Effect of angiotensin II infusion on the human glomerular filtration barrier
Authors: Loon N. , Shemesh O. , Morelli E. , Myers B. D.
Published: December 2017

Angiotensin II (ANG II) infusion has been reported to impair barrier size selectivity and exacerbate proteinuria in the rat. To examine whether this is also true of humans, we infused a pressor dose of ANG II into seven healthy controls and seven nephrotic patients. A prompt depression of glomerular filtration rate (GFR) and renal plasma flow was observed in each group (P less than 0.01). Surprisingly, the excretion rates of albumin (5.3 +/- 1.6 to 2.8 +/- 0.3 in controls and 4,791 +/- 1,244 to 3,833 +/- 800 micrograms/min in nephrotics) and immunoglobulin G (1.5 +/- 0.4 to 0.8 +/- 0.2 and 305 +/- 87 to 255 +/- 94 micrograms/min, respectively) fell significantly during ANG II infusion. Fractional clearances of dextrans of broad size distribution (radii 34–54 A) were uniformly elevated by ANG II infusion in controls but tended to decline in nephrotics. A heteroporous model of the glomerular capillary wall revealed ANG II to have a negligible effect on membrane-pore structure. However, the depressed GFR lowered the rate at which macromolecule-rich filtrate was formed through a subset of nondiscriminatory pores from 272 to 176 microliters/min in controls and from 394 to 334 microliters/min in nephrotics. We conclude that, in striking contrast to the rat, pressor ANG II infusion has little or no influence on barrier size selectivity in humans but exerts an antiproteinuric effect by lowering the filtered protein load.
Adaptation of rabbit renal cortical Na+-H+ exchange activity in chronic hypocapnia
Authors: Hilden S. A. , Johns C. A. , Madias N. E.
Published: December 2017

We have examined the activity and kinetic characteristics of the Na+-H+ exchanger in renal cortical brush-border membrane vesicles (BBMV) prepared from rabbits adapted to chronic hypocapnia in order to address whether this transporter might contribute to the suppressed proximal bicarbonate reabsorption characteristic of this disorder. Chronic hypocapnia was induced by exposing animals to 9% O2 for a 5-day period. In comparison with paired, contemporaneous controls, an average delta PaCO2 of 13 mmHg and an average delta [HCO3-] of 7.3 meq/l were obtained. Chronic hypocapnia led to a significant suppression of the 22Na+ uptake by BBMV; at the 3-s mark, a 30% suppression was observed (chronic hypocapnia, 4.05 +/- 0.43 nmol/mg protein; control, 5.72 +/- 0.39 nmol/mg protein) (P less than 0.01). A significant decrease in the Vmax of the antiporter was noted (chronic hypocapnia, 622.7 +/- 86.8 nmol.mg protein-1.min-1; control 857.5 +/- 64.8 nmol.mg protein-1.min-1) (P less than 0.01), whereas the Km for sodium remained unaltered. The specificity of this adaptation was supported by showing that Na+-dependent uptake of D-[3H]glucose by BBMV was not significantly different between chronic hypocapnia and control. Chronic normocapnic hypoxemia left Na+-H+ exchange activity undisturbed. We conclude that the observed change in the BBMV Na+-H+ antiporter might be responsible, at least in part, for the suppressed renal bicarbonate reabsorption characteristic of chronic hypocapnia and that a consequence of the hypocapnic state itself mediates this adaptation.
pH gradient-stimulated phosphate transport in outer medullary brush-border membranes
Authors: Quamme G. A. , Walker J. J. , Yan T. S.
Published: December 2017

Phosphate transport was studied in brush-border membrane vesicles prepared from outer medullary tissue of the porcine kidney. Phosphate uptake studies were performed in the absence of sodium at 21 degrees C. A 1.2- to 12-fold overshoot, above equilibrium values, was present with intracellular pH (pHin) equal to 8.0 and extracellular pH (pHout) equal to 6.5, which was not evident at pHin = pHout. Concentration-dependence of the pH-stimulate uptake was determined by the difference of uptake in the absence of a pH gradient (pHin = pHout) from that in the presence of a pH gradient over a large range of phosphate concentrations. The uptake was consistent with a single facilitative system characterized by apparent kinetic parameters; with Michaelis constant 149 +/- 11 microM and maximal velocity 4.9 +/- 0.4 nmol.mg protein-1.min-1, n = 3. Phosphate uptake was inhibited by the stilbene derivative 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid with a mean inhibition constant (Ki) value of 0.15 mM (n = 2). In addition, pH gradient-stimulated phosphate uptake was sensitive to furosemide and bumetanide; Ki values of 0.50 +/- 0.05 and 0.11 +/- 0.04 mM, respectively. Arsenate (1 mM) and phosphonoformate (1 mM) inhibited pH-dependent phosphate uptake, whereas sulfate (5 mM), bicarbonate (25 mM), and chloride (100 mM) were without effect, indicating that the transport system is relatively specific to phosphate and its close analogues. pH gradient-stimulated phosphate uptake was not influenced by potassium-diffusional gradients. The data provide evidence for a facilitative process in brush-border membrane vesicles isolated from outer medullary tissue of the pig kidney that is capable of transporting phosphate in the absence of sodium.
Osmotic forces driving water reabsorption in the proximal tubule of the rat kidney
Authors: Green R. , Giebisch G.
Published: December 2017

Simultaneous microperfusion of proximal tubules and peritubular capillaries in kidneys of rats anesthetized with Inactin was used to measure reabsorption of fluid in response to an imposed osmotic gradient. The tubular fluid was isotonic and the peritubular capillaries were made hypertonic with NaCl or NaHCO3. Mean gradients and ionic fluxes were measured. When no gradient was imposed tubular fluid became hypotonic and rate of fluid reabsorption was 0.700 nl.mm-1.min-1. Imposition of a 25 mM NaCl gradient increased fluid flux to 3.887 nl.mm-1.min-1, whereas 25 mM NaHCO3 stimulated 5.226 ml/mm fluid reabsorption. This gave a relative reflection coefficient of NaCl:NaHCO3 of 0.73. Apparent water permeability varied with highest values for the smallest gradients. This suggests the possibility of a compartment in the epithelium that is hypertonic to the peritubular capillaries. The hypertonicity required to account for fluid movement was 6-16 mosmol/kg.
Insulin-like growth factor I stimulates Na-dependent Pi transport in cultured kidney cells
Authors: Caverzasio J. , Bonjour J. P.
Published: December 2017

The effect of recombinant insulin-like growth factor I (IGF-I/somatomedin C) on the transport of inorganic phosphate (Pi) was studied in cultured kidney epithelia. In opossum kidney (OK) epithelia, IGF-I (5 x 10(-10) to 10(-7) M) induced a dose-related stimulation of the Na-dependent Pi transport (NaPiT). A maximal response was observed at 10(-7) M (IGF-I 1.64 +/- 0.12; vehicle 0.90 +/- 0.02 nmol.mg protein-1. 4 min-1, P less than 0.001). Kinetic analysis of the stimulatory effect of IGF-I on NaPiT indicated an increase in Vmax and no change in Km. Insulin also stimulated NaPiT in OK epithelia but only at concentrations 20-40 times higher than IGF-I. The effect of IGF-I on Pi transport was detectable in less than 30 min with a maximal response occurring after 4-5 h. It was selective for NaPiT, since the Na-dependent alanine transport was not affected by IGF-I. Inhibition of protein synthesis by either cycloheximide or cordycepin markedly attenuated the stimulatory effect of IGF-I on NaPiT. The cellular adenosine 3',5'-cyclic monophosphate content was not modified by the growth factor. In conclusion, these data indicate that IGF-I increases NaPiT selectively through a mechanism that involves de novo protein synthesis. These observations suggest that growth and growth hormone-related stimulation of renal Pi transport could be mediated by IGF-I.
Heterogeneity of cAMP effect on endosomal proton transport
Authors: Gurich R. W. , DuBose T. D.
Published: December 2017

The effects of 8-bromoadenosine 3',5'-cyclic monophosphate (8-BrcAMP) on proton transport in endocytotic vesicles (i.e., endosomes) obtained from rabbit renal cortex were investigated. Endosomes were prepared from New Zealand White rabbits following the intravenous injection of horseradish peroxidase. Under high (106 mM) chloride conditions, 5 microM 8-BrcAMP stimulated proton transport by 11 and 12% in fractions 1 and 2, but inhibited proton transport by 10, 8, and 14% in fractions 4, 5, and 6. Two hundred and fifty micromolar 8-BrcAMP inhibited proton transport progressively from 20% in fraction 1 to 50% in fraction 6. Under conditions in which chloride entry was minimized, i.e., low (6 mM) external chloride concentration plus voltage clamping, 5 microM 8-BrcAMP consistently and significantly inhibited proton transport by 40-60% in all six fractions. Under the same low chloride conditions, 250 microM 8-BrcAMP inhibited proton transport by 80-90% in all six fractions. These studies indicate that 8-BrcAMP can modify endosomal transport in a heterogeneous manner, that 8-BrcAMP inhibits the H+-ATPase directly, and that this effect is significantly modified by chloride. Last, these studies suggest that the observed heterogeneity in proton transport arises from interaction of 8-BrcAMP and chloride.
Escherichia coli enterotoxin receptors: localization in opossum kidney, intestine, and testis
Authors: Forte L. R. , Krause W. J. , Freeman R. H.
Published: December 2017

The distribution of receptors for Escherichia coli enterotoxin were examined in opossum kidney, intestine, and testis. E. coli enterotoxin stimulated guanosine 3',5'-cyclic monophosphate (cGMP) production in renal cortex, testis, and small intestinal mucosa but had only a small effect in the colon. Atrial natriuretic factor enhanced the cGMP content of renal cortex and small intestine but had no effect on testis or colon. The enterotoxin receptors were observed to be localized in proximal tubules, to epithelial cells of crypts and villi of small intestine, to crypts of colon, and in seminiferous tubules. Both convoluted and straight portions of proximal tubules exhibited specific binding sites for 125I-labeled enterotoxin. Glomeruli and distal tubules did not have receptors. Binding of 125I-enterotoxin to brush-border membranes of kidney cortex or intestinal mucosa and to testis membranes was markedly temperature dependent. The binding affinities of these receptors for E. coli enterotoxin were similar (i.e., IC50 approximately equal to 0.4-0.5 nM). Daily administration of 20 micrograms of enterotoxin intramuscularly to opossums increased urine cGMP excretion with no apparent changes in urine volume, Na+, or K+ excretion. Thus receptors for heat-stable enterotoxins are localized to proximal tubules of kidney and to enterocytes and seminiferous tubules of intestine and testis, respectively. Apical membranes may be the site of enterotoxin receptors in these epithelia.
Inhibition of Jv by ANF in rat proximal straight tubules requires angiotensin
Authors: Garvin J. L.
Published: December 2017

The effects of atrial natriuretic factor (ANF) on fluid absorption (Jv) by isolated perfused proximal straight tubules of rats were investigated. ANF alone (10(-8) M) added to the bath had no significant effect on absorption. In contrast, when tubules were first treated with 1.6 X 10(-10) M angiotensin II, this same concentration of ANF lowered fluid absorption from 0.99 +/- 0.03 to 0.69 +/- 0.02 nl.mm-1.min-1. A lower dose of ANF, 2 X 10(-10) M, reduced fluid absorption in the presence of angiotensin II from 1.13 +/- 0.06 to 0.65 +/- 0.05 nl.mm-1.min-1, an inhibition of 40%. Since guanosine 3',5'-cyclic monophosphate (cGMP) is reportedly part of the second messenger system of ANF, the effects of dibutyryl-cGMP (DBcGMP) on fluid absorption were studied. This membrane-permeant form of cGMP mimicked the effects of ANF, reducing fluid absorption from 1.15 +/- 0.18 to 0.54 +/- 0.08 nl.mm-1.min-1. These studies suggested the following: 1) ANF can regulate fluid absorption in the proximal nephron; 2) this inhibition occurs only in the presence of angiotensin; and 3) cGMP is part of the second messenger system of ANF in the rat proximal straight tubule, as it is in other tissues.
Glutamine transport in submitochondrial particles
Authors: Sastrasinh S. , Sastrasinh M.
Published: December 2017

Glutamine transport was studied in submitochondrial particles (SMP) to avoid interference from glutamine metabolism. Phosphate-dependent glutaminase activity in SMP was only 0.04% of that in intact mitochondria. The uptake of glutamine in SMP represented both the transport into vesicles and membrane binding (about one-third of total uptake). Sulfhydryl reagents inhibited glutamine uptake in SMP. The uptake of L-[3H]glutamine increased more than twofold in SMP preloaded with 1 mM L-glutamine, an effect that was not seen with 1 mM D-glutamine. The uptake of L-[3H]glutamine was inhibited in the presence of either L-glutamine or L-alanine in the incubation medium. Other amino acids did not inhibit glutamine uptake. Alanine was also shown to trans-stimulate glutamine transport in SMP and cis-inhibit glutamine transport in both SMP and intact mitochondria. Glutamine transport showed a positive cooperativity effect with a Hill coefficient of 1.45. Metabolic acidosis increased the affinity of the transporter for glutamine without any change in other kinetic parameters. These data indicated that mitochondrial glutamine transport occurs via a specific carrier with multiple binding sites and that the transport of glutamine into mitochondria has an important role in increased ammoniagenesis during metabolic acidosis.
Effects of dietary interventions on glomerular pathophysiology
Authors: Diamond J. R.
Published: December 2017

Numerous dietary interventions have been utilized to modify the course of and further elucidate the pathophysiological processes involved in experimental progressive glomerulopathy. Alterations in dietary constituents can affect the glomerular capillary hemodynamic parameters, the permselectivity features of the filtration apparatus, as well as the morphology and function of resident glomerular cells and influxing bone marrow-derived monocytes. The three dietary modifications examined in this review are protein restriction, dietary cholesterol supplementation, and essential fatty acid deficiency. These maneuvers have been chosen from the myriad dietary interventions in the experimental and clinical literature and are not meant to be all inclusive. The implementation of these three dietary modifications, in experimental models of glomerular disease, amply demonstrate the concept of a stratified alteration in glomerular structure and function. Since perturbed glomerular pathobiology, involving the above-mentioned structures and cell types, is believed to contribute to progressive glomerulopathy, a review of these seemingly diverse, yet perhaps, interrelated responses to dietary modifications will only aid us in understanding this process.
Radiocontrast medium-induced declines in renal function: a role for oxygen free radicals
Authors: Bakris G. L. , Lass N. , Gaber A. O. , Jones J. D. , Burnett J. C.
Published: December 2017

Intrarenal injection of radiocontrast medium (RCM) results in transient vasoconstriction and a persistent decline in glomerular filtration rate (GFR). Adenosine modulates this vasoconstrictor response and is postulated to increase oxygen free radical (OFR) generation. We hypothesized that the persistent decline in (GFR that follows RCM administration results in an increased generation of OFR. We evaluated the effects of RCM injection on renal blood flow, inulin clearance, hypoxanthine, xanthine, and malondialdehyde concentrations in four groups of non-volume-expanded, pentobarbital sodium anesthetized dogs in the presence and absence of intravenous allopurinol, 25 mg/min (group 1), intrarenal superoxide dismutase (SOD), 400 U/min (group 2), heat-inactivated intrarenal SOD, 400 U/min (group 3), and simultaneous infusions of intrarenal SOD, 400 U/min, to one kidney and saline to the other (group 4). Both allopurinol and SOD significantly attenuated the fall in GFR after RCM administration over control. Malondialdehyde concentrations were attenuated over control in all treated groups, indicating a decrease in OFR generation. We conclude that intrarenal injection of RCM results in increased production of OFR. Inhibition of OFR production by allopurinol and increased OFR removal by SOD attenuates the effects of RCM on declines in GFR.
Hypothalamic Na(+)-K(+)-ATPase inhibitor characterized in two-sided liposomes containing pure renal Na(+)-K(+)-ATPase
Authors: Anner B. M. , Rey H. G. , Moosmayer M. , Meszoely I. , Haupert G. T.
Published: December 2017

The functional characterization of putative endogenous inhibitors of the Na(+)-K(+)-ATPase has been greatly hindered by spare amounts extractable from biological sources. We therefore used a miniaturized, two-sided test system consisting of ATP-filled liposomes containing dispersed, randomly oriented renal Na(+)-K(+)-ATPase molecules to study effects of a low-molecular-weight, nonpeptidic Na(+)-K(+)-ATPase inhibitor extracted from bovine hypothalamus. With this test system, Na(+)-K(+)-ATPase inhibition produced by a single dose of 0.1 U (congruent to 75 fmol) of the hypothalamic inhibitory factor (HIF) as well as the membrane permeation of a single unit (approximately equal to 750 fmol) became measurable, and an estimation of the minimal number of HIF molecules per unit could be made. By a molecular mechanism involving positive cooperativity, HIF potently and completely blocked active 86Rb+ transport catalyzed by the right-side-out-oriented pump population, with an average 50% inhibitory concentration of 3.5 x 10(-8) M, indicating a roughly 30-fold higher apparent affinity than ouabain. By studying inhibition of the inside-out-oriented pump population, comparison of the membrane permeability of HIF to that of various cardiac glycosides of known hydrophobicity further indicated that HIF is not entirely ouabain-like as HIF penetrates the liposomal membrane, whereas ouabain does not. Besides the cardiac glycosides, HIF is the only compound tested thus far in the purified system that displays such striking transport inhibition. Other known or proposed endogenous Na(+)-K(+)-ATPase inhibitors, including unsaturated fatty acids, palytoxin, dehydroepiandrosterone, and vanadate, produce only partial transport inhibition even at high concentration.
In vivo osmoregulation of aldose reductase mRNA, protein, and sorbitol in renal medulla
Authors: Cowley B. D. , Ferraris J. D. , Carper D. , Burg M. B.
Published: December 2017

Sorbitol accumulates in renal medullary cells by synthesis from glucose in a reaction catalyzed by aldose reductase. Medullary sodium and urea are high and vary with urinary concentration. Sorbitol varies similarly, consistent with its role as a compatible intracellular organic osmolyte. We measured renal medullary sodium, urea, sorbitol, aldose reductase (protein and activity), and aldose reductase mRNA in rats treated to change medullary sodium and urea. In untreated Brattleboro rats all measurements were low and increased after 7 days of treatment with arginine vasopressin. In contrast, when normal rats were water deprived for 3 days, urea increased out of proportion to sodium, and sorbitol, aldose reductase, and aldose reductase mRNA were unchanged. After 2 h of diuresis, normal rats had lower medullary sodium and urea and reduced mRNA and sorbitol; however aldose reductase did not change. These data are consistent with previous results from cultured cells in which altered extracellular sodium, but not urea, leads to rapid changes in aldose reductase mRNA and slow changes (days) in aldose reductase. In addition, acute decreases in extracellular sodium increase leakage of sorbitol from cells. We also confirm previous results showing medullary glycerophosphorylcholine correlates best with urea, whereas the sum of all compatible osmolytes correlates best with sodium.
Net acid transport by isolated perfused inner medullary collecting ducts
Authors: Wall S. M. , Sands J. M. , Flessner M. F. , Nonoguchi H. , Spring K. R. , Knepper M. A.
Published: December 2017

The isolated perfused tubule technique was used to study net acid transport in rat terminal inner medullary collecting duct (IMCD) segments. The stop-flow luminal pH [measured fluorometrically with the acidic form of the pH-sensitive dye 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein in the lumen] fell 0.35 units below the bath pH in tubules from control rats and 0.53 units below the bath in tubules from deoxycorticosterone-treated rats. Tubules from control rats absorbed bicarbonate and secreted ammonium against concentration gradients, although at low rates. In control rats, 10(-8) M vasopressin added to the bath increased bicarbonate absorption almost threefold. Treatment of rats in vivo with deoxycorticosterone significantly increased the rate of bicarbonate absorption in vitro. In vivo NH4Cl loading also significantly increased bicarbonate absorption. Staining microdissected tubules with acridine orange confirmed that the perfused segments lacked intercalated cells. We conclude that the terminal IMCD spontaneously acidifies the lumen despite an absence of intercalated cells. Bicarbonate absorption appears to be regulated by the same factors that affect net acidification in other collecting duct segments.
Inhibition of rat mesangial cell growth by heparan sulfate
Authors: Groggel G. C. , Marinides G. N. , Hovingh P. , Hammond E. , Linker A.
Published: December 2017

The ability of heparan sulfate, an endogenous component of the glomerulus, to regulate the growth of cultured rat mesangial cells was investigated. Heparan sulfate caused a dose-dependent inhibition of rat mesangial cell growth, 85% inhibition compared with controls at the highest dose (1,000 micrograms/ml). Chondroitin sulfate produced no inhibition. The low-sulfated fraction of heparan sulfate (9%) produced more inhibition than the high-sulfated fraction (13%), 90 +/- 1 vs. 71 +/- 2% (P = 0.002). The effects of the heparan sulfate were completely reversible. Treatment of heparan sulfate with heparitinase increased the degree of inhibition, 71 +/- 1 vs. 84 +/- 1% (P less than 0.001). Four different oligosaccharides derived from heparan sulfate and heparin were tested for their ability to inhibit growth. One of the oligosaccharides, low-sulfated (10%), caused significant inhibition, 76 +/- 2%. Heparan sulfate was also able to inhibit the growth of Swiss 3T3 fibroblasts (63 +/- 5%). This inhibition was less marked than that seen with mesangial cells. Thus heparan sulfate was able to significantly inhibit rat mesangial cell growth in culture. Alterations in glomerular heparan sulfate may play an important role in alterations in mesangial cell growth.
Atrial natriuretic peptide-induced changes in renal prostacyclin production in ureteral obstruction
Authors: Himmelstein S. I. , Coffman T. M. , Yarger W. E. , Klotman P. E.
Published: December 2017

Ureteral obstruction is characterized by a marked reduction in renal hemodynamic function that is mediated in part by increased production of the vasoconstrictor eicosanoid thromboxane. However, animals with bilateral ureteral obstruction (BUO) sustain less renal functional impairment than unilaterally obstructed (UUO) animals. Recent evidence suggests that atrial natriuretic peptide (ANP) may be important in maintaining these differences. We therefore investigated the possibility that ANP-induced changes in renal arachidonic acid metabolism may be linked to and important in maintaining the differences between BUO and UUO animals. We measured renal function, renal eicosanoid production, and plasma ANP levels in BUO and UUO animals after the release of 24 h of ureteral obstruction. Renal function was reduced in both groups of obstructed animals compared with sham-operated controls. Inulin and p-aminohippurate clearance were significantly increased in BUO compared with UUO animals. Renal 6-ketoprostaglandin F1 alpha production by BUO kidneys was also significantly increased compared with kidneys from the UUO group or the sham-operated controls. In contrast, thromboxane B2 production by BUO kidneys was significantly reduced compared with UUO kidneys and was not significantly different from controls. Plasma ANP levels of BUO animals were significantly greater than those of UUO or sham-operated animals. When ANP was administered to in situ perfused UUO or BUO kidneys, renal vascular resistance fell significantly, and ANP induced a dramatic increase in 6-ketoprostaglandin F1 alpha production without affecting production of thromboxane B2. Indomethacin blunted the reduction in renal vascular resistance to ANP by 35-50%.(ABSTRACT TRUNCATED AT 250 WORDS)
Cell swelling increases intracellular free [Ca] in cultured toad bladder cells
Authors: Wong S. M. , DeBell M. C. , Chase H. S.
Published: December 2017

We examined the effect of cell swelling on intracellular free calcium concentration ([Ca]i) in cultured toad bladder cells (TB-M) grown as a polarized monolayer on collagen-coated filters. [Ca]i was measured by use of fura-2, fluorescence microscopy, and simple video imaging. In preliminary experiments we determined that reducing ionic strength by 15% had no effect on the Kd of fura-2, indicating that the dye could be used to examine the effects of cell swelling on [Ca]i. Reducing the osmolality of the serosal bathing medium by 15% caused [Ca]i to increase within 10 s from 97 +/- 9 to 354 +/- 88 nM (n = 5). By 2 min [Ca]i had declined to 163 +/- 22 nM. The increase in [Ca]i was not caused by a fall in Na concentration ([Na]) because isosmotic reduction of serosal [Na] did not result in an increase in [Ca]i. The swelling-induced increase in [Ca]i could be abolished by lowering serosal [Ca] to 200 nM and by addition of lanthanum. The calcium-channel blockers nitrendipine and verapamil also inhibited the swelling-induced increase in [Ca]i, although to different degrees. These experiments demonstrate that swelling of cultured toad bladder cells results in a significant increase in [Ca]i by enhancing the rate of calcium entry across the basolateral membrane, possibly through a calcium channel.
Na(+)-H+ antiporter and Na(+)-(HCO3-)n symporter regulate intracellular pH in mouse medullary thick limbs of Henle
Authors: Kikeri D. , Azar S. , Sun A. , Zeidel M. L. , Hebert S. C.
Published: December 2017

To determine mechanisms of intracellular pH (pHi) regulation in mouse medullary thick limbs (MTAL), pHi was measured in MTAL suspensions and in the isolated perfused MTAL by use of 2',7'-bis(carboxyethyl)-5(6)carboxyfluorescein (BCECF). A method to obtain MTAL suspensions from the mouse outer medulla is reported. Characterization of suspensions with microscopy, anti-Tamm-Horsfall antibody labeling, measurement of O2 consumption, and adenosine 3',5'-cyclic monophosphate responses to antidiuretic hormone indicated that these suspensions were highly purified for viable MTAL tubules. The resting pHi was 7.41 +/- 0.02 (means +/- SE) in N-2-hydroxyethylpiperazine-N'-2-ethanesulfonic acid-buffered media and 7.23 +/- 0.02 in CO2- HCO3(-)-buffered media, both at extracellular pH 7.4. MTAL tubules exhibited rapid pHi recovery from intracellular acidification. Recovery of pHi was dependent on luminal Na+ (apparent Km = 13.2 +/- 3.2 mM) and was inhibited by amiloride (apparent Ki = 10.6 microM), consistent with the activity of an apical Na(+)-H+ antiporter. Antiporter activity was enhanced by acidification and was diminished at the resting pHi. Recovery from intracellular alkalinization (rapid withdrawal of CO2- HCO3-) was sensitive to the stilbene anion transport inhibitor 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid, Cl(-)-insensitive, and Na(+)-sensitive, consistent with the activity of a Na(+)-(HCO3-)n symporter. Both transporters were significantly involved in steady-state pHi regulation in the presence of CO2- HCO3-. In contrast, the Na(+)-H+ antiporter played the dominant role in steady-state pHi regulation in the absence of CO2- HCO3-.
Concentration dependence of urea and thiourea transport in rat inner medullary collecting duct
Authors: Chou C. L. , Sands J. M. , Nonoguchi H. , Knepper M. A.
Published: December 2017

The vasopressin-dependent urea permeability of the rat terminal inner medullary collecting duct (IMCD) is much greater than can be explained by lipid-phase permeation or paracellular diffusion, suggesting the presence of vasopressin-stimulated facilitated transport pathway. We used the isolated perfused tubule technique to test whether the urea transport pathway exhibits saturation characteristics consistent with a facilitated pathway. When the luminal urea concentration was varied between 0 and 800 mM (no urea in peritubular bath), the relationship between the urea flux and the luminal concentration was linear with a y-axis intercept that was not significantly different from zero, indicating an absence of saturation in this concentration range. Higher concentrations of urea could not be tested due to technical limitations. However, when thiourea (a urea analogue that shares the urea transport pathway with urea) was substituted for urea in similar experiments, the apparent thiourea permeability fell with increasing thiourea concentration in the range 10-200 mM, indicative of saturation of the urea-thiourea transporter. When the urea concentration was varied in both bath and lumen, the lumen-to-bath urea flux approached a limiting value at 400-500 mM urea, consistent with saturation of the transporter. However, nonspecific inhibition of urea transport by bath urea could not be ruled out in those experiments. We conclude that the urea and thiourea transport pathway in the terminal IMCD exhibits saturation characteristics. However, the urea concentration required to saturate the pathway is apparently high, at least 400-500 mM in one set of experiments and probably greater than 800 mM in another.
Potassium load prevents the decrease of GFR induced by captopril in sodium-depleted rats
Authors: Rathaus M. , Pomeranz A. , Podjarny E. , Bernheim J.
Published: December 2017

Captopril decreases the glomerular filtration rate (GFR) in Na-depleted rats and inhibits the stimulation of glomerular prostanoid synthesis induced by Na depletion. Because K loading stimulates glomerular prostanoid production in normal rats, we studied the effects of K loading in Na-depleted captopril-treated (LNC) rats. Potassium, but not Cl, loading stimulated the glomerular synthesis of 6-ketoprostaglandin F1 alpha (PGF1 alpha) and thromboxane B2 (TxB2). Urinary kallikrein-like activity (UKALLV) and plasma aldosterone increased in K-loaded animals. LNC rats had lower clearances of inulin (CIN) and p-aminohippurate (CPAH) than controls (0.22 +/- 0.02 vs. 0.94 +/- 0.07 and 0.56 +/- 0.12 vs. 2.23 +/- 0.23 ml.min-1.100 g body wt-1, both P less than 0.01). KCl-loaded LNC rats had CIN and CPAH greater than LNC (0.64 +/- 0.16 and 1.90 +/- 0.28 ml.min-1.100 g body wt-1, P less than 0.01). Similar results were observed in LNC rats loaded with a K solution not containing Cl, but not in LNC rats loaded with a mixture of CaCl2, MgCl2, and HCl. In KCl-loaded LNC rats, cyclooxygenase inhibition decreased CIN from 0.49 +/- 0.09 to 0.30 +/- 0.08 ml.min-1.100 g body wt-1 (P less than 0.01). Aprotinin did not affect renal function despite significant decrease of UKALLV. We conclude that K loading prevents the decrease of GFR induced by captopril in Na-depleted rats and that this might be mediated by stimulation of glomerular prostanoid synthesis.
Proliferation and intracellular pH in cultured proximal tubular cells
Authors: Larsson S. H. , Fukuda Y. , Kolare S. , Aperia A.
Published: December 2017

Renal proximal tubule (PT) cells from adult rats will maintain much of their functional characteristics in short-term primary culture [S. Larsson, A. Aperia, and C. Lechene. Am. J. Physiol. 251 (Cell Physiol. 20): C455-C464, 1986]. This study examines the growth regulation of these highly differentiated cells with particular reference to cell density, intracellular pH (pHi), and the expression of the Na(+)-H+ exchanger. PT cells were obtained from young adult rats and studied after 48 h in culture. The mitotic rate was determined as the labeling index (LI) after [3H]thymidine autoradiography, and pHi was determined by 2',7'-bis(carboxyethyl)-5(6)-carboxyfluorescein quantitative fluorescence microscopy in single cells. Cells were grown either continuously in serum (S) or were serum deprived after 24 h (D). The cells were nonconfluent and grew in colonies. We defined the two peripheral layers of cells in a colony as peripheral (P) cells and the remaining cells as central (C). In C cells LI/h and pHi were in the range of what has been observed under in vivo conditions. In S condition LI/h was 2.2 +/- 0.3% and in D condition was 0.3 +/- 0.1%. LI was significantly higher in P than in C cells both under S (2.5 +/- 0.4-fold) and D conditions (5.6 +/- 0.8-fold). The rapidly growing P cells had a significantly lower pHi than the growth-retarded C cells both under S (7.25 +/- 0.02 vs. 7.30 +/- 0.01, P less than 0.05) and D conditions (7.21 +/- 0.02 vs. 7.28 +/- 0.01, P less than 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)
Urea transport in a distributed loop model of the urine-concentrating mechanism
Authors: Layton H. E.
Published: December 2017

Continuously distributed loops of Henle were used in a central core model of the rat kidney's urine-concentrating mechanism to investigate the importance of overlapping loops for three different modes of urea transport in the long loops of Henle: 1) urea-impermeable loops, 2) urea-permeable loops (as indicated by perfused tubule experiments), and 3) loops with urea-permeable descending limbs and active urea transport out of thin ascending limbs. Mode 1 produces high papillary tip osmolality in accordance with tissue slice experiments, but the relative contribution of urea to the osmolality of the central core and the long descending limbs is below experimental measurements. Mode 2 generates no significant osmolality increase in the inner medulla, in agreement with other model studies. Mode 3 produces high papillary tip osmolality with a substantial contribution of urea to the osmolality of the core and the descending limbs, which is more in accordance with experiments. The results suggest that 1) overlapping loops may produce a cascade effect that contributes to the inner medullary concentrating mechanism and that 2) new experiments are needed to more certainly ascertain the urea transport characteristics of the thin ascending limbs.
Effects of endothelin on renal function in dogs and rats
Authors: Banks R. O.
Published: December 2017

Endothelin was infused for 20 min into the left renal artery of pentobarbital-anesthetized dogs at 1 (n = 6) and 10 (n = 5) ng.min-1.kg-1. Renal blood flow (flow probe) increased 6 +/- 2 (SE) and 29 +/- 2% during the first 5 min of endothelin infusion and then slowly decreased to 86 +/- 3 and 29 +/- 2% of control at 20 min, respectively; the low renal blood flow persisted for at least 30 min after endothelin infusion, and there were no systemic effects of the peptide at either dose. These effects of endothelin on renal function were not altered by the angiotensin (ANG) II receptor antagonist, [Sar1,Thr8]ANG II. In the rat, endothelin was infused intravenously into three groups of pentobarbital-anesthetized females for 30 min at 0.1 microgram.min-1.kg-1; five had endothelin only, six had either endothelin + [Sar1,Thr8]ANG II (n = 4, 1.0 micrograms.min-1.kg-1) or endothelin + saralasin (n = 2, 1 and 2 micrograms.kg-1.min-1), and five had endothelin + captopril (5 mg.h-1.kg-1). The inhibitors were infused throughout the entire experiment. During infusion of endothelin alone mean arterial blood pressure increased from 106 +/- 2 to 136 +/- 4 mmHg and the glomerular filtration rate decreased from 2.7 +/- 0.2 to 0.7 +/- 0.3 ml/min. Captopril attenuated the endothelin-induced changes in renal function but not the increase in mean arterial blood pressure, whereas the competitive ANG II receptor antagonists had no effect on either the systemic or renal actions of the peptide. These data demonstrate that endothelin is a potent renal vasoconstrictor with transient vasodilator effects and that the inhibition of kinin degradation may attenuate the renal actions of the peptide.