bluuebunny/crossref_metadata_2025 huggingface dataset:
Ammonia transport by the turtle bladder: relationship to H+ secretion
Authors: Arruda J. A. , Dytko G.
Published: December 2017

The turtle bladder is apparently capable of transporting ammonia in the form of NH3 as well as NH+4. In the present study we examined the relationship of ammonia transport into the mucosal solution to H+ secretion and to chemical reactions in the unstirred layers. The relationship between ammonia transport and H+ secretion was examined before and after inhibition of H+ secretion by acetazolamide, SITS, and the putative inhibitor of the H+ pump dicyclohexylcarbodiimide. All these inhibitors caused a significant decrease in H+ secretion and led to a parallel decrease in the rate of ammonia transport with serosal pH at 6.4. Stimulation of H+ secretion by 1% CO2 increased both H+ secretion and ammonia transport at serosal pH 6.4. At serosal pH 6.4 the changes in H+ secretion were highly correlated with changes in ammonia transport. Ammonia transport at serosal pH 6.4 was electrogenic and inhibited by a low mucosal pH. In contrast, the diffusion of NH3 down an imposed concentration gradient was not correlated with changes in H+ secretion. Chemical reactions in the unstirred layers seem to influence ammonia transport in that increasing serosal nonvolatile buffer concentrations decreased the diffusion of NH3 down the concentration gradient from the serosal into the mucosal solution, probably by decreasing serosal NH3 concentration. Conversely, addition of uncouplers in the mucosal solution in an attempt to decrease the H+ concentration in the mucosal solution unstirred layer decreased the ammonia transport at serosal pH 6.4.
Transmembrane potential of renal papillary epithelial cells: effect of urea and DDAVP
Authors: Sands J. M. , Ivy E. J. , Beeuwkes R.
Published: December 2017

To define how renal papillary epithelial cells respond to wide changes in the ionic and osmotic composition of their environment, measurements were made of the transmembrane potential differences (PD) of rat renal papillary epithelial cells in vitro in media containing 100 mM NaCl, 100 mM KCl, 1.5 mM CaCl2, and 1 mM MgSO4 plus varying amounts of urea and/or sucrose up to 1,400 mM. Glass microelectrodes (resistance 25-75 M Omega) were used. With added sucrose, no change in PD from the initial value of -9.3 +/- 1.3 (SD) mV (n = 29) (cell interior negative) was found. With added urea, alone or while osmolality was maintained nearly constant with sucrose, the PD changed in a triphasic manner, depolarizing to -5.3 mV at 50 mM urea, hyperpolarizing to -20.0 mV at 150 mM urea, and then depolarizing again to -5.5 mV at 1,400 mM urea. When bath potassium was decreased to 10 meQ/liter (choline replacement) the PD hyperpolarized to -46.9 +/- 5.0 (SD) mV (n = 32). DDAVP, a nonpressor vasopressin analogue, and 8-bromo-cAMP depolarized the membrane to -5 mV in the presence of urea but did not change PD when urea was absent. These observations suggest an interaction between urea and ionic movement or conductance in rat renal papillary epithelial cells.
Amiloride inhibition of proximal tubular acidification
Authors: Howlin K. J. , Alpern R. J. , Rector F. C.
Published: December 2017

In brush border membrane vesicles prepared from mammalian kidney cortex, amiloride is a potent inhibitor of the Na+/H+ exchanger. In the present study, in vivo microperfusion was used to examine the effect of luminal amiloride on transport in the rat superficial proximal convoluted tubule. At a perfusion rate of 14 nl/min, addition of 10(-3) M amiloride to artificial early proximal tubular fluid reduced bicarbonate absorption from 103 +/- 7 to 81 +/- 5 pmol mm-1 X min-1 and volume absorption from 2.03 +/- 0.15 to 1.57 +/- 0.06 nl X mm-1 X min-1. Glucose efflux was unchanged, excluding nonspecific inhibition of Na+-K+-ATPase. Luminal amiloride at 10(-4) M did not affect bicarbonate absorption or volume absorption. At a perfusion rate of 41 nl/min, 10(-3) M amiloride reduced bicarbonate absorption from 179 +/- 8 to 114 +/- 9 pmol X mm-1 X min-1, a significantly greater inhibition than that seen in tubules perfused at 14 nl/min. Amiloride at 10(-3) M had no significant effect on sodium chloride absorption as measured by volume flux from an artificial late proximal tubular fluid. The results show that luminal amiloride specifically inhibits proximal acidification and demonstrate involvement of the Na+/H+ antiporter in proximal tubular acidification. However, the inhibition of acidification is less than the inhibition of Na+/H+ exchange predicted by vesicle studies.
Effects of prostaglandins on vasoconstrictor action in isolated renal arterioles
Authors: Edwards R. M.
Published: December 2017

The effects of arachidonic acid, prostaglandins (PG) I2, E2, D2, and F2 alpha on norepinephrine- (NE) and angiotensin II- (ANG II) induced tone were examined in interlobular arteries and afferent and efferent arterioles isolated from rabbit kidney. Arachidonic acid at 10(-5) M produced a rapid relaxation of NE-induced tone in all three vessel types. The vasodilatory effect of arachidonic acid but not acetylcholine was blocked by meclofenamate. In interlobular arteries, PGE2, and PGI2 caused a dose-dependent relaxation of NE-induced tone with a concentration causing the half-maximal response (ED50) of 1.2 and 4.6 X 10(-8) M, respectively. PGD2 caused a small but significant relaxation at 10(-7) M and above, whereas PGF2 alpha was inactive. In afferent arterioles contracted with NE, PGE2 and PGI2 caused identical dose-dependent relaxations. Significant effects were observed at concentrations between 10(-11) and 10(-10) M with ED50 values of 1.7 X 10(-8) M for PGE2 and 8.7 X 10(-9) M for PGI2. PGD2 had significant effects only at 10(-5) M, whereas PGF2 alpha was without effect. In contrast to the preglomerular vessels, efferent arterioles responded only to PGI2 (ED50, 9.7 X 10(-9) M), and the other arachidonic acid metabolites had no effect on lumen diameter. PGI2 antagonized the vasoconstrictive effects of both NE and ANG II in this vessel segment. The results demonstrate that of the prostanoids tested only PGE2 and PGI2 were effective in antagonizing vasoconstrictor stimuli in isolated renal microvessels. Furthermore, the rabbit renal microvasculature displays segmental heterogeneity for the vasodilatory PGs in that PGI2 affected both pre- and postglomerular arterioles, whereas PGE2 was effective only on the preglomerular microvessels.
Cellular contribution to pH-mediated calcium flux in neonatal mouse calvariae
Authors: Bushinsky D. A. , Goldring J. M. , Coe F. L.
Published: December 2017

Net calcium flux from cultured neonatal mouse calvariae into the culture medium is pH dependent, and acidified culture medium causes egress of calcium from bone. To determine whether calcium flux is mediated by pH effects on bone cell function, we cultured calvariae for 24 h with sodium azide, acetazolamide, parathyroid hormone (PTH), 1,25-dihydroxyvitamin D3 [1,25(OH)2D3], or after three successive freeze-thaw cycles, treatments that would be expected to alter bone cell function. We recultured bones for 3 h with the respective treatment and measured calcium flux. Sodium azide and freeze-thaw cycles produced a net influx of calcium (JCa = -22 +/- 7 and -23 +/- 6 nmol X bone-1 X 3 h-1, respectively) compared with net efflux of control bones (JCa = 35 +/- 6) at a similar initial medium pH. Acetazolamide reduced net flux to 0 (JCa = 7 +/- 6). PTH and 1,25(OH)2D3 increased net calcium efflux from bone (JCa = 78 +/- 7 and 74 +/- 10, respectively). Despite changing net flux, the slope dependence of net flux on medium pH was the same in the control group and all five treated groups of bones. The similarity of slopes indicates that the pH dependence of net flux is not a result of pH acting on bone cells but probably an effect of altered mineral equilibria. The difference in net flux at similar pH indicates that calcium efflux is partially inhibited by acetazolamide and stimulated by both PTH and 1,25(OH)2D3.
Sodium-dependent bicarbonate absorption by cortical thick ascending limb of rat kidney
Authors: Good D. W.
Published: December 2017

In vitro microperfusion experiments were performed to investigate the mechanism of bicarbonate absorption in the cortical thick ascending limb of the rat. Tubules were perfused at 1.0-1.5 nl X min-1 X mm-1 and bicarbonate concentration was 25 mM in the perfusate and bath. Bicarbonate absorption rates were determined by microcalorimetry. Control tubules absorbed bicarbonate at a mean rate of 9.5 +/- 0.6 pmol X min-1 X mm-1. The limiting luminal bicarbonate concentration was approximately 5 mM for tubules perfused at slow rates with 25 mM bicarbonate in the bath. Acetazolamide (10(-4)M) in the bath reduced bicarbonate absorption by 76% without significant effect on transepithelial voltage. Removing sodium from the perfusate and bath or removing potassium from the bath reduced bicarbonate absorption and transepithelial voltage to near zero. Adding amiloride (5 X 10(-4) or 10(-3) M) to the perfusate reduced bicarbonate absorption by 60-75% without detectable effect on transepithelial voltage. Adding furosemide (10(-4)M) to the perfusate increased bicarbonate absorption significantly by 40-50% while decreasing transepithelial voltage from 17 to 1.8 mV. Thus, bicarbonate absorption by cortical thick ascending limbs requires carbonic anhydrase activity and sodium transport but is not dependent on transepithelial voltage. When considered together, the results are consistent with mediation of the bicarbonate absorption by apical membrane sodium-hydrogen exchange.
Interaction of insulin with the renal proximal tubular cell
Authors: Hammerman M. R.
Published: December 2017

Insulin is known to regulate both metabolic and transport functions in the renal proximal tubule. Insulin present in plasma and in glomerular ultrafiltrate is known to be degraded at this nephron site. This paper summarizes what is known about these processes and about the mechanisms by which the actions of insulin and the degradation of insulin are effected in the proximal tubular epithelial cell. Recent studies have characterized the binding of insulin to specific receptors present in the proximal tubular basolateral membrane. Binding of insulin to its receptor in this membrane is thought to initiate events that lead to the phosphorylation of that receptor. Such insulin-stimulated phosphorylation may mediate hormonal action. A possible role for insulin-like growth factor II in the modulation of the actions of insulin has been suggested by observations in the kidney and in nonrenal cells. These findings are integrated into a model characterizing the nature of the interaction of insulin with the renal proximal tubular cell.
Effect of 1,25-dihydroxyvitamin D3 on phospholipid composition of rat renal brush border membrane
Authors: Tsutsumi M. , Alvarez U. , Avioli L. V. , Hruska K. A.
Published: December 2017

To analyze the effects of vitamin D on renal tubular cell membrane phospholipid metabolism, the effects of vitamin D depletion and repletion on renal brush border membrane (BBM) phosphatidylethanolamine (PE), phosphatidylcholine (PC), and phosphatidylinositol (PI) were studied. The PC content of BBM from kidneys of rats deprived of vitamin D for 5-6 wk was 33.5 +/- 2.2 nmol Pi/mg protein. This was significantly lower than the PC content of BBM from kidneys of rats supplemented with vitamin D2 for 2 wk, 41.0 +/- 0.4 nmol Pi/mg protein. Vitamin D depletion also decreased the content of BBM PE. The fatty acid composition of BBM PC was altered by vitamin D depletion. Vitamin D depletion increased palmitic acid and decreased stearic, linoleic, and arachidonic acid. Vitamin D repletion with a single physiological dose of 1,25(OH)2D3 (30 pmol), 16 h prior to study tended to increase membrane content of PC and significantly increased the linoleic acid content of the PC fraction. Single-dose vitamin D repletion with a pharmacological dose of 1,25(OH)2D3 (2.4 nmol) produced a significant increase in BBM content of PC and also significantly increased the linoleic acid content of PC. These results demonstrate that vitamin D deficiency affects PC and PE content of rat renal BBM and their fatty acid composition, and that vitamin D repletion with 1,25(OH)2D3 for 16 h partially normalizes the changes in PC.
Effect of metabolic acidosis on proximal tubular total CO2 absorption
Authors: Kunau R. T. , Hart J. I. , Walker K. A.
Published: December 2017

In vivo microperfusion studies of the proximal convoluted tubule of the rat were performed to determine the effect of metabolic acidosis on total CO2 (tCO2) absorption. In series I, tubular perfusion was performed in control and acidotic rats in a manner by which similar mean total CO2 concentrations in the proximal tubule were maintained. Comparable ranges of perfusion rate were studied in both groups. Following 3 days of HCl ingestion, plasma tCO2 was 20.0 +/- 0.9 mM in the acidotic rats whereas it was 29.6 +/- 0.53 mM in control rats. The arterial blood pH values were 7.25 +/- 0.02 vs. 7.43 +/- 0.01. Starting tCO2 perfusate concentrations were identical in both groups, 29.3 and 29.7 mM, as were the concentrations at the end of the perfused segments, 21.2 and 21.9 mM. The absorption of tCO2 (JtCO2, pmol X mm-1 X min-1) was significantly greater in the acidotic rats than in the controls, 576 +/- 39 vs. 256 +/- 21. At all perfusion rates studied, proximal tubular JtCO2 was higher in the acidotic than in the control rats. In series II, similar lengths of the late proximal tubule were perfused at the same rate in control and acidotic rats. Again, JtCO2 was higher in the acidotic rats, 352 +/- 19 vs. 198 +/- 13. The results indicate that at comparable luminal tCO2 concentration and tubular fluid flow rates, tCO2 absorption is significantly increased in the acidotic state. Although other mechanisms cannot be excluded, the finding of an increase in proximal tCO2 absorption in the acidotic rats is in agreement with the presence of an accelerated Na+/H+ exchange rate in brush border membrane vesicles obtained from the renal cortex of animals with metabolic acidosis.
Vasoactive intestinal peptide in the regulation of renin secretion
Authors: Porter J. P. , Thrasher T. N. , Said S. I. , Ganong W. F.
Published: December 2017

We have previously shown that vasoactive intestinal peptide (VIP) is a renin-stimulating factor both in vivo and in vitro. In the present investigation we sought to determine whether VIP exerted this effect by a neural or humoral mechanism. To test for a neural effect, the renal nerves were stimulated on one side for 30 min in anesthetized dogs, and plasma VIP and renin levels were determined in the renal venous effluent. The stimulation significantly increased plasma renin activity in arterial and renal venous plasma but had no effect on VIP concentrations. A humoral action was tested in two ways. First, plasma renin activity was measured before and after elevating circulating levels of endogenously produced VIP using intravenous neostigmine (0.07 mg/kg) in control, renal-denervated, and propranolol-pretreated animals. In all three groups, the elevated plasma level of VIP was associated with a significant increase in plasma renin activity. Second, plasma levels of VIP were determined in conscious dogs with elevated plasma renin activity produced by either a low-salt diet or hemorrhage. In both cases, plasma renin activity was significantly elevated as expected, but plasma levels of VIP were unchanged. These data suggest that the effects of VIP on renin secretion are not mediated by release of the peptide from the renal nerves, the circulating level of endogenously produced VIP can be elevated sufficiently to stimulate renin secretion, but a humoral role of VIP in the elevated plasma renin activity produced by low-salt diet or hemorrhage seems unlikely.+
Effects of KCl infusion on potassium excretion in sheep
Authors: Rabinowitz L. , Sarason R. L. , Yamauchi H.
Published: December 2017

To determine the quantitative relation of K excretion (UKV) to plasma K concentration (PK), three fasted, conscious, mature ewes were infused intravenously with 50 mmol KCl over 15, 30, and 60 min. Control experiments were without infusion. During KCl infusion PK was increased to 7.26 +/- 0.40 (15 min), 6.68 +/- 0.48 (30 min), and 5.59 +/- 0.3 meq/liter (60 min). During all three infusions the increase in UKV relative to the increase in PK was similar. The mean delta UKV/delta PK ratio was 160 +/- 30 (SD) mueq/min per meq/liter (range 102-203). On termination of each infusion PK decreased to control values, but UKV either remained elevated (60-min infusion) or first decreased and then increased (15- and 30-min infusions). The second, delayed kaliuresis began 30-45 min after initiation of KCl infusion and accelerated a return to the level of K balance of the control experiments. A plot of UKV against the corresponding period PK showed that, at a common value of PK, UKV was higher following KCl infusion when PK was dropping than during KCl infusion when PK was rising. The mechanisms responsible for this hysteresis phenomenon are not identified.
Water and electrolyte transport in Henle's loop and distal tubule after renal sympathectomy in the rat
Authors: Bencsath P. , Szenasi G. , Takacs L.
Published: December 2017

The effect of acute renal denervation (AD) on transtubular movement of water and electrolytes in Henle's loop (LH) and distal tubule (DT) of superficial nephrons was studied by the technique of in vivo microperfusion in Inactin-anesthetized hydropenic male rats. In time-control experiments (n = 6) no changes in either whole kidney or single nephron function were detected. Predenervation results of denervation experiments (n = 10) were similar to those of the time-control series. AD resulted in increased urine, sodium, and potassium excretion in the absence of changes of either arterial blood pressure or GFR. Compared with predenervation data, AD led to significant decreases in net transtubular fluxes (J) of water and sodium in both perfused segments with delivery kept constant (delta JNa: LH = 144 +/- 26 peq X min-1, 9.1 +/- 0.3%; DT = 94 +/- 11 peq X min-1, 22.3 +/- 1.1%). Potassium absorption in the loop decreased but an increase in net addition (secretion) of K in the distal tubule on denervation occurred (delta JK = 8.7 +/- 1.9 peq X min-1, 68.7 +/- 3.2%). Use of the reperfusion technique gave similar results. These results indicate that efferent renal sympathetic nerve activity directly influences water, sodium, and potassium transport in the loop of Henle and distal tubule of the anesthetized rat.
Renal interstitial pressure in mineralocorticoid escape
Authors: Burnett J. C. , Haas J. A. , Larson M. S.
Published: December 2017

Studies were performed in normal and DOCA-treated rats to determine renal hydrostatic pressures within superficial peritubular capillaries, the vasa recta, and renal interstitium during mineralocorticoid escape to test the hypothesis that mineralocorticoid escape is associated with elevated renal interstitial hydrostatic pressure. Fractional sodium excretion was greater in the DOCA-treated rats (3.20 +/- 0.51%) compared with control rats (1.23 +/- 0.12%) with no difference in glomerular filtration rate and renal blood flow between the two groups. Superficial peritubular capillary hydrostatic pressure (13.4 +/- 0.6 vs. 8.3 +/- 0.3 mmHg), vasa recta hydrostatic pressure (13.8 +/- 0.5 vs. 9.0 +/- 0.4 mmHg), renal interstitial hydrostatic pressure (9.8 +/- 0.4 vs. 4.5 +/- 0.4 mmHg), and arterial pressure (145 +/- 6 vs. 120 +/- 7 mmHg) were greater in the DOCA-treated compared with the control rats. These studies establish that mineralocorticoid escape is characterized by high renal interstitial hydrostatic pressure.
Effects of volume expansion on renal nerve activity, renal blood flow, and sodium and water excretion in conscious dogs
Authors: Morita H. , Vatner S. F.
Published: December 2017

Effects of acute volume expansion with isotonic isoncotic 3% dextran in saline were examined on renal nerve activity (RNA), renal blood flow, vascular resistance, and sodium and water excretion in conscious dogs. In intact dogs, acute volume expansion increased mean arterial pressure 15 +/- 3 mmHg, left atrial pressure 5.5 +/- 0.6 mmHg, and decreased RNA 88 +/- 2%, whereas renal blood flow did not change and renal vascular resistance increased slightly. When renal perfusion pressure was maintained at control levels, volume expansion decreased RNA 87 +/- 2% and renal vascular resistance 15 +/- 4%. During the 80-min period after volume expansion, urine flow rate increased 0.66 +/- 0.13 ml/min and sodium excretion rose 3.89 +/- 0.54 mueq X min-1 X kg-1, whereas RNA remained depressed. Arterial baroreceptor denervation (ABD) did not diminish responses of RNA, renal blood flow, renal vascular resistance, or sodium and water excretion to volume expansion. After ABD plus bilateral cervical vagotomy, volume expansion did not decrease RNA, and diuretic and natriuretic responses were significantly attenuated (P less than 0.025). However, responses of renal blood flow to volume expansion were not altered significantly. In conscious dogs with renal denervation, responses of renal blood flow to volume expansion were not impaired, whereas diuretic and natriuretic responses were attenuated (P less than 0.025). Thus, in intact conscious dogs, vagally mediated reflex decreases in RNA induced by acute volume expansion exerted a significant effect on sodium and water excretion but little control of renal blood flow and renal vascular resistance.
Natriuresis induced by arginine vasopressin infusion in sheep
Authors: Park R. G. , Congiu M. , Denton D. A. , McKinley M. J.
Published: December 2017

The aim of this study was to investigate whether arginine vasopressin (AVP) is natriuretic in sheep at plasma concentrations comparable to those induced by water deprivation. AVP was infused intravenously at 0.1, 0.2, and 0.5 microgram/h for 24-48 h in sheep allowed free access to water. Infusion of AVP at 0.1 microgram/h did not alter renal Na output, whereas infusion of AVP at both 0.2 and 0.5 microgram/h significantly increased daily output of Na in urine. Significant natriuresis did not occur until 3.5 h after the start of AVP infusion at 0.2 microgram/h. Plasma AVP levels induced by these infusions were 9.8 +/- 1.6 (0.1 microgram/h AVP), 21.9 +/- 7.7 (0.2 microgram/h AVP), and 32.5 +/- 9.0 pg/ml (0.5 microgram/h AVP) after 24 h. These concentrations are within the range found in sheep deprived of water for 3 days. Hypophysectomy abolished increases in plasma AVP concentration but not natriuresis in response to water deprivation. This suggests that increased plasma AVP concentration does not play an essential role in the mechanisms subserving dehydration-induced natriuresis.
Modification of experimental gentamicin nephrotoxicity by selective parathyroidectomy
Authors: Bennett W. M. , Pulliam J. P. , Porter G. A. , Houghton D. C.
Published: December 2017

Dietary calcium loading reduces gentamicin nephrotoxicity in rats. Since parathyroid hormone increases renal brush border membrane anionic phospholipids, the putative gentamicin receptors, the effects of selective parathyroidectomy on gentamicin nephrotoxicity were examined. Male Fisher 344 rats underwent parathyroidectomy or sham surgery. All animals were fed a diet containing 0.5% calcium for 2 wk prior to gentamicin, 20 mg/kg twice daily for 6 and 10 days. Other parathyroidectomized rats were fed a 4% calcium diet for 2 wk and treated similarly with gentamicin On day 6, serum creatinine (mg/100 ml) was 2.0 +/- 0.9 in the sham-operated animals, 1.7 +/- 1.6 in the parathyroidectomized animals on the 0.5% diet, and 0.8 +/- 0.1 in the parathyroidectomized animals on the 4% diet. By 10 days, the sham-operated animals had creatinine values of 6.3 +/- 1.6 (mg/100 ml) compared with 1.7 +/- .9 in the parathyroidectomized animals on the same diet and 0.8 +/- 0.2 in the 4% diet animals. More severe tubular necrosis was present in the sham-operated compared with the parathyroidectomized animals. High calcium diet in the parathyroidectomized animals produced structural and functional protection from gentamicin nephrotoxicity. Human parathyroid hormone (1-34) 20 IU twice daily given subcutaneously to a separate group of parathyroidectomized rats, eliminated the protective effect of parathyroidectomy on renal structure and function. Parathyroidectomy modifies experimental gentamicin nephrotoxicity. The additional protective effect of dietary calcium loading may be independent of parathyroid ablation.
Mechanism of fluid secretion in isolated shark renal proximal tubules
Authors: Sawyer D. B. , Beyenbach K. W.
Published: December 2017

Renal proximal tubules from the glomerular Squalus acanthias were studied for evidence of fluid secretion by closing one end of isolated tubules and leaving the other end open so that secreted fluid could be collected. When tubules were bathed in shark Ringer, fluid secretion rate was 27.6 +/- 3.9 (SE) pl X min-1 X mm-1 (21 tubules). Dibutyryl cAMP stimulated fluid secretion 50% (P less than 0.02, n = 14), furosemide inhibited fluid secretion 50% (P less than 0.01, n = 6), and metabolic inhibitors blocked fluid secretion nearly 100%. Secreted fluid was slightly hyperosmotic to peritubular bath (P less than 0.01, n = 7) but Na, Cl, S, K, and Ca concentrations were not significantly different from bath concentrations (wavelength-dispersive spectroscopy, electron probe analysis). cAMP had no effect on secreted fluid composition, and in some tubules cAMP did not stimulate fluid secretion. In conjunction with previous data we propose that spontaneous fluid secretion is driven by secretion of NaCl. However, finding the mechanism of NaCl and fluid secretion in glomerular renal tubules offers new perspectives of some previously inexplicable phenomena in the renal physiology of fish.
Purine nucleotides stimulate DNA synthesis in kidney epithelial cells in culture
Authors: Kartha S. , Toback F. G.
Published: December 2017

Adenine nucleotides infused into animals with acute renal failure appear to enhance recovery of kidney function and structure. To determine whether these compounds could act by a direct effect on renal cell metabolism, their capacity to stimulate DNA synthesis was evaluated in cultures of monkey kidney epithelial cells (BSC-1 line). AMP and ADP enhanced DNA synthesis by threefold more than was previously observed with other mitogens for these cells. Guanosine and inosine and their nucleotides and adenosine and ATP were also mitogenic but to a lesser extent, whereas pyrimidine derivatives were ineffective. In the presence of AMP, autoradiography of [3H]thymidine-labeled cells indicated that a greater number of cells entered the S phase of the cell cycle, and assessment of cell number revealed increased multiplication. The mitogenic effect of adenine nucleotides was not reproduced by agents that raise the cellular content of cAMP and was serum independent. Adenine nucleotides did not alter DNA synthesis when added to cultures of mouse fibroblasts. These results indicate that provision of exogenous purine nucleosides and nucleotides stimulate DNA synthesis in renal epithelial cells in culture.
Ureteral occlusion decreases phospholipid and cholesterol of renal tubular membranes
Authors: Morrissey J. , Windus D. , Schwab S. , Tannenbaum J. , Klahr S.
Published: December 2017

Unilateral ureteral obstruction of 24 h duration in the dog results in a 20% decrease in the amount of total phospholipids present in basolateral membranes of renal tubular cells obtained from the experimental kidney as compared with the amount of phospholipid in basolateral membranes prepared from the contralateral kidney of the same dogs or from the kidneys of normal sham-operated dogs. There was also a decrease in the content of cholesterol and cholesterol esters of the basolateral membranes from the experimental kidney. By contrast, no significant change in lipid content was observed in brush border membranes obtained from the experimental kidney of dogs with unilateral ureteral obstruction. The decrease in phospholipid content of basolateral membranes was accompanied by a 40% fall in the content of phosphatidylcholine and a 12% fall in sphingomyelin. There was a small (12%) but significant increase in the content of phosphatidylethanolamine in basolateral membranes. The mechanisms responsible for the selective decrease in phospholipid content of basolateral membranes remain to be established. It is postulated that changes in solute transport and altered response to hormones observed in the postobstructed kidney of animals with unilateral ureteral obstruction may be explained, at least in part, by changes in the lipid composition of basolateral membranes.
PGI2 synthesis and excretion in dog kidney: evidence for renal PG compartmentalization
Authors: Boyd R. M. , Nasjletti A. , Heerdt P. M. , Baer P. G.
Published: December 2017

To assess the concept of compartmentalization of renal prostaglandins (PG), we compared entry of PGE2 and the PGI2 metabolite 6-keto-PGF1 alpha into the renal vascular and tubular compartments, in sodium pentobarbital-anesthetized dogs. Renal arterial 6-keto-PGF1 alpha infusion increased both renal venous and urinary 6-keto-PGF1 alpha outflow. In contrast, renal arterial infusion of arachidonic acid (AA) or bradykinin (BK) increased renal venous 6-keto-PGF1 alpha outflow but had no effect on its urinary outflow. Both urinary and renal venous PGE2 outflows increased during AA or BK infusion. Ureteral stopped-flow studies revealed no postglomerular 6-keto-PGF1 alpha entry into tubular fluid. During renal arterial infusion of [3H]PGI2 and inulin, first-pass 3H clearance was 40% of inulin clearance; 35% of urinary 3H was 6-keto-PGF1 alpha, and two other urinary metabolites were found. During renal arterial infusion of [3H]6-keto-PGF1 alpha and inulin, first-pass 3H clearance was 150% of inulin clearance; 75% of urinary 3H was 6-keto-PGF1 alpha, and only one other metabolite was found. We conclude that in the dog PGE2 synthesized in the kidney enters directly into both the renal vascular and tubular compartments, but 6-keto-PGF1 alpha of renal origin enters directly into only the renal vascular compartment.
Roles of urea production, ammonium excretion, and amino acid oxidation in acid-base balance
Authors: Mackenzie W.
Published: December 2017

Atkinson and colleagues recently proposed several concepts that contrast with traditional views: first, that acid-base balance is regulated chiefly by the reactions leading to urea production in the liver; second, that ammonium excretion by the kidney plays no role in acid-base homeostasis; and third, that ammonium does not stimulate ureagenesis (except indirectly). To examine these concepts, plasma ions other than bicarbonate are categorized as 1) fixed cations (Na+, K+, Ca2+, and Mg2+, symbolized M+) and anions (Cl-), 2) buffer anions (A-), 3) other anions (X-), and 4) ammonium plus charged amino groups (N+). Since electroneutrality dictates that M+ + N+ = Cl- + HCO3- + A- + X-, it follows that delta HCO3- = delta(M+ - Cl-) - delta A- - delta X- + delta N+. Therefore acid-base disturbances (changes in HCO3-) can be categorized as to how they affect bodily content and hence plasma concentration of each of these four types of ions. The stoichiometry of ureagenesis, glutamine hydrolysis, ammonium and titratable acid excretion, oxidation of neutral, acidic, and basic amino acids, and oxidation of methionine, phosphoserine, and protein are examined to see how they alter these quantities. It is concluded that 1) although ureagenesis is pH dependent and also counteracts a tendency of amino acid oxidation to cause alkalosis, this tendency is inherently limited by the hyperammonemia (delta N+) that necessarily accompanies it, 2) ammonium excretion is equivalent to hydrogen excretion in its effects on acid-base balance if, and only if, it occurs in exchange for sodium or is accompanied by chloride excretion and only when the glutamate generated by glutamine hydrolysis is oxidized.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of secretin on glomerular dynamics in dogs
Authors: Marchand G. R.
Published: December 2017

These studies were performed to determine whether a role for increased renal plasma flow (RPF) in the regulation of glomerular filtration rate (GFR) could be demonstrated in dogs by infusing the polypeptide hormone secretin, a vasodilator that has been reported to increase GFR. Differences between control and recollection periods were compared by paired t test in five time-control dogs (group 1) and 10 secretin dogs (group 2). In group 2, secretin (100 mU . kg-1 . min-1, ia) significantly increased single-nephron glomerular filtration rate (SNGFR) 11.1 +/- 3.1 nl/min (20%) and glomerular plasma flow 59 +/- 11 nl/min (26%). Similar increases in GFR (26%) and RPF (29%) were observed. Secretin also increased glomerular capillary pressure 5.2 +/- 0.8 mmHg and free-flow proximal tubule pressure 5.5 +/- 1.0 mmHg. Secretin did not significantly affect average effective filtration pressure (EFP) but significantly increased the ultrafiltration coefficient (Kf) 0.74 +/- 0.14 nl . min-1 . mmHg-1. These differences were significantly greater than those observed in group 2. It is concluded that secretin increased SNGFR primarily by an effect on Kf. This is consistent with the marked effect that Kf is predicted to have on glomerular filtration in dogs. The maintenance of EFP agrees with other vasodilator studies and indicates that GFR is only moderately dependent on plasma flow in dogs.
Angiotensin II inhibition on blood pressure and renal hemodynamics in pregnant rats
Authors: Baylis C. , Collins R. C.
Published: December 2017

Late-pregnant (18-20 days) and virgin rats were studied under anesthesia or while awake to investigate the effect of acute angiotensin II (ANG II) inhibition (with saralasin or captopril) on mean arterial blood pressure (AP) and renal hemodynamics. ANG II inhibition had no effect on AP in either anesthetized or awake virgin rats. Saralasin produced no effect on renal hemodynamics although with captopril small increases in renal plasma flow rate (RPF) and decreases in renal vascular resistance (RVR) occurred in virgins. In anesthetized pregnant rats, ANG II inhibition evoked marked decreases in AP. In some rats receiving saralasin, AP was only mildly depressed and RVR fell, leading to increases in glomerular filtration rate and RPF. In others, saralasin produced large decreases in AP, and indices of renal function became unmeasurable because of near cessation of urine flow. All late-pregnant anesthetized rats receiving captopril showed increased RPF irrespective of the magnitude of the fall in AP. In awake pregnant rats no effect on AP was seen with ANG II inhibition. Saralasin had no effect on renal hemodynamics although with captopril a small increase in RPF was observed. These data indicate that the stress of acute surgery and anesthesia produces a dependence of AP on ANG II in the pregnant but not the virgin rat. Under normal pregnant (awake) conditions, however, ANG II inhibition has no net effect on AP.
Cholinergic stimulation of the hypothalamus and natriuresis in rats: role of the renal nerves
Authors: Silva-Netto C. R. , Jackson R. H. , Colindres R. E.
Published: December 2017

The role of the renal nerves in the natriuresis seen after cholinergic stimulation of the hypothalamus was studied in anesthetized rats treated with injection into the lateral hypothalamus (LH) of 1 microgram of carbamylcholine chloride (carbachol) in 1 microliter of 0.15 M NaCl or NaCl alone. Injection of carbachol exhibited diuresis and natriuresis both in acutely denervated kidneys (P less than 0.01) and in contralateral innervated kidneys (P less than 0.01) without changes in glomerular filtration rate (GFR) or renal plasma flow (RPF) (n = 10). Salt and water excretion was unchanged in 10 rats after injection of NaCl. Micropuncture studies in denervated kidneys showed that, after carbachol injection, tubular fluid-to-plasma inulin concentration ratio [(F/P)In] in the late proximal tubule fell from 1.86 +/- 0.08 to 1.64 +/- 0.07 (P less than 0.01) without changes in single-nephron GFR. In nine other carbachol-treated rats in which renal perfusion pressure was maintained low and constant, diuresis and natriuresis, although attenuated, were again observed both in denervated (P less than 0.01) and in contralateral innervated kidneys (P less than 0.05). In another group of 11 animals, efferent renal nerve activity (ERNA) was recorded before and after LH injection of carbachol and isotonic saline. ERNA was significantly depressed for 30 min, only after carbachol injection. Our results suggest that the renal nerves, although involved, are not essential for the natriuretic response after cholinergic stimulation of LH. By exclusion, other factors, presumably hormones, must contribute to the response.
Characterization of the apical membrane ionic permeability of the rabbit proximal convoluted tubule
Authors: Lapointe J. Y. , Laprade R. , Cardinal J.
Published: December 2017

Basolateral membrane potential (psi BL), transepithelial potential (psi T), and the ratio of apical to basolateral membrane resistance (RA/RBL) were measured in rabbit proximal convoluted tubules (PCT) perfused in vitro. Analysis of RA/RBL changes using several luminal perfusates indicates that the cotransport of Na with glucose and alanine would represent 19% of the apical conductance in normal conditions; the cotransport of Na with acetate, citrate, sulfate, and phosphate would represent 7%, whereas Na, K, and Cl diffusion would represent 10, 4, and 0% of this apical conductance, respectively. On the other hand, psi BL values can also be analyzed using the equivalent circuit of the epithelium to obtain the apical membrane equivalent electromotive force (EA) in the presence of each perfusate. These values, as well as the preceding values obtained from RA/RBL measurements, indicate that in the absence of cotransported solutes the transference number for Na diffusion is several times larger than for K diffusion. Among the conductance pathways studied, the transference number sequence would be as follows: Na cotransport with alanine and glucose greater than Na cotransport with anions greater than Na diffusion greater than K diffusion greater than Cl diffusion. This study also suggests the presence of another important but unidentified apical ionic permeation pathway, since the total of the transference numbers obtained from RA/RBL analysis represents only 40% of the total apical membrane conductance and the absolute values of EA are difficult to account for using only the tested apical membrane permeation pathways.
Electrogenic Na+-independent Pi transport in canine renal basolateral membrane vesicles
Authors: Schwab S. J. , Hammerman M. R.
Published: December 2017

To define the mechanism by which Pi exists from the renal proximal tubular cell across the basolateral membrane, we measured 32Pi uptake in basolateral membrane vesicles from dog kidney in the absence of Na+. Preloading of basolateral vesicles with 2 mM Pi transstimulated 32Pi uptake, which is consistent with counterflow. We used measurements of transstimulation to quantitate the transport component of 32Pi uptake. Transstimulation of 32Pi uptake was inhibited less than 30% by concentrations of probenecid as high as 50 mM. In contrast, transstimulation of 35SO4(2-) uptake by intravesicular SO4(2-) was inhibited 92% by 5 mM probenecid. Preloading basolateral vesicles with SO4(2-) did not result in transstimulation of 32Pi uptake. Accumulation of 32Pi in basolateral vesicles above steady state was driven by a membrane potential (intravesicular positive), consistent with Na+-independent Pi transport being accompanied by the net transfer of negative charge across the membrane. We conclude that carrier-mediated, electrogenic Na+-independent 32Pi transport can be demonstrated in basolateral vesicles from dog kidney. This process appears to be mediated, at least in part, via a mechanism different from that by which SO4(2-) is transported. Electrogenic Na+-independent Pi transport may reflect one means by which Pi reabsorbed across the luminal membrane exists from the proximal tubular cell down an electrochemical gradient.
K+ transport by rat colon: adaptation to a low potassium diet
Authors: Tannen R. L. , Marino R. , Dawson D. C.
Published: December 2017

Recent studies with the isolated perfused rat kidney have demonstrated the existence of an intrinsic renal adaptation to conserve K+ in response to ingestion of a low K+ diet for 3 days. To determine whether the colon alters its K+ transport properties in a similar fashion, we measured transmural 86Rb fluxes across sheets of distal colonic epithelium under short-circuit conditions. Preliminary studies using a double-isotope technique demonstrated that 86Rb and 42K fluxes were similar; therefore 86Rb flux was considered equivalent to K+ flux. The distal half of the colon from each rat was divided into two segments, referred to as early and late distal colon. Experiments were carried out using rats fed a K+ -free, control (0.15 mmol/g), and high K+ (1.13 mmol/g) powdered diet of otherwise identical electrolyte content. Net K+ secretion (Jnet) by the early distal colon was reduced from 0.45 in the controls to -0.02 mueq X cm-2 X h-1 by a low K+ diet as a result of a decrease in serosal-to-mucosal flux (Jsm), with no change in mucosal-to-serosal flux (Jms). Conductance (GT) and short-circuit current (Isc) were unchanged. Jnet by the late distal colon averaged 0.17 in the controls and 0.01 mueq X cm-2 X h-1 with a low K+ diet, but this difference was not significant statistically. In comparison with the controls, a high K+ diet had no effect on Jnet by the early distal colon (0.48 mueq X cm-2 X h-1) but increased Jnet by the late distal colon substantially (0.77 mueq X cm-2 X h-1).(ABSTRACT TRUNCATED AT 250 WORDS)
Role of thromboxane in control of arterial pressure and renal function in young spontaneously hypertensive rats
Authors: Grone H. J. , Grippo R. S. , Arendshorst W. J. , Dunn M. J.
Published: December 2017

As platelet and renal thromboxane (TX)A2 synthesis are increased in spontaneously hypertensive rats (SHR), we tested the hypothesis that increased renal TXA2 synthesis may cause the reduction in glomerular filtration rate (GFR), renal plasma flow (RPF), and the increase in arterial pressure in SHR of the Okamoto-Aoki strain. A selective inhibitor of TXA2 synthetase (UK 38485) was given acutely, with or without a TXA2 receptor antagonist (EP-092), to 6- to 8-wk-old SHR and age-matched Wistar-Kyoto rats (WKY) and chronically for 5.5 wk to 3.5-wk-old SHR. Inhibition of TXA2, measured by the stable metabolite TXB2, in the acute experiments was greater than 95% in serum and greater than 80% in glomeruli; in the chronic studies, it was greater than 65% in glomeruli. There was no endoperoxide shunting to vasodilatory and natriuretic prostaglandins (PGE2, PGI2) in glomeruli after TXA2 inhibition. Before drug administration, GFR and RPF were reduced and renal vascular resistance (RVR) was increased in SHR. During acute blockade of renal TXA2 synthesis, with or without a TXA2 receptor antagonist, there was no significant change in GFR, RPF, or RVR in WKY and SHR. Inhibition of TXA2 did not affect urine flow or sodium excretion in anesthetized or conscious WKY or SHR. Mean arterial pressure did not fall in treated SHR and WKY. Chronic TXA2 synthesis inhibition did not improve GFR or RPF in SHR, and systolic arterial pressure was not altered. These findings show that enhanced serum and glomerular TXA2 synthesis do not significantly contribute to the reduction in renal function and are not essential for the development of hypertension in young SHR.
Ammonium as a substrate for Na+-K+-ATPase in rabbit proximal tubules
Authors: Kurtz I. , Balaban R. S.
Published: December 2017

The role of the ammonium ion (NH+4) as a substrate for Na+-K+-ATPase was determined in intact rabbit proximal tubules. Since ouabain-sensitive oxygen consumption and Na+-K+-ATPase transport activity are tightly coupled in the proximal tubule with a stoichiometry of 12 K+ pumped/oxygen consumed, we used the ouabain-sensitive oxygen consumption of rabbit proximal tubule suspensions as an assay of Na+-K+-ATPase pump activity. The addition of NH+4 to K+-depleted tubules in nominally K+-free media resulted in a dose-dependent increase in oxygen consumption with an apparent affinity (Km) of 0.4 mM NH+4. Oxygen consumption was increased by 39.3 +/- 3% over control (n = 7) by 5 mM NH4Cl. This stimulation was completely inhibited by the addition of 5 X 10(-4) M ouabain. Under the same conditions, the addition of 5 mM KCl stimulated oxygen consumption by 52.4 +/- 2.9% (n = 7) with a Km of 0.5 mM. This stimulation was also completely inhibited by ouabain. Ouabain was also found to decrease the initial rate of NH+4 uptake into the proximal tubule cells. K+ and NH+4 competed with each other for active uptake into tubule cells. These results demonstrate that NH+4 can substitute for K+ on the Na+-K+-ATPase of the rabbit proximal tubule cell. Based on these data we have developed a kinetic model that predicts that the competition between NH+4 and K+ for transport on the Na+-K+-ATPase is not significant in the cortical labyrinth but potentially very significant in the inner medulla.
Localization of atrial natriuretic peptide binding sites within the rat kidney
Authors: Healy D. P. , Fanestil D. D.
Published: December 2017

Although synthetic atrial natriuretic peptides (ANP) have potent natriuretic/diuretic properties, the renal mechanisms underlying these effects are not yet clearly defined. To determine the possible sites of action for ANP within the kidney, we have localized 125I-ANP binding sites by in vitro autoradiography. Slices of rat kidney were incubated with 150 pM 125I-ANP [alpha-rat ANP (alpha-rANP), 28 amino acids] alone or in the presence of 10 nM or 1 microM unlabeled ANP. Autoradiography was performed using LKB Ultrofilm or emulsion-coated cover slips together with histochemical/immunohistochemical staining of specific tubular segments. High-affinity 125I-ANP binding sites were concentrated over glomeruli and to a lesser extent over the arterial vasculature. Lower-affinity binding sites were seen over proximal tubules and inner medullary collecting ducts. The remainder of the nephron was unlabeled. The localization of high-affinity 125I-ANP binding sites in rat kidney is consistent with a glomerular filtration/hemodynamic mechanism as the principal means by which ANP promotes natriuresis/diuresis.