bluuebunny/crossref_metadata_2025 huggingface dataset:
Furosemide-sensitive thallium fluxes in smooth muscle of rabbit uterus
Authors: Johns A. , Cutshaw S. V.
Published: December 2017

The furosemide-sensitive uptake of thallium represents approximately equal to 50% of the total uptake of thallium by rabbit uterus and requires Cl- and Na+. The furosemide-sensitive uptake of thallium is stimulated by other ions at low concentrations with the rank order Li+ greater than Tl+ greater than K+ = Rb+ greater than Cs+ and is inhibited by these ions at high concentrations with the rank order Tl+ greater than K+ = Rb+ greater than Cs+ greater than Li+, suggesting multiple cation binding sites on the carrier. Uptake of 36Cl- is inhibited by furosemide in the presence of ouabain. Thallium efflux and 36Cl efflux in the presence of ouabain is inhibited by furosemide. The chloride concentration regulates the proportion of thallium uptake that is ouabain sensitive and furosemide sensitive without altering the total uptake. It is suggested that the furosemide-sensitive uptake of thallium reflects a Na+-Cl- -K+ exchange system that could be classified as a cotransport or countertransport of any two of these ions and also could be the smooth muscle chloride pump.
Hydrogen ion permeability of the rabbit proximal convoluted tubule
Authors: Hamm L. L. , Pucacco L. R. , Kokko J. P. , Jacobson H. R.
Published: December 2017

Acidification of luminal fluid in the proximal convoluted tubule has been modeled as a pump-leak system. Using isolated perfused rabbit proximal convoluted tubules in a HCO-3/CO2-free in vitro environment, we studied “H+ leak” by imposing pH gradients across the tubule and measuring the change in pH from perfusate to collected fluid. Active acidification was inhibited by acetazolamide with and without hypothermia. At 21 degrees C a symmetrical H+ leak with an apparent permeability coefficient of approximately 0.15 cm X s-1 was found with either a lumen-to-bath or bath-to-lumen [H+] gradient. At 37 degrees C a much higher apparent permeability coefficient was found that was dependent on luminal lactate. Phosphate movement did not affect H+ fluxes significantly. Without luminal lactate, the apparent permeability coefficient was 0.31 cm X s-1. Although this permeability coefficient is larger than other ionic permeability coefficients in this segment, it is not sufficient to account for a significant H+ leak compared with rates of acidification or bicarbonate reabsorption. To investigate the role of Na+-H+ exchange in mediating the observed H+ leak, we perfused tubules with low [Na+] solutions with and without amiloride (10(-3) M). Neither the lower [Na+] nor the presence of amiloride diminished the apparent [H+] permeability coefficient. We conclude that a H+ leak pathway independent of Na+-H+ exchange is present in the proximal convoluted tubule.
Elevated 1,25(OH)2D3, intestinal absorption, and renal mineral conservation in male rats
Authors: Bushinsky D. A. , Favus M. J. , Coe F. L.
Published: December 2017

We studied the physiological importance of elevated serum 1,25-dihydroxy-vitamin D3 [1,25(OH)2D3] in male rats. Male and female rats of equal weight consumed either a high calcium diet (1.20% calcium; HCD), a low calcium diet (0.02% calcium; LCD), or a normal calcium diet (0.60% calcium; NCD). With all three diets, serum 1,25(OH)2D3 was higher in males than females and rose in both sexes with decreasing diet calcium. There was a direct correlation between serum 1,25(OH)2D3 and proximal duodenal 45Ca uptake (r = 0.667; P less than 0.001). With NCD, we performed a balance study and found a direct correlation between serum 1,25(OH)2D3 and both 5-day fractional calcium absorption (r = 0.703; P less than 0.01) and fractional phosphorus absorption (r = 0.679; P less than 0.01). In addition, serum 1,25(OH)2D3 was directly correlated with 5-day calcium retention (r = 0.772; P less than 0.001) and phosphorus retention (r = 0.830; P less than 0.001). Males grew faster than females (F ratio = 1,194; P less than 0.001). Elevated 1,25(OH)2D3 in males appears to be of biological significance and may help satisfy a greater, growth-related, need for calcium.
Phosphatidylcholine metabolism during renal growth and regeneration
Authors: Toback F. G.
Published: December 2017

Phosphatidylcholine, the most abundant phospholipid in renal cellular membranes, is synthesized predominantly via the Kennedy pathway in normal and growing kidney tissue. Augmented biosynthesis of phosphatidylcholine is one of the earliest responses to growth signals in renal cells. During potassium depletion, regeneration after acute tubular necrosis, and compensatory growth after uninephrectomy increased membrane phosphatidylcholine biosynthesis precedes the appearance of new organelles and surface structures and the onset of cell division. The increment in phosphatidylcholine biosynthesis in the growing kidneys of potassium-depleted rats appears to be mediated by enhanced cellular uptake of the precursor choline and activation of the enzyme cytidine diphosphocholine:1,2-diacylglycerol cholinephosphotransferase. Specific amino acids, cations, and polyamines can modify the activity of this microsomal enzyme in normal and growing renal cells. Phospholipase A also plays a regulatory role in phosphatidylcholine metabolism because inhibition of this catabolic enzyme favors phospholipid accretion and kidney growth during potassium depletion, whereas stimulation of the enzyme leads to brisk phospholipid breakdown and a decrease in tissue mass during potassium repletion.
Structural prerequisites for the hypotensive action of parathyroid hormone
Authors: Ellison D. H. , McCarron D. A.
Published: December 2017

We assessed the vascular, phosphaturic, and calcemic responses to several synthetic parathyroid hormone (PTH) analogues. Bovine (b) PTH (1-34), human (h) PTH (1-34), hPTH (53-84), [ Nle8 , Nle18 , Tyr34 ]bPTH (1-34), and [ Nle8 , Nle18 , Tyr34 ]bPTH (3-34) were administered in doses between 1 and 500 micrograms/kg as bolus intravenous injections to male Wistar-Kyoto rats aged 18-26 wk. Antagonism of the action of PTH was assessed in rats pretreated with 10 or 100 micrograms/kg [ Nle8 , Nle18 , Tyr34 ]bPTH (3-34) followed by 10 micrograms/kg of bPTH (1-34), or with 10 micrograms/kg hPTH (53-84) followed by 10 micrograms/kg hPTH (1-34). Bovine PTH (1-34), hPTH (1-34), and [ Nle8 , Nle18 , Tyr34 ]bPTH (1-34) produced virtually identical log dose-dependent hypotension, with 100 micrograms/kg of each analogue producing a 56% reduction in mean arterial pressure. Neither hPTH (53-84) nor [ Nle8 , Nle18 , Tyr34 ]bPTH (3-34) demonstrated any effect on mean arterial pressure at doses up to 500 micrograms/kg. Pretreatment with the inactive analogues failed to antagonize the vasodilating response to either bPTH (1-34) or hPTH (1-34). The vasoactive analogues significantly increased urinary phosphorus excretion while the inactive analogues did not modify it. hPTH (1-34) produced a modest decrease in serum Ca2+ at 1 min after injection. The results document that the vasodilating effect of PTH is a specific action of the peptide. Deletion of the first two amino acid residues abolishes both the phosphaturic and hypotensive effects of the peptide. Acute changes in serum Ca2+ do not appear to be a prerequisite for the vasodilatory response. Inactive analogues of PTH do not antagonize the vascular actions of the peptide.
Role of uremia, brain calcium, and parathyroid hormone on changes in electroencephalogram in chronic renal failure
Authors: Akmal M. , Goldstein D. A. , Multani S. , Massry S. G.
Published: December 2017

Acute uremia is associated with increased calcium (Ca) in brain and changes in electroencephalogram (EEG), and both derangements are related to excess parathyroid hormone (PTH). Also changes in EEG in patients with chronic renal failure (CRF) correlated directly with blood levels of PTH, and fall in PTH was followed by improvement in EEG. We examined whether chronic uremia per se has an effect on brain calcium or EEG. Uremia was produced by 5/6 nephrectomy and maintained for 32-70 wk in seven thyroparathyroidectomized (TPTX) and seven control dogs. There were no differences in creatinine clearance and serum electrolytes except for HCO3, which was lower in control animals (P less than 0.01). Serum PTH was undetectable in TPTX dogs but was significantly elevated in control animals (32.3 +/- 3.3 mu leq /ml). Calcium in gray and white matter was significantly increased in both groups but much higher in control animals. The percent waves of less than 7 Hz in EEG were similar in both groups prior to uremia (TPTX 4.6 +/- 0.8 vs. control 4.2 +/- 0.5%) but remained unchanged in TPTX animals and increased significantly in control dogs (19.0 +/- 1.3%) after uremia. These data suggest that CRF per se is associated with marked rise in Ca in both gray and white matter and increment is higher in the presence of PTH. Disturbance in EEG in a state of CRF requires the presence of excess PTH and is prevented despite increased Ca in brain if hyperparathyroidism is not allowed to develop.
Role of metabolic CO2 production in the generation of elevated renal cortical PCO2
Authors: DuBose T. D. , Caflisch C. R. , Bidani A.
Published: December 2017

Several possible explanations for the elevated CO2 tension observed in structures of the renal cortex have been proposed. The present study was designed to investigate the contribution of renal metabolic CO2 production and removal and the role of incomplete equilibration of the CO2 added to peritubular plasma in an environment devoid of carbonic anhydrase. PCO2 was measured in vivo with PCO2 microelectrodes in early (EP) and late proximal (LP) tubules and stellate vessels (SV) during control conditions and after hyperoncotic albumin, aortic constriction, vanadate, rotenone, or 2,4-dinitrophenol (2,4-DNP) per renal artery, and carbonic anhydrase infusion. In all groups values for PCO2 in EP, LP, and SV sites were indistinguishable but significantly higher than systemic arterial PCO2. PCO2 increased to 71.4 +/- 1.4 mmHg with hyperoncotic albumin and to 87.0 +/- 1.8 mmHg after 2,4-DNP (P less than 0.001). During aortic constriction, vanadate infusion, and rotenone per renal artery, PCO2 fell to 53.7 +/- 0.9, 55.2 +/- 2.5, and 57.3 +/- 1.3, respectively (P less than 0.001). Renal O2 consumption decreased significantly after rotenone (-38.1 +/- 5.6 to -13.3 +/- 2.7 mumol X min-1 X kg-1) and increased significantly after 2,4-DNP (-35.7 +/- 5.9 to -75.9 +/- 6.9 mumol X min-1 X kg-1). These findings demonstrate that renal energy utilization and metabolic CO2 production represents an important source of renal cortical PCO2. Carbonic anhydrase infusion resulted in a decrease in PCO2 to 58.2 +/- 1.2 mmHg (P less than 0.01).(ABSTRACT TRUNCATED AT 250 WORDS)
Luminal influences on potassium secretion: low sodium concentration
Authors: Good D. W. , Velazquez H. , Wright F. S.
Published: December 2017

In vivo microperfusion techniques were employed in anesthetized rats to determine whether K secretion by renal distal tubules requires the presence of Na in luminal fluid, and, if it does, in what concentration range do changes in Na concentration have the most effect. In a first series of experiments Na in perfusion fluid was replaced at constant Cl with tetramethylammonium (TMA). When the perfusion fluid Na concentration was reduced from 96 or 34 mM to 10 or 3 mM, K secretion was reduced by 50-60% and transepithelial voltage ( VTE ) was reduced by 40-60%. In a second series of experiments, in which NaCl was replaced with urea, perfusion fluid Na concentration again was reduced to 3 mM, and K secretion and VTE were reduced. In a third series of experiments, Na was replaced with rubidium. The reduced K secretion could not be explained solely by changes in electrical driving forces. The results indicate that some luminal Na (half-maximal concentration approx 10 mM) is necessary to permit K secretion to proceed at a normal rate. Considering prior measurements of luminal Na concentration in rat distal tubules, it is unlikely that changes in luminal Na concentration play an important role in regulating the rate of distal K secretion.
Interactions between gluconeogenesis and sodium transport in rabbit proximal tubule
Authors: Gullans S. R. , Brazy P. C. , Dennis V. W. , Mandel L. J.
Published: December 2017

Gluconeogenesis and sodium transport are ATP-requiring functions of the renal proximal tubule. Previously observed interactions between these processes indicated that they may compete for cellular energy. We have reevaluated this interaction in the rabbit proximal tubule using two preparations: suspensions of cortical tubules and isolated perfused tubules. In the presence of lactate and alanine, net glucose synthesis was 22.3 +/- 1.3 nmol X mg protein-1 .30 min-1. Additions of valerate, butyrate, or succinate increased this rate by factors of 2-3 without affecting cellular ATP levels or net fluid absorption (Jv). Inhibition of ATP production with rotenone, which we have previously shown to inhibit Jv [Am. J. Physiol. 243 (Renal Fluid Electrolyte Physiol. 12): F133-F140, 1982], greatly decreased the gluconeogenic rate, but this was modulated by the type of gluconeogenic substrate used. Increasing Na-K-ATPase activity with nystatin or decreasing it with ouabain had widely differing effects, which also depended on the substrate regimen. We conclude that the interaction between gluconeogenesis and active sodium transport cannot be described by a simple competition for ATP. Rather, under normal circumstances, the renal proximal tubule can meet the energetic demands of both gluconeogenesis and sodium transport, and control of these processes is multifactorial and sensitive to fatty acid metabolism.
Effect of perfusate phosphate concentration on responses to PTH in isolated rat kidney
Authors: Scheinman S. J. , Coulson R.
Published: December 2017

We studied the excretion of electrolytes and adenosine 3',5'-cyclic monophosphate (cAMP) by rat kidneys perfused for 2 or 3 h at several concentrations of phosphate (Pi). Fractional phosphate excretion increased with higher perfusate Pi concentrations (up to 4.0 mM Pi) without parathyroid hormone (PTH), but no tubular maximum for phosphate reabsorption was reached. The addition of synthetic bovine 1-34 PTH (bPTH) gave a dose-related phosphaturia that depended on the perfusate Pi level. The urinary cAMP response to doses of bPTH was highly dependent on perfusate Pi concentration: with 20 nM bPTH, urinary cAMP was 211 +/- 94 pmol/ml glomerular filtration rate at 1.2 mM Pi and was 3,998 +/- 711 at 4.0 mM Pi (P less than 0.001). Without bPTH, cAMP excretion did not differ among Pi levels. Calcium-to-sodium clearance ratio rose with time in kidneys perfused without bPTH but fell with the addition of as little as 0.02 nM bPTH, regardless of Pi concentration. Variations in Pi or bPTH did not affect fractional magnesium excretion, which fell by 68% through 3 h of perfusion (P less than 0.001). These data suggest that the effects of Pi concentration on renal electrolyte excretion are consistent with changes in the filtered Pi load but that extracellular Pi concentrations dramatically alter the renal cAMP response to bPTH in the isolated perfused kidney.
Comparison of calcium and sodium transport in early and late rat distal tubules: effect of amiloride
Authors: Costanzo L. S.
Published: December 2017

In vivo tubular microperfusion experiments were performed in rats to compare the function of the early and late rat distal convoluted tubule and to examine the effect of amiloride on distal Na and Ca reabsorption. In clearance experiments, amiloride (6 micrograms/min) reduced fractional Ca excretion (P less than 0.05) and the calcium-to-sodium clearance ratio (P less than 0.001) without affecting fractional Na excretion. The in vivo microperfusion experiments revealed a higher rate of osmotic water flow in late distal convoluted tubules than in early tubules (P less than 0.001), while Na and Ca transport rates were comparable. The addition of 10(-5) M amiloride to the luminal perfusate inhibited net fluid reabsorption (P less than 0.05) and Na reabsorption (P less than 0.01) and enhanced Ca reabsorption (P less than 0.005) in late segments of the distal tubule. The drug did not change early distal function. The degree of enhancement of Ca transport was highly correlated with the degree of inhibition of Na transport, suggesting that the two effects are related. We suggest that increased Ca reabsorption is a result of luminal membrane hyperpolarization or of increased rates of Ca-Na exchange.
Potential effects of renin activation on the regulation of renin production
Authors: Hsueh W. A.
Published: December 2017

In normal humans nearly half the renin in plasma and kidney is inactive. Human inactive renin can be activated by a variety of proteases and by exposure to low pH and is a putative biosynthetic precursor of renin, i.e., prorenin. Pulse-labeling studies in a human renin-secreting tumor suggest that renin is synthesized as a prepro- and proform, both of which are inactive. Using the cDNA probe to deduce the amino acid sequence of precursor renin from the nucleotide sequence of human kidney mRNA, the prosegment was estimated to be 46 amino acids long, similar to differences in molecular weight between active and inactive renin. In plasma of diabetic patients with nephropathy and the syndrome of hyporeninemic hypoaldosteronism, inactive renin levels are increased 3-5 times normal. The inability to activate renin in this syndrome strongly implies that conversion of inactive (pro-) renin to active renin may be physiologically relevant to active renin production. Furthermore, in normal humans profound stimulation of active renin can be accompanied by a reciprocal drop in circulating inactive renin levels. The beta-adrenergic system and prostaglandins are two major, but independent, mechanisms of stimulating renin release. Studies in our laboratory suggest that prostaglandins and the beta-adrenergic system may act at different sites in renin production: beta-stimulation may act at early steps in renin biosynthesis, while prostaglandins may act preferentially at later steps that possibly involve conversion of inactive to active renin. Proof of this hypothesis lies in purification of inactive renin to determine whether it is prorenin and in the use of the renin cDNA probe to study pre- vs. posttranslational events in renin processing.(ABSTRACT TRUNCATED AT 250 WORDS)
Renal autoregulation in chronically catheterized conscious rats
Authors: Conrad K. P. , Brinck-Johnsen T. , Gellai M. , Valtin H.
Published: December 2017

We examined renal hemodynamics and arterial plasma renin activity (PRA) concurrently in trained chronically catheterized conscious rats during decreased and elevated renal arterial pressure (RAP). Control RAP had an absolute value of 112 +/- 2 mmHg (mean +/- SE). During inflation of a suprarenal aortic cuff, glomerular filtration rate (GFR) and effective renal plasma flow (ERPF) were autoregulated down to 82% of control RAP. Within this range GFR averaged 107 +/- 5% and ERPF 114 +/- 10% of the control value. During inflation of the infrarenal aortic cuff, RAP increased by 24 +/- 2% to an absolute level of 139 +/- 5 mmHg; this elevation was associated with autoregulation of both GFR (100 +/- 5% of control) and ERPF (94 +/- 6% of control). Arterial PRA had an absolute value during control conditions of 2.1 +/- 0.2 ng ANG I X ml-1 X h-1. It was not significantly altered within the autoregulatory range, being 104 +/- 10% of control during lowered RAP and 120 +/- 15% of control during elevated RAP. Nor, in separate experiments, was PRA changed significantly during the transient state, i.e., at 5, 10, or 30 min after RAP was lowered to an autoregulatory level. These studies demonstrate that, in the conscious rat, there is considerable autoregulatory capacity both below and above resting arterial pressure, and that GFR and ERPF are autoregulated concomitantly. Arterial PRA was not altered significantly within the autoregulatory range.
Effect of epinephrine on renal potassium excretion in the isolated perfused rat kidney
Authors: Katz L. D. , D'Avella J. , DeFronzo R. A.
Published: December 2017

The effects of beta-agonists (epinephrine, isoproterenol, and ITP) and beta-antagonists (propranolol, metoprolol, and butoxamine) on renal potassium excretion were examined using the isolated perfused rat kidney preparation. Following 30 min of control perfusion, one of the above beta-adrenergic agonists or antagonists was added to the perfusion medium. Following epinephrine, a combined beta 1- and beta 2-agonist, urinary potassium excretion (UKV; 0.55 +/- 0.55 vs. 0.36 +/- 0.04 mueq/min, P less than 0.001) and fractional excretion of potassium (FEK; 24.6 +/- 2.4 vs. 18.2 +/- 2.0%, P less than 0.001) both decreased. When isoproterenol, a nonspecific beta-agonist, was added to the perfusate, UKV (0.49 +/- 0.10 vs. 0.27 +/- 0.04 mueq/min, P less than 0.02) and FEK (29.0 +/- 5.2 vs. 16.3 +/- 2.9%, P less than 0.01) again decreased. ITP, a specific beta 1-agonist also caused a decrease in UKV (0.60 +/- 0.13 vs. 0.39 +/- 0.04 mueq/min, P less than 0.02) and FEK (30.2 +/- 5.1 vs. 17.8 +/- 2.8%, P less than 0.02). In contrast, when propranolol, a nonspecific beta-antagonist, was added to the perfusate, the opposite effects on renal potassium handling were observed. UKV (0.45 +/- 0.05 vs. 0.70 +/- 0.07 mueq/min, P less than 0.001) and FEK (23.0 +/- 2.1 vs. 42.5 +/- 3.1%, P less than 0.001) both increased. Metoprolol (50 ng/ml), a specific beta 1-antagonist, increased UKV (0.56 +/- 0.10 vs. 0.68 +/- 0.15 mueq/min, P less than 0.02) and FEK (31.0 +/- 3.8 vs. 48.0 +/- 7.1%, P less than 0.02). A similar effect was observed when a higher dose of metoprolol (200 ng/ml) was employed.(ABSTRACT TRUNCATED AT 250 WORDS)
Effect of an osmotic gradient on antidiuretic hormone-induced endocytosis and hydroosmosis in the toad urinary bladder
Authors: Masur S. K. , Cooper S. , Rubin M. S.
Published: December 2017

The luminal (apical) border of the epithelium of the bladder in the well-hydrated toad is relatively impermeable, so the bladder usually stores hyposmotic urine. When antidiuretic hormone (ADH) increases apical membrane osmotic permeability dramatically, water is resorbed from hyposmotic mucosal solution; in the presence of hyposmotic or isosmotic mucosal solutions, ADH concomitantly induces exocytosis at the apical border of granule-rich (G) cells. Then ADH induces endocytosis at this border. We describe how an osmotic gradient affects ADH-induced endocytosis and hydroosmosis in vitro. We can assess ADH-induced endocytosis in gradient and no-gradient bladders by applying a double-marker technique that distinguishes among endocytosis, completed internalization of previously surface-attached membrane, and surface invagination by comparing the number of horseradish peroxidase (HRP) uptake bodies (endocytosis) with the number of ruthenium red (RR)-delineated bodies (surface invaginations). With this approach we find that gradient bladders have approximately six times more ADH-induced endocytosis than no-gradient bladders during 45-60 min of ADH stimulation. Furthermore, at 60 min approximately 50% of the HRP-containing structures in no-gradient bladders remain surface connected compared with approximately 1% in gradient bladders. In parallel physiological studies, no-gradient bladders reach and maintain higher induced osmotic permeabilities than gradient bladders. These findings support the hypothesis that endocytosis plays an active role in reestablishing impermeable apical surface characteristics in toad bladder.
Renal osmotic effect of mannitol in the neonatal and adult dog
Authors: Kleinman L. I. , Disney T. A.
Published: December 2017

The renal response to mannitol loading was studied in 21 newborn dogs aged 1-19 days and in 12 adult dogs. One group of animals (protocol B) underwent distal nephron blockade with ethacrynic acid and amiloride prior to and during infusion of mannitol to estimate proximal tubule function. The other group of animals (protocol A) received mannitol without the diuretics. Mannitol was infused at progressively increasing dosages, resulting in progressively increasing mannitol excretion rates. For all groups of animals, as mannitol excretion rates increased, urine flow and sodium, potassium, and chloride excretion rates increased. However, there was no correlation between mannitol excretion and bicarbonate excretion. The osmotic effect of mannitol was quantitated from the slope of the plot of mannitol excretion vs. sodium excretion (dNa/dMan). In both pups and adults dNa/dMan was greater in protocol B (1.47 for pups, 0.70 for adults) than in protocol A (0.18 for pups, 0.07 for adults). In addition, in protocol B dNa/dMan was greater in the newborn than in the adult and decreased logarithmically with age in pups. In protocol B, as mannitol excretion increased, the urine-to-plasma sodium ratio declined in adults but did not change in pups. Urine-to-plasma osmolality ratio remained at unity throughout the experiment in both age groups in protocol B. These results indicate that 1) the osmotic effect of mannitol is greater in the immature than in the mature kidney, and 2) the greater osmotic effect in the neonatal kidney is related to inability of the immature proximal tubule to generate and sustain a transtubular sodium gradient.
Antidiuretic effect of endogenous oxytocin in dehydrated Brattleboro homozygous rats
Authors: Edwards B. R. , LaRochelle F. T.
Published: December 2017

Despite the absence of vasopressin, Brattleboro homozygous (DI) rats concentrate their urine to hypertonic levels when deprived of drinking water for 24 h. Glomerular filtration rate (GFR) falls concurrently and might contribute to the increased concentrating ability. The present studies concerned the time course of the changes in concentrating ability and GFR during the early hours of dehydration. Experiments were performed in 10 chronically catheterized conscious DI rats in the normally hydrated control state and during 3 h of fluid deprivation. Urine osmolality (Uosmol) increased from 97 +/- 6 (SE) to 325 +/- 11 mosmol/kg H2O at 3 h. Averaged over the 3 h, neither GFR nor effective renal blood flow changed significantly (103 +/- 2 and 106 +/- 4% of control, respectively). Fractional excretion of sodium (FENa) rose markedly from 0.3 +/- 0.1 to 1.3 +/- 0.1% at its peak. Clearly, a fall in GFR cannot explain the rise in Uosmol during the first 3 h. Plasma oxytocin (OT) increased from 5.6 +/- 0.8 to 36.4 +/- 4.5 pg/ml after 3 h of dehydration. In additional experiments, d(CH2)5-D-Phe-VAVP, an antidiuretic antagonist (anti-ADH), was administered to eight DI rats after 3-h dehydration. Control, 3-h dehydration, and post-anti-ADH values were, respectively: for Uosmol, 102 +/- 7, 347 +/- 14, 145 +/- 11 mosmol/kg H2O; for GFR, 1,003 +/- 43, 1,042 +/- 59, 866 +/- 54 microliter X min-1 X 100 g body wt-1; for FENa, 0.4 +/- 0.1, 1.4 +/- 0.1, 0.5 +/- 0.1%. The decreases following anti-ADH were all statistically significant. We conclude that OT is released during the early hours of dehydration in the DI rat and has at least three renal effects. It causes a natriuresis, it maintains renal hemodynamics and GFR during the volume contraction, and it elicits a weak antidiuretic response.
Uptake of Pi in basolateral vesicles after release of unilateral ureteral obstruction
Authors: Schwab S. J. , Klahr S. , Hammerman M. R.
Published: December 2017

We previously demonstrated Na+-dependent 32Pi uptake in basolateral membrane vesicles from kidneys of normal dogs. We postulated that this reflects Na+-dependent Pi transport across the basolateral membrane into the proximal tubular cell in vivo that subserves cellular needs for Pi. To ascertain whether Pi transport across the basolateral membrane was enhanced in a condition in which delivery of Pi across the luminal membrane would be markedly decreased, we measured Na+-dependent 32Pi uptake in basolateral vesicles isolated from postobstructed and control kidneys of dogs following release of unilateral ureteral obstruction. Clearance of creatinine and filtered load of Pi were significantly decreased in postobstructed compared with control kidneys. Na+-dependent 32Pi uptake was increased in basolateral vesicles from postobstructed compared with control kidneys, as reflected by increased initial rate of uptake and an increased overshoot of 32Pi transport. Our findings are consistent with an adaptation resulting in increased transport of Pi across the basolateral membrane of the proximal tubular cell in unilateral ureteral obstruction. This process may provide required Pi to the cell under conditions in which decreased Pi is available for transport across the brush border membrane.
Inter- and intracompartmental osmotic gradients within the rat cochlea
Authors: Sterkers O. , Ferrary E. , Amiel C.
Published: December 2017

The osmolality and the electrochemical composition of the endolymph, a potassium-rich positively polarized extracellular fluid in the cochlea, was studied in the rat. Endolymph of each cochlear turn was hyperosmotic to perilymph and plasma. Osmolalities (mosmol/kg H2O) were 329 +/- 2.9 (mean +/- SE) (n = 13) in basal turn endolymph, 322 +/- 2.7 (n = 9) in middle turn endolymph, 317 +/- 5.2 (n = 3) in apical turn endolymph, 289 +/- 3.1 (n = 14) in perilymph of the scala vestibuli, and 298 +/- 1.8 (n = 7) in plasma. Moreover, differences in osmolality and electrochemical composition of endolymph, involving resting potential and K and Cl concentrations, were observed between the basal and the middle cochlear turns, suggesting the presence of an electrical and osmotic gradient within endolymph, declining from the base to the apex of the cochlea. The active potassium transport into endolymph, located presumably in the stria vascularis, could account for both the internal and external osmotic gradients.
Estimated lean body mass as an index for normalization of body fluid volumes in humans
Authors: Boer P.
Published: December 2017

Blood volume was measured in 66 healthy subjects (38 males, 28 females), and extracellular fluid volume in 54 subjects (31 males, 23 females). Volumes were normalized against body weight, height, body surface area, leanness index, and lean body mass (estimated from body weight and height). The regression lines of body fluid volumes against lean body mass passed through the origin on extrapolation and were not different for males and females. None of the other indices fulfilled these criteria. It is concluded that estimated lean body mass is a suitable index for normalization of body fluid volumes. A single set of normal reference values can be used for males and females.
Metabolic machinery of the alligator kidney
Authors: Lemieux G. , Craan A. G. , Quenneville A. , Lemieux C. , Berkofsky J. , Lewis V. S.
Published: December 2017

Crocodilians such as caimans and alligators are uricotelic and ammoniotelic animals. They are carnivorous but they excrete ammonium ions in an alkaline urine. The metabolic organization of the kidney of the Mississippi alligator was studied by measuring the renal metabolite profile, the activities of enzymes, and the behavior of kidney tubules in vitro. The liver and tail muscle were also studied. Both awake and anesthetized animals were in a state of low plasma bicarbonate and low blood pH with high plasma lactate concentration. This did not prevent the excretion of an alkaline urine (pH 7.76). alpha-Ketoglutarate was low in all three tissues and lactate was high. Glutamate concentration and glutamate dehydrogenase activity were highest in the kidney with a low equilibrium constant for alanine aminotransferase (KGPT). Glutaminase I was found only in the kidney. It could not be detected in liver or muscle. Glutamine synthetase was found only in the liver. Phosphoenolpyruvate carboxykinase (PEPCK) was present in both liver and kidney. Alanine aminotransferase and malic enzyme showed high activity in the kidney but were inconspicuous in liver and muscle. Malate dehydrogenase and lactate dehydrogenase were present in all three tissues. Renal tubules incubated with glutamine and alanine were ammoniagenic and gluconeogenic. Lactate was gluconeogenic. Enzyme activities were measured at both 30 and 37 degrees C. The studies on renal tubules were also performed at these two temperatures. Temperature had little effect on the data including acid-base values in the blood. Our findings demonstrate that the kidney of the alligator is perfectly equipped for various metabolic functions and especially for ammoniagenesis and gluconeogenesis.
Mechanism of chronic hypocalciuria with chlorthalidone: reduced calcium absorption
Authors: Bushinsky D. A. , Favus M. J. , Coe F. L.
Published: December 2017

Chlorthalidone, like other benzothiadiazides, lowers urine calcium excretion chronically. If intestinal calcium absorption did not fall or bone accretion did not increase, serum calcium and the filtered load of calcium would increase and urine calcium would return to pretreatment levels. To determine whether overall intestinal calcium absorption fell, we fed chlorthalidone (5 mg X kg body wt-1 X 24 h-1) to 10 adult male rats eating 15 g/day of a 0.6% calcium diet. Compared with 10 control rats, chlorthalidone reduced urine calcium [2.1 +/- 0.1 (SE) vs. 5.8 +/- 0.5 mg/6 days; P less than 0.001]. Fecal calcium rose (307 +/- 9 vs. 257 +/- 12; P less than 0.005) because percent intestinal calcium absorption fell (41 +/- 2 vs. 52 +/- 2; P less than 0.002). Twenty other rats given the same diet were injected subcutaneously with 1,25(OH)2D3 (50 ng/day). In these rats, chlorthalidone reduced urine calcium (23 +/- 3 vs. 59 +/- 3; P less than 0.001) and percent intestinal calcium absorption (60 +/- 1 vs. 66 +/- 1; P less than 0.01). With or without 1,25(OH)2D3, chronic administration of chlorthalidone reduces intestinal calcium absorption, and this reduction seems to be the mechanism that permits urine calcium excretion to remain low.
Axial heterogeneity in the rat proximal convoluted tubule. II. Osmolality and osmotic water permeability
Authors: Liu F. Y. , Cogan M. G. , Rector F. C.
Published: December 2017

To assess whether proximal luminal fluid becomes hypotonic with respect to plasma, free-flow micropuncture measurements were made sequentially from the end-proximal tubule to Bowman's space in 10 tubules of hydropenic Munich-Wistar rats. Osmolality in Bowman's space was 2.8 +/- 0.3 mosmol less than in plasma. Tubular fluid osmolality fell along the tubule and by the end-proximal tubule was 7.5 +/- 0.7 mosmol/kg less than in plasma or 4.7 mosmol/kg less than in Bowman's space. Since luminal fluid became hypotonic, the reabsorbate was hypertonic. The transepithelial osmotic water permeability (Pf) was calculated using simultaneously measured water reabsorption rates. The osmotic gradient responsible for water reabsorption was assumed to be either lumen-to-reabsorbate or lumen-to-peritubular plasma, with a reflection coefficient for sodium chloride of 0.7-1.0. The Pf was then estimated to be between 0.2 and 2.0 cm/s in the first millimeter of tubule and to have fallen to 0.1-0.2 cm/s by the end of the tubule. In conclusion, luminal hypotonicity develops in the rat proximal convoluted tubule and must be considered as part of the osmotic driving force for water reabsorption.
ADH or theophylline-induced changes in intracellular free and membrane-bound calcium
Authors: Burch R. M. , Halushka P. V.
Published: December 2017

Ca2+ is thought to play a role in the enhancement of water permeability of toad urinary bladder epithelial cells by antidiuretic hormone (ADH) or theophylline. This study examined the effects of ADH and theophylline on intracellular free Ca2+ ([Ca2+]i) and total cellular exchangeable Ca2+ in isolated toad bladder epithelial cells. ADH or theophylline enhanced water permeability maximally by 15-25 min after a 4-min lag. 45Ca2+ efflux, a probe for total cellular exchangeable (plasma membrane plus intracellular) Ca2+, was enhanced by ADH within 2 min and returned to control by 8 min. Chlortetracycline fluorescence, a probe for intracellular Ca2+ only, was not affected, suggesting that ADH released only plasma membrane-bound Ca2+. Theophylline enhanced 45Ca2+ efflux and decreased chlortetracycline fluorescence, suggesting release of Ca2+ from intracellular sources. Both agents decreased [Ca2+]i as assessed by quin-2 fluorescence with a time course similar to the enhancement in water permeability. The results suggest that the changes in membrane-bound Ca2+ and [Ca2+]i induced by ADH and theophylline may play a role in the enhanced permeability to water in response to these agents.
Adaptation of phosphate transport in phosphate-deprived LLC-PK1 cells
Authors: Caverzasio J. , Brown C. D. , Biber J. , Bonjour J. P. , Murer H.
Published: December 2017

Sodium-dependent transport of phosphate was studied in LLC-PK1 cells that had been deprived of phosphate (Pi). Compared with control cells (fed with 2 mM Pi) a twofold increase in the rate of Na-Pi cotransport was observed in cells incubated for 15 h in a phosphate-free medium, whereas transport of L-alanine and the specific activity of alkaline phosphatase were not changed. The same adaptive response was observed with apical membrane vesicles isolated from Pi-deprived cells. In both experimental systems Pi deprivation caused a change in the Vmax but not in the apparent Km (for Pi) of the cotransport system. Adaptation of the Na-Pi cotransport was triggered by free phosphate concentrations between 0 and 100 microM. Over the first 20 h the adaptive response was found to be a linear process that could be prevented by 70 microM cycloheximide. Adapted cells that were re-treated with phosphate showed a rapid (less than 3 h) decrease in the Na-Pi transport. The data suggest that LLC-PK1 cells adapt to low Pi conditions by increasing the rate of the Na-Pi cotransport, which is located in the apical membrane. Two mechanisms may be involved in the adaptive response: a long-term process involving new protein synthesis, and a short-term response involving activation-inactivation of transport systems already existing.
Bradykinin stimulates Cl secretion and prostaglandin E2 release by canine tracheal epithelium
Authors: Leikauf G. D. , Ueki I. F. , Nadel J. A. , Widdicombe J. H.
Published: December 2017

Bradykinin increased mean short-circuit current (Isc) when added either to the mucosal (KD = 1.1 nM; delta Imaxsc = 29.8 +/- 4.4 microA/cm2) or submucosal bath (KD = 108 nM; delta Imaxsc = 27.1 +/- 4.9 microA/cm2). Bumetanide or replacement of Cl reduced the maximal change in Isc. In paired tissues, the increase in net 36Cl flux toward the mucosa equaled the change in Isc. Net 22Na flux toward the submucosa was unchanged. Involvement of intramural nerves was ruled out because bradykinin-induced increases in Isc were not inhibited by phentolamine, propranolol, atropine, or tetrodotoxin. A direct action of bradykinin on the epithelium was also made probable by the autoradiographic demonstration of specific bradykinin binding sites. The antagonists of arachidonic acid metabolism, indomethacin and eicosa-5,8,11,14-tetraynoic acid, inhibited the increase in Isc induced by bradykinin. Finally, prostaglandin E2 release was significantly increased by submucosal addition of bradykinin, and this effect was abolished by pretreatment with indomethacin. We conclude that bradykinin stimulates Cl secretion in canine tracheal epithelium by increasing prostaglandin release.
Prostaglandins in the sodium excretory response to altered renal arterial pressure in dogs
Authors: Carmines P. K. , Bell P. D. , Roman R. J. , Work J. , Navar L. G.
Published: December 2017

Acute variations in renal arterial pressure are associated with corresponding alterations in absolute and fractional sodium excretion even under conditions of highly efficient autoregulation of renal blood flow (RBF) and glomerular filtration rate (GFR). Since prostaglandins recently have been implicated in the regulation of sodium excretion, we investigated the hypothesis that the renal prostaglandin system participates in "pressure natriuresis." Anesthetized sodium-replete dogs were subjected to partial carotid artery constriction to elevate systemic arterial pressure. Under these control conditions, sodium excretion was 103 +/- 18 mueq/min (n = 17) and urinary prostaglandin E2 excretion averaged 4.6 +/- 1.5 ng/min (n = 8). Decreases in renal arterial pressure within the auto-regulatory range reduced sodium excretion (2.1%/mmHg) and prostaglandin E2 excretion (1.7%/mmHg), whereas GFR and RBF were not affected. There was a significant correlation between the changes in sodium and prostaglandin E2 excretion rates (r = 0.932, P less than 0.01). In nine dogs treated with indomethacin, sodium excretion was reduced by 70% while GFR and autoregulatory capability were unaffected. There was a marked attenuation of the effect of changes in arterial pressure on sodium excretion, with this parameter exhibiting changes averaging 0.6%/mmHg (P less than 0.001). These observations suggest that the renal prostaglandin system may exert an important influence on the pressure-natriuresis mechanism.
Effects of selective inhibition of thromboxane synthesis on renal function in humans
Authors: Zipser R. D.
Published: December 2017

Thromboxane A2, a potent vasoconstrictor, is a major metabolite of arachidonic acid in the human kidney. To determine the role of thromboxanes in renal hemodynamics, we administered the new thromboxane inhibitor dazmegrel or placebo to 20 healthy volunteers for 14 days in a double-blind protocol. Dazmegrel reduced urinary thromboxane B2 by an average of 68% and serum thromboxane B2 by 79%, without affecting urinary excretion of the prostacyclin metabolite 6-ketoprostaglandin F 1 alpha. Neither p-aminohippurate clearance nor inulin clearance were altered by thromboxane inhibition. Thus it is unlikely that thromboxane A2 plays a major role in the regulation of glomerular function in healthy humans.
Juxtamedullary nephrons during acute metabolic alkalosis in the rat
Authors: Frommer J. P. , Wesson D. E. , Laski M. E. , Kurtzman N. A.
Published: December 2017

The renal handling of bicarbonate during acute metabolic alkalosis was examined in Munich-Wistar rats using micropuncture techniques. Group I received an acute bicarbonate load, and fractional delivery of total CO2 (tCO2) (FDtCO2) to the superficial late distal tubule (LD) was significantly lower than to the base of the papillary collecting duct (B) (18.4 +/- 1.7 vs. 22.9 +/- 1.5%; P less than 0.01), indicating net addition of bicarbonate between LD and B. When acutely bicarbonate-loaded rats had their deep nephrons destroyed with bromoethylamine hydrobromide (BEA) (group II), net addition of tCO2 between LD and B was abolished and net reabsorption uncovered (FDtCO2 LD: 28.0 +/- 3.6 vs. B: 17.5 +/- 2.5%; P less than 0.01). The infusion of amiloride (2.5 mg/kg body wt) to alkalotic rats treated with BEA (group III) completely inhibited distal bicarbonate reabsorption but did not reestablish addition (FDtCO2 LD: 27.6 +/- 1.6 vs. B: 26.1 +/- 3.7%; P = NS). The values obtained for sham-operated animals (group IV) were the same for group I. The patterns that were observed between LD and B were reproduced for the four groups of animals when FDtCO2 LD was compared with the fractional excretion of bicarbonate in the urine of the intact contralateral kidney. These studies suggest that juxtamedullary nephrons contribute a higher load of bicarbonate than superficial nephrons to the final urine during acute metabolic alkalosis in the rat.
Effect of 6-aminonicotinamide on renin release in isolated rat kidney: possible role for the pentose pathway
Authors: Rostand S. G. , Work J.
Published: December 2017

To study the association between renal renin release and the pentose pathway, we perfused nonfiltering kidneys from Sprague-Dawley rats with Krebs-Ringer bicarbonate buffer containing 5 mM glucose and 14 g/100 ml bovine serum albumin in the presence or in the absence of 0.25 mM 6-aminonicotinamide (6AN), an inhibitor of glucose-6-phosphate dehydrogenase, the rate-limiting step of the pentose pathway. Eleven kidneys perfused in the absence of 6AN had a renin secretion rate of 7.4 +/- 2.2 ng ANG I X min-1 X ml-1. In six kidneys perfused in the presence of 6AN, renin release was depressed to 0.56 +/- 0.24 ng ANG I X min-1 X ml-1. The renal renin content for four control kidneys was 56 +/- 3.3 ng ANG I X mg-1 X h-1 while in four kidneys perfused with 6AN renal renin content was lower, 35 +/- 2.9 ng ANG I X mg-1 X h-1. In the presence of 5 mM lactate, the renin release of eight nonfiltering kidneys was 0.31 +/- 0.06 ng ANG I X min-1 X ml-1. The addition of 6AN did not further depress renin secretion in the presence of lactate. 6-Aminonicotinamide also completely blocked furosemide-stimulated renin release without having any effect on glomerular filtration rate or furosemide-induced natriuresis. However, 6AN did not inhibit stimulation of renin secretion by isoproterenol. We conclude that 6-aminonicotinamide interferes with renin release by nonfiltering kidneys and also inhibits furosemide-stimulated renin release but does not affect beta-adrenergic-stimulated renin secretion. Glucose but not lactate is important for maintaining augmented rates of renin secretion in nonfiltering kidneys. 6-Aminonicotinamide significantly reduced renal renin content in the presence of glucose.(ABSTRACT TRUNCATED AT 250 WORDS)
Blockade of colchicine-induced inhibition of vasopressin-stimulated osmotic water flow: failure to influence microtubule formation
Authors: Baron D. A. , Burch R. M. , Halushka P. V. , Spicer S. S.
Published: December 2017

Colchicine inhibits vasopressin-induced osmotic water flow across isolated toad urinary bladder. Concomitantly, colchicine has been shown to reduce the relative cytoplasmic volume fraction of microtubules in the apical granular cells of this epithelium that have been shown previously to mediate the hydroosmotic effect of vasopressin. Therefore, an intact cytoskeleton has been postulated to be a requirement for a full response to vasopressin. Since it has been demonstrated recently that cyclooxygenase inhibitors (meclofenamic acid) abrogate the inhibition by colchicine of vasopressin-stimulated water flow, we tested by stereological criteria the hypothesis that colchicine in the presence of meclofenamic acid does not prevent the polymerization of tubulin. Our results show that the relative cytoplasmic volume fraction of microtubules was reduced 75% by colchicine in the presence or absence of meclofenamic acid. An alternative explanation of the inhibitory action of colchicine is its ability in the toad urinary bladder to enhance the endogenous synthesis of and sensitivity to prostaglandin E, a potent negative modulator of vasopressin-stimulated water flow. An intact microtubular component of the cytoskeleton does not appear to be required for a maximal response to a physiological dose of vasopressin.