Biomedical subjects

W H Dantzler

Publications and source records attributed to W H Dantzler.

At least 73 records · Page 4Linked to original sources

PubMed1989

Glomerular filtration rate in conscious unrestrained starlings under dehydration.

Glomerular filtration rate (GFR) was measured in conscious unrestrained starlings, Sturnis vulgaris. Alzet osmotic minipumps were inserted into the peritoneal cavity under lidocaine local anesthesia and served to infuse the GFR marker [14C]sodium ferrocyanide. GFR was measured in hydrated birds and again after a 24-h period of water deprivation. GFR in dehydrated birds was 1.15 +/- 0.09 ml.min-1.kg-1, significantly lower (P less than 0.001) than the 2.71 +/- 0.31 ml.min-1.kg-1 in fully hydrated animals. In addition, the GFR of the hydrated birds was significantly lower (P less than 0.01) than values of 4.43 +/- 0.24 ml.min-1.kg-1 measured in hydrated anesthetized birds during micropuncture studies. A 24-h period of water deprivation caused significant increases in plasma osmolality and concentration of sodium, chloride, and phosphate. The osmolality and concentrations of calcium, magnesium, and phosphate were significantly elevated in both cloacal urine supernatant and in ureteral urine of dehydrated birds. In both hydrated and dehydrated states, the concentration of magnesium, phosphate, potassium, and total osmolality were significantly higher in cloacal urine than in ureteral urine.

Animals↗

PubMed1989

Membrane dynamics in relation to fluid absorption in reptilian proximal renal tubules.

Net fluid absorption (Jv), cell volume, and cell membrane area have been studied in isolated, perfused snake (Thamnophis spp.) proximal tubules. With Na+ in both perfusate and bathing medium, Jv averages approximately 0.9 nl.min-1.mm-1. When choline replaces Na+ in perfusate, Jv nearly ceases. When choline also replaces Na+ in bathing medium, so that both solutions are identical, Jv returns to the control rate. The results are the same when tetramethylammonium replaces Na+, when sucrose replaces Na+ and the equivalent amount of Cl-, and when methyl sulfate replaces Cl- alone. However, when Li+ replaces Na+ in perfusate alone or in both perfusate and bathing medium, Jv is unchanged. Jv at control rates is isosmotic and can be partially inhibited by cold and cyanide. When choline replaces Na+ in perfusate and bathing medium, cell volume doubles, and intercellular space volume nearly quintuples. The areas of the lateral and apical cell membranes also approximately double, so that the surface area-to-volume ratio remains constant. These morphological changes in the absence of Na+ occur concomitantly with maintenance of Jv, suggesting that they may play a permissive role in such maintenance.

Absorption↗

PubMed1989

Brush-border TEA transport in intact proximal tubules and isolated membrane vesicles.

The efflux of the organic cation, tetraethylammonium (TEA), across proximal cell luminal membranes was studied using intact, perfused rabbit proximal tubules and isolated rabbit cortical brush-border membrane vesicles (BBMV). Increases of either the extravesicular H+ concentration (from pH 7.5 to pH 6.5) or the extravesicular concentration of unlabeled TEA (from 0.1 to 0.5 mM) increased the rate of efflux of radioactively labeled TEA from BBMV. Similarly, when proximal tubules were preloaded with labeled TEA and then submerged in a mineral oil bath, a rapid increase in either the H+ concentration (from pH 7.5 to pH 5.8) or the TEA concentration (from 0 to 1 mM) of the tubular perfusate produced an acute increase in efflux of the labeled TEA across the luminal brush-border membrane. These results with intact tubules and isolated membranes are consistent with previous suggestions that TEA transport across the brush border of proximal tubule cells involves a carrier-mediated countertransport process and represent the first demonstration with intact proximal tubules that the secretory flux of TEA occurs by an exchange with H+.

Animals↗

PubMed1988

Enzymatic and transport characteristics of isolated snake renal brush-border membranes.

Brush-border membranes (BBM) of proximal tubules were isolated from the kidney of the garter snake (Thamnophis sirtalis) by a procedure involving hypotonic lysis, Ca precipitation, and differential centrifugation. The isolated membranes were enriched 15-fold in brush-border enzyme activities (alkaline phosphatase, gamma-glutamyl transpeptidase) compared with whole kidney homogenates and were substantially free of other contaminating membranes. The yield of the BBM preparation was 40%. The BBM vesicular transport of several organic solutes was characterized by a rapid filtration technique at 25 degrees C. D-glucose, p-aminohippurate (PAH), and urate entered the same osmotically active space (2-3 microliter/mg protein) and binding was minimal (less than 20% for PAH). An uptake overshoot for 3-O-methyl-D-glucose (20 microM) by reptilian BBM was observed only in the presence of an inwardly directed NaCl gradient and was abolished by 0.1 mM phlorizin. Reptilian BBM exhibited Na-gradient-stimulated uptake of PAH (90 microM) with an overshoot that was inhibited by other organic acids and by 4-acetamido-4'-isothiocyanostilbene-2, 2'-disulfonic acid (SITS). In contrast, urate uptake (30 microM) appeared to be Na independent and not appreciably affected by other organic anions or SITS. The presence of specific transport systems for organic solutes in the isolated membrane preparation distinctly characterizes the BBM of reptilian kidney.

3-O-Methylglucose↗

PubMed1988

TEA transport by snake renal tubules: choline effects, countertransport, H+-TEA exchange.

Tetraethylammonium (TEA) transport by isolated perfused snake (Thamnophis spp.) proximal renal tubules was examined for effects of choline and evidence of countertransport of organic cations and H+-TEA exchange. Choline in perfusate significantly inhibited unidirectional lumen-to-bath flux of TEA and accumulation of labeled TEA by tubule cells, and choline in bath significantly inhibited unidirectional bath-to-lumen flux of TEA and accumulation of labeled TEA by tubule cells. These data indicate that choline inhibits transport of TEA into the cells across both the luminal and peritubular membranes and suggest that it may share the TEA transporter. To examine transport at single membranes in intact tubules, we examined the efflux of labeled TEA across the luminal membrane of tubules covered with oil and across the peritubular membrane of tubules with oil-filled lumens. Unlabeled TEA, choline, and low pH in the perfusate stimulated efflux of labeled TEA across the luminal membrane. These data suggest that TEA transport across the luminal membrane can involve countertransport of organic cations and H+-TEA exchange. Unlabeled TEA, choline, and, to a small extent, low pH in the bath stimulated the efflux of labeled TEA across the peritubular membrane. These data suggest that TEA transport across the peritubular membrane can involve countertransport of organic cations and, possibly, H+-TEA exchange. The efflux data across both membranes further support the idea that choline may share the TEA transporter.

Animals↗

PubMed1988

Amino acid transport by juxtamedullary nephrons: distal reabsorption and recycling.

Amino acid transport by juxtamedullary (JM) nephrons and its relationship to transport by superficial cortical (SC) nephrons and to function of vasa recta and collecting ducts were examined in vivo and in situ by free-flow micropuncture of Henle's loops, collecting ducts, and vasa recta and by continuous microinfusion of Henle's loops in exposed rat papillae. Fractional deliveries (FDs) of six neutral amino acids, two acidic amino acids, and taurine to tips of Henle's loops of JM nephrons could be substantially below those to early distal loops of SC nephrons, indicating that reabsorption before loop tips could be greater in JM than in SC nephrons. FDs to collecting ducts lower than to JM loop tips suggested reabsorption distal to loop tips. This was confirmed by continuous microinfusion of ascending limbs of Henle's loops. Distal site of reabsorption is unknown, but amino acids may move passively out of the thin ascending limb and be recycled into vasa recta and descending limb. Recycling of amino acids was supported by high FDs to tips of Henle's loops (sometimes greater than 1.0), higher concentrations in ascending than in descending vasa recta at same papilla level, and high mean concentrations in vasa recta.

Amino Acids↗

PubMed1987

Potassium secretion by nasal salt glands of desert lizard Sauromalus obesus.

Potassium secretion by the nasal salt glands of the herbivorous desert lizard Sauromalus obesus was determined in vivo by a new technique. Intraperitoneal injection of KCl rapidly increased the potassium secretion rate from 0.28 to 15.35 mumol X 100 g-1 X h-1. A second identical intraperitoneal injection, given 15 h after the first, further increased potassium secretion to 50.09 mumol X 100 g-1 X h-1. This was associated with a doubling of plasma K+ concentration and salt gland Na+-K+-adenosinetriphosphatase (ATPase) activity. Neither salt gland weight or residual (Mg2+) ATPase activity were affected. In an isolated perfused head preparation, potassium secretion from the nasal salt glands was stimulated from 0.99 to 10.76 mumol X 100 g-1 X h-1 by methacholine and to 14.68 mumol X 100 g-1 X h-1 by forskolin. In this perfused preparation, simultaneous determination of salt gland perfusion flow (using radiolabeled microspheres) and the rate of potassium secretion revealed that the secreting glands removed 68% of the perfusing potassium ions. Calculations indicated that secretion at the maximal rate observed in vivo would necessitate a fourfold increase in the rate of blood flow to the gland.

Adenosine Triphosphatases↗

PubMed1987

NMN transport by snake renal tubules: choline effects, countertransport, H+-NMN exchange.

N1-methylnicotinamide (NMN) transport by isolated perfused snake (Thamnophis spp.) proximal renal tubules was examined for effects of choline and evidence of countertransport of organic cations and H+-NMN exchange. Choline had no effect on NMN transport, supporting the concept of multiple organic cation transport processes. A transconcentration of unlabeled NMN had no effect on unidirectional transepithelial fluxes of labeled NMN. Low pH in the bath enhanced the lumen-to-bath flux of labeled NMN and, at the same time, reduced the intracellular concentration of labeled NMN, but low pH in the perfusate had no effect on the bath-to-lumen flux of labeled NMN. To examine transport at single membranes more directly in intact tubules, we examined efflux of labeled NMN across the luminal membrane of tubules covered with oil and across the peritubular membrane of tubules with oil-filled lumens. Neither unlabeled NMN nor low pH in the perfusate had any effect on efflux across the luminal membrane, providing no evidence of countertransport or H+-NMN exchange across this membrane. However, unlabeled NMN and low pH in the bath both significantly stimulated efflux across the peritubular membrane, providing evidence that both countertransport of organic cations and H+-NMN exchange may play a role in transport of NMN across this membrane.

Animals↗

PubMed1986

Plasma levels and renal handling of endogenous amino acids in snakes: a comparative study.

Plasma levels of 22 endogenous amino acids were measured by ion-exchange chromatography in four species of snakes: Thamnophis sirtalis, T. radix, Aipysurus laevis, and Python molurus. Despite considerable interspecific variation in the amino acid composition, all species showed relatively high plasma concentrations of histidine, a feature apparently unique to reptiles. The renal handling of these amino acids was studied by renal clearance methods. As in other vertebrates, net tubular absorption of filtered amino acids predominated. However, net tubular secretion of taurine, cysteic acid and/or phosphoserine and beta-alanine was observed, with taurine being the predominant amino acid secreted. The percentage reabsorption of the total amino acids filtered by the snake kidneys ranged from 79 to 95%. Evidence for the postrenal absorption of amino acids in these reptiles is presented. In species that normally undergo hibernation (Thamnophis spp.), the ability of the kidney to reabsorb amino acids was depressed by cold acclimation. Cold acclimation significantly decreased plasma levels of all amino acids except taurine, whose concentration increased. The increase in plasma taurine level may have resulted from cellular osmoregulation. Under these conditions, renal excretion of taurine increased concomitantly with the increase in plasma taurine concentration.

Amino Acids↗

PubMed1986

Renal secretion of amino acids in ophidian reptiles.

Net renal tubular secretion of endogenous beta-amino acids (taurine, beta-alanine, beta-aminoisobutyric acid) and their endogenous analogue (L-cysteic acid) was revealed in the olive sea snake, Aipysurus laevis, and in the garter snake, Thamnophis sirtalis, by renal clearance methods. The net secretory rates ranged from 16 to 795 nmol X kg-1 X h-1, with taurine being secreted at the highest rates. These rates of secretion are comparable to those observed in marine fish, the only other group of vertebrates exhibiting renal tubular secretion of L-amino acids under physiological conditions. However, only some snakes (8-58%) demonstrated net tubular secretion; the others (0-58%) showed net tubular reabsorption of these amino acids. Net tubular secretion was consistently observed whenever the filtered load of the amino acid was low, and net reabsorption was apparent whenever the filtered load was high; the two variables being significantly correlated. An analysis of the net amino acid transport rates, both secretory and reabsorptive, as a function of the filtered load suggests that in snakes the beta-amino acids are reabsorbed and secreted at discrete tubular sites, with the secretory sites located beyond the major reabsorptive sites. Taurine, beta-alanine, and L-cysteic acid appear to share a common transport system in the snake renal tubule cells.

Amino Acids↗

PubMed1986

N1-methylnicotinamide transport by isolated perfused snake proximal renal tubules.

N1-methylnicotinamide (NMN) transport was studied in isolated perfused snake (Thamnophis spp.) proximal renal tubules. Unidirectional lumen-to-bath (Jl----bNMN) and bath-to-lumen (Jb----lNMN) fluxes saturated. Although Jl----bNMN and Jb----lNMN were similar, mean Jl----bNMN tended to exceed mean Jb----lNMN at all concentrations studied. Direct measurements confirmed a net reabsorptive flux equal to the difference between the unidirectional fluxes. This transport, opposite in direction to tetraethylammonium (TEA) transport, was not inhibited by TEA. Transport into the cells across both the luminal and peritubular membranes during flux measurements was apparently down an electrochemical gradient by a mediated process that was sodium dependent. Inhibition with NMN analogues suggested that transport into the cells across the luminal membrane during Jl----bNMN was more specific than transport into the cells across the peritubular membrane during Jb----lNMN. Transport out of the cells across both the luminal and peritubular membranes during flux measurements was apparently against an electrochemical gradient.

Animals↗

PubMed1986

Morphological changes with Na+-free fluid absorption in isolated perfused snake tubules.

Snake (Thamnophis spp.) proximal renal tubules were perfused and bathed in vitro either with medium containing sodium or with medium in which the sodium was replaced with choline. Net fluid absorption was measured by changes in volume marker concentration, and cell volumes and cell membrane surface areas were measured by ultrastructural morphometric methods. Net fluid absorption did not differ significantly in the presence or absence of sodium. However, during the 20-25-min perfusion in the absence of sodium, significant morphological changes took place. The volume of the cells, doubled and the volume of the intercellular spaces nearly quintupled. The areas of the lateral and apical cell membranes approximately doubled, but their surface densities remained essentially constant. Therefore the larger cells in the absence of sodium had proportionally enlarged surface areas, so that the volume-to-surface area ratio remained constant. These morphological changes occurred concomitantly with the maintenance of net fluid absorption and might play a permissive role in such maintenance in the absence of sodium.

Absorption↗

PubMed1985

Effects of SITS on urate transport by isolated, perfused snake renal tubules.

Effects of an inhibitor of membrane anion-exchange transport processes, 4-acetamido-4'-isothiocyano-2,2'-disulfonic stilbene (SITS), on urate transport by isolated, perfused snake (Thamnophis spp.) proximal renal tubules were studied. SITS (10(-4) mol/l) in the luminal perfusate had absolutely no effect on net urate secretion (Jneturate) or on net fluid absorption (JV). This observation is compatible with other data that give no support to the concept of a mediated transport step for urate from the cells to the lumen. SITS (10(-4) mol/l) in the bathing medium reversibly inhibited Jneturate without affecting JV. At the time of maximum inhibition of Jneturate, the concentration of urate in the cell water was increased and the apparent permeability of the luminal membrane to urate was decreased, but the urate efflux across the peritubular membrane and the apparent permeability of the peritubular membrane to urate were unchanged. There was no evidence of significant intracellular binding or trapping of urate. Although an increase in the initial rate of urate transport into the cells across the peritubular membrane could not be demonstrated conclusively in nonperfused tubules, the results still suggest that SITS in the bathing medium may inhibit Jneturate by inhibiting urate movement from the cells to the lumen while actually enhancing transport from the bathing medium into the cells.

4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfo↗

PubMed1985

Renal function in sea snakes. I. Glomerular filtration rate and water handling.

Renal clearance studies were performed on anesthetized sea snakes (Aipysurus laevis) under various salt and volume loads. The median values for the control glomerular filtration rate (GFR) and urine flow rate (V) were 0.78 and 0.11 ml X kg-1 X h-1, respectively. Acute salt loading with 1 mol/l NaCl significantly increased V to 0.68 ml X kg-1 X h-1, whereas acute water loading significantly decreased GFR to 0.17 ml X kg-1 X h-1. Acute loading with either isosmotic NaCl or seawater did not significantly alter either V or GFR. Chronic loading with water or seawater by intraperitoneal injection significantly increased both GFR and V. No consistent relationship between plasma osmolality and GFR was observed. Instead a threshold-type relationship existed between GFR and plasma K concentration. Within each treatment group, high plasma K concentrations were correlated with low GFRs. There was an abrupt increase in GFR at low plasma K concentrations, the inflection point ranging from 2.5 to 4 mmol/l K depending on the experimental treatment. A curvilinear relationship existed between V and GFR; as GFR increased, V approached a maximal limiting value. At low GFRs (less than 0.2 ml X kg-1 X h-1), V often exceeded GFR, indicating net fluid secretion that was correlated with net Na movement. In addition, there was an inverse relationship between urine-to-plasma osmolality ratio and V. At low values of V, urine osmolalities modestly exceeded those of the plasma. Overall, renal function of A. laevis appears to be adapted to conserve water.

Animals↗

PubMed1985

Renal function in sea snakes. II. Sodium, potassium, and magnesium excretion.

Renal clearance studies performed on the sea snake Aipysurus laevis demonstrated net tubular reabsorption of Na and both net tubular secretion and reabsorption of Mg and K. Fractional excretion of Na (FENa) was 0.05 under control conditions and increased markedly with hyperosmotic salt loading. Within each group, however, higher glomerular filtration rates were accompanied by disproportionately greater Na reabsorption. FEMg was 0.66 under control conditions and increased with Mg loading. The rate of Mg secretion was positively correlated with the urine flow rate. However, Mg loading caused a flow-independent increase in Mg secretion that was correlated with increasing plasma Mg concentration. FEK was 0.86 under control conditions and increased with K loading as a result of enhanced K secretion by the renal tubules. Like renal Mg secretion, renal K secretion showed a flow-dependent component as well as a flow-independent component related to plasma K concentration.

Animals↗

PubMed1985

Comparative aspects of glomerular filtration in vertebrates.

Glomerular ultrafiltration of the plasma is a fundamental component of vertebrate renal function. The importance of the glomerulus is reflected by its near-universal presence and great elaboration among the vertebrates. Although the general structural features and functional properties of the glomerulus appear to be largely similar among diverse groups, there exists considerable variation in the magnitude of the rate of filtration. The kidney is the primary vertebrate organ responsible for water and metabolic waste excretion, and glomerular filtration plays an important role in these functions. Therefore, the magnitude of the GFR appears to be influenced primarily by the rates of water influx and metabolism. Major phylogenetic differences in morphological, physiological and metabolic design have a decisive impact on the magnitude of the GFR. The endothermic classes, with more numerous glomeruli, high metabolic rates, and high ultrafiltration pressures, have proportionately higher rates of glomerular filtration than the ectothermic groups. As a group, the reptiles, with presumably the lowest rates of water influx, exhibit the lowest GFRs. Within each class, there are trends toward species with greater access to free water having higher GFRs (e.g. fresh water vs. marine; mesic vs. xeric. The clearest examples exist for the teleosts, with marine forms having lower GFRs than their fresh water relatives. The coupling of the GFR to environmental influences is also demonstrated by the response of the animal to environmentally imposed perturbations, such as dehydration. In terrestrial animals during dehydration, reductions in the rate of glomerular filtration occur reducing the rate of urinary water loss. And increases in GFR appears to be important in the rapid elimination of water loads in nonmammalian vertebrates. This short-term modulation of the GFR occurs by either changing glomerular plasma flow or glomerular capillary hydrostatic pressure, or both. In addition, shifts in the filtering populations of glomeruli can take place, as has been demonstrated in birds. Although the mediators of these effects have not been unequivocally identified, several hormones, including antidiuretic hormone, angiotensin, and catecholamines, have been implicated.

Animals↗

PubMed1984

Endocrine regulation of avian renal function.

The avian kidney contains reptilian-type (RT) nephrons that do not function in concert and mammalian-type (MT) nephrons that do function in concert to permit production of concentrated urine. Significant data on endocrine regulation of renal function are available only for antidiuretic hormone (arginine vasotocin, AVT) and parathyroid hormone (PTH). Plasma AVT increases and number of filtering RT nephrons decrease when plasma osmolality increases. Small doses of AVT reduce the number of filtering RT nephrons, and all RT nephrons filter following acute neurohypophysectomy. In addition to changing tubule permeability to water, AVT affects the concentrating mechanism by reducing the number of filtering RT nephrons and flow through collecting ducts. Both net tubular reabsorption and net tubular secretion of PO4 occur. Parathyroidectomy (PTX) stimulates PO4 reabsorption, and PTH replacement decreases reabsorption and stimulates secretion, apparently in proximal tubules of RT nephrons. PTX stimulates and PTH replacement inhibits Na-dependent PO4 transport by renal brush border membrane vesicles. PTH also stimulates Ca2+ reabsorption but apparently not long the proximal tubule of RT nephrons.

Animals↗

PubMed1984

Lack of effect of low [Ca2+], La3+, and pyrazinoate on urate transport by isolated, perfused snake renal tubules.

Effects of low medium calcium concentration, of lanthanum, and of pyrazinoate on urate transport by isolated, perfused snake (Thamnophis spp.) distal-proximal renal tubules were studied. Removal of calcium from perfusate with 0.18 mmol/l calcium in bathing medium had no effect on net urate secretion (J net urate) or on net fluid absorption (Jv). In the presence of calcium (1.8 mmol/l), lanthanum (2.0 mmol/l) in perfusate alone, in bathing medium alone, or in both perfusate and bathing medium had no effect on J net urate. These findings suggest that urate transport, in contrast to para-aminohippurate (PAH) transport, is not sensitive to calcium entry into the cells and support the concept that urate and PAH are transported by separate mechanisms in these renal tubules. Pyrazinoate (1.0 mmol/l) in the bathing medium had no effect on J net urate or Jv. These findings do not support the idea of a primary urate secretory process uniquely sensitive to pyrazinoate among the vertebrates.

Animals↗