Biomedical subjects

G J Schwartz

Publications and source records attributed to G J Schwartz.

At least 19 recordsLinked to original sources

PubMed2007

Basolateral carbonic anhydrase IV in the proximal tubule is a glycosylphosphatidylinositol-anchored protein.

Carbonic anhydrase (CA) IV facilitates HCO(3) reabsorption in the renal proximal tubule by catalyzing the reversible hydration of CO(2). CAIV is tethered to cell membranes via a glycosylphosphatidylinositol (GPI) lipid anchor. As there is basolateral as well as apical CAIV staining in proximal tubule, the molecular identity of basolateral CAIV was examined. Biotinylation of confluent monolayers of rat inner medullary collecting duct cells stably transfected with rabbit CAIV showed apical and basolateral CAIV, and in the cell transfectants expressing high levels of CAIV, a transmembrane form was targeted to the basolateral membrane. Basolateral expression of CAIV ( approximately 46 kDa) was confirmed in normal kidney tissue by Western blotting of vesicle fractions enriched for basolateral membranes by Percoll density fractionation. We examined the mode of membrane linkage of basolaterally expressed CAIV in the kidney cortex. CAIV detected in basolateral or apical membrane vesicles exhibited similar molecular size by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis following deglycosylation, and was equally sensitive to phosphatidylinositol-specific phospholipase C digestion, indicating that CAIV is expressed on the basolateral membrane as a GPI-anchored protein. Half of the hydratase activity of basolateral vesicles was resistant to SDS denaturation, compatible with being CAIV. Thus, GPI-anchored CAIV resides in the basolateral membrane of proximal tubule epithelia where it may facilitate HCO(3) reabsorption via association with kNBC1.

Animals↗

PubMed2006

The role of carbonic anhydrases in renal physiology.

Carbonic anhydrase (CA) catalyzes the reversible hydration of CO(2). CA is expressed in most segments of the kidney. CAII and CAIV predominate in human and rabbit kidneys; in rodent kidneys, CAXII, and CAXIV are also present. CAIX is expressed by renal cell carcinoma (RCC). Most of these isoforms, except for rodent CAIV, have high turnover rates. CAII is a cytoplasmic enzyme, whereas the others are membrane-associated; CAIV is anchored by glycosylphosphatidylinositol linkage. Membrane polarity is apical for CAXIV, basolateral for CAXII, and apical and basolateral for CAIV. Luminal membrane CAs facilitate the dehydration of carbonic acid (H(2)CO(3)) that is formed when secreted protons combine with filtered bicarbonate. Basolateral CA enhances the efflux of bicarbonate via dehydration of H(2)CO(3). CAII and CAIV can associate with bicarbonate transporters (e.g., AE1, kNBC1, NBC3, and SCL26A6), and proton antiporter, NHE1 in a membrane protein complex called a transport metabolon. CAXII and CAXIV may also be associated with transporters in normal kidney and CAIX in RCCs. The multiplicity of CAs implicates their importance in acid-base and other solute transport along the nephron. For example, CAII on the cytoplasmic face and CAIV on the extracellular surface provide the 'push' and 'pull' for bicarbonate transport by supplying and dissipating substrate respectively.

Acid-Base Equilibrium↗

PubMed2006

Glomerular filtration rate via plasma iohexol disappearance: pilot study for chronic kidney disease in children.

To guide the design of a nation-wide cohort study of chronic kidney disease in children, we determined how iohexol plasma disappearance curves could be used in children to measure glomerular filtration rate (GFR). Iohexol (5 ml) was administered intravenously and blood samples were obtained at 10, 20, 30, 60, 120, 240, 300, and 360 min after injection (N=29) and assayed by high performance liquid chromatography. Four urines were also collected following the injection. Intra-assay coefficient of variation (CV) in serum was 1.3% at 100 mg/l, 2.6% at 15 mg/l, and 3.4% for duplicate unknowns. GFR(9) was computed from iohexol dose and area under the nine-point blood disappearance curve, using double exponential modeling. Only 2.8% of 254 data points deviated by >3 CV from the curves. GFR(4) calculated from 10, 30, 120, and 300 min points correlated well with GFR(9) (r=0.999) and showed no bias (means+/-s.d. of GFR(9) and GFR(4)=59.3+/-36.3 and 59.4+/-36.0 ml/min per 1.73 m(2)). Relationship of GFR(9) and one-compartment GFR followed quadratic equation as previously reported by Brochner-Mortensen, allowing GFR to be calculated from 120 and 300 min points. This GFR(2) correlated well with GFR(9) (r=0.986). Estimated GFR from Schwartz height/creatinine formula correlated with GFR(9)(r=0.934) but overestimated GFR by 12.2 ml/min per 1.73 m(2). Urine iohexol clearance was poorly correlated (r=0.770) with GFR(9) owing to variability in urine collections (median CV=24%). GFR can be measured accurately using four-point iohexol plasma disappearance (in most cases, two points suffice); estimated GFR and urinary clearances are less useful.

Adolescent↗

PubMed2004

Acute and chronic administration of immunomodulators induces anorexia in Zucker rats.

To investigate the possible involvement of leptin signaling in lipopolysaccharide (LPS) anorexia, we compared the anorectic effect of LPS in genetically obese (fa/fa) Zucker rats and in their lean (Fa/?) counterparts. The effects of interleukin-1beta (IL-1beta) and muramyl dipeptide (MDP) were also tested. LPS [100 microg/kg body weight (BW)], IL-1beta (2 microg/kg BW) and MDP (2.2 mg/kg BW) injected intraperitoneally (i.p.) at lights out reduced food intake similarly in obese and lean rats. LPS injection at 500 or 1000 microg/kg BW (i.p.) also reduced food intake and BW similarly in obese and lean rats, but obese regained BW faster than lean rats. LPS (2.45 microg or 9.8 microg/h/rat) administered chronically with i.p. implanted osmotic pumps reduced food intake similarly on experimental day 1, regardless of the genotype. After day 3, the lean rats' anorectic response and recovery were dose-dependent, whereas the anorectic response in obese rats was minimally affected by dose (significant dose effect only on day 3). Again, obese rats regained lost BW faster than lean rats. These results do not support a role for leptin as the sole mediator of anorexia induced by bacterial products (LPS and MDP) and IL-1beta.

Analysis of Variance↗

PubMed2004

Role for CD14, TLR2, and TLR4 in bacterial product-induced anorexia.

The cell surface component CD14 and the toll-like receptors 2 and 4 (TLR2 and TLR4) are important in mediating the immune responses to bacterial products in mammals. Using mice genetically deficient in CD14, TLR2, or TLR4, we studied the role of these molecules in the anorectic effects of LPS and muramyl dipeptide (MDP). CD14 or TLR2 knockout (KO) and TLR4-deficient (TLR4-DEF) mice as well as corresponding wild-type (WT) colittermates were injected intraperitoneally at dark onset with LPS (2 microg/mouse), MDP (10 mg/kg), interleukin-1 beta (IL-1 beta, 150 ng/mouse), or vehicle, and food intake was recorded. LPS and MDP reduced food intake in WT mice of all genotypes tested. The anorectic effect of LPS was attenuated (P < 0.04) in CD14-KO and TLR4-DEF mice but not in TLR2-KO (P > 0.05). The anorectic effect of MDP was blunted in CD14-KO and TLR2-KO (P < 0.02) mice but not in TLR4-DEF mice. IL-1 beta reduced food intake similarly in all genotypes tested. These results indicate that CD14 is involved in mediating the anorectic effects of both LPS and MDP. Furthermore, TLR4 and TLR2 are specifically involved in mediating the anorectic effects of LPS and MDP, respectively. The results are consistent with the hypothesis that TLR4 functions as the true LPS receptor and that TLR2 is involved in recognition of gram-positive bacterial products.

Acetylmuramyl-Alanyl-Isoglutamine↗

PubMed2002

A role for cyclooxygenase-2 in lipopolysaccharide-induced anorexia in rats.

Because nonselective cycloooxygenase (COX) inhibition attenuated anorexia after lipopolysaccharide (LPS) administration, we tested the ability of resveratrol (2.5, 10, and 40 mg/kg) and NS-398 (2.5, 10, and 40 mg/kg), selective inhibitors of the two COX isoforms COX-1 and -2, respectively, to attenuate LPS (100 microg/kg ip)-induced anorexia. NS-398 (10 and 40 mg/kg) administered with LPS at lights out attenuated LPS-induced anorexia, whereas resveratrol at all doses tested did not. Because prostaglandin (PG) E(2) is considered the major metabolite synthesized by COX, we measured plasma and cerebrospinal fluid (CSF) PGE(2) levels after LPS administration. LPS induced a time-dependent increase of PGE(2) in CSF but not in plasma. NS-398 (5, 10, and 40 mg/kg) blocked the LPS-induced increase in CSF PGE(2), whereas resveratrol (10 mg/kg) did not. These results support a role of COX-2 in mediating the anorectic response to peripheral LPS and point at PGE(2) as a potential neuromodulator involved in this response.

Analgesics, Non-Narcotic↗

PubMed2001

Excessive sugar intake alters binding to dopamine and mu-opioid receptors in the brain.

Palatable food stimulates neural systems implicated in drug dependence; thus sugar might have effects like a drug of abuse. Rats were given 25% glucose solution with chow for 12 h followed by 12 h of food deprivation each day. They doubled their glucose intake in 10 days and developed a pattern of excessive intake in the first hour of daily access. After 30 days, receptor binding was compared to chow-fed controls. Dopamine D-1 receptor binding increased significantly in the accumbens core and shell. In contrast, D-2 binding decreased in the dorsal striatum. Binding to dopamine transporter increased in the midbrain. Opioid mu-1 receptor binding increased significantly in the cingulate cortex, hippocampus, locus coeruleus and accumbens shell. Thus, intermittent, excessive sugar intake sensitized D-1 and mu-1 receptors much like some drugs of abuse.

Animals↗

PubMed2001

Pro-inflammatory and anti-inflammatory cytokine mRNA induction in the periphery and brain following intraperitoneal administration of bacterial lipopolysaccharide.

Gram-negative bacteria-derived lipopolysaccharide (LPS or endotoxin) is known to play an important role in immune and neurological manifestations during bacterial infections. LPS exerts its effects through cytokines, and peripheral or brain administration of LPS activates cytokine production in the brain. In this study, we investigated cytokine and neuropeptide mRNA profiles in specific brain regions and peripheral organs, as well as serum tumor necrosis factor (TNF)-alpha protein levels, in response to the intraperitoneal administration of LPS. For the first time, the simultaneous analysis of interleukin (IL)-1beta system components (ligand, signaling receptor, receptor accessory proteins, receptor antagonist), TNF-alpha, transforming growth factor (TGF)-beta1, glycoprotein 130 (IL-6 receptor signal transducer), OB protein (leptin) receptor, neuropeptide Y, and pro-opiomelanocortin (opioid peptide precursor) mRNAs was done in samples from specific brain regions in response to peripherally administered LPS. The same brain region/organ sample was assayed for all cytokine mRNA components. Peripherally administered LPS up-regulated pro-inflammatory cytokine (IL-1beta and/or TNF-alpha) mRNAs within the cerebral cortex, cerebellum, hippocampus, spleen, liver, and adipose tissue. LPS also increased plasma levels of TNF-alpha protein. LPS did not up-regulate inhibitory (anti-inflammatory) cytokine (IL-1 receptor antagonist and TGF-beta1) mRNAs in most brain regions (except for IL-1 receptor antagonist in the cerebral cortex and for TGF-beta1 in the hippocampus), while they were increased in the liver, and IL-1 receptor antagonist was up-regulated in the spleen and adipose tissue. Overall, peripherally administered LPS modulated the levels of IL-1beta system components within the brain and periphery, but did not affect the neuropeptide-related components studied. The data suggest specificity of transcriptional changes induced by LPS and that cytokine component up-regulation in specific brain regions is relevant to the neurological and neuropsychiatric manifestations associated with peripheral LPS challenge.

Activin Receptors, Type I↗

PubMed2001

Neonatal Borna disease virus infection (BDV)-induced damage to the cerebellum is associated with sensorimotor deficits in developing Lewis rats.

Neonatal Borna disease virus (BDV) infection of the brain produces developmental damage to the cerebellum in Lewis rats, with minimal classical inflammatory responses. In the present study, we assessed the consequences of this damage by measuring motor coordination and postural skills in developing (postnatal days 4 to 30) Lewis rats that were neonatally infected with BDV. Neonatal BDV infection-induced motor impairments were selective and correlated with the time course of BDV damage to cerebellar development. BDV-induced motor deficits were not seen until the end of postnatal week 2. By postnatal week 3, BDV-infected rats had deficits in negative geotropism, fore- and hind limb placing and grasping. BDV-infected rats also exhibited deficits in the ability to hold on to a bar and to cross a suspended bar. Neonatal BDV infection induced impairments in the acoustic startle response. Compared to controls, neonatally BDV-infected rats exhibited attenuated habituation of the acoustic startle at postnatal day (PND) 23 and decreased startle responsiveness at PND 30. Prepulse inhibition of the acoustic startle remained unaltered in BDV-infected rats. The data demonstrate that neonatal BDV brain infection of rats can be a valuable animal model system for studying the relationship between abnormal brain development and resultant behavioral deficits. Further studies of this model may elucidate specific pathogenic mechanisms that that may have implications in the study of neurodevelopmental human disorders.

Animals↗

PubMed2001

Leptin amplifies the feeding inhibition and neural activation arising from a gastric nutrient preload.

Leptin affects food intake by reducing meal size, suggesting that it may modulate the efficacy of within-meal satiety signals. To assess whether leptin would amplify the feeding inhibitory actions of a nutrient gastric preload, we compared liquid diet food intake and patterns of c-Fos activation in response to intraventricular leptin (3.5 microg), intragastric Ensure (10 ml over 10 min), or their combination. Leptin alone did not affect Ensure intake but significantly increased the suppression of intake produced by the intragastric preload. Within the nucleus of the solitary tract (NTS), leptin alone did not stimulate c-Fos but significantly elevated the number of c-Fos positive cells in response to intragastric Ensure at medial and rostral levels. Within the paraventricular nucleus (PVN), both leptin and the gastric load stimulated c-Fos expression, but the combination resulted in significantly greater number of c-Fos positive cells. These data demonstrate that leptin modulates the feeding inhibition produced by meal-related signals and suggest that this modulation occurs at the levels of the NTS and PVN.

Animals↗

PubMed2001

Influence of dispersants on the bioavailability and trophic transfer of petroleum hydrocarbons to larval topsmelt (Atherinops affinis).

Use of chemical dispersants as oil spill clean-up agents may alter the normal behavior of petroleum hydrocarbons (PH) by increasing their functional water solubility, resulting in increased bioavailability and altered interactions between dispersant, oil, and biological membranes. The objective of this research was to determine the impact of dispersing agents on PH bioavailability and trophic transfer to larval fish from primary levels of a marine food chain. Uptake, bioaccumulation, depuration, and metabolic transformation of a model PH, [14C]naphthalene, were measured and compared for Prudhoe Bay crude oil (PBCO) dispersed with Corexit 9527(R) (DO) and undispersed preparations of the water-accommodated fraction (WAF) of PBCO. The model food chain consisted of a primary producer, Isochrysis galbana; and a primary consumer, the rotifer, Brachionus plicatilis; and larval topsmelt, Atherinops affinis. Direct aqueous (AQ) exposure was compared with combined aqueous and dietary (AQ&D) exposure. Dispersants altered the uptake and depuration processes of naphthalene, independent of aqueous concentrations, in primary trophic species of a marine food chain. The amount of naphthalene taken up by topsmelt was initially significantly (P < or = 0.05) enhanced in the presence of dispersant, reaching a maximum more quickly than undispersed samples. Dispersion treatment significantly increased naphthalene dispension in topsmelt (P < or = 0.05) from both AQ and AQ&D exposures. No significant change in naphthalene uptake by fish was observed with the addition of contaminated food for either WAF or DO medium; however, both uptake and depuration rate constants varied significantly with route of exposure consistent with greater naphthalene turnover. The majority (> or = 72%) of naphthalene-derived radioactivity from fish tissue following all exposures was in the parent form, with smaller quantities of alpha- and beta-naphthols, alpha- and beta-naphthyl sulfates, and an unidentified derivative.

Animals↗

PubMed2001

Within-meal gut feedback signaling.

During a meal, multiple gastrointestinal sites are stimulated by ingested nutrients and their digestion products, initiating local gastrointestinal actions and producing a variety of potential feedback signals that can contribute to meal termination. During ingestion, gastric emptying is rapid, allowing a significant portion of ingested nutrients to enter the intestine. Gastric and duodenal vagal afferent fibers increase their electrophysiological activity in relation to the mechanical presence of ingested nutrients. On reaching the duodenum, nutrients also activate vagal chemosensitive elements and stimulate the release of a variety of brain gut peptides including cholecystokinin (CCK). CCK also activates vagal afferent fibers directly and modifies the response properties of vagal mechanosensitive fibers to gastric and duodenal loads. Blocking or eliminating these feedback signals results in increased meal size demonstrating their role in meal termination.

Afferent Pathways↗

PubMed2001

Distal renal tubular acidosis with severe hypokalaemia, probably caused by colonic H(+)-K(+)-ATPase deficiency.

We describe a 21 month old male infant who presented with failure to thrive associated with severe hypokalaemia and metabolic acidosis, together with hypomagnesaemia. Evaluation revealed marked renal and probable faecal potassium wasting, distal renal tubular acidosis, mild urinary magnesium wasting, and a normal gastric pH (gastric H(+)-K(+)-ATPase). Hypokalaemic forms of metabolic acidosis, such as diabetic ketoacidosis and proximal renal tubular acidosis were ruled out from the clinical picture. The hypokalaemia of distal renal tubular acidosis usually improves with alkali therapy, but this was not observed: despite correction of acidosis with 5 mmol/kg potassium citrate per day, an additional 5 mmol/kg potassium chloride was required to bring serum potassium to 3.5 mmol/l. At 3 years of age potassium was provided in the absence of potential alkali and acidosis ensued; serum bicarbonate fell to 10 mmol/l. Although a specific genetic analysis is not yet possible, the abnormalities are consistent with a novel form of distal renal tubular acidosis. The pathophysiology probably does not stem from defects in the vacuolar H(+)-ATPase but more likely from deficient activity of the colonic isoform of H(+)-K(+)-ATPase that is resident in the medullary collecting duct and mediates potassium absorption and proton secretion.

Acidosis, Renal Tubular↗

PubMed2001

Meal-related stimuli differentially induce c-Fos activation in the nucleus of the solitary tract.

Feedback signals arising from the oral cavity and upper gastrointestinal tract contribute to the control of meal size. To assess how these signals are integrated at central sites involved in ingestive control, we compared levels of c-Fos activation in the nucleus of the solitary tract (NTS) and area postrema (AP) in response to meal ingestion or gastric and duodenal infusions in the rat. Ingestion of a liquid diet to satiety induced significant fos-like immunoreactivity (FLI) at multiple levels of the NTS and within the AP. The restriction of intake to one-half the normal ingestion of a rat did not result in significant FLI, although gastric infusion of this liquid diet volume did. Fast bolus infusion resulted in greater FLI than did the same volume infused at a rate to mimic that of normal ingestion. Prior experience with gastric infusions did not affect the amounts of FLI within the NTS or AP. In rats with pyloric cuffs blocking flow from the stomach to the intestine, combined gastric load and duodenal nutrient elicited significantly greater FLI than either gastric or duodenal infusions alone. These data demonstrate that neural activation arising from meal-related stimuli are integrated at the level of the NTS.

Animals↗

PubMed2001

Intracerebroventricular CART peptide reduces rat ingestive behavior and alters licking microstructure.

Intracerebroventricular administration of cocaine- and amphetamine-regulated transcript (CART) peptides reduces food intake and increases c-Fos in brain areas involved in the control of feeding. To discern behavioral mechanisms through which CART alters the microstructure of feeding, we injected CART-(55--102) (0.1, 0.5, 1, 2 microg, and saline controls) into the lateral ventricle of male Sprague-Dawley rats 5 min before dark onset and, using lickometers, monitored the ingestion of an Ensure liquid diet for the first 6 h of dark. At a threshold dose of 1 microg, CART dose dependently 1) decreased intake of Ensure in licks; 2) decreased meal size, but did not alter meal duration or number; 3) reduced initial lick rate of meals; and 4) significantly reduced burst number, licks/burst, and licks/cluster. CART dose dependently increased interlick interval (0.5 microg threshold, 192 +/- 4 vs. 183 +/- 3 ms, control; 1 microg: 201 +/- 1 ms; 2 microg: 214 +/- 6 ms). These data suggest that altered oral motor function, and possibly palatability perception, may be fundamental to the anorexigenic action of CART.

Animals↗

PubMed2001

A role for NPY overexpression in the dorsomedial hypothalamus in hyperphagia and obesity of OLETF rats.

Otsuka Long-Evans Tokushima Fatty (OLETF) rats lacking CCK-A receptors are hyperphagic, obese, and diabetic. We have previously demonstrated that these rats have a peripheral satiety deficit resulting in increased meal size. To examine the potential role of hypothalamic pathways in the hyperphagia and obesity of OLETF rats, we compared patterns of hypothalamic neuropeptide Y (NPY), proopiomelanocortin (POMC), and leptin receptor mRNA expression in ad libitum-fed Long-Evans Tokushima (LETO) and OLETF rats and food-restricted OLETF rats that were pair-fed to the intake of LETO controls. Pair feeding OLETF rats prevented their increased body weight and elevated levels of plasma insulin and leptin and normalized their elevated POMC and decreased NPY mRNA expression in the arcuate nucleus. In contrast, NPY expression was upregulated in the dorsomedial hypothalamus (DMH) in pair-fed OLETF rats. A similar DMH NPY overexpression was evident in 5-wk-old preobese OLETF rats. These findings suggest a role for DMH NPY upregulation in the etiology of OLETF hyperphagia and obesity.

Age Factors↗

PubMed2001

Intracerebroventricular CART peptide reduces food intake and alters motor behavior at a hindbrain site.

Peptides from cocaine- and amphetamine-regulated transcript (CART) reduce food intake in rats when injected into the lateral ventricle. Hypothalamic and hindbrain sites important in the control of feeding contain CART-immunoreactive fibers. To further define the site of CART's anorectic action, we compared feeding and other behavioral responses to third or fourth ventricular (3V, 4V) CART-(55-102) in 6-h food-deprived rats, both before and after cerebral aqueduct occlusion. 3V CART reduced the volume of Ensure consumed and resulted in fewer observations of eating and grooming within the 30-min test session. These reductions were significantly attenuated by aqueduct obstruction. 4V CART suppressed Ensure intake and resulted in decreased observations of feeding both with and without aqueduct blockade. 3V CART produced flat-backed postures and movement-associated tremors that were prevented by aqueduct obstruction. 4V CART also produced these signs, both with and without aqueduct blockade. We conclude that the major hypophagic effect of intracerebroventricular CART is mediated at a hindbrain site. The association of CART-induced feeding suppression with altered motor behavior questions the specificity of intracerebroventricular CART for actions on feeding.

Animals↗

PubMed2001

Role of basolateral carbonic anhydrase in proximal tubular fluid and bicarbonate absorption.

Membrane-bound carbonic anhydrase (CA) is critical to renal acidification. The role of CA activity on the basolateral membrane of the proximal tubule has not been defined clearly. To investigate this issue in microperfused rabbit proximal straight tubules in vitro, we measured fluid and HCO(3)(-) absorption and cell pH before and after the extracellular CA inhibitor p-fluorobenzyl-aminobenzolamide was applied in the bath to inhibit only basolateral CA. This inhibitor was 1% as permeant as acetazolamide. Neutral dextran (2 g/dl, molecular mass 70,000) was used as a colloid to support fluid absorption because albumin could affect CO(2) diffusion and rheogenic HCO(3)(-) efflux. Indeed, dextran in the bath stimulated fluid absorption by 55% over albumin. Basolateral CA inhibition reduced fluid absorption ( approximately 30%) and markedly decreased HCO(3)(-) absorption ( approximately 60%), both reversible when CA was added to the bathing solution. In the presence of luminal CA inhibition, which reduced fluid ( approximately 16%) and HCO(3)(-) ( approximately 66%) absorption, inhibition of basolateral CA further decreased the absorption of fluid (to 74% of baseline) and HCO(3)(-) (to 22% of baseline). CA inhibition also alkalinized cell pH by approximately 0.2 units, suggesting the presence of an alkaline disequilibrium pH in the interspace, which would secondarily block HCO(3)(-) exit from the cell and thereby decrease luminal proton secretion (HCO(3)(-) absorption). These data clearly indicate that basolateral CA has an important role in mediating fluid and especially HCO(3)(-) absorption in the proximal straight tubule.

Absorption↗