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Biomedical subjects

S Segal

Publications and source records attributed to S Segal.

At least 289 records · Page 16Linked to original sources
PubMed1987

Metabolic fate of glutamate carbon in rat renal tubules. Studies with 13C nuclear magnetic resonance and gas chromatography-mass spectrometry.

13C-n.m.r. spectroscopy and g.c.-m.s. were used to determine the metabolic fate of glutamate carbon in rat kidney. The main purpose was to characterize the effect of chronic metabolic acidosis on the utilization of glutamate carbon. Renal tubules obtained from normal and chronically acidotic rats were incubated in Krebs buffer, pH 7.4, in the presence of 2.5 mM-[3-13C]glutamate. During the course of incubation the concentrations of total glucose and NH3 were significantly (P less than 0.05) higher in tissue from acidotic rats. The levels of some tricarboxylic-acid-cycle intermediates were higher (P less than 0.05) in control tissue. In control tissue, 13C-n.m.r. spectra demonstrated a significantly higher rate of 13C appearance of aspartate, glutamine and [2,4-13C]glutamate. However, in acidosis the resonances of [13C]glucose carbon atoms were significantly higher. In the control, approx. 15% of glutamate carbon was accounted for by [13C]glucose formation as against 30% in chronic acidosis. However, in control tissue, 44% of glutamate carbon utilization was accounted for by recycling to glutamate and formation of aspartate, glutamine and GABA. In acidosis, only 11% was so recovered. Analysis of 15NH3 formation during the course of incubation with 2.5 mM-[15N]glutamate demonstrated a positive association between the appearance of [13C]glucose and 15NH3 both in the control and in acidosis. The data suggest that the control of gluconeogenesis and ammoniagenesis in acidosis is, in part, referable to a diminution in the rate of the reductive amination of alpha-oxoglutarate, that of the transamination reaction and that of glutamine synthesis.

Acidosis, Renal Tubular↗
PubMed1987

Cystine and lysine transport in cultured human renal epithelial cells.

The transport of the amino acids, cystine and lysine, was studied in epithelial cell lines propagated from human kidney cortex. Cystine uptake data were reproducible in different cell lines and did not vary over several cell passages of an individual cell line. The transport of this disulfide amino acid was sodium-dependent with kinetic analysis showing one apparent Kt system of 0.09 mmol/L and Vmax of 0.054 mmol/L cell water/min. Studies of the kinetics of lysine transport, however, revealed two uptake systems with apparent high and low affinities with Kt of 0.14 mmol/L and 5 mmol/L and Vmax of 0.041 and 0.167 mmol/L cell water/min, respectively. Glutamate appeared to be the most potent inhibitor of cystine uptake by these cultured human renal cells and this interaction was competitive. Although cystine did not inhibit lysine uptake, arginine and ornithine were shown to be major inhibitors, thus providing evidence for the presence of a shared dibasic amino acid transport system.

Arginine↗
PubMed1987

Effect of cystine dimethylester on renal solute handling and isolated renal tubule transport in the rat: a new model of the Fanconi syndrome.

The effect of cystine dimethylester on the renal handling of phosphate, glucose, alpha-amino nitrogen, amino acids, and protein in vivo and on the uptake of lysine, glycine, taurine, and alpha-methyl glucoside by isolated renal tubules in vitro was studied in adult male rats. Parenteral administration of 400 mumol twice a day for four days of cystine dimethylester led to an increased urine volume, and excretion of phosphate, glucose, alpha-amino nitrogen, and the amino acids glutamine, proline, alanine, 1/2 cystine, ornithine, lysine, histidine, and glycine. Cystine dimethylester treatment did not affect the creatine clearance nor were any renal anatomic abnormalities noted. Intracellular cysteine, but not cystine, was increased in the kidney after the four days of treatment. Pre-incubation of isolated renal tubules with 2 mmol/L cystine dimethylester for ten minutes markedly inhibited the uptake of 0.025 mmol/L lysine, 0.1 mmol/L glycine, 0.01 mmol/L taurine, and 2 mmol/L alpha-methyl glucoside. Incubation with 2 mmol/L cystine dimethylester for ten minutes did not affect the ability of the renal tubule to exclude trypan blue dye, although longer incubation times did lead to significant staining. The intracellular cystine concentration of the renal tubule did rise significantly after incubation with cystine dimethylester, a biochemical correlate of the human disease cystinosis. These studies indicate that cystine dimethylester can induce an experimental form of the Fanconi syndrome both in vivo and in vitro and offers a new model for investigating the mechanisms underlying this enigmatic disorder.

Amino Acids↗
PubMed1987

A new delivery system for contraceptive steroids.

Long-acting forms of contraception that take advantage of the tissue compatibility of silicone rubber, a polymer of dimethylsiloxane, have been developed. The most advanced type of subdermal contraceptive capsule contains about 36 to 40 mg of levonorgestrel and is 30 mm in length and 2.4 mm in diameter (Norplant). The set of six implants is placed under the skin of the upper arm with a 10-gauge trocar with the use of a local anesthetic. The basis for the antifertility effect of these implants is continuous, low-dose progestogen therapy without the use of estrogen. The capsules release a total of approximately 39 micrograms of levonorgestrel each day. The blood progestogen level achieved through this microabsorption delivery system is 0.25 to 0.3 ng/ml. There is a sufficient supply of steroid in the capsules to maintain this blood progestogen level for 5 to 6 years. Since the capsules can be removed at any time, this contraceptive method is voluntarily reversible. The effectiveness of these subdermal implants has been evaluated in long-term studies that have progressed for well over 5 years. Therefore one clinic visit eliminates nearly 2000 days of concern over having to remember to take a pill on schedule. There has been sufficient experience to assure that fertility recurs promptly after removal of the subdermal implants.

Clinical Trials as Topic↗
PubMed1987

Characterization of amino acid metabolism by cultured rat kidney cells: study with 15N.

The present study evaluates the metabolism of glutamine and glutamate by normal rat kidney (NRK) cells. The major aim was to evaluate the effect of acute acidosis on the metabolism of amino acid and ammonia formation by cultured NRK cells. Experiments at either pH 7.0 or 7.4 were conducted with phosphate-buffered saline supplemented with either 1 mM [5-15N]glutamine, [2-15N]glutamine, or [15N]glutamate. Incubation with either glutamine or glutamate as a precursor showed that production of ammonia and glucose was increased significantly at pH 7.0 vs. 7.4. The disappearance [corrected] of glutamine and glutamate was linear during a 60-min incubation at either pH. In experiments with [5-15N]glutamine, we found that approximately 57 and 43% of ammonia N was derived from 5-N of glutamine at pH 7.4 and 7.0, respectively. Experiments with [2-15N]glutamine or [15N]glutamate indicated that approximately 43 and 47% of 2-N glutamine and glutamate N utilization, respectively, was accounted for by ammonia production at pH 7.0. Similarly, 28 and 29% of NH3 was derived from 2-N of glutamine or glutamate N by activity of glutamate dehydrogenase at pH 7.4. In addition to 15NH3 formation, three major metabolic pathways of [2-15N]glutamine or [15N]glutamate disposal were identified: 1) transamination reactions involving the pH-independent formation of [15N] aspartate and [15N]alanine; 2) the synthesis of [6-15NH2]adenine nucleotide, a process more active at pH 7.4 vs. 7.0; and 3) glutamine synthesis from [15N]glutamate, especially at pH 7.4. The data indicate that NRK cells in culture consume glutamine and glutamate and generate ammonia and various amino acids, depending on the H+ concentration in the media. The studies suggest that these cell lines may provide a useful model for studying various aspects of the effect of pH on rat renal ammoniagenesis.

Amino Acids↗
PubMed1987

Cysteine and glutathione levels in developing rat kidney and liver.

Intracellular levels of cysteine (CSH) and reduced glutathione (GSH) in the kidney and liver of rats from the newborn to the adult period have been determined using a sensitive high performance liquid chromatography method. In the kidney, the intracellular level of free CSH increased 4-fold from 1 to 4 nmol/mg protein with GSH levels which ranged from 20 to 25 nmol/mg protein from the 10th to 21st postnatal day, respectively. In contrast, intracellular free hepatic CSH showed a biphasic pattern with development. Intracellular free hepatic GSH, on the other hand, increased 2-fold over the 3- to 21-day postnatal period. In adult tissues, intracellular levels of free CSH and GSH decreased as compared with levels in 21-day postnatal animals. When ratios of CSH to GSH were compared between tissues from the 3-day-old postnatal and adult rat, CSH:GSH increased approximately 4-fold in the kidney and decreased 2- to 3-fold in the liver.

Animals↗
PubMed1986

Assessment of binding of L-cystine and L-lysine by rat renal brush-border membranes.

Cystine and lysine bind to isolated rat renal brush-border vesicles. Three methods to determine the extent of amino acid binding to the membranes have been compared, one relying on the osmotic reactivity of the vesicle, a second by trichloroacetic acid precipitation of membrane-bound material and a third by initial rate analysis. For cystine, all methods yield comparable results at early time points, indicating the trichloroacetic acid method is a simple and valuable tool for binding estimation under initial-rate or near initial-rate conditions. For lysine, initial rate analysis and osmotic perturbation are the methods of choice since lysine co-precipitates with trichloroacetic acid.

Animals↗
PubMed1986

Characteristics of lysine uptake by isolated renal cortical tubule fragments from mature and immature dogs.

The uptake of L-lysine was examined in isolated renal cortical tubule fragments from adult and 1-week-old dogs. Lysine uptake by adult tubules was initially more rapid than that by the immature tubules. This uptake by mature tubules reached a steady state after 30 min of incubation, while the newborn tubules still had not reached a steady state by 90 min of incubation. Because a steady state of lysine uptake was not attained with the immature tubules, their uptake of lysine exceeded that of the adult after 60 min of incubation. Kinetic studies revealed that lysine was taken up by one saturable transport system with a Km of 0.56 mM and Vmax of 6.18 mmol/liter intercellular fluid per 5 min in the adult and one saturable transport system in the 1-week-old with a Km of 0.38 mM and Vmax of 3.66 mmol/l intracellular fluid per 5 min. Lysine also entered the renal tubule cells in both age groups via a diffusional pathway with a kd of 0.35 min-1 in the adult and 0.30 min-1 in the newborn. Cystine competitively inhibited lysine uptake by adult dog tubules with a Ki of 0.61 mM. The other dibasic amino acids, ornithine and arginine, also inhibited lysine uptake in both the adult and the newborn.

Age Factors↗
PubMed1986

L-cystine transport by papain-treated rat renal brush-border membrane vesicles.

In papain-treated rat renal brush-border membrane vesicles, cystine uptake was enhanced under sodium gradient conditions. This effect was not observed when sodium was equilibrated across the vesicle membrane or when sodium was completely absent from the incubation medium. The increased rate of cystine uptake occurred within the first two minutes of incubation and coincided with the period of increased flux of sodium known to occur after papain treatment. Under sodium gradient conditions, the Vmax of cystine uptake by treated vesicles was 65% greater while the Km was 25% lower than the value observed in untreated membranes. The increased cystine uptake after papain treatment occurred when medium cystine was in the electroneutral form. In the absence of a sodium gradient, cystine uptake by control membranes was insensitive to changes in membrane potential and this was unaltered after papain treatment. Exposure of the membranes to papain also resulted in a profound decrease in cystine binding which occurs in native membranes incubated with cystine. The fact that cystine uptake is unchanged under sodium equilibration and even enhanced under sodium gradient conditions suggests that the component of cystine binding is not essential for cystine transport and may represent non-specific binding to membrane proteins.

Animals↗
PubMed1986

Effect of 5-amino-4-imidazolecarboxamide riboside on renal ammoniagenesis. Study with [15N]aspartate.

[15N]Aspartate and 5-amino-4-imidazolecarboxamide riboside (AICAriboside) were used to evaluate the contribution of the purine nucleotide cycle to ammonia production in renal tubules isolated from control and chronically acidotic rats. Addition of 1 mM AICAriboside to incubation medium containing 2.5 mM [15N] aspartate significantly stimulated production of 15NH3 and 15N in the 6-amino group of adenine nucleotides during a 30-min incubation. In tubules from both control and acidotic animals, the levels of ATP, AMP, and NH3 were increased. In contrast, 5 mM AICAriboside inhibited 15NH3 production and reduced the total purine nucleotide content. In tubules from acidotic rats, enrichment in 15NH3 exceeded that in the 6-amino group of the adenine nucleotides, indicating that no precursor-product relationship existed between the purine nucleotide cycle and ammonia. Conversely, in tubules from control rats, 15N enrichment in the 6-amino group of the adenine nucleotides exceeded that in NH3. This relationship obtained whether or not AICAriboside was included in the incubation mixture. The current investigations show that the metabolism of aspartate through the purine nucleotide cycle is lower in renal tubules obtained from chronically acidotic rats than in control tubules. The observations indicate that AICAriboside has a biphasic effect on renal ammoniagenesis and adenine nucleotide synthesis, and suggest a possible clinical use of AICAriboside in cases of impaired ammonia formation in renal failure.

Adenosine Diphosphate↗
PubMed1986

Modulation of protein kinase C and Ca2+ lipid-independent protein kinase in lymphoma induced by Moloney murine leukemia virus in BALB/c mice.

We investigated the possible role of protein kinase C (PKC) in the progression of Moloney murine leukemia virus (Mo-MuLV)-induced lymphoma in BALB/c mice. Mice injected with Mo-MuLV on the first day after birth developed lymphoma within 1 1/2-3 months. The development of lymphoma was characterized by a gradual increase in the number of spleen cells. However, no analogous changes could be detected in the thymuses of these mice, although cells of both organs were found to be virus producers as early as 3-4 weeks after inoculation. PKC activity, which was assayed in extracts of spleen and thymus cells, declined gradually during the development of lymphoma. Concomitantly with this decline, a progressive appearance of Ca2+/lipid-independent protein kinase activity was observed. TPA treatment of intact cells from normal mice reduced the level of soluble PKC activity, while inducing Ca2+/lipid-independent phosphorylation. By contrast, TPA had no effect on these enzymatic activities in cells derived from leukemic mice. Spleen enlargement caused by injection of a non-leukemogenic inflammatory agent such as mineral oil was ineffective in this respect, suggesting that the PKC-Ca2+/lipid-independent protein kinase modulation is associated with the virally induced leukemogenesis.

Animals↗
PubMed1986

Survey of bereaved parents.

A retrospective study in Vancouver was designed to evaluate parents' perceptions of support received after the death of a child up to 5 years old. The families were contacted with the help of health care professionals and the news media. A standardized questionnaire was used in a personal interview or occasionally by mail. The contact with health care professionals after the child's death was frequently considered by the 61 families not to have been helpful: 80% of the families judged the information or counselling they had received to be inadequate, and over 50% had received none; many listed comments and behaviour that they considered harmful. The families desired both full medical information and grief support; what forms such support could take are suggested.

Adult↗
PubMed1986

Establishment and characterization of a novel bone-marrow-derived macrophage-like accessory cell line.

An accessory cell line, designated line A, was generated from bone marrow stem cells which differentiated in vitro in response to colony-stimulating factor (CSF) in substratum cultures. The cells were found to constitutively secrete large amounts of CSF, the activity of which was neutralized by anti-CSF-1 antibodies. Cells of line A and its supernatants potentiate the suboptimal response of thymocytes to PHA, manifesting an interleukin-1 (IL-1)-like activity. Culture fluids of this line also reconstitute the response to T cell mitogens of spleen cells depleted of adherent accessory cells. It was also found that cells of line A bear low levels of surface Ia, and they efficiently present soluble antigen to proliferating memory T cells. Constitutive prostaglandin secretion, which sometimes masks antigen-presenting capacity, was also demonstrated. Cells of line A are poorly phagocytic, do not secrete lysozyme, and lack Fc and complement receptors. However, they manifest strong cytoplasmic nonspecific esterase staining and an ectoenzyme profile resembling that of elicited inflammatory macrophages. In addition, the cell surface antigen Mac-2 was demonstrated, while stainings with anti-Mac-1 and anti-Mac-3 were negative. Thus, line A may represent a unique subpopulation of immunoregulatory accessory cells, the features of which are discussed.

Animals↗
PubMed1986

Cystine-glutamate transport interactions in rat renal cortical tubules, brushborder vesicles, and cultured renal tubule cells.

Glutamate had no significant effect on the uptake of 0.025 mM cystine by isolated rat renal cortical tubules and brushborder membrane vesicles in contrast to lysine which significantly inhibits cystine transport. Glutamate, however, markedly inhibited cystine uptake by rat renal tubule cells grown in a serum-free, hormonally defined media for 5 days. Lysine also inhibited cystine transport in these cultured renal tubule cells.

Animals↗
PubMed1986

Characteristics of cultured human renal cortical epithelia.

Nine human kidney epithelial cell lines, isolated from small biopsied material and from whole kidney, were propagated in both a hormonally defined medium and a medium supplemented with serum. At confluency, hemicysts or domes, typical of cultured epithelial cells, were formed by these cells. Monolayers had junctional complexes between cells and the presence of numerous microvilli on the cell surface. Parathyroid hormone markedly stimulated these cells to produce cyclic AMP. They also contained high levels of gamma-glutamyltranspeptidase, leucine aminopeptidase, and maltase, enzymes that are associated with the brush-border membrane of the proximal tubule. The cultured cells demonstrated the ability to transport amino acids and alpha-methylglucoside, a substrate actively transported only by the proximal tubule in the kidney. Based on these findings, the cultured cells reflected a number of characteristics associated with the proximal tubule. These renal epithelial cell lines may provide a useful model for studying various aspects of human renal physiology and biochemistry.

Adult↗