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Biomedical subjects

M Field

Publications and source records attributed to M Field.

At least 55 records · Page 3Linked to original sources
PubMed1987

Antidiarrheal therapy. Prospects for new agents.

Successful treatment of severe diarrhea has traditionally relied upon opiates or opiate derivatives. Recent advances in our understanding of intestinal fluid and electrolyte absorption have provided the opportunity to develop therapeutic agents specific for various points in the secretory and absorptive process. Present and proposed antidiarrheal agents, in addition to antimotility activity, will be capable of stimulating intestinal fluid absorption, inhibiting intestinal fluid secretion, or both. The mechanism(s) of action and clinical implications for proposed antidiarrheal agents are reviewed.

Antidiarrheals↗
PubMed1987

Na-K-2Cl cotransport in winter flounder intestine and bovine kidney outer medulla: [3H] bumetanide binding and effects of furosemide analogues.

The effects of several sulfamoyl benzoic acid derivatives on Na-K-Cl cotransport were investigated in winter flounder intestine. The relative efficacy (IC50 values) and order of potency of these derivatives were benzmetanide, 5 X 10(-8) M greater than bumetanide 3 X 10(-7) M greater than piretanide 3 X 10(-6) M greater than furosemide 7 X 10(-6) M greater than amino piretanide 1 X 10(-5) 3-amino-4-penoxy-5-sulfamoyl benzoic acid. Binding of [3H] bumetanide was studied in microsomal membranes from winter flounder intestine and compared to that in bovine kidney outer medulla. Binding was also studied in brush-border membranes from winter flounder intestine. The estimated values for Kd and number of binding sites (n) were: bovine kidney, Kd = 1.6 X 10(-7), n = 10.5 pmol/mg protein; winter flounder intestine, Kd 1.2 X 10(-7), n = 7.3 pmol/mg protein, and brush-border membranes from winter flounder, Kd = 5.3 X 10(-7), n = 20.4 pmol/mg protein. The estimated Kd for bumetanide binding to winter flounder brush-border membranes derived from association and dissociation kinetics was 6.8 X 10(-7) M. The similarity in magnitudes of IC50 and Kd for bumetanide suggests that the brush-border cotransporter is ordinarily rate-limiting for transmural salt absorption and that bumetanide specifically binds to the cotransporter. Measurement of bumetanide binding at various concentrations of Na, K and Cl showed that optimal binding required all three ions to be present at about 5 mM concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1987

Characteristics and functions of Na-K-Cl cotransport in epithelial tissues.

This review summarizes our present understanding of Na-K-Cl cotransport and its physiological role in absorption and secretion of electrolytes and water in epithelial tissues. In the past several years an extensive literature about this cotransporter has developed due to its widespread distribution in a variety of cell types and its essential role in fluid and electrolyte transport in several epithelial tissues. We summarize this literature and speculate on the future characterization of this transport system. Although this review focuses on cotransport as it relates to absorptive and secretory processes in epithelia, important information concerning the pharmacology, stoichiometry, and regulation of Na-K-Cl cotransport in nonepithelial systems (i.e., erythrocytes, fibroblasts, squid axon, etc.) has been included to supplement areas that are less well established in the epithelial literature.

Affinity Labels↗
PubMed1987

Homologous desensitization to prostaglandins in rabbit ileum.

Prostaglandins (PG's) increase short-circuit current (Isc), inhibit NaCl absorption, and stimulate Cl secretion in rabbit ileum. These changes occur with the following PGs; E2, E1, nitrilo-I2 and, to a lesser extent, with A2, D2, and F2 alpha. Arachidonic acid (AA) also stimulates secretion. The PG- or AA-stimulated Isc does not persist, however, and on prolonged exposure tachyphylaxis develops. Resensitization of the Isc response to PGE2 is rapid, being essentially complete in 15 min after the PG is removed. Desensitization to AA is not reflected by diminished PG generation. PGE2 release from the mucosa after AA addition is constant, although the AA-stimulated Isc decreases. Isc measurements indicate that PGE2 at slightly below its EC50 partially desensitizes and a near-maximal concentration completely desensitizes to PGE2 but does not, however, inhibit the subsequent change in Isc caused by theophylline or vasoactive intestinal peptide (VIP). Adenosine 3',5'-cyclic monophosphate (cAMP) measurements suggest that desensitization applies to cAMP production. PGE2 (10(-5) M) increases mucosal cAMP three- to sevenfold, but this elevation is transient; a second challenge dose, which fails to elicit a Isc change, also fails to increase mucosal cAMP. Adenylate cyclase measurements from untreated and PGE2-treated enterocytes demonstrate a decrease in stimulation by PGE2 but not in stimulation by VIP, fluoride, or 5-guanylylimidodiphosphate.

Adenylyl Cyclases↗
PubMed1987

Tyrosine transport in winter flounder intestine: interaction with Na+-K+-2Cl- cotransport.

Tyrosine absorption across the brush border of the intestinal epithelium of the winter flounder Pseudopleuronectes americanus was studied in Ussing chambers modified to determine early rates of uptake. At 0.1 mM tyrosine, the 4-min rate of uptake (influx) of tyrosine across the brush border averaged 37.5 nmol X cm-2 X h-1. Omission of Na decreased influx by 60%, indicating that tyrosine influx occurs, at least in part, by a Na-coupled process. Ouabain inhibited influx by 80%. Inhibition of brush border Na+-K+-2Cl- cotransport by bumetanide, 8-bromo-cyclic GMP, or Cl replacement stimulated tyrosine influx 2.5- to 4-fold. However, atriopeptin III, which also inhibits Na+-K+-2Cl- cotransport, did not stimulate tyrosine influx. Cyclic AMP, which does not appear to inhibit ion cotransport, did not stimulate tyrosine influx. Both cyclic GMP and bumetanide also stimulated the net mucosa-to-serosa tyrosine flux (43 and 29%, respectively) and increased the cellular concentration of tyrosine by 50%. Thus tyrosine's influx is increased to a greater extent than is its transmural flux or its cellular concentration, suggesting that the main change occurs at the brush border and represents large increases in both influx and efflux of tyrosine across this membrane.

Animals↗
PubMed1987

Intestinal adaptation to diabetes. Altered Na-dependent nutrient absorption in streptozocin-treated chronically diabetic rats.

To examine the pattern and mechanisms of enhanced intestinal nutrient absorption in diabetes, we measured intestinal transport of 3-O-methylglucose (3OMG), l-alanine (ALA), and SO4 in male Lewis rats made diabetic with streptozocin. Diabetes enhanced 3OMG absorption fivefold in ileum and threefold in jejunum; ALA absorption increased twofold in ileum but not at all in jejunum; ileal SO4 transport was unaffected. Increases in 3OMG and ALA transport were due solely to increases in maximum velocity. The enhancement of ileal glucose absorption was half-maximal in 40-45 d, could be reversed by 10 d of treatment with insulin and did not result from adrenergic denervation. The density of glucose carriers per milligram brush border protein (measured as [3H]phlorizin binding sites) was not altered but there was a sixfold increase in the number of glucose-inhibitable [3H]phlorizin-binding sites in the intact epithelium. Generalized mucosal hypertrophy accounted for less than 30% of this increase. We conclude that the intestine adapts to streptozocin-induced diabetes through recruitment of additional brush border carriers for sugar, probably in the midvillus-to-crypt region.

3-O-Methylglucose↗
PubMed1987

MRL-lpr/lpr mice show an impairment of IgG aggregate removal which relates to parameters of disease activity.

MRL-lpr/lpr mice show an age-related impairment in the removal of heat-aggregated IgG (HAGG) from the circulation. The female mice, which have an earlier mortality than their male counterparts, clear HAGG more slowly than the male animals. Delay in clearance of this probe of mononuclear phagocytic system (MPS) function relates directly to high levels of circulating immune complexes (CIC) and to significant renal damage. In addition it relates indirectly to hepatic and splenic uptake of HAGG. MPS saturation plays a significant role in the pathogenesis of the disease seen in MRL-lpr/lpr mice.

Aging↗
PubMed1986

Relationship between lipid fluidity and water permeability of bovine tracheal epithelial cell apical membranes.

Apical membrane vesicles were prepared from bovine tracheal epithelial cells. These membranes were enriched in alkaline phosphatase specific activity 35-fold compared to cellular homogenates. Steady-state fluorescence polarization studies of these membranes, using three fluorophores, demonstrated that they possessed a relatively low fluidity. Studies using the probe 1,6-diphenyl-1,3,5-hexatriene detected thermotropic transitions at 25.7 +/- 0.4 and 26.8 +/- 0.6 degrees C in these membranes and their liposomes, respectively. Analysis of the composition of these membranes revealed a fatty acyl saturation index of 0.59 +/- 0.02, a protein/lipid ratio (w/w) of 0.60 +/- 0.06, a cholesterol/phospholipid ratio (mol/mol) of 0.83 +/- 0.11, and a sphingomyelin/lecithin ratio (mol/mol) of 0.64 +/- 0.10. Membrane vesicles were osmotically active when studied by a stopped-flow nephelometric technique. Arrhenius plots of rates of osmotic water efflux demonstrated break points at approximately 28 and 18 degrees C, with activation energies of 16.7 +/- 0.2 kcal mol-1 from 35 to 28 degrees C, 8.3 +/- 0.5 kcal mol-1 from 28 to 18 degrees C, and approximately 3.0 kcal mol-1 below 18 degrees C. Treatment of membrane vesicles with benzyl alcohol, a known fluidizer, decreased lipid order (increased fluidity) and increased the rate of osmotic water efflux. The present results suggest that water crosses tracheal epithelial cell apical membranes by solubility-diffusion across the lipid domain and that increases in fluidity correlate with increases in the water permeability of these membranes.

Animals↗
PubMed1986

Stoichiometry and ion affinities of the Na-K-Cl cotransport system in the intestine of the winter flounder (Pseudopleuronectes americanus).

Na-K-Cl cotransport stoichiometry and affinities for Na, K and Cl were determined in flounder intestine. Measurement of simultaneous NaCl and RbCl influxes resulted in ratios of 2.2 for Cl/Na and 1.8 for Cl/Rb. The effect of Na and Rb on Rb influx showed first order kinetics with K1/2 values of 5 and 4.5 mM and Hill coefficients of 0.9 and 1.2, respectively. The effect of Cl on rubidium influx showed a sigmoidal relationship with K1/2 of 20 mM and a Hill coefficient of 2.0. The effects of variations in Na and Cl concentration on short-circuit current (Isc) were also determined. The K1/2 for Na was 7 mM with a Hill coefficient of 0.9 and the K1/2 for Cl was 46 mM with a Hill coefficient of 1.9. Based on the simultaneous influx measurements, a cotransport stoichiometry of 1Na:1K:2Cl is concluded. The Hill coefficients for Cl suggest a high degree of cooperativity between Cl binding sites. Measurements of the ratio of net Na and Cl transepithelial fluxes under short-circuit conditions (using a low Na Ringer solution to minimize the passive Na flux) indicate that the Cl/Na flux ratio is approximately 2:1. Therefore, Na recycling from serosa to mucosa does not significantly contribute to the Isc. Addition of serosal ouabain (100 microM) inhibited Rb influx, indicating that Na-K-Cl cotransport is inhibited by ouabain. This finding suggests that a feedback mechanism exists between the Na-K-ATPase on the basolateral membrane and the apical Na-K-2Cl cotransporter.

Animals↗
PubMed1986

Changes in intracellular sodium with chloride secretion in dog tracheal epithelium.

Na-selective microelectrodes were employed to investigate the mechanism of Cl secretion by canine tracheal epithelium. In control tissues with a mean short-circuit current (Isc) of 30.1 microA/cm2, the intracellular Na activity (aiNa) was 10.7 mM. Following steady-state stimulation of Cl secretion with epinephrine (Isc = 126.4 microA/cm2), aiNa was 21.3 mM. These data indicate that there is sufficient energy in the Na gradient to drive Cl secretion by this tissue. When analyzed with simple kinetic models for the Na-K pump, they also suggest that the basolateral entry step involves the Na-K-2Cl cotransporter.

Animals↗
PubMed1986

Secretagogue-induced changes in membrane calcium permeability in chicken and chinchilla ileal mucosa. Selective inhibition by loperamide.

Substance P (SP), neurotensin (NT), bombesin (BB), serotonin (5HT), and carbamylcholine (CCH) transiently increase electrogenic anion secretion in chinchilla and chicken ileum. SP and CCH also transiently inhibit amiloride-sensitive Na/H exchange in isolated chicken enterocytes. Loperamide (LP) inhibits the short-circuit current responses caused by SP, NT, and BB, but not those caused by CCH, 5HT, Ca ionophore, or cyclic nucleotides. Similarly, LP inhibits the effects of SP, but not those of CCH, on Na/H exchange. LP inhibition of the SP effects was further studied in isolated chicken enterocytes. CCH and SP transiently increased cytosolic Ca activity by 20-50 nmol/liter, but only the response to SP was inhibited by LP (10(-5) M) and by the absence of extracellular Ca. We conclude SP and CCH effects on intestinal electrolyte transport are mediated by increasing enterocyte Ca activity and LP specifically inhibits peptide hormone-activated Ca entry by an opiate receptor-independent mechanism.

Amiloride↗
PubMed1986

Experimental diabetic diarrhea in rats. Intestinal mucosal denervation hypersensitivity and treatment with clonidine.

Diarrhea in streptozocin-induced chronically diabetic rats is caused by an impaired adrenergic regulation of intestinal fluid and electrolyte transport. Stimulation of alpha 2-adrenergic receptors on enterocytes normally promotes NaCl absorption and inhibits HCO3 secretion. The purpose of this study was to determine if adrenergic denervation of intestinal mucosa in chronically diabetic rats alters postsynaptic receptor response, and if the alpha 2-adrenergic agonist clonidine could correct observed fluid malabsorption. Mucosal norepinephrine stores, a measure of adrenergic tone, were markedly reduced in diabetic rats compared with nondiabetic littermates. In vitro, short-circuit current changes to exogenously added l-epinephrine were significantly greater in diabetics, suggesting that denervation hypersensitivity was due to increased numbers of postsynaptic alpha 2-adrenergic receptors. In vivo loop studies demonstrated net fluid secretion in the ileum and colon of diabetics. In diabetics, clonidine reversed the secretion to absorption, but it had no effect on fluid absorption in controls. We conclude that diabetic diarrhea in streptozocin-induced chronically diabetic rats is due to impaired adrenergic regulation of mucosal ion transport, accompanied by a postsynaptic denervation hypersensitivity that can be reversed by clonidine, and accompanied by net intestinal fluid secretion that can be effectively reversed with clonidine.

Adrenergic alpha-Agonists↗
PubMed1985

The production of small IgG aggregates by glutaraldehyde cross-linking.

Reaction conditions have been determined for the production of soluble IgG polymers in the size range 10 S to 30 S by covalent cross-linking with glutaraldehyde. This size range is comparable with that of the immune complexes which are frequently found in the circulation of patients with certain autoimmune diseases such as rheumatoid arthritis and systemic lupus erythematosus. The yield of IgG aggregates in this size range is far greater than has been reported for cross-linking by other bifunctional reagents or for aggregation by heating. Glutaraldehyde cross-linked IgG polymers are stable and biologically reactive. They can also be labelled with fluorescein and freeze-dried with minimal loss of integrity or reactivity.

Aldehydes↗
PubMed1985

Soluble IgG aggregates produced by heating remain stable on freeze-drying.

IgG aggregates produced by heating gamma globulin solutions were freeze-dried, kept at 4 degrees C and reconstituted up to 4 months later. By comparison with frozen (-20 degrees C) preparations, only minimal changes in biological reactivity and in physical integrity occurred during this period. These results demonstrate that freeze-dried preparations of heat-aggregated IgG are potentially useful as a reference reagent for the comparative evaluation and standardisation of immune complex assays.

Antigen-Antibody Complex↗
PubMed1985

Osmotic water permeability of small intestinal brush-border membranes.

A stopped-flow nephelometric technique was used to examine osmotic water flow across small intestinal brush-border membranes. Brush-border membrane vesicles (BBMV) were prepared from rat small intestine by calcium precipitation. Scattered 500 nm light intensity at 90 degrees to incident was a linear function of the number of vesicles in suspension, and of the reciprocal of the suspending medium osmolality. When BBMV were mixed with hyperosmotic mannitol solutions there was a rapid increase in the intensity of scattered light that could be fit to a single exponential function. The rate constant for vesicle shrinking varied with temperature and the size of the imposed osmotic gradient. At 25 degrees C and an initial osmotic gradient of 50 mOsm, the rate constant was 1.43 +/- 0.044 sec-1. An Arrhenius plot of the temperature dependence of vesicle shrinking showed a break at about 25 degrees C with an activation energy of 9.75 +/- 1.04 kcal/mole from 11 to 25 degrees C and 17.2 +/- 0.55 kcal/mole from 25 to 37 degrees C. The pore-forming antibiotic gramicidin increased the rate of osmotically driven water efflux and decreased the activation energy of the process to 4.51 +/- 0.25 kcal/mole. Gramicidin also increased the sodium permeability of these membranes as measured by the rate of vesicle reswelling in hyperosmotic NaSCN medium. Gramicidin had no effect on mannitol permeability. Assuming spherical vesicles of 0.1 micron radius, an osmotic permeability coefficient of 1.2 X 10(-3) cm/sec can be estimated for the native brush-border membranes at 25 degrees C.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1985

Cryolumpectomy for breast cancer: an experimental study.

The effects of cryosurgical procedures and surgical excision in preventing the local recurrence of mammary adenocarcinoma were studied in BALB/cfC3H mice carrying syngeneic, virus-induced mammary adenocarcinomas transplanted into the fourth mammary fat pad. In this report we present evidence demonstrating that cryosurgical procedures involving multiple freeze-thaw cycles followed by tumor excision markedly reduce the local recurrence rate of mouse mammary cancer. Surgical resection without cryotreatment resulted in an 80% local recurrence rate; in contrast, cryotreatment consisting of three freeze-thaw cycles before excision prevented local tumor recurrence in 70% of the animals. The use of cryotherapy and local excision (cryolumpectomy) in the treatment of human breast cancer is discussed.

Adenocarcinoma↗
PubMed1985

Alpha 2-adrenergic receptor-mediated regulation of intestinal calcium transport.

The role of alpha 2-adrenergic receptors in the regulation of intestinal Ca2+ transport was studied in vitro in rabbit proximal colon and distal ileum. Unidirectional mucosal-to-serosal and serosal-to-mucosal fluxes (Jm----s and Js----m) of 45Ca2+ were measured across isolated mucosal sheets bathed on both sides with identical Ringer solutions (1.25 mM Ca2+) and short-circuited. In the proximal colon, mucosal-to-epithelial influx (Jm----e) of Ca2+ was also determined. Proximal colonic mucosa secreted Ca2+ (in nmol X h-1 X cm-2, Jm----s = 12.1 and Js----m = 42.2). Epinephrine (10 microM) abolished Ca2+ secretion (Jm----s = 24.1 and Js----m = 24.9) but did not affect Jm----e (21.4 in controls and 23.6 after epinephrine). These effects were mediated by alpha 2-adrenergic receptors: yohimbine abolished the effect of epinephrine, but prazosin and propranolol did not; furthermore, clonidine mimicked the effects of epinephrine, whereas methoxamine and isoproterenol had no effect. Ileal mucosa did not transport Ca2+ spontaneously; epinephrine (10 microM) increased Jm----s in the ileum without affecting Js----m, thereby stimulating net Ca2+ absorption. The mechanism for these alpha 2-receptor-mediated effects was examined in proximal colon. The effect of epinephrine on Jm----s was dependent on serosal Na+ but was unaffected by ouabain or the Na+-Ca2+ exchange inhibitor, benzamil. The effect of epinephrine on Js----m was dependent on serosal Na+ and was blocked by both ouabain and benzamil. In the absence of epinephrine benzamil did not alter Jm----s or Js----m.(ABSTRACT TRUNCATED AT 250 WORDS)

Adrenergic alpha-Agonists↗