PubMed Health⌕ Search

Biomedical subjects

M G Currie

Publications and source records attributed to M G Currie.

At least 55 records · Page 3Linked to original sources
PubMed1995

Potentiation of nitric oxide-mediated vascular relaxation by SC52608, a superoxide dismutase mimic.

Nitric oxide (NO) produced by the vascular endothelium is an endogenous contributor to the regulation of vascular relaxation and the maintenance of blood pressure. The effective half-life of NO and the relaxation of aortic rings by NO is enhanced by a reduction in the concentration of superoxide radicals with superoxide dismutase (SOD). In the current study, SC52608, a newly synthesized SOD mimic with a manganese core, was tested for its ability to potentiate the activity of NO both in vitro and in vivo. SC52608 relaxation of rat aortic segments was endothelium dependent as well as concentration dependent. The maximum relaxation following KCl contraction was 44% with 300 microM SC52608. Cyclic GMP concentrations in the segments were increased 1.6- and 3.2-fold with 5 and 300 microM SC52608, respectively. N-monomethyl-I-arginine pretreatment of aortic rings abolished the relaxation and cyclic GMP accumulation mediated by SC52608. In a smooth muscle cell reporter system of nitric oxide synthase activity, SC52608 potentiated the increase in cyclic GMP elicited by NO in a concentration-dependent manner with a maximum increase of 5.2-fold at 100 microM. Injection of SC52608 into conscious, restrained rats resulted in a dose-dependent decrease of blood pressure. Therefore, the data suggest that SC52608 potentiates the actions of nitric oxide on vascular tone, cyclic GMP, and blood pressure by enhancing the half-life of NO through a mechanism that mimics the action of SOD.

Animals↗
PubMed1994

L-N6-(1-iminoethyl)lysine: a selective inhibitor of inducible nitric oxide synthase.

L-N6-(1-Iminoethyl)lysine (L-NIL) has been synthesized and is shown to be both a potent and selective inhibitor of mouse inducible nitric oxide synthase (miNOS). L-NIL has an IC50 of 3.3 microM for miNOS compared to an IC50 of 92 microM for rat brain constitutive NOS indicating that L-NIL is 28-fold more selective for inducible NOS. L-N5-(1-Iminoethyl)ornithine (L-NIO), which differs from L-NIL by having one less methylene group, has very similar potency for inducible NOS, but lacks selectivity. DL-N7-(1-Iminoethyl)homolysine was also synthesized and found to be substantially less potent than L-NIL or L-NIO, with intermediate selectivity for inducible NOS. These data suggest that L-NIL may be useful as a selective inhibitor of inducible NOS for determining the role of this enzyme in disease models.

Amino Acid Oxidoreductases↗
PubMed1994

Potentiation of osteoclast bone-resorption activity by inhibition of nitric oxide synthase.

We have examined the effects of modulating nitric oxide (NO) levels on osteoclast-mediated bone resorption in vitro and the effects of nitric oxide synthase (NOS) inhibitors on bone mineral density in vivo. Diaphorase-based histochemical staining for NOS activity of bone sections or highly enriched osteoclast cultures suggested that osteoclasts exhibit substantial NOS activity that may account for basal NO production. Chicken osteoclasts were cultured for 36 hr on bovine bone slices in the presence or absence of the NO-generating agent sodium nitroprusside or the NOS inhibitors N-nitro-L-arginine methyl ester and aminoguanidine. Nitroprusside markedly decreased the number of bone pits and the average pit area in comparison with control cultures. On the other hand, NOS inhibition by N-nitro-L-arginine methyl ester or aminoguanidine dramatically increased the number of bone pits and the average resorption area per pit. In a model of osteoporosis, aminoguanidine potentiated the loss of bone mineral density in ovariectomized rats. Aminoguanidine also caused a loss of bone mineral density in the sham-operated rats. Inhibition of NOS activity in vitro and in vivo resulted in an apparent potentiation of osteoclast activity. These findings suggest that endogenous NO production in osteoclast cultures may regulate resorption activity. The modulation of NOS and NO levels by cells within the bone microenvironment may be a sensitive mechanism for local control of osteoclast bone resorption.

Amino Acid Oxidoreductases↗
PubMed1994

Manganese potentiation of nitric oxide-mediated vascular relaxation.

The half-life of nitric oxide (NO) and the relaxation of aortic-rings are enhanced by superoxide dismutase. Manganese and manganese-containing preparations have been reported to mimic superoxide dismutase activity. In the current study, manganese was tested for its ability to potentiate the activity of NO both in vitro and in vivo. Manganese relaxation of aortic segments was endothelium dependent as well as concentration dependent. Cyclic GMP concentrations in the segments were increased 2- and 4-fold with 5 and 300 microM manganese, respectively. N-Monomethyl-L-arginine pretreatment of aortic rings abolished the relaxation and cyclic GMP accumulation mediated by manganese. Infusion of manganese into conscious, restrained rats resulted in a decrease of blood pressure which was abolished by N-nitro-L-arginine pretreatment. Therefore, manganese may prolong the half-life of NO by a mechanism that mimics the action of superoxide dismutase resulting in potentiation of NO actions in vascular tissue.

Amino Acid Oxidoreductases↗
PubMed1994

Correlation between vascular and cellular responses to atrial natriuretic peptide and to sodium nitroprusside.

Atrial natriuretic peptide (ANP) and sodium nitroprusside (SNP) increase cGMP in vascular smooth muscle cells and act as vasodilators in some, but not all, blood vessels. In this present study, we attempted to correlate the ability of these two agents to dilate blood vessels with the ability to increase cGMP in cultured vascular smooth muscle cells. In the isolated guinea pig heart, SNP dose-dependently increased coronary flow while ANP was ineffective. In smooth muscle cells cultured from the coronary system, SNP increased intracellular cGMP in a dose-dependent manner while ANP had no effect on cGMP in these cells. In isolated guinea-pig thoracic aorta, precontracted with K+, both ANP and SNP produced relaxation and ANP was the more potent. In smooth muscle cells cultured from the aorta, ANP and SNP increased cGMP and the potency relationship was similar to the intact vessel. These results support the view that phenotypic properties of vascular smooth muscle cells can account for differences in the response of blood vessels to vasodilators.

Analysis of Variance↗
PubMed1994

Nitric oxide participates in the regulation of pancreatic acinar cell secretion.

The role of nitric oxide (NO) in the regulation of exocrine secretion was investigated in isolated rat pancreatic acini. NO synthase activity was detected in the extract of acini and purified by ion-exchange and 2',5'-ADP agarose chromatographies. Enzyme activity was determined by conversion of 3H-arginine to 3H-citrulline, by measurement of nitrite (a breakdown product of NO) and by generation of cyclic GMP. Treatment of acini with L-arginine increased nitrite as well as cyclic GMP and amylase release, which were prevented by the nitric oxide synthase inhibitors N-monomethyl-arginine [NMMA] and NG-nitro-L-arginine [NNA]. These nitric oxide inhibitors also blocked carbachol-induced amylase release as well as elevation of acinar cell cyclic GMP. NNA was a potent inhibitor of carbamylcholine-induced amylase release (est. Ki = 2.2 uM). Nitric oxide apparently participates significantly in the overall control of pancreatic acinar cell secretory function.

Amino Acid Oxidoreductases↗
PubMed1994

Endogenous nitric oxide enhances prostaglandin production in a model of renal inflammation.

The interaction between nitric oxide (NO) and cyclooxygenase (COX) was studied in a rabbit model of renal inflammation, the ureteral obstructed hydronephrotic kidney (HNK). Ex vivo perfusion of the HNK but not the control kidney (e.g., unobstructed contralateral kidney, CLK), led to a time-dependent release of nitrite (NO2-), a breakdown product of NO. Stimulation of the HNK with bradykinin (BK) evoked a time-dependent increase in prostaglandin E2 (PGE2) production. NG-monomethyl-L-arginine (L-NMMA), which blocks the activity of both constitutive and inducible nitric oxide synthase (cNOS and iNOS), aminoguanidine, a recently described selective iNOS inhibitor, dexamethasone, or cycloheximide abolished the release of NO2- and attenuated the exaggerated BK-induced PGE2 production. This supports the existence of iNOS and COX-2 in the HNK. In the CLK, BK elicited release of both NO2- and PGE2 but this did not augment with time. L-NMMA but not aminoguanidine, dexamethasone, or cycloheximide attenuated NO2- and PGE2 release indicative of the presence of constitutive but not inducible NOS or COX. The current study suggests that the endogenous release of NO from cNOS in the CLK activates a constitutive COX resulting in optimal PGE2 release by BK. In addition, in the HNK, NO release from iNOS activates the induced COX resulting in markedly increased release of proinflammatory prostaglandin. The broader implication of this study is that the cyclooxygenase isozymes are potential receptor targets for nitric oxide.

Amino Acid Oxidoreductases↗
PubMed1994

Endotoxin-induced uveitis in the rat is attenuated by inhibition of nitric oxide production.

PURPOSE: These experiments were undertaken to assess the role of increased nitric oxide production in the pathogenesis of vascular dysfunction associated with endotoxin-induced uveitis. METHODS: Lipopolysaccharides (LPS) (100 micrograms of Salmonella minnesota) was injected into foot-pads of Lewis rats randomly assigned to an untreated group or to a group treated with subcutaneous injections of aminoguanidine, a selective inhibitor of the inducible isoform of nitric oxide synthase (iNOS). Controls included untreated and aminoguanidine-treated rats. Twenty to 24 hours later, blood flow and vascular 125I-albumin permeation were quantified in ocular tissues. Eyes were graded histologically for leukocyte infiltration into the anterior uvea and anterior chamber, and leukocyte counts were performed on aqueous fluid. Plasma nitrate levels were measured fluorometrically after enzymatic reduction to nitrite. RESULTS: Lipopolysaccharides markedly increased plasma nitrate levels and 125I-albumin permeation in aqueous fluid, retina, anterior uvea, and choroid-sclera. Blood flow was increased only in the anterior uvea. Aminoguanidine normalized plasma nitrate levels and prevented or significantly ameliorated the 125I-albumin permeation and blood flow changes in ocular tissues. The increased aqueous fluid content of lymphocytes and neutrophils in LPS-treated rats, as well as the increased histologic score of iritis, were significantly reduced by aminoguanidine. CONCLUSIONS: These results suggest that the hemodynamic and vascular permeability changes associated with endotoxin-induced uveitis are mediated in large part by increased production of nitric oxide.

Albumins↗
PubMed1994

Distribution of heat-stable enterotoxin/guanylin receptors in the intestinal tract of man and other mammals.

The human intestinal tract, as well as that of several eutherian and metatherian mammals, was examined for the distribution of heat-stable enterotoxin (ST)/guanylin receptors. These receptors were confined to the intestinal epithelium lining the lumen and forming the intestinal glands throughout the length of both the small intestine and colon of all species examined. In man and most other mammalian species, there appeared to be a decrease in receptor density distally along the longitudinal axis of the small intestine. ST/guanylin receptors were not observed in other strata forming the gut wall. Along the vertical axis of the human small intestine (villus/crypt unit), as well as that of most other mammals, receptor density was greatest in enterocytes located near the base of villi and in those forming the proximal portion of the intestinal glands. ST/guanylin receptors were for the most part confined to the region of the plasmalemma forming the microvillus border. In the colon of man and the other species examined, receptor density was greatest in enterocytes forming the proximal region of the intestinal glands. Receptors were present in the intestinal epithelium lining the lumen of the colon, but generally were fewer in number. The distribution of cellular cGMP accumulation responses to E. coli ST and guanylin in the opossum (Didelphis virginiana) and raccoon (Procyon lotor) revealed that proximal small intestine had greater magnitudes of cGMP responses than did the distal small intestine. Proximal colon had greater cGMP responses than distal colon, which had no significant cGMP responses to either ST or guanylin.

Animals↗
PubMed1993

Guanylin mRNA is expressed in villous enterocytes of the rat small intestine and superficial epithelia of the rat colon.

Guanylin, and endogenous ligand for the Escherichia coli heat-stable enterotoxin receptor, is a recently characterized intestinal peptide. To understand the possible physiologic function of guanylin, we examined the cellular location of guanylin mRNA expression in the rat intestine. Intestinal cells were sequentially isolated from villous tip to crypt in rat jejunum and ileum. Northern blots of total RNA identified a single 0.65 kb guanylin transcript predominantly in the villous cell fractions. In situ hybridization studies demonstrated maximal signal intensity in villous cells in rat ileum and surface epithelial cells in the colon. In the ileum, the signal was nonuniform in distribution in the surface epithelial cells, with focal areas of intense signal in clusters of columnar absorptive cells. In both colon and ileum, signal intensity was near background level in deep crypt cells, lamina propria, and muscularis.

Animals↗
PubMed1993

Nitric oxide activates cyclooxygenase enzymes.

We have evaluated the role of nitric oxide (NO) on the activity of the constitutive and induced forms of cyclooxygenase (COX; COX-1 and COX-2, respectively). Induction of NO synthase (NOS) and COX (COX-2) in the mouse macrophage cell line RAW264.7 by Escherichia coli lipopolysaccharide (1 microgram/ml, 18 h) caused an increase in the release of nitrite (NO2-) and prostaglandin E2 (PGE2), products of NOS and COX, respectively. Production of both NO2- and PGE2 was blocked by the NOS inhibitors NG-monomethyl-L-arginine or aminoguanidine. The effects of NG-monomethyl-L-arginine or aminoguanidine were reversed by coincubation with L-Arg, the precursor for NO synthesis, but not by D-Arg. RAW264.7 cells stimulated for 18 h with lipopolysaccharide in L-Arg-free medium (to reduce NO generation by the endogenous NOS pathway) failed to release NO2- and accumulated at least 4-fold less PGE2 when compared to cells in the presence of L-Arg. PGE2 production elicited by a 15-min arachidonic acid treatment of lipopolysaccharide-induced RAW264.7 cells in L-Arg-deficient medium was decreased 3-fold when compared to the release obtained with cells induced in medium containing L-Arg. To examine the NO activation of the induced form of COX in the absence of an endogenous L-Arg, human fetal fibroblasts were first stimulated for 18 h with interleukin 1 beta. These cells released PGE2 but not NO2-, consistent with the induction of COX but not NOS in the fibroblast. Exogenous NO either as a gaseous solution or released by a NO donor, sodium nitroprusside or glyceryl trinitrate, increased COX activity in the interleukin 1 beta-stimulated fibroblasts by 5-fold; these effects were abolished by coincubation with hemoglobin (10 microM), which binds and inactivates NO, but not by methylene blue, an inhibitor of the soluble guanylate cyclase. Furthermore, sodium nitroprusside (0.25-1 mM) increased arachidonic acid-stimulated PGE2 production by murine recombinant COX-1 and COX-2. These results demonstrate that NO enhances COX activity through a mechanism independent of cGMP and suggest that, in conditions in which both the NOS and COX systems are present, there is an NO-mediated increase in the production of proinflammatory prostaglandins that may result in an exacerbated inflammatory response. The data suggest that NO directly interacts with COX to cause an increase in the enzymatic activity.

Amino Acid Oxidoreductases↗
PubMed1993

Selective inhibition of the inducible nitric oxide synthase by aminoguanidine.

Overproduction of the free radical nitric oxide (NO) has been implicated in the pathogenesis of a variety of inflammatory and immunologically mediated diseases as well as complications of diabetes. In the present study we have demonstrated that aminoguanidine selectively inhibits the cytokine-inducible isoform of NO synthase which appears to be responsible for the excess production of NO linked to these disease states. By using organ, cell, and enzyme-based measurements we have shown that aminoguanidine is equipotent to NG-monomethyl-L-arginine (L-NMA) as an inhibitor of the cytokine-induced isoform of NO synthase but is 10 to 100-fold less potent as an inhibitor of the constitutive isoform. Thus, aminoguanidine may be useful as a selective inhibitor of the inducible NO synthase in the treatment of disease states characterized by the pathological overproduction of NO.

Amino Acid Oxidoreductases↗
PubMed1993

Induction of nitric oxide synthase regulates atrial natriuretic peptide receptors in vascular smooth muscle cells.

In a previous study, we reported that cyclic GMP (cGMP) selectively down-regulates the atrial natriuretic peptide clearance receptor (ANPC receptor) in the vascular endothelial cells. The aim of the present study is to determine whether nitric oxide (NO) regulates ANP receptor by accumulating intracellular cGMP in cultured rabbit aortic smooth muscle cells. Treatment with interleukin-1 beta (IL-1), a cytokine known to induce NO synthase, dose-dependently increased the basal level of intracellular cGMP with a concomitant increase of nitrite in the conditioned media. These effects of IL-1 were attenuated in the presence of N omega-nitro-L-arginine. IL-1 (40 pM) significantly (P < 0.01) decreased [125I]atriopeptin III binding to the cells, an effect that was inhibited by N omega-nitro-L-arginine. Treatment with sodium nitroprusside (SNP) which releases NO also decreased [125I]atriopeptin III binding to the cells. In addition, further decrease in [125I]atriopeptin III binding following IL-1 or SNP treatment was observed in the presence of 0.1 mM zaprinast, a cGMP-specific phosphodiesterase inhibitor. Scatchard analysis of the binding data in the treated cells showed a decrease in Bmax without a significant change in Kd. Affinity cross-linking of [125I]atriopeptin III to the treated cells demonstrated a decrease in 70-kDa band corresponding to the ANPC receptor. MEanwhile, intracellular cGMP response to atriopeptin III was significantly (P < 0.01) enhanced in the cells pretreated with IL-1 or SNP despite the decrease in receptor density. These findings suggest that NO down-regulates the ANPC receptor by the accumulation of intracellular cGMP in cultured rabbit aortic smooth muscle cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Oxidoreductases↗
PubMed1993

A fluorometric assay for the measurement of nitrite in biological samples.

The increasing importance of nitric oxide synthase has been underscored by the elucidation of its role in a growing number of normal and pathophysiological processes. Therefore, techniques for detection of nitrite/nitrate, oxidation products of the enzymatic conversion of arginine to citrulline and nitric oxide, should serve as useful tools in defining the contribution of NO synthase to these processes. We have developed a rapid and sensitive fluorometric assay for quantification of nitrite/nitrate based upon the reaction of nitrite with 2,3-diaminonaphthalene to form the fluorescent product, 1-(H)-naphthotriazole. The assay can be used to detect 10 nM nitrite, making it 50-100 times more sensitive than the well-known Griess assay. Moreover, the assay is adaptable to a 96-well plate format, facilitating the handling of a large number of samples including conditioned media from cell culture or the nitrite generated by the purified enzyme. Nitrite/nitrate levels in blood can also be monitored using this assay when it is combined with a filtration step (to remove hemoglobin) followed by conversion of the nitrate to nitrite by nitrate reductase. Thus, this fluorometric method combines speed and sensitivity with the handling of a large number of samples for the quantification of nitrite generated from in vivo and in vitro sources.

2-Naphthylamine↗
PubMed1993

Guanylin stimulation of Cl- secretion in human intestinal T84 cells via cyclic guanosine monophosphate.

Intestinal salt and fluid secretion is stimulated by Escherichia coli heat-stable enterotoxins (ST) through activation of a membrane guanylate cyclase found in the intestine. Guanylin is an endogenous intestinal peptide that has structural similarity to the bacterial peptides. Synthetic preparations of guanylin or E. coli ST 5-17 stimulated Cl- secretion in T84 cells cultured on semipermeable membranes as measured by increases in short circuit current (Isc). The guanylin/ST receptors appeared to be on the apical surface of T84 cells, since addition of guanylin to the apical, but not basolateral, reservoir stimulated Isc. Bumetanide added to the basolateral side effectively inhibited the Isc responses of T84 cells to either guanylin or ST 5-17. Guanylin appeared to be about one-tenth as potent as ST in stimulating transepithelial Cl- secretion. Guanylin and E. coli ST 5-17 both caused massive (> 1,000-fold) increases in cGMP levels in T84 cells, but guanylin was less potent than ST. Both peptides fully inhibited the binding of 125I-ST to receptor sites on intact T84 cells. The radioligand binding data obtained with guanylin or ST 5-17 best fit a model predicting two receptors with different affinity for these ligands. The Ki values for guanylin were 19 +/- 5 nM and 1.3 +/- 0.5 microM, whereas the Ki values for ST 5-17 were 78 +/- 38 pM and 4.9 +/- 1.4 nM. We conclude that guanylin stimulated Cl- secretion via the second messenger, cGMP, in T84 human colon cells. At least two guanylin receptors with different affinities for these ligands may exist in the cultured T84 cells. It may be postulated that guanylin is an endogenous hormone that controls intestinal Cl- secretion by a paracrine mechanism via cGMP and that E. coli ST stimulates Cl- secretion by virtue of an opportunistic mechanism through activation of guanylin receptors.

Bacterial Toxins↗
PubMed1993

Prevention of diabetic vascular dysfunction by guanidines. Inhibition of nitric oxide synthase versus advanced glycation end-product formation.

This study was undertaken to compare the ability of two guanidine compounds (aminoguanidine and methylguanidine), with different in vitro effects on NO synthase activity and AGE formation, to inhibit diabetic vascular dysfunction developing early after the onset of diabetes. In rats with STZ-induced diabetes of 5-wk duration, regional vascular [125I]albumin permeation was increased about two- to threefold in ocular tissues, sciatic nerve, and aorta; in general, both guanidine compounds normalized albumin permeation in diabetic rats without affecting it in controls. Methylguanidine was only approximately 7% as effective as aminoguanidine as an inhibitor of AGE formation from L-lysine and G6P; both compounds were poor inhibitors of AR. Methylguanidine was approximately 1-5% as potent as aminoguanidine and L-NMMA as an inhibitor of the cytokine- and endotoxin-inducible isoform of NO synthase. In contrast, the potency of methylguanidine as an inhibitor of the constitutive isoform of NO synthase was comparable to that of aminoguanidine, and both guanidine compounds were much less effective than L-NMMA. These observations suggest a role for a relative or absolute increase in NO production in the pathogenesis of early diabetic vascular dysfunction and raise the possibility that inhibition of diabetic vascular functional changes by aminoguanidine may reflect inhibition of NO synthase activity rather than, or in addition to, prevention of AGE formation.

Aldehyde Reductase↗