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Biomedical subjects

C Duffy

Publications and source records attributed to C Duffy.

At least 37 records · Page 2Linked to original sources
PubMed1996

Ex vivo measurement of brain tissue nitrite and nitrate accurately reflects nitric oxide synthase activity in vivo.

The ex vivo tissue concentration of nitrite and nitrate (NOx) was found to correlate closely with the activity of nitric oxide synthase (NOS; EC 1.14.13.39) in various brain regions. Systemic administration of the nonselective NOS inhibitor N omega-nitro-L-arginine (L-NA) at doses that completely inhibited both central and peripheral NOS, depleted whole-brain and CSF NOx by up to 75% but had no effect on plasma NOx. Selective inhibition of central NOS by intracerebroventricular administration of L-NA methyl ester produced similar decreases in levels of whole-brain NOx. A residual concentration of NOx of 10-15 microM remained in all brain regions even after complete inhibition of brain NOS. Brain NOx content decreased rapidly and in parallel with the inhibition of brain NOS. The ex vivo measurement of levels of brain NOx was found to reflect the in vivo efficacy of several different types of NOS inhibitor: L-NA, N omega-monomethyl-l-arginine, and 7-nitroindazole. Intraperitoneal administration of the NOS substrate L-arginine increased brain NOx concentrations by up to 150% of control values. These results demonstrate that the ex vivo measurement of levels of brain tissue NOx is a rapid, reliable, and straightforward technique to determine NOS activity in vivo. This method can be used to assess both the regional distribution and the degree of inhibition of NOS activity in vivo.

Animals↗
PubMed1996

Investigation of the role of inositol and the phosphatidylinositol signal transduction system in mouse embryonic stem cells.

The aims of this study were to investigate in mouse embryonic stem cells (1) the requirement for myo-inositol for cell proliferation, (2) the incorporation of inositol into the phosphoinositides and inositol phosphates of the phosphatidylinositol (PtdIns) signal transduction system and (3) the effect of serum growth factors on PtdIns turnover. Exogenous myo-inositol was not essential for embryonic stem cell proliferation. Lithium, an inhibitor of endogenous inositol recycling, inhibited embryonic stem cell proliferation but this effect was not reversible by the addition of high concentrations of exogenous inositol. [3H]inositol was incorporated into the phosphoinositides, PtdIns, PtdIns4P and PtdIns(4,5)P2 in similar proportions as reported for other cells. [3H]inositol was also incorporated into a fourth lipid, tentatively identified as an inositolglycan. [3H]inositol was also incorporated into a number of inositol phosphates, with the greatest amount of incorporation after 24 h into an inositol pentakisphosphate. After serum starvation for 24 h, the addition of 10% whole or dialysed serum for 2 or 20 min increased (P < 0.05) incorporation into inositol tris- and tetrakisphosphates. These results demonstrate the presence of PtdIns system components in embryonic stem cells and increased PtdIns turnover in response to serum growth factors.

Animals↗
PubMed1995

Determination of brain nitric oxide synthase inhibition in vivo: ex vivo assays of nitric oxide synthase can give incorrect results.

The in vivo potencies of N omega-nitro-L-arginine (L-NA), N omega-monomethyl-L-arginine (L-NMMA) and N omega-iminoethyl-L-ornithine (L-NIO) against brain nitric oxide synthase (NOS) were determined by assessing their ability to inhibit harmaline-induced increases in rat cerebellar cGMP. L-NA, L-NIO and L-NMMA were all able to completely prevent the harmaline-induced increase in cGMP with ID50s of 0.5, 30 and 55 mg/kg, respectively, and with the same order of potency as that seen for inhibition of cerebellar NOS in vitro. The inhibitory effects of low doses of L-NA on cerebellar cGMP were maintained for at least 8 hr. The ID50 of L-NA for inhibition of cerebellar cGMP in vivo was similar to its ID50 for inhibition of cerebellar NOS ex vivo but only when NOS activity was assayed as an initial rate. However, doses of L-NMMA and L-NIO that inhibited harmaline-induced increases in cerebellar cGMP in vivo by 50% failed to inhibit NOS ex vivo. The methyl ester of L-NA, L-NAME, produced substantial inhibition of cerebellar NOS ex vivo when given either orally, intraperitoneally or intravenously but with a slower onset of action than L-NA. These results demonstrate that measurement of NOS activity ex vivo can accurately reflect the degree of inhibition of NOS in vivo with inhibitors that dissociate slowly from the enzyme such as L-NA, but only when the initial rate of NOS activity is measured.

Amino Acid Oxidoreductases↗
PubMed1995

Substantial regional and hemispheric differences in brain nitric oxide synthase (NOS) inhibition following intracerebroventricular administration of N omega-nitro-L-arginine (L-NA) and its methyl ester (L-NAME).

Nitric oxide synthase (NOS) enzyme activity was determined in a comprehensive selection of regions of the rat brain. The effects of lateral ventricular administration of N omega-nitro-L-arginine (L-NA, 30 micrograms) and its methyl ester (L-NAME, 3-100 micrograms) on NOS activity were examined in the ipsilateral and contralateral areas of 4 of these brain regions and in the cerebellum. NOS activity was determined using a new and rapid ex vivo assay method which ensures minimal dissociation of the enzyme-inhibitor complex. Following infusion of L-NAME, NOS activity was rapidly and dose-dependently inhibited in all brain regions studied (cerebral cortex, striatum, hippocampus, cerebellum and thalamus). However, NOS activity of brain regions within the contralateral hemisphere was inhibited significantly less than in ipsilateral regions, with the exception of the thalamus. The degree of NOS inhibition varied markedly between brain regions within each hemisphere and correlated with their ventricular proximity to the site of NOS inhibitor administration. Therefore, NOS in the thalamus was inhibited most effectively and NOS in the cerebral cortex the least. Within the cerebral cortex further regional differences could be observed, with NOS in the frontal/parietal areas inhibited more effectively than NOS in the temporal/occipital areas. Maximal inhibition of NOS was sustained for approx 6 hr after administration of 30 and 100 micrograms L-NAME. No inhibition of NOS was observed 24 hr after administration. Lateral ventricular administration of the metabolite and active moiety of L-NAME, L-NA, resulted in a similar degree of inhibition and time of inhibitory onset. In contrast, when L-NAME was administered i.p., a significant delay in the onset of NOS inhibition was observed in the above brain regions compared to L-NA. However, no regional or hemispheric differences in NOS inhibition were detected following peripheral administration of these inhibitors. These results indicate that central administration of NOS inhibitors yields a complex pattern of NOS inhibition and that data obtained on brain physiology following the i.c.v. administration of NOS inhibitors, or for that matter any other CNS effector, should therefore be interpreted with extreme caution.

Animals↗
PubMed1994

Potent and selective inhibition of human nitric oxide synthases. Selective inhibition of neuronal nitric oxide synthase by S-methyl-L-thiocitrulline and S-ethyl-L-thiocitrulline.

Potent and selective inhibition of neuronal nitric oxide synthase (nNOS) compared to endothelial NOS (eNOS) and inducible NOS (iNOS) may be useful to treat cerebral ischemia (stroke) and other neurodegenerative diseases. S-Methyl-L-thiocitrulline (Me-TC) and S-ethyl-L-thiocitrulline (Et-TC) inhibited the oxidation of L-arginine and the L-arginine-independent oxidation of NADPH by nNOS from human brain. Me-TC and Et-TC were slow, tight binding inhibitors of nNOS with second-order association rate constants (kon) of 2.6 x 10(5) M-1 s-1 and 1.3 x 10(5) M-1 s-1, respectively. The respective dissociation rate constants (koff) were 3 x 10(-4) s-1 and 0.7 x 10(-4) s-1. Thus, the Kd values calculated from koff/kon were 1.2 and 0.5 nM, respectively. L-Arginine was a competitive inhibitor of Me-TC and Et-TC binding with competition constant (Ks) values of 2.2 and 2.7 microM, respectively. The Km of nNOS for L-arginine was 1.6 microM. The active site concentration of nNOS was estimated by titration with Et-TC. Based on this active site concentration, a kcat of 0.4 s-1 for the oxidation of L-arginine, was calculated. Me-TC and Et-TC were less potent inhibitors of human iNOS (Ki values of 34 and 17 nM, respectively) and human eNOS (Ki values of 11 and 24 nM). Thus, Me-TC and Et-TC were 10- and 50-fold, respectively, more potent inhibitors of nNOS than eNOS. Furthermore, Me-TC was also 17-fold selective for rat nNOS in neuronal tissue compared to rat eNOS in vascular endothelium, suggesting that Me-TC may be selective for nNOS in vivo and therefore, may be therapeutically useful to treat neurodegenerative diseases.

Amino Acid Oxidoreductases↗
PubMed1989

Asthma: a provincial study.

To identify factors contributing to increased mortality and morbidity we prospectively evaluated 200 consecutive adult (greater than 17 years) asthmatic presentations (105 patients) referred to Gisborne Hospital over a 28 month period between 1985 and 1987 using a modified protocol adapted from previous national studies. In the moderate asthmatic group (113 presentations, 56%), 6% failed to use beta agonists prior to admission and 43% were not on regular steroid inhaler therapy. No patient had a crisis plan although 45 (22.5%) had received oral steroid therapy before admission. Poor drug compliance was twice as common in the Maori. Fifty-eight percent of patients were on regular long term oral theophylline whereas 48 (43%) patients with moderate and severe asthma were not on corticosteroid inhalers. We conclude that patient education and more liberal use of steroid inhalers have the greatest potential for improving morbidity and mortality.

Administration, Inhalation↗
PubMed1988

Determinants of low serum concentrations of salicylates in patients with Kawasaki disease.

The mechanisms leading to the previously reported difficulties in achieving therapeutic serum concentrations of salicylates in Kawasaki disease were studied in eight children, once during the acute (febrile) phase and again during the nonfebrile (subacute) phase of the disease. Salicylate bioavailability was impaired during the acute phase of the disease (47.7% +/- 6.6%), and increased significantly thereafter to 75.1% +/- 9.3%. During the febrile phase there was a significant correlation between salicylate bioavailability and steady-state serum concentrations. Salicylate renal clearance was significantly higher during the febrile phase (14.45 +/- 2.5 mL/kg.h), compared with the nonfebrile phase (7 +/- 1.6 mL/kg.h, P less than 0.05). The change in salicylate clearance could be explained by decreased protein binding in the acute phase (82.5% +/- 1.9%) with substantially more free salicylates caused by significantly lower serum albumin concentrations. Changes in urine metabolites during the acute and subacute phases were consistent with the changes in dose administered (100 mg/kg in the acute phase vs 10 mg/kg in the subacute phase). The pattern of metabolites excreted in the urine of children with Kawasaki disease receiving 100 mg/kg was similar to that in children with juvenile rheumatoid arthritis receiving the same dose.

Arthritis, Juvenile↗
PubMed1987

Trichinella spiralis in an agricultural ecosystem. II. Evidence for natural transmission of Trichinella spiralis spiralis from domestic swine to wildlife.

Epidemiological investigations of an outbreak of trichinellosis were carried out in a domestic swine herd and it was established that the parasite also occurred in rats, and in skunks, opossums, and raccoons. Because considerable uncertainty exists regarding the role of sylvatic trichinellosis as a reservoir for the synanthropic cycle, studies were conducted to determine the genetic nature of the various isolates from this ecosystem. Pig infectivity trials, isoenzyme analyses, and repetitive DNA sequence analyses were performed. The results showed that all isolates from the farm environs were genetically similar and that they are related to Trichinella spiralis isolated from domestic pigs. The implication of these findings, in contrast to studies on isolates from wildlife elsewhere, is that this parasite is transmitted from domestic swine to sylvatic hosts and that any control or eradication efforts must take into account the potential for reinfection of hogs from wild animals.

Animals↗
PubMed1981

Long-term potentiation in the hippocampal slice: evidence for stimulated secretion of newly synthesized proteins.

Long-term potentiation of the hippocampal slice preparation results in an increase in the incorporation of labeled valine into the proteins destined for secretion into the extracellular medium. Double-labeling methods established that the increased secretion of the labeled proteins was limited to the potentiated region of a slice; incorporation of labeled valine was increased in the hippocampus if potentiation was through the Schaffer collaterals and in the dentate if potentiation was through the perforant path. Controls for nonspecific stimulation showed no changes. There appears to be a link between long-term potentiation and the metabolic processes that lead to protein synthesis in the hippocampal slice system.

Animals↗
PubMed1980

The pH and titratable acidity of stored CPD blood.

Blood stored in citrate-phosphate-dextrose (CPD) solution for periods up to 20 days had a mean pH 6.71. The mean metabolic hydrogen ion excess was 32 mmol/litre and the mean respiratory hydrogen ion excess was 80 mmol/litre. These results for CPD blood are compared with those obtained on acid-citrate-dextrose blood. A prediction is made that clnically, only small variations in metabolic and respiratory acid-base balance would be produced directly due to the acid and base loads in transfused blood.

Acid-Base Equilibrium↗