PubMed Health⌕ Search

Biomedical subjects

K R Elliott

Publications and source records attributed to K R Elliott.

At least 19 recordsLinked to original sources
PubMed2001

Effect of lipopolysaccharide and cytokines on oxidative metabolism in neonatal rat hepatocytes.

BACKGROUND/PURPOSE: Lipopolysaccharide (LPS) and cytokines produced during neonatal sepsis trigger free radical production, which eventually results in inhibition of liver metabolism. Studies in adults have indicated a hypermetabolic response to sepsis; however, evidence for a hypermetabolic response in neonates is equivocal. This study was carried out to determine whether LPS and cytokines can cause liver hypermetabolism in neonates. METHODS: The initial bacterial insult and cytokine cascade were mimicked by the addition of lipopolysaccharide (Escherichia coli 055:B5), tumour necrosis factor (TNF-alpha), and interleukin-6 (IL6) during the isolation of hepatocytes by collagenase digestion from 11- to 13-day-old Wistar rats. Hepatocyte oxygen consumption was measured polarographically with cells respiring on palmitate (0.5 mmol/L). Myxothiazol, a specific inhibitor of mitochondrial respiration, was used to distinguish extra- and intramitochondrial oxygen consumption. Morphologic changes were assessed by electron microscopy. RESULTS: The addition of LPS, TNF-alpha and IL6 during hepatocyte isolation resulted in a 10% decrease in cell yield (P <.05) compared with untreated controls; however, cell viability was unchanged (n = 31). Both total and extramitochondrial oxygen consumption were significantly greater in treated cells compared with untreated controls (P <.05, Student's t test). Electron microscopy indicated that LPS, TNF-alpha, and IL6 did not cause ultrastructural changes to hepatocytes. CONCLUSIONS: The increase in oxygen consumption was predominantly extramitochondrial and likely to be caused by increased oxygen requirement for cytosolic detoxification and repair purposes. This study shows that liver hypermetabolism metabolism can occur in response to LPS and cytokines. However, during in vivo neonatal sepsis, additional free radical damage may blunt this hypermetabolic response.

Animals↗
PubMed1999

New imidazo(1,2-a)pyrazine derivatives with bronchodilatory and cyclic nucleotide phosphodiesterase inhibitory activities.

New imidazo[1,2-a]pyrazine derivatives have been synthesized either by direct cyclization from pyrazines or by electrophilic substitutions. The presence of electron donating groups on position 8 greatly enhances the reactivity of the heterocycle towards such reactions on position 3 of the heterocycle. The activities of these derivatives in trachealis muscle relaxation and in inhibiting cyclic nucleotide phosphodiesterase (PDE) isoenzyme types III and IV have been assessed. All compounds demonstrated significantly higher relaxant potency than theophylline. All the derivatives were moderately potent in inhibiting the type IV isoenzyme of PDE but only those with a cyano group on position 2 were potent in inhibiting the type III isoenzyme.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1999

Comparisons of flux control exerted by mitochondrial outer-membrane carnitine palmitoyltransferase over ketogenesis in hepatocytes and mitochondria isolated from suckling or adult rats.

The primary aim of this paper was to calculate and report flux control coefficients for mitochondrial outer-membrane carnitine palmitoyltransferase (CPT I) over hepatic ketogenesis because its role in controlling this pathway during the neonatal period is of academic importance and immediate clinical relevance. Using hepatocytes isolated from suckling rats as our model system, we measured CPT I activity and carbon flux from palmitate to ketone bodies and to CO2 in the absence and presence of a range of concentrations of etomoxir. (This is converted in situ to etomoxir-CoA which is a specific inhibitor of the enzyme.) From these data we calculated the individual flux control coefficients for CPT I over ketogenesis, CO2 production and total carbon flux (0.51 +/- 0.03; -1.30 +/- 0.26; 0.55 +/- 0.07, respectively) and compared them with equivalent coefficients calculated by similar analyses [Drynan, L., Quant, P.A. & Zammit, V.A. (1996) Biochem. J. 317, 791-795] in hepatocytes isolated from adult rats (0.85 +/- 0.20; 0.23 +/- 0.06; 1.06 +/- 0.29). CPT I exerts significantly less control over ketogenesis in hepatocytes isolated from suckling rats than those from adult rats. In the suckling systems the flux control coefficients for CPT I over ketogenesis specifically and over total carbon flux (< 0.6) are not consistent with the enzyme being rate-limiting. Broadly similar results were obtained and conclusions drawn by reanalysis of previous data {from experiments in mitochondria isolated from suckling or adult rats [Krauss, S., Lascelles, C.V., Zammit, V.A. & Quant, P.A. (1996) Biochem. J. 319, 427-433]} using a different approach of control analysis, although it is not strictly valid to compare flux control coefficients from different systems. Our overall conclusion is that flux control coefficients for CPT I over oxidative fluxes from palmitate (or palmitoyl-CoA) differ markedly according to (a) the metabolic state, (b) the stage of development, (c) the specific pathway studied and (d) the model system.

Animals↗
PubMed1997

Effects of SCA40 on bovine trachealis muscle and on cyclic nucleotide phosphodiesterases.

While UK-93,928 (1-[[3-(6,9-dihydro-6-oxo-9-propyl-1H-purin-2-yl)-4-ethoxyphenyl] sulfonyl]-4-methylpiperazine; 5 nM-5 microM) was devoid of relaxant activity, benzafentrine, isoprenaline, levcromakalim and SCA40 (6-bromo-8-methylaminoimidazo[1,2-a]pyrazine-2-carbonitrile) each relaxed histamine (460 microM)-precontracted bovine isolated trachealis. Each of these relaxants was antagonised by a K+-rich (80 mM) medium. Except in the case of levcromakalim, nifedipine (1 microM) offset this antagonism. Charybdotoxin (100 nM) antagonised isoprenaline in a nifedipine-sensitive manner but did not antagonise SCA40 or benzafentrine. Iberiotoxin (100 nM) did not antagonise SCA40. Acting on tissue precontracted with carbachol, SCA40 potentiated isoprenaline but did not potentiate sodium nitroprusside. While levcromakalim (1 and 10 microM) induced hyperpolarisation, SCA40 (1 and 10 microM) induced little change in the membrane potential of bovine trachealis. In trachealis preloaded with 86Rb+, levcromakalim (1 and 10 microM) promoted efflux of the radiotracer while SCA40 (1 and 10 microM) had no effect. Tested as an inhibitor of isoenzymes of cyclic nucleotide phosphodiesterase, SCA40 was most potent against the type III, less potent against the type IV and least potent against the type I isoenzyme. It is concluded that neither inhibition of phosphodiesterase type V nor the promotion of BKCa channel opening explains the tracheal smooth muscle relaxant activity of SCA40. This compound relaxes bovine tracheal smooth muscle mainly by inhibiting phosphodiesterase isoenzyme types III and IV.

Animals↗
PubMed1997

The role of a cAMP-dependent pathway in the uterine relaxant action of relaxin in rats.

The aim of this study was to investigate the role of the adenylyl cyclase pathway, and in particular cyclic AMP-dependent protein kinase A, in the relaxant action of relaxin in the isolated uterus of the nonpregnant rat. The purportedly selective inhibitor of cAMP-dependent protein kinase A N-[2-(methylamino) ethyl]-5-isoquinolinesulfonamide hydrochloride (H-8) (at 100 mumol l-7) antagonized relaxin, salbutamol (an agonist at beta-adrenoceptors) and levcromakalim (a K+ channel opener) to a similar extent (by factors of 3.1, 1.9 and 2.8, respectively), demonstrating that it is not a selective inhibitor. Relaxin and levcromakalim were less potent and had smaller, maximal, relaxant effects in longitudinal myometrium than in intact uterus cut in the longitudinal plane. By contrast, nifedipine (a Ca2+ channel blocker) was equipotent in the two preparations and salbutamol only slightly less potent in the longitudinal myometrium. Relaxin did not alter the cyclic AMP-dependent protein kinase A activity ratio in longitudinal myometrium, but did increase the activity ratio by a factor of 2.0 +/- 0.2 in the intact uterus. Salbutamol, the positive control, increased this activity ratio in both longitudinal myometrium (by 1.9 +/- 0.3 times) and in the intact uterus (by 3.8 +/- 0.3 times), whereas the negative control levcromakalim had no effect. Relaxin seems to act as a relaxant of longitudinal myometrium by a cyclic AMP-independent mechanism but possibly interacts with the circular myometrium or endometrium to release a relaxant factor via a cyclic-AMP-dependent mechanism.

Adrenergic beta-Agonists↗
PubMed1995

Further analysis of the mechanisms underlying the tracheal relaxant action of SCA40.

1. SCA40 (1nM-10 microM), isoprenaline (1-300 nM) and levcromakalim (100 nM-10 microM) each produced concentration-dependent suppression of the spontaneous tone of guinea-pig isolated trachea. Propranolol (1 microM) markedly (approximately 150 fold) antagonized isoprenaline but did not antagonize SCA40. The tracheal relaxant action of SCA40 was unaffected by suramin (100 microM) or 8-(p)-sulphophenyltheophylline (8-SPT; 140 microM). 2. An isosmolar, K(+)-rich (80 mM) Krebs solution increased tracheal tone, antagonized SCA40 (approximately 60 fold), antagonized isoprenaline (approximately 20 fold) and very profoundly depressed the log concentration-effect curve for levcromakalim. Nifedipine (1 microM) did not itself modify the relaxant actions of SCA40, isoprenaline or levcromakalim. However, nifedipine prevented the rise in tissue tone and the antagonism of SCA40 and isoprenaline induced by the K(+)-rich medium. In contrast, nifedipine did not prevent the equivalent antagonism of levcromakalim. 3. Charybdotoxin (100 nM) increased tracheal tone, antagonized SCA40 (approximately 4 fold) and antagonized isoprenaline (approximately 3 fold). Nifedipine (1 microM) prevented the rise in tissue tone and the antagonism of SCA40 and isoprenaline induced by charybdotoxin. 4. Quinine (30 microM) caused little or no change in tissue tone and did not modify the relaxant action of isoprenaline. However, quinine antagonized SCA40 (approximately 2 fold). Nifedipine (1 microM) prevented the antagonism of SCA40 induced by quinine. 5. Tested on spontaneously-beating guinea-pig isolated atria SCA40 (1 nM-10 microM) increased the rate of beating in a concentration-dependent manner. Over the concentration-range 1 microM-10 microM, SCA40 also caused an increase in the force of atrial contraction. 6. Intracellular electrophysiological recording from guinea-pig isolated trachealis showed that the relaxant effects of SCA40 (1 micro M) were often accompanied by the suppression of spontaneous electrical slow waves but no change in resting membrane potential. When the concentration of SCA40 was raised to 10 micro M, its relaxant activity was accompanied both by slow wave suppression and by plasmalemmal hyperpolarization.7. SCA40 (10 nM- 100 micro M) more potently inhibited the activity of cyclic AMP phosphodiesterase (PDE)than that of cyclic GMP PDE derived from homogenates of guinea-pig trachealis. Theophylline(1 micro M- 1O mM) also inhibited these enzymes but was less potent than SCA40 in each case and did not exhibit selectivity for inhibition of cyclic AMP hydrolysis.8. Tested against the activity of the isoenzymes of cyclic nucleotide PDE derived from human blood cells and lung tissue, SCA40 proved highly potent against the type III isoenzyme. It was markedly less potent against the type IV and type V isoenzymes and even less potent against the isoenzymes types I and II.9. It is concluded that the tracheal relaxant action of SCA40 (1 nM- 1 micro M) does not involve the activation of beta-adrenoceptors or P1 or P2 purinoceptors. Furthermore, this action is unlikely to depend upon the opening of BKca channels with consequent cellular hyperpolarization and voltage-dependent inhibition of Ca2+ influx. The tracheal relaxant action of SCA40 (up to 1 micro M) is more likely to depend upon its selective inhibition of the type III isoenzyme of cyclic nucleotide PDE. At concentrations above 1 micro M, SCA40 exerts more general inhibition of the isoenzymes of cyclic nucleotide PDE and may then promote the opening of BKca channels.

Animals↗
PubMed1991

Biochemical and electrical aspects of the tracheal relaxant action of AH 21-132.

In Triton X-100-skinned trachealis muscle, neither papaverine nor AH 21-132 modified responses to Ca2+. The (-)-enantiomer of AH 21-132 was more potent than the (+)-enantiomer both in relaxing intact trachealis muscle and in inhibiting tracheal cAMP phosphodiesterase (PDE). AH 21-132 (0.6 microM) potentiated forskolin in causing tracheal relaxation but did not potentiate isoprenaline, cromakalim or sodium nitrate. AH 21-132 (2 microM) potentiated all four agents in relaxing the trachea. AH 21-132 (1 microM) potentiated forskolin in increasing tissue cAMP content and, in higher concentration, itself increased tissue cAMP. Electrical effects of AH 21-132 included suppression of spontaneous slow waves and cellular hyperpolarisation. It is concluded that AH 21-132 lacks a direct depressant effect on the intracellular contractile machinery. The weight of evidence suggests that AH 21-132-induced relaxation results from inhibition of cAMP-PDE. However, in common with other PDE inhibitors. AH 21-132 increases tissue cAMP content only at concentration greater than that required to cause full relaxation.

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

Mechanical, biochemical and electrophysiological studies of RP 49356 and cromakalim in guinea-pig and bovine trachealis muscle.

Experiments have been performed using guinea-pig and bovine trachealis in order to determine whether cromakalim and RP 49356 share the same relaxant action and to analyse the mechanisms underlying this action. RP 49356 was approximately 3 times less potent than cromakalim in suppressing the spontaneous tone of guinea-pig trachea and, like cromakalim, was antagonised by glibenclamide and by phentolamine. Biochemical studies showed that relaxant concentrations of cromakalim and RP 49356 did not alter the cAMP or cGMP content of guinea-pig trachealis muscle and did not inhibit cAMP or cGMP hydrolysis by tracheal homogenates. Like cromakalim, RP 49356 caused marked hyperpolarisation of guinea-pig trachealis cells. Patch clamp recording using inside-out membrane patches from bovine trachealis showed that cromakalim, RP 49356, glibenclamide and phentolamine were each without effect on the open state probability (Popen) of large conductance, Ca(2+)-activated K(+)-channels. We conclude that cromakalim and RP 49356 share a similar action in opening K(+)-channels in the trachealis cell membrane. This action probably does not involve the intracellular accumulation of cyclic nucleotides and the channel involved is not the large conductance, Ca(2+)-dependent K(+)-channel.

2',3'-Cyclic-Nucleotide Phosphodiesterases↗
PubMed1991

The isoenzyme selectivity of AH 21-132 as an inhibitor of cyclic nucleotide phosphodiesterase activity.

The smooth muscle relaxant, AH 21-132, was tested for its inhibitory effect on the cyclic nucleotide phosphodiesterase (PDE) activities fractionated from guinea-pig cardiac ventricle and bovine trachealis muscle. Both tissues yielded significant PDE-I and PDE-II activities. The cardiac ventricle also contained a significant amount of PDE-III whilst the trachealis contained PDE-IV. AH 21-132 inhibited PDE-III and PDE-IV selectively (Ki values 0.30-0.55 microM) compared with PDE-I and PDE-II (Ki values 20-140 microM).

3',5'-Cyclic-AMP Phosphodiesterases↗
PubMed1991

The bronchodilator action of AH 21-132.

The benzonaphthyridine derivative, AH 21-132, has non-specific relaxant effects in isolated airways smooth muscle. The action of AH 21-132 in trachealis muscle is not antagonised by propranolol but AH 21-132 is slightly potentiated by epithelium removal. Electrophysiological recording from guinea-pig trachealis shows that AH 21-132-induced relaxation is accompanied by suppression of electrical slow waves and by cellular hyperpolarisation. Unlike theophylline, AH 21-132 does not cause spasm of cooled (12 degrees C), indomethacin-treated trachealis muscle, nor does it act as an antagonist at adenosine A1 receptors. AH 21-132 does not depress the Ca2+ sensitivity or responsiveness of Triton X-100 skinned trachealis fibres. In tracheal relaxant concentrations, AH 21-132 selectively inhibits cAMP phosphodiesterase (PDE) compared with cGMP-PDE. The (-)-enantiomer of AH 21-132 is more potent than its (+)-enantiomer both in causing tracheal relaxation and in inhibiting cAMP-PDE. When tested on PDE isoenzymes separated from bovine trachealis and guinea-pig cardiac ventricles, AH 21-132 exhibits selectivity as an inhibitor of the isoenzyme types III and IV. AH 21-132 increases the trachealis content of cAMP and cGMP, but only in concentration greater than that required fully to suppress the mechanical tone of the tissue. AH 21-132 has bronchodilator activity in anaesthetised, ventilated guinea-pigs when administered intraduodenally, intravenously or by inhalation. Inhaled AH 21-132 also provides bronchodilatation in healthy human volunteers in whom bronchoconstriction has been induced by inhaled methacholine.

Animals↗