Search PubMed⌕ Search

Biomedical subjects

J R Hoult

Publications and source records attributed to J R Hoult.

At least 73 records · Page 4Linked to original sources
PubMed1986

Inhibition by ethanol and mepacrine of phospholipase-dependent prostaglandin release from the isolated perfused rat lung.

To investigate the possibility that millimolar concentrations of ethanol have a membrane-directed inhibitory effect on phospholipase A2 and prostanoid generation (suggested from previous platelet experiments), we studied the release of prostacyclin, thromboxane A2 and prostaglandin E2 from isolated perfused rat lung. Prostanoid release was evoked by arachidonic acid, bradykinin and ionophore A23187 and was measured after extraction by radioimmunoassay. In these experiments, prostanoid release is dependent upon biosynthesis from fatty acid precursors as there is no endogenous prostanoid storage pool. Arachidonic acid and bradykinin caused enhanced release of more prostacyclin than thromboxane A2 with much less prostaglandin E2 and no detectable prostaglandin F2 alpha, whereas A23187 released equal proportions of prostacyclin and thromboxane A2 with less prostaglandin E2. Ethanol at 50 mM resembled mepacrine (46 microM) in that prostanoid release in response to bradykinin and A23187 was highly significantly reduced with little effect on release induced by arachidonic acid. We suggest that ethanol, like mepacrine, interferes with prostaglandin generation by an action at the phospholipase step. This may be secondary to a physical effect on membrane configuration.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Failure of anti-inflammatory steroids to inhibit prostaglandin release from the hydronephrotic rabbit kidney.

The release of prostaglandins E2, F2 alpha, I2 and thromboxane A2 from isolated perfused normal and hydronephrotic rabbit kidneys was investigated by extraction and radioimmunoassay. In both types of kidneys, basal PG efflux increased with time and was not altered by co-perfusion with dexamethasone or hydrocortisone. Several vasoactive substances at 1 to 4 micrograms (e.g., bradykinin, angiotensin II, substance P, noradrenaline and vasopressin) caused release of additional amounts of prostaglandins. PGE2 and 6-keto PGF1 alpha were the major prostanoids detected, but substantial amounts of PGF2 alpha were also found. Thromboxane A2 was not released from normal kidneys. In hydronephrotic kidneys there was greatly augmented release of prostaglandins E2 and I2, some increases in PGF2 alpha, and the appearance of substantial amounts of thromboxane A2 (measured as immunoreactive TXB2) when the kidneys were challenged with angiotensin, bradykinin and vasopressin, and smaller augmentation of the response to noradrenaline and substance P. There was no evidence that these evoked increases in renal PG output could be inhibited by dexamethasone or hydrocortisone. Some explanations for the failure of steroids to alter prostanoid metabolism from arachidonate in rabbit kidney are discussed, and it is proposed that there are clear exceptions to the concept that steroids inhibit prostaglandin generation in intact tissues.

Angiotensin II↗
PubMed1986

Kinin-induced prostaglandin release in rat colon does not display serosal/mucosal 'sidedness' after epithelial removal.

Release of prostaglandin E2 (PGE2) from rat colon in response to 1 microM lysylbradykinin (LBk) displayed 'sidedness' in preparations with an intact epithelial cell layer (PGE2 release, sensitivity to LBk and inhibition by indomethacin all occurred on the serosal side only). Preparations with histologically-verified removal of the epithelial layer and which were impermeable to prostaglandins (i.e. intact) continued to demonstrate LBk-induced PGE2 generation, but this and indomethacin inhibition did not display sidedness. The results show that kinin-induced PGE2 derives principally from cells in the lamina propria and not from the epithelial cells as previously supposed, and that the apparent sidedness of LBk responsiveness, PGE2 generation and its inhibition by indomethacin results from the barrier property of the epithelial cells and is not indicative of an asymmetric response.

Animals↗
PubMed1986

Identification of 6-oxo-prostaglandin E1 as a naturally occurring prostanoid generated by rat lung.

The spontaneous release of prostanoids from rat isolated perfused lungs was studied after acid/organic extraction of perfusates by bioassay, radioimmunoassay, thin layer and high performance liquid chromatographic methods and by gas chromatography-negative ion mass spectroscopy (g.c.n.i.m.s.). An acid/organic extractable anti-aggregatory vasodilator prostaglandin which inhibited the twitch response of the field-stimulated guinea-pig vas deferens was released from the Krebs-perfused rat lung in nanogram amounts similar to those of other detected prostanoids. Parallel biological assay suggested that this prostaglandin had very closely similar pharmacological activity to authentic 6-oxo-prostaglandin E1 (6-oxo-PGE1), a metabolite of prostacyclin (PGI2) generated by the action of the enzyme 9-hydroxyprostaglandin dehydrogenase (9-PGDH). 6-oxo-PGE1 was identified conclusively in extracts of rat lung perfusate by thin layer chromatography, high performance liquid chromatography and g.c./m.s. combined with bioassay (inhibition of platelet aggregation), and its covalent structure was defined by g.c. negative ion chemical ionization mass spectroscopy. The rank order of spontaneous release of prostanoids (measured by radioimmunoassay) from the perfused rat lung was 6-oxo-PGF1 alpha greater than thromboxane B2 (TXB2) greater than PGE2 greater than 6-oxo-PGE1 (measured biologically) greater than PGF2 alpha. Release of all five prostanoids was inhibited by indomethacin, but only that of 6-oxo-PGE1 was inhibited by naringenin. Rat lung 100,000 g cytosolic supernatants contained 9-PGDH activity capable of removing 9 beta-tritium from labelled prostacyclin and forming an acid/organic extractable 6-oxo-PGE1-like anti-aggregatory substance. This 9-PGDH activity was inhibited by naringenin (IC50 10.3 microM). 6 The relevance of these findings to the possible physiological role of 6-oxo-PGE1 in the lung is discussed, and we propose that 6-oxo-PGE, should be accorded the status ofa physiologically relevant, naturally occurring metabolite of arachidonic acid.

Alprostadil↗
PubMed1986

Pharmacological and biochemical actions of sulphasalazine.

This review considers recent pharmacological and biochemical studies of sulphasalazine and its colonic metabolites, 5-aminosalicylic acid and sulphapyridine, in relation to the use of the parent drug for the treatment of ulcerative colitis and, more recently, rheumatoid arthritis. Several factors make it difficult to analyse the mode of action of sulphasalazine, such as the aetiology and variable course of the conditions it is used to treat, lack of suitable animal models, and the question of which moiety of the drug is active. An important feature of the pharmacokinetics of the drug after oral administration is the significance of the azo cleavage of sulphasalazine due to bacterial action. The effects of sulphasalazine on the metabolism of arachidonic acid to prostaglandins and leukotrienes have been widely studied because of the evidence that these substances are formed in increased amounts in inflammatory bowel diseases. The effects are complex, but it appears that sulphasalazine and 5-aminosalicylic acid are weak and very weak inhibitors, respectively, of both cyclo-oxygenase- and lipoxygenase-dependent pathways. The overall pharmacological profile may favour a more marked inhibition of the lipoxygenase pathway because of the additional ability of 5-aminosalicylic acid to enhance prostanoid production and of sulphasalazine to inhibit prostaglandin inactivation. Drugs with selective lipoxygenase inhibitory actions in the colon should thus be sought so as not to compromise the prostaglandin pathway. Other properties of sulphasalazine, including its immunosuppressive, antifolate, lymphocyte inhibitory and leucocyte modulatory actions, are also discussed in the context of the therapeutic uses of the drug.(ABSTRACT TRUNCATED AT 250 WORDS)

Anti-Inflammatory Agents, Non-Steroidal↗
PubMed1985

Actions of flavonoids and the novel anti-inflammatory flavone, hypolaetin-8-glucoside, on prostaglandin biosynthesis and inactivation.

The newly identified plant-derived flavone-glycoside hypolaetin-8-glucoside, which has anti-inflammatory and gastric ulcer protective properties, and its corresponding aglycone, hypolaetin, were tested for effects on prostaglandin biosynthesis and degradation. They were compared with four other flavonoids, viz. rutin and its corresponding aglycone, quercetin, and the aglycones isoscutellarein and kaempferol. Over the range 10-1000 microM the glycosides rutin and hypolaetin-8-glucoside stimulated prostaglandin formation by sheep seminal vesicle microsomes incubated with radiolabelled arachidonic acid; the other compounds were essentially inactive. Over 5-5000 microM rutin and hypolaetin-8-glucoside enhanced the release of prostacyclin (and other prostanoids) from fragments of rat caecum incubated in the absence of additional arachidonic acid; the four aglycones compounds did not stimulate prostacyclin release but some reduced it at 5000 microM. However, the glycosides did not affect the enzymatic inactivation of radiolabelled prostaglandin F2 alpha by semi-purified bovine lung prostaglandin 15-hydroxydehydrogenase (PGDH) or in 100,000 g supernatants prepared from homogenised rat stomach. Three of the four aglycones (quercetin, kaempferol, isoscutellarein, in descending order of potency) were inhibitory to PGDH with ID50 values in the range 130-2100 microM. The results show that the capacity of flavonoids to enhance prostaglandin formation is associated with the presence of glycosidic substitution, whereas PGDH inhibition requires its absence. The relevance of this biochemical profile of hypolaetin-8-glucoside to its anti-inflammatory gastroprotective effects in vivo is discussed.

Animals↗
PubMed1985

Age-dependent changes in the synthesis and catabolism of 6 oxo PGE1 and other prostanoids by the rat kidney in vitro.

Synthesis and catabolism of 6 oxo PGE1 was assessed in 100,000 g cell-free supernatant fractions of kidneys obtained from rats aged 20, 34 and 70 days. In addition the release of PGI2, TxA2 (measured as 6 oxo PGF1 alpha and TxB2, respectively), PGE2 and PGF2 alpha from kidney slices prepared from these three groups of rats was determined using specific radioimmunoassays. The conversion of PGI2 to 6 oxo PGE1 (but not 13,14 dihydro 15 oxo PGF2 alpha to 13,14 dihydro 15 oxo PGE2) was detected in supernatant fractions of kidneys from 20 day rats. Slices prepared from the kidneys of these animals spontaneously released significant amounts of three prostanoids (6 oxo PGF1 alpha greater than PGE2 greater than PGF2 alpha greater than TxB2 = 0). No formation of 6 oxo PGE1 from exogenous PGI2 was demonstrated in renal 100,000 g supernates from 34 and 70 day rats even though these supernates avidly oxidised 13,14 dihydro 15 oxo PGF2 alpha to 13,14 dihydro 15 oxo PGE2. In these animals the rank order of prostanoid release from kidney slices was PGE2 greater than 6 oxo PGF1 alpha greater than PGF2 alpha greater than TxB2 = 0. The catabolism of 6 oxo PGE1 is also age-dependent. In 20 and 34 day old rats 6 oxo PGE1 and PGE1 incubated with renal 100,000 g supernates undergo loss of biological activity as determined by the ability to inhibit ADP induced human platelet aggregation. In contrast, kidney 100,000 g supernates prepared from 70 day rats convert 6 oxo PGE1 to an unidentified metabolite with more potent anti-aggregatory activity. The possibility that 6 oxo PGE1 has a biological role in the developing rat kidney is discussed.

Age Factors↗
PubMed1985

Phorbol myristate acetate enhances human polymorphonuclear neutrophil release of granular enzymes but inhibits chemokinesis.

The effects of the co-carcinogenic phorbol ester, phorbol myristate acetate (PMA), on N-formyl-Met-Leu-Phe (FMLP)-induced human polymorphonuclear leukocyte chemokinesis and release of granular lysozyme and beta-glucuronidase were compared with those of the inactive phorbol didecanoate (PDD). Release of the enzymes was enhanced by PMA but was unaffected by PDD which also had no effect on chemokinesis. In contrast, FMLP-induced chemokinesis was completely suppressed by PMA in a dose-dependent fashion (ID50 = 3.5 nM). PMA also inhibited the FMLP-induced increase in cytoplasmic calcium level, measured by the fluorescent indicator quin-2. These and other results suggest that although the diacylglycerol/protein kinase C system is involved in the positive regulation of certain neutrophil functions (degranulation and superoxide generation), if it is very powerfully stimulated, as with PMA, it has inhibitory actions on other neutrophil properties such as motility.

Calcium↗
PubMed1985

Highly potent inhibition of prostaglandin 15-hydroxydehydrogenase in-vitro and of prostaglandin inactivation in perfused lung by the new azobenzene analogue, Ph CL 28A.

The new azobenzene analogue Ph CL 28A (2-hydroxy-5-(3,5-dimethoxycarbonyl-benzoyl)-benzene acetic acid) potently inhibited prostaglandin 15-hydroxydehydrogenase (PGDH) in the nanomolar range in-vitro and inhibited prostaglandin inactivation in rat perfused lung at similar concentrations, and is the most potent PGDH inhibitor yet available. It was synthesized because electronegative substituents in the B ring of homosalazine enhance PGDH inhibitory potency. Ph CL 28A inhibited human placental PGDH non-competitively with regard both to substrate PGF2 alpha (Ki = 18.7 +/- 0.9 nM) and the NAD+ cofactor (Ki = 57.6 +/- 2.9 nM); inhibition was greatly reduced at pH greater than or equal to 8.0. Ph CL 28A hydrolyses spontaneously in alkali (t1/2 at pH 9.0 = 45 h) to the less active dicarboxylic acid (IC50 human placental PGDH 1.6 microM versus 0.028 microM for Ph CL 28A). The new analogue is 1000 X more active than the parent compound sulphasalazine from which it derives. The IC50 values for five azobenzene analogues in rat perfused lung (Ph CL 28A = 72 nM) correlated strongly with those obtained using purified PGDH (r = 0.99), suggesting that they inhibit pulmonary prostaglandin degradation at the enzyme step rather than at the hypothetical carrier. The new compound will be a useful probe for PGDH structure and function.

Animals↗
PubMed1985

Effects of hypolaetin-8-glucoside and related flavonoids on soybean lipoxygenase and snake venom phospholipase A2.

Hypolaetin-8-glucoside, a novel flavonoid isolated from Sideritis mugronensis and possessing anti-inflammatory and gastroprotective properties in the rat, was compared with the structurally related flavonoids hypolaetin, isoscutellarein, rutin, quercetin and kaempferol for inhibitory effects on the enzymes soybean 15-lipoxygenase and snake venom phospholipase A2. The aglycone flavonoids dose-dependently inhibited snake venom phospholipase A2 but the glycosides hypolaetin-8-glucoside and rutin were inactive. All 6 flavonoids inhibited soybean 15-lipoxygenase with no differences between glycosides and aglycones, although flavonols appeared more active than flavones. The inhibition of these enzyme activities cannot explain the anti-inflammatory action of hypolaetin-8-glucoside, unless a significant proportion of the drug reaches the target tissue as the aglycone, hypolaetin.

Animals↗
PubMed1984

Enzymatic inactivation of 6-keto-prostaglandin E1 in vitro: comparison with prostaglandin E1.

The inactivation of 6-keto PGE1, a biologically active and stable metabolite of prostacyclin, was studied in 100,000 g cytosolic supernatants by bioassay on rat stomach strip (contraction) and human platelets (inhibition of ADP-induced aggregation). PGE1 was used as a reference compound. Both PGs were inactivated in supernatants from colon, kidney and liver of rat, rabbit and guinea-pig. Inactivation was time- and NAD+ -dependent and was generally greater for PGE1 than 6-keto-PGE1. The enzyme responsible for 6-keto-PGE1 inactivation in cytosolic supernatants is distinct from prostaglandin 15-hydroxydehydrogenase and 9-keto reductase, is not inhibitable by sulphasalazine-like drugs and its activity is recoverable after precipitation by ammonium sulphate. We conclude that 6-keto-PGE1 can be inactivated by enzymes with wide tissue distribution, but further studies are needed for identification of these novel enzymes and the products formed as well as to assess their significance in the intact animal.

Alprostadil↗
PubMed1984

Total profiling by GC/NICIMS of the major cyclo-oxygenase products from antigen and leukotriene-challenged guinea-pig lung.

Separation and quantitation of all the major cyclo-oxygenase products in perfused guinea-pig lungs challenged with antigen or leukotrienes C4 and D4 were achieved using a novel combined capillary column gas chromatography/negative ion chemical ionization mass spectrometric (GC/NICIMS) method. In descending order of magnitude, unchallenged lungs released thromboxane B2 (TXB2) plus its pulmonary metabolite (TXDK) greater than 6-keto-PGF1 alpha plus its 13,14-dihydro-15-keto metabolite (K2H1F1 alpha) greater than PGE2 plus PGF2 alpha greater than PGD2; after ovalbumin anaphylaxis there were increases of X 26 in TXB2 plus TXDK, X 28 in PGD2 and histamine (measured fluorometrically) but of only X 3 in 6-keto-PGF1 alpha plus K2H2F1 alpha and PGE2 plus PGF2 alpha. FPL55712 treatment greatly reduced the release of TXB2 and 6-keto-PGF1 alpha and their metabolites (showing this to be a secondary effect mediated by leukotriene action) but did not affect PGD2 output. LTC4 and LTD4 themselves induced the release of TXB2 and TXDK, as did bradykinin, but neither substance caused appreciable PGD2 release. Aside from illustrating the great value of the GC/NICIMS method for simultaneously determining all cyclooxygenase products, the main conclusions are: (i) PGD2 may be an in vitro marker for activation of lung inflammatory cells; (ii) prostacyclin and thromboxanes are actively metabolized in situ in the lung; and (iii) 'pathological subversion' of pulmonary function by anaphylaxis, leukotrienes or bradykinin principally causes thromboxane release from unknown target cells, with a smaller release of prostacyclin which may be compensatory in nature.

Anaphylaxis↗
PubMed1983

Thromboxane A2 analogues inhibit the metabolism of thromboxane B2 in perfused guinea-pig lung.

The effect of four thromboxane A2-like analogues as inhibitors of thromboxane B2 uptake and metabolism to 13,14-dihydro-15-keto-thromboxane B2 was studied in the perfused guinea-pig lung. We used 5-min infusions containing 1 muCi [3H]thromboxane B2 (10 ng/ml) and measured uptake/accumulation (as tissue to medium ratio) and metabolism to 13,14-dihydro-15-ketothromboxane B2 by radio-TLC. The results showed that thromboxane B2 metabolism is saturable and exhibits substantial dose-dependent inhibition of both processes by U46619 and U44069 endoperoxide analogues (50% inhibition, ID50, in the range 0.5-0.9 microM), pinane thromboxane A2 (a thromboxane A2 partial agonist, ID50 against metabolism, 0.7 microM) and the thromboxane A2 mimetic EPO11 (ID50 against metabolism, 2.6 microM). These agents affected uptake and enzyme transformation steps differentially, thus strengthening the evidence that thromboxane B2 metabolism is a multi-step, uptake-dependent process in this tissue. U46619 did not affect prostaglandin F2 alpha metabolism, nor did prostaglandin F2 alpha inhibit thromboxane B2 metabolism, confirming that thromboxane B2 uptake/metabolism is distinct from the process which handles prostaglandins. Of the four analogues, only pinane thromboxane was a significant substrate for 15-hydroxyprostaglandin dehydrogenase and it was also the best inhibitor of 15-hydroxyprostaglandin dehydrogenase in purified enzyme preparations. These results advance our understanding of the inactivation in lung of thromboxane B2 and invite study of thromboxane A2 itself.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1983

Inhibition of prostaglandin 15-hydroxydehydrogenase by sulphasalazine and a novel series of potent analogues.

The ability of sulphasalazine, its colonic metabolites and various analogues to inhibit prostaglandin inactivation by two purified preparations of type INAD+-dependent prostaglandin 15-hydroxydehydrogenase or in various 100,000 g cytosolic supernatants was investigated using PGF2 alpha as substrate and radio-TLC. Bovine lung and human placental PGDH were inhibited in a dose-dependent and apparently non-competitive manner by sulphasalazine and most of the 26 salazine/sulphasalazine analogues tested, but the potencies of the analogues varied considerably. In a survey of structure-activity effects testing 30 drugs at a fixed dose (50 microM) in six test systems, it was established that only two aromatic rings are needed and that optimal PGDH inhibition requires -CH2COOH and -OH at positions 1 and 2 in the salicyl C ring system. Homosalazine was thus established as the type compound of a novel series of powerful PGDH inhibitors. Electronegative substituents meta or para in ring B produce compounds with greater than 150 X inhibitory potency of sulphasalazine, and a significant linear correlation (r = 0.82, P less than 0.002) was found between the inhibitory activity and the Hammett sigma substituent constant in this series of ten homosalazine analogues.

Animals↗
PubMed1983

Selective inhibition of thromboxane B2 accumulation and metabolism in perfused guinea-pig lung.

1 U46619, a prostaglandin H2 endoperoxide analogue and thromboxane A2 agonist, dose-dependently inhibited accumulation and metabolism of thromboxane B2 in the isolated perfused lung of the guinea-pig. At similar doses prostaglandins E1, E2, F1 alpha, F2 alpha, I2, 5, 6-trans-PGE2 and 8-iso-PGE1 were ineffective. 2 U46619 did not affect accumulation and metabolism of prostaglandin F2 alpha under similar conditions. 3 The pulmonary disposition of thromboxane B2, which occurs by uptake into pulmonary cells or binding to a specific macromolecular component, is mediated by a mechanism distinct from that handling prostaglandin F2 alpha. The possible relevance of these findings to the pulmonary disposition of thromboxane A2 is discussed.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1983

6-Keto-prostaglandin E1: its formation by platelets from prostacyclin and resistance to pulmonary degradation.

6-Keto-prostaglandin E1 is a novel biologically active product of the metabolism of prostacyclin in liver and platelets. Further evidence for this bioconversion was obtained in stirred suspensions of platelet rich plasma (PRP) and resuspended platelets (RSP) by sampling and simultaneous assay on a superfusion cascade (rabbit coeliac artery, rat stomach fundus strip) and on human platelet aggregation. Incubation of prostacyclin in saline led to rapid loss of bioactivity (t1/2 3.2 min); its stability was prolonged in platelet poor plasma (t1/2 25.1 min). However, in PRP and RSP a more spasmogenic product was generated transiently. 6-Keto-PGE1, was 3.0 and 2.5 times more potent on the two bioassay tissues, respectively, but approximately 3 times less so as inhibitor of platelet aggregation. 6-Keto-PGE1 is not extensively metabolised in the isolated perfused rat lung (20.4 or 4.2%, depending on protocol), compared with PGE1 (84.3 or 78.5%), and is a much poorer substrate for the principal prostaglandin metabolising enzyme, prostaglandin 15-hydroxydehydrogenase. These data show that 6-keto-PGE1 is a biologically active but pulmonary-resistant product of prostacyclin metabolism but does not resolve the claim that it might have physiological relevance.

Alprostadil↗
PubMed1982

Thromboxane B2 uptake and metabolism in isolated perfused lung. Identification and comparison with prostaglandin F2 alpha.

Thromboxane B2 was metabolised in isolated perfused guinea-pig lungs to a product identified by negative ion chemical ionisation mass spectrometry as 13,14-dihydro-15-ketothromboxane B2. Conversion was measured by radio TLC and was greater in guinea-pig than rat lungs (29.1 vs. 13.8% at 10 ng/ml), but similar in lungs from normal and sensitized guinea-pigs. Thromboxane B2 metabolism was less than that of prostaglandin F2 alpha but, like it, was prevented at 5 degrees C and reduced by cycloheximide pretreatment. Tissue to medium ratio in perfused guinea-pig lungs was 3.4 for thromboxane B2, but 0.2 for insulin (showing that thromboxane B2 is accumulated within the lung) and was altered after experimental manipulations. Neither lung slices, crude homogenates, cytosolic and microsomal fractions nor purified prostaglandin 15-hydroxydehydrogenase metabolised thromboxane B2 in vitro, although prostaglandin F2 alpha was extensively inactivated. Quantitative partition coefficient and albumin-binding data confirm that thromboxane B2 lacks prominent lipophilicity, implying that cellular uptake in lung must be carrier-mediated. We conclude that thromboxane B2 is a substrate for pulmonary degradation which may form a route for the biological inactivation of thromboxane A2. Its resistance to prostaglandin 15-hydroxydehydrogenase as conventionally tested remains paradoxical and is discussed.

Animals↗