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R W Bryant

Publications and source records attributed to R W Bryant.

At least 73 records · Page 4Linked to original sources
PubMed1983

Characterization of 11-HETE and 15-HETE, together with prostacyclin, as major products of the cyclooxygenase pathway in cultured rat aorta smooth muscle cells.

Arachidonic acid is the precursor of several potent derivatives that regulate physiological functions in the cardiovascular system. Thromboxane (TXA2) and prostacyclin (PGI2) are synthesized by the cyclooxygenase enzyme. The proaggregatory and vasoconstrictive TXA2 produced by platelets is opposed in vivo by the antiaggregatory and vasodilating activity of PGI2 synthesized by blood vessels. Arachidonic acid is also converted via a 5-lipoxygenase to leukotrienes, the vasoconstrictive components of SRSA. We have shown that this latter pathway is regulated by 15-HETE, a product of the 15-lipoxygenase present in lymphocytes. Confluent cultures of rat aorta smooth muscle cells (RSM) were superfused briefly with [14C]arachidonic acid. The products were isolated and analyzed by thin-layer chromatography-radioautography, high performance liquid chromatography, and gas-liquid chromatography-mass spectrometry. Prostacyclin (PGI2) was identified as the major product both by its biological properties in a platelet aggregation assay and by the mass spectrum of its tetra-trimethylsilylether-methyl ester derivative. Minor quantities of PGE2, PGD2, and PGF2 alpha were also synthesized. Three other compounds with chromatographic properties of mono-hydroxy eicosanoic acids were also formed in major amounts. These were shown to be cyclooxygenase products since their synthesis, together with that of prostacyclin, was blocked by the cyclooxygenase inhibitors aspirin (0.2 mM) and indomethacin (10 microM). Quantities of the hydroxy-eicosanoids were isolated from large scale incubations by silicic acid chromatography. Following methylation and reduction with platinum oxide/H2, the compounds were converted to their trimethylsilylether derivatives and analyzed by gas-liquid chromatography-mass spectrometry. The compounds were identified as 11-hydroxy-5,8,12,14-eicosatetraenoic acid (11-HETE), 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE), and hydroxy-5,8,10-heptadeca-trienoic acid (HHT) by simultaneous ion monitoring of characteristic ions at M/e ratios of 287, 258, 229 for 11-HETE and 343, 314, 173 for 15-HETE, and by comparison with the mass spectra of authentic samples. Rat smooth muscle cells, prelabeled by 24-hour incubation with [14C]arachidonic acid, released large amounts of prostacyclin together with enhanced amounts of 11- and 15-HETE in response to physiological levels of thrombin (0.5-5 units/ml). These experiments demonstrate that, in addition to the thromboxane antagonist prostacyclin, vascular smooth muscle cells produce significant quantities of the leukotriene inhibitor 15-HETE via the cyclooxygenase pathway in response to physiological stimuli such as thrombin. The release of both prostacyclin and 15-HETE by vascular smooth muscle cells may thus play an important role in vascular homeostasis.

Animals↗
PubMed1982

Regulation of leukocyte and platelet lipoxygenases by hydroxyeicosanoids.

During allergic and inflammatory reactions, arachidonic acid is oxidized by lipoxygenases to a variety of biologically active products, including leukotrienes. The mechanisms for regulation of the different lipoxygenase activities are not well defined. We report here that [14C]arachidonic acid metabolism by the 5- and 15-lipoxygenase activities in rabbit leukocytes and the 12-lipoxygenase in rabbit platelets is inhibited by various hydroxyeicosatetraenoic acids (HETEs). 15-HETE was the most effective inhibitor of the 5- and 12-lipoxygenases, whereas similar inhibitory potencies were observed for 5-HETE and 12-HETE acting on the 15-lipoxygenase. These three enzyme pathways were all least sensitive to their own products HETEs. To determine which structural characteristics of 15-HETE are essential for inhibition of the 5-lipoxygenase, various derivatives were prepared and purified by high pressure liquid chromatography, and their structures were confirmed by gas chromatography-mass spectrometry. The inhibitory potencies of 15-HETE analogs with different degrees of unsaturation were in the order of three double bonds greater than 4 greater than 2 greater than 0. 15-Hydroperoxy-5,8,11,13-eicosatetraenoic acid (15-HPETE) was four times more potent than 15-HETE. The 15-acetoxy, 15-keto and methyl ester derivatives were of comparable activity to 15-HETE, and the 15-acetoxy methyl ester derivative was less potent. Based upon the observed patterns of inhibition, we postulate that complex interregulatory relationships exist between the various lipoxygenases, and that cells containing these lipoxygenases may interact with each other via their lipoxygenase metabolites.

12-Hydroxy-5,8,10,14-eicosatetraenoic Acid↗
PubMed1982

Role of lipoxygenases in regulation of PHA and phorbol ester-induced mitogenesis.

The experiments described here confirm the critical involvement of products of arachidonic acid metabolism in immune cell function. The results suggest opposing activities of the cyclo-oxygenase versus the lipoxygenases products in these systems. However, in contrast to the situation with the prostaglandins, where addition of the pure compounds has reproduced the effects predicted from the inhibitor studies, identification of the specific lipoxygenase products involved and the induction of the predicted biological response by addition of these compounds remains to be accomplished.

Animals↗
PubMed1980

Inhibition of leukotriene biosynthesis by the leukocyte product 15-hydroxy-5,8,11,13-eicosatetraenoic acid.

Rabbit peritoneal polymorphonuclear leukocytes, elicited with glycogen, metabolized added [1-14C]arachidonic acid to the 5-lipoxygenase products 5-hydroxy-6,8,11,14-eicosatetraenoic acid and 5,12-dihydroxy-6,8,10,14-eicosatetraenoic acid (leukotriene B) and the 15-lipoxygenase product 15-hydroxy-5,8,11,13-eicosatetraenoic acid. These metabolites were isolated by high pressure liquid chromatography and converted to the trimethylsilyl-ether methyl ester derivatives, and the structures were confirmed by gas chromatography-mass spectrometry. When polymorphonuclear leukocytes were preincubated with 15-HETE (16 microM), the formation of 5-hydroxy-6,8,11,14-eicosatetraenoic acid and 5,12-dihydroxy-6,8,10,14-eicostatetraenoic acid from [1-14C]arachidonic acid was strongly suppressed. The concentration required for 50% inhibition of the 5-lipoxygenase pathway in these cells was approximately 6 microM, which is comparable to the concentrations (0.20 to 1.8 microM) of 15-hydroxy-5,8,11,13-eicosatetraenoic acid produced in incubations of polymorphonuclear leukocytes with arachidonic acid alone. Recent reports indicate that slow-reacting substance of anaphylaxis (leukotriene C/D) and chemotactic substance leukotriene B are arachidonic acid metabolites formed via the 5-lipoxygenase pathway. Our observations thus suggest that 15-hydroxy-5,8,11,13-eicosatetraenoic acid can regulate the formation of these vasoactive and inflammatory mediators intracellularly.

Animals↗
PubMed1980

15-hydroxy-5,8,11,13-eicosatetraenoic acid: A potent and selective inhibitor of platelet lipoxygenase.

The functional interrelationships between the cyclooxygenase and lipoxygenase systems for arachidonic acid metabolism in platelets have not yet been clarified. Although a number of specific inhibitors of the cyclooxygenase, such as aspirin and indomethacin, have been described, few inhibitors of the lipoxygenase have been found. Several hydroxy and hydroperoxy derivatives of arachidonic acid were prepared and purified by high performance liquid chromatography, and their structures were confirmed by gas chromatography-mass spectrometry. The effect of these compounds on oxygenation of [1-14C]arachidonic acid by platelet cyclooxygenase and lipoxygenase enzymes was monitored both with an oxygen electrode and by analysis of radioactive products formed. It was found that 15-hydroxy-5,8,11,13-eicosatetraenoic acid selectively inhibited platelet lipoxygenase activity at micromolar concentrations (I50 = 8 microM) without inhibiting the cyclooxygenase. The 15-hydroperoxy analog, although more potent, was less selective, whereas neither 12-hydroxy-5,8,10,14-eicosatetraenoic acid nor 12-hydroxy-9-octadecenoic acid (ricinoleic acid) appeared to affect either enzyme. The high degree of selectivity of the 15-hydroxy derivative of eicosatetraenoic acid makes it the most suitable inhibitor so far discovered for studying the functions of the platelet lipoxygenase system.

Arachidonic Acids↗
PubMed1980

The static creep of amalgams from fifteen alloys.

The static creep of amalgams prepared from fifteen conventional Ag3Sn and higher copper alloys was investigated one week after packing. The rate at which the different alloys develop resistance to creep was compared by testing amalgams at a number of times other than one week. A microfine lathe-cut alloy possesses the highest static creep and the single melt high copper type of alloy the lowest. An admixed high copper group of alloys possesses static creep similar to the silver-copper dispersed alloys. The rate at which amalgam develops a resistance to creep is dependent on the alloy type.

Copper↗
PubMed1980

X-ray mapping of dental amalgam using the electron microprobe.

Tin, copper, silver and mercury X-ray maps were obtained for amalgams prepared from three "high copper" commercial alloys. The data obtained from quantitative analysis of a silver-copper dispersed amalgam was subjected to major element analysis. X-ray mapping was found to reflect accurately the relative quantity of an element present in different regions of a map, thereby providing a reliable qualitative, part-quantitative analysis of the structure of the amalgam.

Chemical Phenomena↗
PubMed1980

Arousal of a specific and persistent sodium appetite in the rat with continuous intracerebroventricular infusion of angiotensin II.

1. Prolonged exposure of the brain of the normal Na-replete rat to angiotensin II produced a marked and persistent Na appetite. In a first series of experiments, short-term, repeated systemic injections of isoprenaline or renin (both of which raise circulating angiotensin levels), and repeated intracranial injections of angiotensin II evoked increased ingestion of 2 . 7% NaCl. In the second series of experiments, continuous infusions of angiotensin II directly into the brain evoked extremely large intakes of 3% NaCl. 2. In addition to large intakes of hypertonic NaCl some rats drank daily volumes of water that exceeded their body weight. 3. Not only did the animals drink large volumes of 3% NaCl some rats drank daily volumes of water that exceeded their body weight. 3. Not only did the animals drink large volumes of 3% NaCl during continuous angiotensin II infusion, but after termination of the infusion they continued to ingest NaCl at a rate comparable to that of the adrenalectomized rat. In most of the animals the persistent NaCl intake diminished over several days, but other animals continued to drink NaCl for as long as their intake was measured (up to 7 months). 4. The response to continuous infusion of angiotensin II was dose-dependent. Both water and 3% NaCl intake increased over a dose range of 6 ng h-1 to 6000 ng h-1. The persistence of the sodium appetitite was also dose-dependent across the same range of doses. 5. Angiotensin-induced salt appetite is specific for Na. Animals did not drink 0 . 5 M-NH4Cl and only occasionally drank minimal amounts of 0 . 5 M-KCl during continuous infusion. 6. The large water turnover was not responsible for the Na appetite. Rats given access to 3% NaCl only during infusion of angiotensin copiously. Animals that were not infused but were given saccharine-flavoured water in order to increase their water intakes did not drink 3% NaCl offered at the same time even though fluid intake was high. Rats that did not receive intracranial infusions but were infused intragastrically with volumes of water equal to or exceeding the amounts that were drunk during angiotensin infusion did not drink the 3% NaCl but did drink some water. 7. Records of the drinking by rats infused with angiotensin show that firstly the onset of drinking after the start of angiotensin infusion varied from animal to animal, secondly, NaCl drinking was not temporally linked to water intake, although this was observed occasionally, and thirdly, most of the drinking occurred during the night although angiotensin was infused continuously throughtout the nychthemeron. 8. Therefore, increases in angiotensin levels, probably with other factors such as increased levels of aldosterone or ACTH, result in Na appetite. The hormonal changes may alter the animals' preception of salt making it more acceptable. By means that are not yet understood the increased accceptability of salt persists after the termination of angiotensin infusion.

Angiotensin II↗