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Biomedical subjects

H H Tai

Publications and source records attributed to H H Tai.

At least 127 records · Page 7Linked to original sources
PubMed1987

Hypoxia provokes leukotriene-dependent neutrophil sequestration in perfused rabbit hearts.

Isolated rabbit hearts were perfused with salt solution containing autologous 111In-labeled neutrophils to determine whether 1) hypoxia provoked myocardial neutrophil sequestration, 2) neutrophil accumulation could be suppressed by inhibition of lipoxygenase and 3) hypoxic myocardium generated radioimmunoassayable leukotriene B4 (LTB4). Whereas accumulation of 111In-labeled neutrophils by normoxic hearts was minimal, induction of acute myocardial hypoxia by perfusion with hypoxic medium caused a rapid uptake of 111In-labeled neutrophils. Sequestered neutrophils were not released during a subsequent 20-min normoxic perfusion period. Hypoxia-induced neutrophil uptake was prevented by nordihydroguaiaretic acid (NDGA) or diethylcarbamazine (DEC), two structurally different inhibitors of lipoxygenase. Although no radioimmunoassayable LTB4 could be detected in neutrophil-free perfusate from normoxic or hypoxic preparations, hypoxia caused an approximate 2-fold increase in myocardial tissue levels of LTB4. Tissue levels of LTB4 reverted to control values after 20 min of normoxic perfusion. Infusion of exogenous LTB4 also provoked myocardial neutrophil uptake. Viewed collectively, these observations suggest that in isolated buffer-perfused rabbit hearts hypoxia induces LTB4 release from resident myocardial cells, which promotes avid neutrophil sequestration.

Animals↗
PubMed1986

Monoclonal antibodies to thromboxane synthase from porcine lung. Production and application to development of a tandem immunoradiometric assay.

Two hybridoma cell lines secreting antibodies against thromboxane synthase of porcine lung were produced. Clone TS1 secretes IgG2a antibody of lower affinity, while clone TS2 secretes IgG1 antibody of higher affinity. Both antibodies (when bound to rabbit anti-mouse IgG-Staphylococcus aureus complex) can immunoprecipitate thromboxane synthase from crude enzyme preparations in an active form suggesting that binding was not directed at the active site. Each antibody showed a distinctive pattern of cross-reactivity with thromboxane synthase from different porcine tissues. Neither of the antibodies cross-reacted with the enzyme from tissues of other species tested, indicating the heterogeneous nature of the enzyme among species. Competitive binding assay revealed that TS1 and TS2 recognized different determinants on the enzyme. The fact that two antibodies bind to separate epitopes on the same enzyme allows the development of a sensitive tandem immunoradiometric assay. The assay, based on binding of 125I-TS2 to thromboxane synthase immobilized on TS1-S. aureus complex, was linear with 7.5 approximately 75 ng of purified lung thromboxane synthase as standards and applicable to enzyme preparations regardless of their purity. The concentration of immunoreactive thromboxane synthase in porcine tissues as determined by this assay followed the order of platelet greater than colon greater than duodenum greater than lung greater than kidney greater than stomach. The fact that gastrointestinal tract is enriched with thromboxane synthase suggests that thromboxane may have significant physiological roles to be recognized in these organs.

Animals↗
PubMed1986

Immunoaffinity purification and characterization of thromboxane synthase from porcine lung.

Thromboxane synthase has been purified 620-fold from porcine lung microsomes by a three-step purification procedure including Lubrol-PX solubilization, reactive blue-agarose chromatography, and immunoaffinity chromatography. The purified enzyme exhibited a single protein band (53,000 daltons) on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Rabbit antiserum raised against the purified enzyme immunoprecipitated thromboxane synthase activity from crude enzyme preparations of porcine lung, cow lung, and human platelets, indicating the existence of structural homology of the enzyme in these species. Immunoblotting experiment identified the same polypeptide (53,000 daltons) in porcine lung and a polypeptide of 50,000 daltons in human platelets, confirming the identity of the enzyme and the specificity of the antiserum. Purified thromboxane synthase is a hemoprotein with a Soret-like absorption peak at 418 nm. The enzyme reaction has a Km for 15-hydroxy-9 alpha, 11 alpha-peroxidoprosta-5, 13-dienoic acid of 12 microM, an optimal pH of 7.5, and an optimal temperature of reaction at 30 degrees C. Purified thromboxane synthase catalyzed the formation of both thromboxane B2 and 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT). The ratios of HHT to thromboxane B2 varied from 1.6 to 2.1 dependent on the reaction conditions. Except that HHT was formed at a greater rate, the formation of HHT and that of thromboxane responded identically to pH, temperature, substrate concentration, kinetics of formation, metal ions, and inhibitors suggesting that the two products are probably formed at the same active site via a common intermediate. Thromboxane synthase was irreversibly inactivated by 15-hydroxy-9 alpha, 11 alpha-peroxidoprosta-5,13-dienoic acid during catalysis and by treatment of 15-hydroperoxyeicosatetraenoic acid. The irreversible inactivation, however, could be protected by reversible inhibitors such as sodium (E)-3-[4-(1-imidazolylmethyl)phenyl]-2-propenoate and 15-hydroxy-11 alpha,9 alpha-(epoxymethano)-prosta-5,13-dienoic acid, suggesting that the inactivation occurred at the active site of the enzyme. The catalytic inactivation of thromboxane synthase and the greater rate of formation of HHT in thromboxane-synthesizing system may probably play important regulatory roles in the control of thromboxane synthesis.

Animals↗
PubMed1986

Cigarette smoke-induced alterations in the release of arachidonate metabolites by pulmonary alveolar macrophage from selenium-fed and selenium-deficient rats.

Male weanling F-344 rats were maintained on selenium-supplemented or -deficient diets and were exposed to fresh cigarette smoke daily for 28 weeks. The deficient status of animals was demonstrated by a significant reduction in the pulmonary and hepatic glutathione peroxidase (GSH-Px) activity of rats on selenium-deficient diet. Sham and smoke treatment did not influence the GSH-Px activity in either diet group. Elevated levels of blood carboxyhemoglobin and pulmonary aryl hydrocarbon hydroxylase activity in the smoke-exposed rats of both diet groups indicated effective inhalation of cigarette smoke by animals. Studies of the extracellular release of arachidonate metabolites by pulmonary alveolar macrophages (PAMs) indicated that resting cells released small amounts of prostaglandin E2 (PGE2), thromboxane B2 (TXB2) and leukotriene B4 (LTB4). Upon phagocytic challenge by opsonized zymosan particles, the release of the three metabolites was substantially increased in all diet and treatment groups. While the release of cyclooxygenase products, PGE2 and TXB2, remained unaffected by cigarette smoke, an inhibition of approximately 50% in the release of lipoxygenase product, LTB4, was observed in cells from selenium-fed animals. In selenium-deficient animals, cigarette smoke almost completely inhibited (greater than 80%) the zymosan-stimulated release of LTB4 by PAMs and additionally caused about 50% reduction in TXB2 release. These results suggest a specific inhibition of lipoxygenase pathway by cigarette smoke in PAMs of selenium-fed rats and suggest that cigarette smoke may additionally impair enzymes of the cyclooxygenase pathway in PAMs of selenium-deficient animals.

Administration, Oral↗
PubMed1986

Streptococcus pneumoniae-induced alterations in levels of circulating thromboxane and prostacyclin: dissociation from granulocytopenia, thrombocytopenia, and pulmonary leukostasis.

The role of thromboxane (Tx) A2 in Streptococcus pneumoniae-induced granulocytopenia, thrombocytopenia, and pulmonary leukostasis is unclear. Rabbits were injected with 0.85% NaCl, nonviable pneumococci, or nonviable pneumococci after pretreatment with TxA2 synthetase inhibition. Blood was obtained immediately before and at times after injection for granulocyte and platelet counts and assays of TxB2 and 6-keto prostaglandin F1 alpha (6-ketoPGF1 alpha). Animals were evaluated for pulmonary leukostasis histologically and biochemically (myeloperoxidase activity). Pneumococcal challenge induced significant granulocytopenia (P less than .001), thrombocytopenia (P less than .001), and elevations in levels of both TxB2 (P less than .05) and 6-ketoPGF1 alpha (P less than .001) as well as pulmonary leukostasis (P less than .001). TxA2 synthetase inhibition blocked the pneumococcus-induced elevation in level of TxB2 without significantly altering levels of circulating granulocytes, platelets, or 6-ketoPGF1 alpha. Pulmonary leukostasis was not blocked. In another group of pneumococcus-challenged animals, no significant transpulmonary gradients of either TxB2 or 6-ketoPGF1 alpha were found.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

Development of cyclooxygenase and lipoxygenase metabolites of arachidonic acid after transient cerebral ischemia.

Vasoactive arachidonic acid metabolites are postulated to play a role in the pathogenesis of cerebral ischemia. In order to characterize the local generation of cyclooxygenase and lipoxygenase metabolites of arachidonic acid in transient ischemia with reperfusion, Mongolian gerbils were studied for regional cerebral blood flow (CBF), using the hydrogen clearance technique, and for cerebral levels of the thromboxane metabolite TXB2, and prostaglandins 6-keto-PGF1 alpha and PGE2, as well as the leukotriene LTB4. The gerbils were anesthetized with pentobarbital, and half of the animals were pretreated with the cyclooxygenase inhibitor indomethacin. All received 10 or 20 minutes of dense forebrain ischemia followed by reperfusion of 10 minutes, 50 minutes, or 100 minutes. A separate control group received no ischemic lesion. Regional CBF decreased significantly from 23.7 +/- 2.6 to 4.3 +/- 1.7 cc/100 gm/min during ischemia (p less than 0.01). Reperfusion resulted in initially normal flows (22.5 +/- 5.1 cc/100 gm/min) followed by a progressive hypoperfusion (11.3 +/- 2.7 cc/100 gm/min). All metabolites showed parallel significant (p less than 0.05) increases after transient ischemia and reperfusion compared to baseline levels (values (in pg/mg protein) were: TXB2 45.5 +/- 7.1 vs 23.3 +/- 3.6; 6-keto-PGF1 alpha 262.8 +/- 47.9 vs 175.8 +/- 26.8; PGE2 256.5 +/- 35.6 vs 112.5 +/- 11.2; and LTB4 37.8 +/- 4.6 vs 24.6 +/- 6). These levels were all significantly decreased (p less than 0.05) by pretreatment with indomethacin except for the leukotriene LTB4, which was increased. Transient cerebral ischemia results in a reperfusion abnormality and the local generation of cyclooxygenase products, which are reduced by pretreatment with indomethacin; however, cyclooxygenase inhibition may result in increased substrate availability for the lipoxygenase system. Studies of such an interaction may lead to new understandings of the pharmacological modification of detrimental vascular changes after transient cerebral ischemia.

6-Ketoprostaglandin F1 alpha↗
PubMed1986

High-sensitivity radioimmunoassay screening method for fentanyl.

A radioiodinated analog of fentanyl was synthesized for use with a commercially available radioimmunoassay for fentanyl. The sensitivity of the modified assay was at least 100 times greater than that of the original assay. Using this modified assay, concentrations of fentanyl as low as 1 pg/ml of fentanyl or fentanyl equivalents in equine urine were detected. Doses of fentanyl 100 times smaller than the minimum dose for a pharmacologic effect were detectable and a pharmacologically effective dose of fentanyl was detectable for up to 96 hours or more. The high sensitivity of the assay indicated that large numbers of urine samples (ie, 10 to 20) probably could be pooled and screened simultaneously, which would result in an economical analysis for fentanyl in the urine of horses after a race. Sufentanil and its metabolites also were detectable, using this assay, but at only about 1% of the efficiency at which fentanyl was detectable.

Animals↗
PubMed1986

Calmodulin and acetylcholine receptor clustering in embryonic chick myotubes.

We have used the calmodulin antagonists, trifluoperazine (TFP) and calmidazolium, to study the potential role of this protein in the movement of acetylcholine receptors (AChRs) to and from the myotube membrane, as well as in the formation of clusters of AChRs within the plasma membrane. Neither calmidazolium (up to 10(-6) M) nor TFP (10(-5) M) inhibited receptor degradation or the incorporation of new receptors (12 to 24 h). In addition, neither drug blocked the increased synthesis of receptors induced by chick brain extract, nor significantly affected AChR clusters already in the plane of the membrane at the time of drug addition. However, both drugs blocked new receptor clusters (induced by a basement membrane extract from Torpedo electric organ) from forming. These results indicate that receptors can move to and from the cell membrane in a calmodulin-independent fashion, but movement in the plane of the membrane to form a cluster requires the participation of calmodulin.

Animals↗
PubMed1985

Inactivation of pulmonary NAD+-dependent 15-hydroxyprostaglandin dehydrogenase by acrolein.

Acrolein, a highly reactive aldehyde found in cigarette smoke, was shown to induce time-dependent inactivation of NAD+-linked 15-hydroxyprostaglandin dehydrogenase from porcine lung. The inactivation process followed pseudo-first-order kinetics and was irreversible. Inactivation by acrolein can be prevented by prior incubation of the enzyme with GSH but not by subsequent addition of GSH during assay. Inactivation can be also protected fully by prior incubation of the enzyme with NAD+, but only partially with prostaglandin E1. The results suggest that acrolein alkylates the enzyme at the coenzyme binding site and inactivates the enzyme. Inactivation of pulmonary NAD+-linked 15-hydroxyprostaglandin dehydrogenase by acrolein may alter cellular and circulating thromboxane/prostacyclin ratios and subsequently disturb vascular homeostasis and augment inflammatory and anaphylactic responses in smokers.

Acrolein↗
PubMed1985

Selective inhibition of leukotriene B4 biosynthesis in rat pulmonary alveolar macrophages by dietary selenium deficiency.

Weanling male Fisher 344 rats were maintained on low selenium basal and Se-supplemented diets for 38 weeks. A several fold reduction in the glutathione peroxidase activity of the lung and liver tissues in rats maintained on low Se basal diet established their Se-deficient status. Analysis of the supernatants from resting pulmonary alveolar macrophage suspensions showed negligible extracellular release of PGE2, TXB2 and LTB4 in both diet groups. A challenge with opsonized zymosan particles increased the release of the same three arachidonic acid metabolites by several fold in both diet groups. The differences between the two diet groups with respect to the secretion of the products of the cyclooxygenase pathway, PGE2 and TXB2 were negligible. By contrast, a significant reduction in the extracellular release of LTB4 was observed in cells from animals on low selenium basal diet. These results suggest a selective inhibition of LTB4 biosynthesis in pulmonary alveolar macrophages by dietary deficiency of selenium.

Animals↗
PubMed1985

Synergistic stimulation of thromboxane biosynthesis by calcium ionophore and phorbol ester or thrombin in human platelets.

Phorbol ester PMA and low concentrations of calcium ionophore A-23187, which given separately have minimal effect in stimulating thromboxane synthesis in human platelets, showed marked synergism when given simultaneously. A similar synergism can be also demonstrated between thrombin or collagen and low concentrations of A-23187 but not of PMA. Simultaneous addition of thrombin and PMA results in less synthesis of thromboxane than that of thrombin alone. These studies suggest that protein kinase C activation by agonists may not only induce but also regulate thromboxane synthesis in human platelets.

Blood Platelets↗
PubMed1985

Induction of a decrease in renal NAD+-dependent 15-hydroxyprostaglandin dehydrogenase activity by estradiol in rats.

The effect of estradiol administration on renal and pulmonary NAD+-dependent 15-hydroxyprostaglandin dehydrogenase activities in rats was studied. Estradiol induced a significant decrease in renal but not in pulmonary enzyme activity. Kinetic parameters for the renal enzyme from control and treated groups were compared. An identical apparent Km for prostaglandin E2 was obtained for the enzyme from both groups. Vmax in the treated group was progressively decreased and plateaued 1 day after estradiol injection. The estradiol-induced decrease in renal enzyme activity was blocked by an anti-estrogen, nafoxidine, suggesting that the effect of estradiol was a was a receptor-mediated event. The decrease in renal prostaglandin catabolic enzyme activity induced by estradiol may result in prolonging the half-life of circulating prostacyclin and may account, in part, for the anti-thrombogenic effect of estradiol.

Animals↗
PubMed1985

12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) is an excellent substrate for NAD+-dependent 15-hydroxyprostaglandin dehydrogenase.

12-L-hydroxy-5,8,10-heptadecatrienoic acid (HHT) was found to be an excellent substrate for NAD+ dependent 15-hydroxyprostaglandin dehydrogenase from porcine kidney. Kcat/Km value of HHT was comparable to that of prostaglandin E although HHT is not a prostanoic acid derivative. Product of enzyme catalyzed oxidation of HHT was identified as 12-keto-5,8,10-heptadecatrienoic acid by gas chromatography-mass spectrometry. The fact that HHT is an excellent substrate for 15-hydroxyprostaglandin dehydrogenase suggest that HHT may have profound unrecognized biological actions and its inactivation may be via oxidation of the hydroxyl group.

Animals↗
PubMed1985

Gossypol, a potent inhibitor of arachidonate 5- and 12-lipoxygenases.

Gossypol inhibited 5- and 12-lipoxygenases of rat basophilic leukemia (RBL-1) cells with ID50 of 0.3 microM and 0.7 microM, respectively. Nearly two orders of magnitude of higher concentration of gossypol was required to inhibit prostaglandin synthetase. The inhibition was of a non-competitive type with respect to arachidonate.

Animals↗
PubMed1985

Polyamine and prostaglandin markers in focal cerebral ischemia.

This study examines the pathophysiology of stroke secondary to focal cerebral ischemia. The interaction of arachidonic acid metabolites and polyamines, a class of ubiquitous ornithine-derived molecules with important membrane effects on edema, Ca++-dependent endocytosis, platelet function, and prostaglandin (PG) formation, are correlated with regional changes in H2 clearance, cerebral blood flow (rCBF), ischemic edema, and somatosensory evoked responses (SSERs) after middle cerebral artery (MCA) occlusion. Thirty cats were studied up to 3 hours before and 6 hours after right MCA occlusion. Four areas of brain showing different levels of perfusion after MCA occlusion were sampled for tissue levels of PGs: 6-keto-PGF1 alpha, PGE2, and as well as thromboxane B2 (TXB2), ornithine decarboxylase activity (ODC) (a measure of polyamine activity) and gravimetric determination of cerebral edema. After right MCA occlusion, right hemisphere SSER amplitude decreased and interpeak latency increased markedly. rCBF was distributed into zones of dense, partial, and no ischemia ranging from 12.6 to 59.4 ml/100 g/minute. Ischemic edema was distributed inversely to rCBF and was increased in areas of dense ischemia (85.2 +/- 0.5%) and ischemia (82.7 +/- 0.7%), but not in partially ischemic or control areas. 6-Keto-PGF1 alpha (1257.3 pg/mg), PGE2 (1628.5 pg/mg), and TXB2 (1572.8 pg/mg) were all significantly (P less than 0.05) increased in areas of partial ischemia that had not yet developed edema. ODC levels were significantly elevated (3812 pmole/g/hour, P less than 0.05) and increased with time in areas of slightly denser ischemia that showed an intermediate increase in edema, but not the presence of infarction. This is the first demonstration that ODC, the rate-limiting enzyme for polyamine synthesis, is stimulated by cerebral ischemia.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗