Search PubMed⌕ Search

Biomedical subjects

H H Tai

Publications and source records attributed to H H Tai.

At least 145 records · Page 8Linked to original sources
PubMed1984

Calcium stimulation of a novel 12-lipoxygenase from rat basophilic leukemia (RBL-1) cells.

Cytosolic fraction of RBL-1 cells transformed arachidonic acid to 12-HETE in addition to the well-recognized 5-hydroxyeicosatetraenoic acid (5-HETE) in the presence of Ca2+, Mg2+ or Mn2+. The identity of 12-HETE was confirmed by gas chromatography-mass spectrometry. Syntheses of 12-HETE and 5-HETE were catalyzed by separate lipoxygenases, since the formation of each product showed differential sensitivity to inhibitors and temperature. 12-Lipoxygenase from RBL-1 cells was also found to be distinct from the enzyme from platelets in calcium sensitivity.

Animals↗
PubMed1984

Pulmonary NAD+-linked 15-hydroxyprostaglandin dehydrogenase activity is decreased by cigarette smoking.

Male rats were exposed to freshly generated cigarette smoke once daily for 4 to 13 weeks. Inhalation of smoke was verified by elevated level of carboxyhemoglobin. NAD+-dependent 15-hydroxyprostaglandin dehydrogenase activity, the key enzyme responsible for biological inactivation of prostaglandins, was found to decrease in lung but not in kidney or stomach following cigarette smoke exposure. The consequence of impaired pulmonary metabolism of prostaglandins and thromboxane may result in alteration of vascular homeostasis and subsequently lead to cardiovascular disorders commonly found in smokers.

Animals↗
PubMed1984

Changes in prostacyclin and thromboxane biosynthesis and their catabolic enzyme activity in kidneys of aging rats.

The effects of aging on the prostacyclin and thromboxane biosynthesis and prostaglandin catabolic enzyme activity in rat kidney were investigated. The prostacyclin biosynthesis, using arachidonic acid as substrate, was the greatest in young kidneys (2 months old) and then progressively decreased in mature (12 months old) and old (24 months old) kidneys, while thromboxane biosynthetic activity showed no significant change as a function of age. When prostaglandin H2 was used as substrate, the prostacyclin and thromboxane biosynthesis showed similar results as when arachidonic acid was used as substrate; the prostacyclin biosynthesis progressively decreased and thromboxane biosynthesis showed no significant change as a function of age. The fatty acid cyclooxygenase in kidney was measured by a specific radioimmunoassay. No significant change in renal fatty acid cyclooxygenase as a function of age was found. Thus, we concluded that the progressive decrease in renal prostacyclin biosynthesis as a function of age is due to a defect in prostacyclin synthetase in aged kidneys. The prostaglandin catabolic enzyme, NAD+-dependent 15-hydroxyprostaglandin dehydrogenase, in kidneys was also investigated. The enzyme activity progressively decreased as a function of age, which suggested a decrease in the metabolism of thromboxane A2 in aged kidneys. The present results, indicating a decrease in renal prostacyclin biosynthesis and renal 15-hydroxyprostaglandin dehydrogenase activity with aging, might contribute to a plausible explanation of the progressive decrease in renal functions in the elderly.

6-Ketoprostaglandin F1 alpha↗
PubMed1984

A radioimmunoassay for prostaglandin endoperoxide synthetase.

A radioimmunoassay for prostaglandin endoperoxide synthetase has been developed. The antiserum was produced in rabbits by repeated immunization with the purified sheep seminal vesicular enzyme. The enzyme was labeled by chloramine T mediated radioiodination and purified by Sephadex G-25 gel filtration followed by hydroxyapatite column chromatography. Separation of bound from free enzyme was achieved by double antibody method. The radioimmunoassay was capable of detecting 1 ng per assay tube. The antiserum was found to crossreact with the enzyme from various animal tissues. Subcellular localization of the enzyme in sheep seminal vesicular gland indicated that distribution of immunoreactive enzyme in subcellular fractions correlated well with that of enzyme activity with highest enrichment in the microsomal fraction. Application of radioimmunoassay to the measurement of immunoreactive enzyme in kidneys of normotensive and genetically hypertensive rats revealed that the level was significantly increased in hypertensive rats at 18 weeks but not at 10 weeks of age. The level of immunoreactive enzyme also correlated well with that of enzyme activity. The availability of a radioimmunoassay will provide a valuable tool for probing the structure and function of the enzyme in various physiological and pathophysiological states.

Animals↗
PubMed1984

Platelet-activating factor raises airway and vascular pressures and induces edema in lungs perfused with platelet-free solution.

The effects of synthetic platelet-activating factor (PAF) on guinea pig lung were examined in isolated lungs perfused with platelet-free Krebs-Ringer solution. When PAF (1 microgram) was injected into the pulmonary artery (PA), it markedly increased airway pressure (maximal increase, 84.7%) and moderately raised PA pressure (maximal increase, 22.8%). The same dose also provoked a massive (29-fold) release of thromboxane B2 (TXB2), the stable metabolite of TXA2, into the perfusate, beginning before the increases in airway and PA pressures. The concentration of 6 keto-PGF1 alpha, the stable metabolite of prostacyclin, also increased (to 5 times control levels) about 70 s after peak release of TXB2. Indomethacin completely blocked TXB2 release, reduced the magnitude of airway pressure increase by 79%, and shortened its duration, as well as the duration of the PA pressure rise. Larger concentrations of PAF (3 and 10 micrograms) produced even greater increments in airway and PA pressures, but these were only moderately attenuated by indomethacin. Also, PAF increased extravascular lung water, as evidenced by increases in wet/dry lung weight and lung/body weight ratios. In a concentration of 0.1 microgram, PAF had no effects on airway or PA pressures, nor did it stimulate TXB2 or 6-keto-PGF1 alpha release. Lyso-PAF was similarly ineffective. We conclude that PAF induces airway constriction, pulmonary hypertension, and pulmonary edema in guinea pig lung independently of platelets. These effects are associated with stimulated synthesis of TXA2, but the mechanisms of their production remain to be determined.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Cigarette smoking stimulates lipoxygenase but not cyclooxygenase pathway in platelets.

Male rats were exposed to freshly generated cigarette smoke once daily for 4 to 8 weeks. Inhalation of smoke was verified by elevated level of carboxyhemoglobin. Arachidonate metabolism through lipoxygenase and cyclooxygenase pathways in platelets was determined. Cigarette smoking increased 12-lipoxygenase activity significantly without affecting the cyclooxygenase pathway. In view of platelet-leukocyte interactions and potent chemotactic activity of 12-HETE for aortic smooth muscle cell migration, increased 12-lipoxygenase activity may predispose individuals to atherosclerosis, thromboembolism and emphysema commonly found in smokers.

Animals↗
PubMed1983

Diglyceride/monoglyceride lipases pathway is not essential for arachidonate release in thrombin-activated human platelets.

Human platelets prelabeled with arachidonate exhibited a rapid and transient rise in arachidonoyl monoglyceride in addition to arachidonoyl diglyceride following thrombin stimulation. Substantial release of arachidonate and its metabolites also occurred at the early phase. Preincubation of labeled platelets with RHC 80267, a potent inhibitor of diglyceride lipase, prior to thrombin stimulation abolished the transient rise in monoglyceride but not the increase in diglyceride and the release of arachidonate and its metabolites. These results suggest that diglyceride does metabolize to monoglyceride and release arachidonate in intact platelets. However, the diglyceride/monoglyceride lipases pathway does not appear to be essential in releasing arachidonate during thrombin stimulation.

Arachidonic Acid↗
PubMed1983

Changes in arachidonate metabolism in aortas and platelets in aging rats.

Prostacyclin formation by aortas, thromboxane biosynthesis and 12-lipoxygenase pathway in platelets as a function of age was investigated. Our results indicate an age-related decrease in prostacyclin production by aortas, while no significant change in thromboxane biosynthesis in platelets from mature (12 month old) to senescent (24 month old) rats was observed. Evidence is also presented indicating a decrease in 12-L-hydroperoxy-5,8,10,14-eicosatetraenoic acid (12-HPETE) peroxidase activity in platelets as a function of age.

6-Ketoprostaglandin F1 alpha↗
PubMed1983

Induction of fatty acid cyclooxygenase in rat aortic smooth muscle cells by estradiol.

We have previously reported that estradiol stimulates prostacyclin biosynthesis in cultured rat aortic smooth muscle cells by increasing fatty acid cyclooxygenase activity, and induction of new protein biosynthesis is involved since the effect of estradiol is blocked by cycloheximide treatment. In order to see whether estradiol stimulates de novo biosynthesis of fatty acid cyclooxygenase in cells, a specific radioimmunoassay of fatty acid cyclooxygenase was used to measure the enzyme. Estradiol significantly increased immunoreactive fatty acid cyclooxygenase in cells. Consequently, increase in cyclooxygenase activity results in the production of more prostaglandin endoperoxides for final increased synthesis of prostacyclin in these cells.

Animals↗
PubMed1982

Resolution into two different forms and study of the properties of phosphatidylinositol-specific phospholipase C from human platelet cytosol.

Two forms of phosphatidylinositol-specific phospholipase C from human platelet cytosol were resolved by DEAE-cellulose chromatography and purified further by hydrophobic chromatography. Both forms utilized phosphatidylinositol as the best substrate. However, the enzyme did not distinguish 2-arachidonylphosphatidylinositol from 2-oleoylphosphatidylinositol although the former substrate was known to be a predominant species in human platelets. Both forms exhibited pH optimum at 7.0. Both activities were inhibited completely by 1 mM EDTA and the inhibited preparations could be restored to full activity or to 60% by free Ca2+ or Co2+, respectively, at 100 microM. Higher concentrations of either ion were inhibitory. Other metal ions were ineffective. Addition of calmodulin in the presence of Ca2+ did not show any additional effect. Both forms were inhibited comparably by various phospholipids, fatty acids and detergents, suggesting that phosphatidylinositol in membranes might be a poor substrate for the enzyme. Initiation of phosphatidylinositol breakdown through the phospholipase C pathway may require additional activator(s). A variety of anti-platelet drugs, including phenylthiazines, local anesthetics and mepacrine, were found to be potent inhibitors of the enzyme, suggesting that these drugs might inhibit platelet function by inhibiting the early phase of arachidonate release.

Blood Platelets↗
PubMed1982

Stimulation of 12-lipoxygenase activity in rat platelets by 17 beta-estradiol.

The effects of estradiol on the endogenous fatty acid (specifically, arachidonic acid) composition of cellular phospholipid fractions and the 12-lipoxygenase activity in rat platelets in vivo were studied. Estradiol had no significant effect on the endogenous fatty acid composition of cellular phospholipid fractions. However, estradiol significantly increased 12-lipoxygenase activity in platelets in a dose-dependent manner. The stimulatory effect of estradiol on platelet lipoxygenase was blocked by the anti-estrogen nafoxidine hydrochloride which was injected simultaneously together with estradiol in vivo, suggesting that the effect in target cells was due directly to estradiol.

Animals↗