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Biomedical subjects

H H Tai

Publications and source records attributed to H H Tai.

At least 181 records · Page 10Linked to original sources
PubMed1980

Radioimmunological assay of prostacyclin synthetase activity.

A radioimmunoassay for 6-oxoprostaglandin F1 alpha has been developed. 6-Oxoprostaglandin F1 alpha antiplasma was produced in rabbits by repeated immunization with 6-oxoprostaglandin F1 alpha coupled to bovine serum albumin. [125I] -labelled hapten with high specific radioactivity was prepared by radioiodination of 6-oxoprostaglandin F1 alpha-tyrosine methyl ester conjugate followed by purification with thin layer chromatography. The antibodies showed good specificity toward 6-oxoprostaglandin F1 alpha and crossreacted only significantly with prostaglandin F1 alpha. The radioimmunoassay was applied to the determination of prostacyclin synthetase activity in swine aorta microsomes using arachidonic acid and prostaglandin H2 as indirect and direct substrates. The enzyme assay was validated by the criteria that the formation of 6-oxoprostaglandin F1 alpha, immunoreactivity from either substrates was both time and enzyme protein dependent, and was inhibitable by specific inhibitors of the enzyme system.

6-Ketoprostaglandin F1 alpha↗
PubMed1980

Inhibition of thromboxane synthesis and platelet aggregation by pyridine and its derivatives.

Pyridine inhibited the conversion of PG endoperoxide to TXA2 catalyzed by TX synthetase from human platelet and swine lung microsomes. The inhibitory potency of pyridine is abolished by derivatizing pyridine at the 2-position but is increased by introducing hydrophobic substituents at 3- or 4-positions, with 3-substituted pyridines being the most potent inhibitors. Inhibition by pyridine and its derivatives was also selective, since other enzymes in the arachidonic acid cascade were not significantly affected. Pyridine and the active derivatives also inhibited human platelet aggregation induced by arachidonic acid or ADP.

Animals↗
PubMed1978

Studies on the thromboxane synthesizing system in human platelet microsomes.

The thromboxane synthesizing system from human platelets has been characterized by using arachidonic acid and prostaglandin endoperoxide as indirect and direct substrates. The synthesis of thromboxanes from either substrates catalyzed by the microsomal fraction was monitored by measuring the formation of thromboxane B2 immunoreactivity. Both hemoglobin and phenolic compounds were required for the maximal synthesis of thromboxane B2 from arachidonic acid but not from prostaglandin endoperoxide. Studies on the kinetics of the formation of thromboxane B2 from either substrates indicated that the synthesis of prostaglandin endoperoxide intermediate is the rate-limiting step in the overall production of thromboxanes from arachidonic acid. Effect of the microsomal protein concentrations on the rate of formation of thromboxane B2 showed concave upward relationship suggesting the possible involvement of endogenous stimulator(s) in thromboxane synthetase catalyzed reaction. A variety of compounds including sulfhydryl inhibitors, prostaglandin endoperoxide analog, prostaglandin antagonist, N-0164, and N-substituted imidazoles could directly inhibit the thromboxane synthetase, while nonsteroidal antiinflammatory drugs apparently affected the prostaglandin endoperoxide synthetase which catalyzes the synthesis of the immediate precursor of thromboxanes.

Arachidonic Acids↗
PubMed1978

Transformation of arachidonate into 6-oxoprostaglandin F1 alpha, thromboxane B2 and prostaglandin E2 by sheep lung microsomal fraction.

In the presence of haemoglobin and isoproterenol, the microsomal fraction of sheep lung catalysed the conversion of arachidonate predominantly into thromboxane B2 and to a lesser extent into 6-oxoprostaglandin F1alpha. Very little prostaglandin E2 and prostaglandin F2alpha were formed. If reduced glutathione was added in combination with haemoglobin and isoproterenol, the synthesis of prostaglandin E2 was favoured over that of thromboxane B2 and 6-oxoprostaglandin F1alpha. The identities of these products were confirmed by t.l.c. and by combined g.l.c.-mass spectrometry. These results indicate that microsomal fraction of sheep lung possesses active prostaglandin synthase, prostacyclin synthase and thromboxane synthase activities.

Animals↗
PubMed1978

Impairment of secretin release in celiac sprue.

Plasma secretin concentrations and pH in the second portion of duodenum were measured in the fasting state and during duodenal infusion of HCl in five patients with untreated celiac sprue, five celiac sprue patients after gluten-free diets, and five normal subjects. Mean fasting plasma secretin concentrations were insignificantly lower in untreated sprue patients (4.1 +/- 1.4 pg/ml) than in normal subjects (5.7 +/- 0.59 pg/ml). During 30-min intraduodenal infusions of 0.1 N HCl at 0.20 mEqH+/min, mean plasma secretin concentrations were significantly lower in untreated sprue patients (5.8 +/- 1.8 pg/ml) than in normal subjects (25.4 +/- 1.60 pg/ml, P less than 0.01). The increases in mean secretin concentrations over fasting were 2.1 +/- 0.82 pg/ml in untreated sprue patients compared to 19.7 +/- 1.47 pg/ml in normal subjects (P less than 0.01), a ninefold difference. The results indicate that endogenous release of secretin in response to duodenal acidification is impaired in patients with celiac sprue.

Adult↗
PubMed1978

Plasma secretin concentrations in fasting and postprandial state in man.

Plasma immunoreactive secretin concentrations were determined in both healthy subjects and patients with duodenal ulcer. The modified radioimmunoassay method could detect significant increases in the plasma secretin concentrations when 0.05 N HCl was infused intraduodenally at a rate of 1.1 and 2.2 ml/min. The mean fasting plasma secretin concentration of 13 normal healthy subjects was 4.4 +/- 0.38 pg/ml which was significantly less (P less than 0.01) than that of 13 duodenal ulcer patients, 6.9 +/- 0.64 pg/ml. In both groups ingestion of a meat-containing meal resulted in significant increase in the plasma secretin concentrations. Recording of pH from proximal duodenum indicated that pH fell periodically below 4.5 during the postprandial period, indicating that only a short segment of proximal duodenum was exposed to acid after meal. The postprandial rise in plasma secretin levels was abolished when antral pH was raised 5.5 by intragastric infusion of 0.3 N NaHCO3 solution. These observations indicate that although fasting plasma secretin levels are low, the plasma secretin levels increase significantly after ingestion of a meal. This increase appears to be attributable to an increased amount of acid delivered to the proximal duodenum, and patients with duodenal ulcer were found to release more secretin during the postprandial period than normal subjects.

Adult↗
PubMed1976

Mechanism of prostaglandin biosynthesis in rabbit kidney medulla. A rate-limiting step and the differential stimulatory actions of L-adrenaline and glutathione.

Microsomal prostaglandin synthase (EC 1.14.99.1) from rabbit kidney medulla was assayed with [5,6,8,9,11,12,14,15-3H]-and [1-14C]-arachidonic acid as the substrate. The ratios of prostaglandin F2 alpha to prostaglandin E2 and to prostaglandin D2 were determined by both 3H and 14C labelling. When 3H was used as a label the ratios were much higher than with 14C labelling indicating that the removal of hydrogen at C-9 or C-11 was the rate-limiting step in the biosynthesis of prostaglandin E2 or prostaglandin D2. This finding shows that the octatritiated arachidonic acid is not the appropriate substrate marker for studying the regulation of the synthesis of different prostaglandins by various agents. When the enzyme assay was carried out in the presence of SnCL2, which was capable of accumulating exclusively prostaglandin F2alpha at the expenses of prostaglandin E2 and prostaglandin D2, the addition of L-adrenaline to the microsomal fraction either alone or with reduced glutathione equally stimulated the formation of prostaglandin F2alpha, whereas the addition of reduced glutathione to the microsomal fraction either alone or with L-adrenaline produced no additional effect. These results suggest that endoperoxide is formed as the common intermediate for the biosynthesis of three different prostaglandins in rabbit kidney medulla, and that L-adrenaline stimulates the synthesis of endoperoxide, whereas reduced glutathione facilitates the formation of prostaglandins from endoperoxide.

Animals↗
PubMed1976

Enzymatic synthesis of (15s)-[15-3h]prostaglandins and their use in the development of a simple and sensitive assay for 15-hydroxyprostaglandin dehydrogenase.

The stereospecificity of swine renal NAD+-dependent 15-hydroxyprostaglandin dehydrogenase has been determined. It was found that the enzyme is a B-side specific dehydrogenase. (15S)-[15-3H]Prostaglandins were synthesized by stereospecific transfer of the tritium label of D-[1-3H]galactose to prostaglandins by coupling 15-hydroxyprostaglandin dehydrogenase with beta-D-galactose dehydrogenase, an enzyme of the same stereospecificity. A simple and sensitive assay for 15-hydroxyprostaglandin dehydrogenase was developed based on the stereospecific transfer of the tritium label of tritiated prostaglandins to glutamate by coupling 15-hydroxyprostaglandin dehydrogenase with glutamate dehydrogenase. The amount of prostaglandin oxidized is determined by the radioactivity of labeled glutamate present in the supernatant after charcoal precipitation of labeled prostaglandin. Concurrent assays with the present tritium release method and the thin-layer chromatography method indicated excellent correlation. The assay was employed to study some of the properties of swine renal 15-hydroxyprostaglandin dehydrogenase in crude extract and the distribution of enzyme activity in various tissues of rat. Enzyme activity was linear for the first 10 min studied and was nonlinear with increasing amounts of crude enzyme, indicating the possible presence of endogenous inhibitor(s). Apparent Km's for PGE2, PGF2alpha, and PGA2 were found to be 2.5, 12.5, and 3.9 muM, respectively. The distribution pattern indicated high levels of enzyme activity in gastrointestinal tract, lung, kidney, and spleen. The assay method may prove to be valuable for studying enzyme turnover and enzyme regulation by hormonal and pharmacological agents.

Alcohol Oxidoreductases↗