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Biomedical subjects

H H Tai

Publications and source records attributed to H H Tai.

At least 163 records · Page 9Linked to original sources
PubMed1982

Hypoxia stimulates prostacyclin generation by dog lung in vitro.

We have investigated the possibility that pulmonary biosynthesis of prostacyclin and thromboxane A2 (TXA2) may be affected by variations in PO2. Fresh lung homogenated from 8 dogs were incubated for 1 hour at 37 degrees C in Krebs-Ringer solution, at high (492 mmHg) or low (53 mmHg) PO2. After incubation, the stable metabolites of prostacyclin (6-keto-PGF1) and of TXA2 (TXB2) were measured by radioimmunoassay. The basal ("pre-incubation") levels of these metabolites, measured in tubes in which biosynthesis was arrested by the addition of indomethacin (10 g/ml), were 0.76 +/- 0.15 and 0.76 +/- 0.11 ng/mg wet wt. for 6-keto-PGF1 alpha, in high and low PO2, respectively, and 0.97 +/- 0.09 and 0.82 +/- 0.15 x 10(-1) ng/mg wet wt. for TXB2, in high and low PO2 respectively. Synthesis during incubation in other tubes was estimated by subtracting basal values from those measured at the end of incubation. More 6-keto-PGF1 alpha was formed in homogenates exposed to low PO2 (3.01 +/- 0.45) than in those exposed kept at high PO2 (1.89 +/- 0.37, p less than 0.001), but equal amounts of TXB2 were bound under both conditions. These results suggest that hypoxia may stimulate pulmonary prostacyclin synthesis; a pulmonary vasodilator, prostacyclin may help modulate hypoxic vasoconstriction in the lung.

6-Ketoprostaglandin F1 alpha↗
PubMed1982

A radioimmunoassay for 6-ketoprostaglandin E1.

A radioimmunoassay for 6-ketoprostaglandin E1 has been developed. 6-keto-prostaglandin E1 antibodies were produced in rabbits by repeated immunization with 6-ketoprostaglandin E1 coupled to bovine serum albumin. [125]-labeled hapten with high specific radioactivity was prepared by radioiodination of 6-ketoprostaglandin in E1-tyrosine methyl ester conjugate followed by purification with thin layer chromatography. The antibodies showed good specificity toward 6-ketoprostaglandin E1 and crossreacted only significantly with prostaglandin E1. The sensitivity of the assay was 10 pg per assay tube. Application of the radioimmunoassay was demonstrated by the detection of immunoreactive 6-ketoprostaglandin E1 from 6-ketoprostaglandin F1 alpha catalyzed by swine renal NADP+-linked 9-hydroxyprostaglandin dehydrogenase.

Alprostadil↗
PubMed1981

Purification of thromboxane synthetase and evidence of two distinct mechanisms for the formation of 12-L-hydroxy-5,8,10-heptadecatrienoic acid by porcine lung microsomes.

Synthesis of thromboxane B2 and 12-L-hydroxy-5,8,10-heptadecatrienoic acid by crude microsomes and by partially purified thromboxane synthetase from porcine lung has been studied. Formation of both compounds catalyzed by the purified enzyme is inhibited similarly by imidazole or increased temperature (52 degrees C). However, during the initial stages of purification only the production of thromboxane B2 was diminished by imidazole or increased temperature, indicating the presence of an additional mechanism for the formation of 12-L-hydroxy-5,8,10-heptadecatrienoic acid. This novel mechanism is attributed to the effect of nondialyzable heat-stable factor(s) present in the crude preparation which stimulates the formation of 12-L-hydroxy-5,8,10-heptadecatrienoic acid from prostaglandin H2 in a time-dependent manner.

Animals↗
PubMed1981

Abnormal platelet response to thromboxane A2.

To determine the pathogenetic mechanism of a hereditary primary platelet release disorder, arachidonic acid metabolism via the cyclooxygenase pathway was investigated. The propositus' platelets exhibited defective release reaction and second-wave aggregation when stimulated by sodium arachidonate or U46619, a thromboxane A2 (TXA2) agonist. The lack of platelet response to U46619 suggested that the defect was beyond the thromboxane synthetase level. Furthermore, thromboxane B2 (TXB2) formation in the propositus' platelets (558.52 ng/10(8) platelets) was within the normal range (574.29 +/- SD 27.39 ng/10(8) platelets) and TXA2 formation appeared to be adequate for aggregating normal platelets. The results were indicative of an abnormal platelet response to TXA2. Failure of the propositus' platelets to aggregate in response to TXA2 formed in normal platelet-rich plasma induced by arachidonate confirmed this notion. To gain further insight, platelet cyclic (c) AMP content was determined. Prostacyclin induced a significant elevation of the propositus' platelet cAMP level comparable to normal values. U46619 suppressed prostaglandin I2-induced cAMP elevation in normal subjects but had no such effect in the patient. We conclude that the primary release disorder observed in this kindred is due to an abnormal platelet respnse to TXA2 possibly because of TXA2/PGH2 receptor abnormalities.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1980

9-Hydroxyprostaglandin dehydrogenase from rat kidney. Purification to homogeneity and partial characterization.

A 9-hydroxyprostaglandin dehydrogenase has been purified from rat kidney to apparent homogeneity. The molecular weight of the enzyme as determined by gel filtration was 33,000. Electrophoresis in sodium dodecyl sulfate gave a value of 34,000 indicating the absence of subunits. The enzyme catalyzes NAD+-specific irreversible oxidation of 15-keto-13,14-dihydro-prostaglandin F2 alpha as well as of 15-keto-PGF2 alpha and PGF2 alpha although at a lesser degree. It does not catalyze the oxidation of 6-keto-PGF1 alpha. The enzyme was sensitive to sulfhydryl inhibitors and was inhibited by prostaglandins, fatty acids, triiodothyroacetic acid, and indomethacin.

Animals↗
PubMed1980

NAD+-dependent 15-hydroxyprostaglandin dehydrogenase from porcine kidney. I. Purification and partial characterization.

The cytoplasmic NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (11 alpha, 15-dihydroxy-9-oxoprost-13-enoate:NAD+ 15-oxidoreductase, EC 1.1.1.141) from porcine kidney was purified to a specific activity of 1.2 unit per mg protein by a series of chromatographic techniques including affinity chromatography. The native molecular weight of the enzyme was estimated to be 45 000. Substrate specificity studies indicated that the enzyme was NAD+-specific and was able to catabolize readily various prostaglandins, with the exception of prostaglandin B and thromboxane B. The enzyme was inhibited by sulfhydryl inhibitors, diuretic drugs and various fatty acids.

Animals↗
PubMed1980

NAD+-dependent 15-hgydroxyprostaglandin dehydrogenase from porcine kidney. II. Kinetic studies.

The kinetic mechanism of porcine renal NAD+-dependent 15-hydroxyprostaglandin dehydrogenase (11 alpha, 15-dihydroxy-9-oxoprost-13-enoate:NAD+ 15-oxidoreductase, EC 1.1.1.141) was investigated. Initial velocity studies gave intersecting double reciprocal plots that conform to a sequential mechanism. Product inhibition studies indicated that 15-keto-prostaglandin E2 exhibited linear non-competitive inhibtion with respect to either prostaglandin E2 or NAD+, and NADH yielded linear competitive inhibition with respect to NAD+. Dead-end inhibition studies showed that adenosine-5'-diphosphoribose inhibited the enzyme competitively with respect to NAD+ as expected, but inhibited the enzyme non-competitively with respect to prostaglandin, E2. Alternate substrate studies indicated that a mixture of 3-acetyl-NAD+ and NAD+ gave a concave upward double reciprocal plot, while a mixture of prostaglandin E2 and prostaglandin F2 alpha yielded a linear plot. These results are consistent with an ordered Bi-Bi mechanism where NAD+ is added first, followed by prostaglandin E2, and 15-keto-prostaglandin E2 is released, followed by NADH.

Animals↗
PubMed1980

Synthesis of [5,6-3H]arachidonic acid and its use in development of a sensitive assay for prostacyclin synthetase.

[5,6-3H]arachidonic acid has been prepared by catalytic reduction of eicosa-cis-8,11,14-trien-5-ynoic acid (IV) over Lindlar catalyst. When either [5,6-3H]arachidonic acid or [5,6-3H]PGH2 is converted into PGI2 by swine aortic microsomes, the tritium at C-6 is lost to the medium. Thus, the progress of this enzymic rearrangement may be monitored by following the rate of tritium release. As swine aortic microsomes contain only low levels of cyclooxygenase, it is necessary to fortify the system with ram seminal vesicular microsomes (rich in cyclooxygenase) when [5,6-3H]arachidonic acid is used as the indirect substrate.

8,11,14-Eicosatrienoic Acid↗