Selective activation of some dihydrodiols of several polycyclic aromatic hydrocarbons to mutagenic products by prostaglandin synthetase.

The ability of prostaglandin synthetase (PGS) to cooxidize benzo(a)pyrene, benzo(a)anthracene, chrysene, and several of their dihydrodiol derivatives to mutagenic products was tested with Salmonella typhimurium strains TA98 and TA100. The microsomal fraction of ram seminal vesicles, a known source of PGS, in the presence of the PGS substrate arachidonic acid, metabolized benzo(a)pyrene-7,8-dihydrodiol, benzo(a)anthracene-3,4-dihydrodiol, and chrysene-1,2-dihydrodiol to mutagenic products. This activity was inhibited by the PGS inhibitor indomethacin.

The horseradish peroxidase-catalyzed oxidation of 3,5,3',5'-tetramethylbenzidine. Free radical and charge-transfer complex intermediates.

Benzidine and related compounds are well known substrates for horseradish peroxidase/H2O2 oxidation. Typically, two different colored products are formed. In this paper, we study the oxidation of 3,5,3',5'-tetramethylbenzidine.

Oxidative metabolism of diethylstilbestrol by prostaglandin synthetase.

The cooxidative metabolism of the transplacental carcinogen, diethylstilbestrol (DES), was examined using ram seminal vesicle microsomes. The major extractable metabolite was beta-dienestrol (Z,Z-DIES) and represented about 35% of the added DES in 3-min incubations supplemented with arachidonic acid. Its formation was dependent upon the presence of arachidonic acid, whereas reduced nicotinamide adenine dinucleotide phosphate failed to elicit Z,Z-DIES above background.

Chemical structure of the adducts formed by the oxidation of benzidine in the presence of phenols.

Bioactivation of carcinogens by peroxidases has received increasing attention since the discovery of the oxidation of carcinogens by prostaglandin hydroperoxidase. Benzidine and 3,5,3',5'-tetramethylbenzidine are oxidized by horseradish peroxidase and prostaglandin synthase to two-electron oxidation products (di-imines). Di-imines readily react with the phenolic anti-oxidant butylated hydroxyanisole to form adducts.

Prostacyclin and thromboxane A2 release in isolated rat lungs.

The influence of platelets and platelet membranes on the generation of prostacyclin (PGI2) and thromboxane A2 (TXA2) by isolated rat lung and porcine aortic endothelial cell, as measured by RIA of their stable end-products, 6-oxo-PGF1 alpha and TXB2 respectively, was studied. After introduction of either aspirin-treated platelets or membranes from aspirin-treated platelets to the perfusate, a 5-fold increase in the amount of 6-oxo-PGF1 alpha and TXB2 in the perfusate was observed. Treatment of the lung with aspirin produced a 50% reduction in the platelet-stimulated release of PGI2 and TXA2.

Metabolism of N-alkyl compounds during the biosynthesis of prostaglandins. N-Dealkylation during prostaglandin biosynthesis.

The microsomal fraction of ram seminal vesicles (RSV), when fortified with arachidonic acid, catalyzed the dealkylation of various N-methyl compounds. These included an analogous series of monomethyl- and dimethyl-substituted anilines as well as the drugs aminopyrine and benzphetamine. In contrast, S-alkyl and O-alkyl compounds were poor substrates for dealkylation by RSV microsomes fortified with fatty acid.

Prostaglandin endoperoxide synthetase-dependent cooxidation of acetaminophen to intermediates which covalently bind in vitro to rabbit renal medullary microsomes.

The metabolism of acetaminophen during prostaglandin biosynthesis was studied in vitro. [3H]Acetaminophen was rapidly metabolized by ram seminal vesicle microsomes to an intermediate(s) which covalently binds to microsomal protein. Arachidonic acid, a substrate for the fatty acid cyclooxygenase component of prostaglandin endoperoxide synthetase (PES), was required to support binding.

A free radical mechanism of prostaglandin synthase-dependent aminopyrine demethylation.

The mechanism of prostaglandin synthase-dependent N-dealkylation has been investigated using an enzyme preparation derived from ram seminal vesicles. Incubation of an N-alkyl substrate, aminopyrine, with enzyme and arachidonic acid, 15-hydroperoxyarachidonic acid, or tert-butyl hydroperoxide resulted in the formation of the transient aminopyrine free radical species. Formation of this radical species, which was detected by electron paramagnetic resonance spectroscopy and/or absorbance at 580 nm, was maximal approximately 30 s following initiation of the reaction and declined thereafter.

Respiratory movements alter the generation of prostacyclin and thromboxane A2 in isolated rat lungs: the influence of arachidonic acid-pathway inhibitors on the ratio between pulmonary prostacyclin and thromboxane A2.

The influence of hyperventilation on the spontaneous generation of prostacyclin and thromboxane A2 by isolated rat lungs was studied. Both prostacyclin and thromboxane A2, as measured by RIA of their stable end-products, 6-oxo-PGF1 alpha and TXB2 respectively, were continuously released into the perfusate. However, the concentration of prostacyclin in the perfusate was higher than thromboxane A2.

Separation of prostaglandins, thromboxane, hydroxy fatty acids and arachidonic acid by high pressure liquid chromatography.

Separation of the major metabolites of arachidonic acid (AA) produced by the cyclo-oxygenase and the lipoxygenases was achieved by using reverse phase high-pressure liquid chromatography. Prostaglandins (PGs), thromboxane B2 (TXB2), and AA were separated on a C-18 radial compression column. An initial isocratic elution resolved the PGs and TXB2 which was followed by a linear gradient in order to elute AA.

Prostaglandin and thromboxane production by fibroblasts and vascular endothelial cells.

We have compared the production of prostaglandins in fibroblast-like cells and endothelial cells in culture. Of the fibroblasts studied 10T1/2, SHE, BP6T and KD produce significant amounts of PGI2, PGE2 and PGF2F2 under optimal culture conditions, but only 3T3 and BHK produce TXA2 in addition to PGI2. The adult bovine aortic endothelial cells (ABAE) and fetal bovine heart endothelium (FBHE) synthesise PGI2 but not TXA2, either from endogenous or exogenous substrates.

A carbon-centered free radical intermediate in the prostaglandin synthetase oxidation of arachidonic acid. Spin trapping and oxygen uptake studies.

The ESR spin-trapping technique has been used to identify a free radical involved in the oxygenation of arachidonic acid by ram seminal vesicle microsomes. The ESR spectrum of the radical adduct indicates that a carbon-centered arachidonic acid free radical has been observed. The formation of this species is inhibited by indomethacin, but not by phenol, and it is probably the first intermediate formed during the prostaglandin synthetase-catalyzed oxidation of arachidonic acid.

Enhanced thromboxane B2 release from challenged guinea pig lung after oxygen exposure.

The effects of exposure to 100% oxygen (O2) on the release of thromboxane B2 (TXB2) and prostaglandins (PG) from guinea pig lungs during anaphylaxis were studied. Lungs from sensitized guinea pigs were isolated, perfused, and challenged. Serologic examination of the perfusate showed that larger amounts of TXB2, 6-keto-PGF1 alpha, PGE2, and PGF2 alpha were released from the lungs of animals previously exposed to 100% O2 for 72 h.

Studies on the persistence of basic amines in the rabbit lung.

We have investigated the time-course of the pulmonary deposition of imipramine (IMIP) following a single iv injection into rabbits. A pool of IMIP and its demethylated metabolites, which exhibited considerable persistence (half-life of decay = 4 hr), was formed in the lung. This pool, now called the slowly effluxable pool (SEP), appears to be synonymous with the noneffluxable pool (NEP), which we have previously shown to be formed with IMIP in the isolated perfused lung (PL).

Inhibition of pulmonary prostaglandin metabolism by exposure of animals to oxygen or nitrogen dioxide.

The effects of exposure of animals to 100% O2 and NO2 on the rate of prostaglandin metabolism by lung and kidney were studied in vitro. Exposure of guinea pigs to 100% O2 for 48 h inhibited the metabolism of prostaglandin F2 alpha by both NAD+- and NADP+-dependent prostaglandin dehydrogenase in lung, but had no effect on the metabolism in kidney. Succinate dehydrogenase, but not glucose 6-phosphate dehydrogenase, in guinea-pig lung was inhibited by exposure to 100% O2.