Identification of the major urinary metabolite of prostaglandin E3 in the rat

[11,12-3H2]Prostaglandin E3 was administered subcutaneously into male Sprague-Dawley rats in doses of 0.4 microgram-10 mg/kg body weight. 40-60% of the administered radioactivity was excreted in the urine. The major metabolite was isolated by solid phase extraction followed by three steps of high-performance liquid chromatography. The structure of the major metabolite (5-11% of the administered radioactivity) was 7 alpha,11 alpha-dihydroxy-5-ketotetranorprosta-9,13-dienoic acid as shown by gas-liquid chromatography-mass spectrometry and by its conversion into 11 alpha-hydroxy-5-ketotetranorprosta-4(8),9, 13-trienoic acid.

Influence of dietary partially hydrogenated vegetable and marine oils on membrane composition and function of liver microsomes and platelets in the rat

The aim of the present study was to investigate the influence of partially hydrogenated vegetable and marine oils on membrane composition and function of liver microsomes and platelets with particular reference to the metabolism of linoleic acid and the production of arachidonic acid metabolites. Four groups of male weanling rats were fed linoleic acid supplemented diets containing 20% (w/w) of partially hydrogenated low erucic acid rapeseed oil (HLRSO), partially hydrogenated herring oil (HHO), olive oil (OO) and trierucin + triolein (TE) for 10 weeks. An additional two groups were fed partially hydrogenated low erucic acid rapeseed oil and partially hydrogenated herring oil without linoleic acid supplementation (HLRSO- and HHO-, respectively). Substantial amounts of trans fatty acids were incorporated into liver microsomes (12.6% in group HLRSO) and platelets (7.0% in group HLRSO-). This incorporation was not dependent on the dietary linoleic acid level. Hepatic microsomal delta5 -desaturase activity was significantly increased after HLRSO feeding compared to 00 feeding. Delta6 -Desaturase activity did not vary in the linoleic acid supplemented groups. Both delta5 -and delta6 -desaturase activities were significantly increased in groups without linoleic acid supplementation. Docosenoic acid was incorporated into platelet phospholipids in contrast to liver microsomes. In the platelet, docosenoic acid seemed to have a special preference for phosphatidylserine. Very small amounts were incorporated into platelet phosphatidylinositol. Feeding diets HLRSO, HHO and 00 did not influence rat platelet cyclooxygenase or 12-lipoxygenase activity. Platelets from rats fed TE, however, produced significantly less 12-hydroxy-5,8,10,14-eicosatetraenoic acid (12-HETE) than platelets from rats fed OO. Feeding of HLRSO- and HHO- resulted in a significantly diminished production of the arachidonic acid metabolites 12-HETE, 12-hydroxy-5,8,10-heptadecatrienoic acid (HHT) and 6-keto-prostaglandin F1alpha in stimulated platelets and aorta. Thus, high dietary levels of trans isomers of monoenoic acids do not interfere with platelet cyclooxygenase or lipoxygenase activity provided sufficient amounts of linoleic acid are available.

Formation of 15-HETE as a major hydroxyeicosatetraenoic acid in the atherosclerotic vessel wall

Atherosclerosis was induced in New Zealand White rabbits through cholesterol feeding. Aortae were taken out from treated animals and incubated with arachidonic acid. Aortae from cholesterol-fed animals converted arachidonic acid into 15-hydroxy-5,8,11,13-eicosatetraenoic acid (15-HETE). This conversion was not seen in aortae from control animals. The immediate precursor of 15-HETE, 15-HPETE, is an inhibitor of prostacyclin synthetase and might hamper prostacyclin production.

Validation of radioimmunoassay for estradiol-17 beta by isotope dilution-mass spectrometry and by a test of radiochemical purity

Isotope dilution-mass spectrometry (ID-MS) was used as a reference method to determine the concentration of estradiol-17 beta (E2) in five different plasma pools (concentrations ranging from 0.040 to 65 nmol/l). The same plasma pools were also subjected to radioimmunoassay (RIA) using five different antisera of largely varying specificity. With the best antiserum (E), a direct RIA apparently gave accurate results (i.e. results statistically indistinguishable from those obtained by ID-MS) at all levels except the lowest one (0.040 nmol/l). It was shown, however, that the apparent accuracy of this RIA to some extent could be due to a lowering effect of lipids in the serum masking a lack of specificity of the antibodies. With the least specific antiserum (A), accurate results were obtained only after chromatography. However, in the assay of the lowest concentration of E2 with this antiserum there was a significant overestimation, even after chromatography. The other three antisera (B, C, D) of average quality gave accurate results in assays of plasma diethyl ether extracts in various numbers of the plasma pools tested, depending on their intrinsic specificity. This specificity was not correlated with the cross-reaction reported for individual antisera. ID-MS is difficult to use in most laboratories. We demonstrate here that the validity of a RIA may in this case be assessed by a relatively simple method, the test of radiochemical purity (RP-test). This test is based on the measurements of specific activity (e.g. dpm/pg) in small consecutive fractions of the chromatographic zone which is usually employed for the RIA.