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Biomedical subjects

W S Powell

Publications and source records attributed to W S Powell.

At least 109 records · Page 6Linked to original sources
PubMed1979

Metabolism of prostaglandins, prostaglandin analogs and thromboxane B2 by lung and liver microsomes from pregnant rabbits.

Liver microsomes from pregnant rabbits converted prostaglandins F2 alpha, E1, and E2 to their 20-hydroxy metabolites along with smaller amounts of the corresponding 19-hydroxy compounds. Prostaglandins E1 and E2 were also reduced to prostaglandins F1 alpha and F2 alpha, respectively, and prostaglandin E1 was isomerized to 8-isoprostaglandin E1. The above products were also identified after incubation of prostaglandins with liver microsomes from non-pregnant rabbits. In this case, the yield of 20-hydroxy metabolites was much lower. Thromboxane B2 and a number of prostaglandin F2 alpha analogs were also hydroxylated by lung and liver microsomes from pregnant rabbits. The relative rates of hydroxylation by lung microsomes were: prostaglandin E2 approximately prostaglandin F2 alpha approximately 16,16-dimethylprostaglandin F2 alpha approximately 13,14-didehydroprostaglandin F2 alpha greater than thromboxane B2 greater than 15-methylprostaglandin F2 alpha approximately 17-phenyl-18,19,-20-trinorprostaglandin F2 alpha approximately ent-13,14-didehydro-15-epiprostaglandin F2 alpha. Similar results were obtained with liver microsomes except that thromboxane B2 was a relatively poorer substrate for hydroxylation.

Animals↗
PubMed1978

Formation of 20-hydroxyprostaglandins by lungs of pregnant rabbits.

Homogenates or particulate fractions (1,000 to 100,000 X g) from lungs of pregnant rabbits were incubated with prostaglandins or prostaglandin metabolites and the products were purified by chromatography and identified by gas chromatography-mass spectrometry. In the presence of NADPH, particulate fractions from pregnant rabbit lungs converted prostaglandins E1, E2, and F2alpha as well as 13,14-dihydro-15-oxoprostaglandin E2 and 13, 14-dihydro-15-oxoprostaglandin F2alpha to their 20-hydroxy derivatives. In the cases of the 3 primary prostaglandins, the corresponding omega-carboxylic acids were also isolated. The omega-hydroxylation reaction occurred in the presence of the microsomal fraction. The mitochondrial fraction was much less active whereas the cytosol fraction converted prostaglandins to their 13, 14-dihydro-15-oxo derivatives. When prostaglandin F2alpha was incubated with homogenates of lungs from pregnant rabbits, omega-oxidation was combined with oxidation of the 15-hydroxyl group and reduction of the 13, 14-double bond to give 13, 14-dihydro-20-hydroxy-15-oxoprostaglandin F2alpha as well as the corresponding derivative with an omega-carboxylic acid group. Lungs from nonpregnant rabbits were much less active than lungs from pregnant rabbits in the omega-oxidation of prostaglandins.

Animals↗
PubMed1978

Biosynthesis of prostaglandins and thromboxane B2 by fetal lung homogenates.

The conversion of arachidonic acid to prostaglandins (PG's) and thromboxane B2 (TXB2) was investigated in homogenates from fetal and adult bovine and rabbit lungs. Adult bovine lungs were very active in converting arachidonic acid (100 microgram/g tissue) to both PGE2 (10.7 microgram/g tissue) and TXB2 (6.2 microgram/g tissue. Smaller amounts of PGF2alpha (0.9 microgram/g) and 6-oxoPGF1alpha were formed. Homogenates from fetal calf lungs during the third trimester of pregnancy were quite active in converting arachidonic acid to PGE2, but formed very little TXB2, PGF2alpha or 6-oxoPGF1alpha. Homogenates from rabbit lungs converted arachidonic acid (100 microgram/g) mainly to PGE2, both before and after birth. The amount of PGE2 formed increased during gestation to a maximum of about 6 microgram/g tissue at 28 days of gestation. It then decreased to a minimum (1.5 microgram/g) which was observed 8 days after birth, followed by an increase to about 4 microgram/g in older rabbits.

Animals↗
PubMed1976

Localization of a prostaglandin F2alpha receptor in bovine Corpus luteum plasma membranes.

The distribution of a prostaglandin F2alpha receptor in various subcellular fractions from bovine corpora lutea obtained by differential and gradient centrifugation paralleled very closely the distribution in these fractions of 5'-nucleotidase, a marker enzyme for plasma membranes. The fractions most enriched in the receptor and 5'-nucleotidase were relatively free of mitochondria and lysosomes but were contaminated to some extent by elements of the endoplasmic reticulum. From these results it can be concluded that the prostaglandin F2alpha receptor is localized on the plasma membranes of the corpus luteum cells. A simple method is described for the purification of plasma membranes from bovine corpora lutea by differential centrifugation.

Animals↗
PubMed1975

Interactions between prostaglandin analogues and a receptor in bovine Corpora lutea. Correlation of dissociation constants with luteolytic potencies in hamsters.

The dissociation constants for the interactions between some prostaglandin analogues and a prostaglandin F2 receptor in bovine corpora lutea were determined. These values were compared to the antifertility potencies of these compounds in hamsters and the rates of metabolism by 15-hydro-syprostaglandin dehydrogenase. The most active analogues with regard to both affinity for the receptor and luteolytic potency were 17-phenyl-18, 19, 20-trinorprostaglandin F2alpha and 15-methylprostaglandin F2alpha. The alkyl side chain of prostaglandins could be modified considerably without altering the affinity for the receptor. In this way metabolism by 15-hydroxyprostaglandin dehydrogenase could be blocked. Some of these compounds -ad greatly increased luteolytic effects. Substitution of a phenyl group for the 3 terminal carbon units of the alkyl side chain of prostaglandins increased both the affinity for the receptor and the luteolytic activity in vivo. 7-oxa-13-prostynoic acid, an antagonist of the luteolytic effect of prostaglandin F2alpha in vivo was a weak competitive inhibitor of the interation between prostaglandin F2alpha and the receptor.

Animals↗
PubMed1975

Occurrence and properties of a prostaglandin F2alpha receptor in bovine corpora lutea.

Prostaglandin F2alpha was specifically bound by a particulate fraction from bovine corpora lutea. The rate constants for the association (7.5 X 10(3) M-1 S-1) and dissociation (2.1 X 10-4 S-1) reactions gave a dissociation constant of 2.8 X 10(-8) M which is similar to that determined from a Scatchard plot of binding data at equilibrium (5 X 10(-8) M). The receptor was stable for several hours at 23 degrees C but was rapidly destroyed at 37 degrees C. The pH optimum for the binding reaction was 6.3. The receptor had high specificity for prostaglandin F2alpha and had much lower affinities for other prostaglandins. Luteinizing and follicle-stimulating hormones had no effect on the prostaglandin F2alpha-receptor interaction.

Animals↗
PubMedDate not supplied

Synthesis of prostaglandins and thromboxane B2 by cholesterol-fed rabbits.

Alterations in the synthesis of thromboxane A2 (TxA2) and prostacyclin have been implicated in the development of atherosclerosis. We measured the amounts of the degradation products of these substances, TxB2 and 6-oxo-prostaglandin F1 alpha (6-oxo-PGF1 alpha), respectively, as well as PGE2, that were synthesized by slices and the luminal surfaces of aortas from rabbits fed either a control diet or a diet supplemented with cholesterol and peanut oil. For these studies, we developed conditions that were designed to minimize the autoinactivation of cyclooxygenase during removal and preparation of the tissue. Pretreatment of aortas with a medium containing ibuprofen and EDTA resulted in an approximately twofold increase in 6-oxo-PGF1 alpha production upon subsequent incubation. Despite the increased lipid peroxidation associated with atherosclerotic lesions, we observed no changes in either aortic 6-oxo-PGF1 alpha production or in the levels of its major urinary metabolite, 2,3-dinor-6-oxo-PGF1 alpha, after as long as 15 weeks of dietary supplementation with cholesterol and peanut oil. Similarly, synthesis of PGE2 by aortic slices and the aortic lumen was the same in cholesterol-fed and control rabbits. In contrast to aortic 6-oxo-PGF1 alpha and PGE2 synthesis, there was a dramatic 10-fold increase in TxB2 released from slices of thoracic aorta after 15 weeks on the atherogenic diet. This was much greater than the approximately twofold increase in the synthesis of TxB2 by the luminal surface of the thoracic aorta, suggesting that the primary site of TxB2 synthesis in the aorta is in the inner part of the blood vessel.(ABSTRACT TRUNCATED AT 250 WORDS)

6-Ketoprostaglandin F1 alpha↗