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D L Venton

Publications and source records attributed to D L Venton.

54 records · Page 3Linked to original sources
PubMed1983

2-(6-carboxyhexyl)cyclopentanone hexylhydrazone. A potent and time-dependent inhibitor of platelet aggregation.

Two new azaprostanoids, a hydrazone (3) and hydrazide (4), have been prepared by the condensation of 2-(6-carboxyhexyl)cyclopentanone with n-hexylhydrazine and caproic acid hydrazide. Preliminary results with the stable hydrazide 4 indicate that it inhibits arachidonic acid (AA) induced human platelet aggregation and that, unlike 13-azaprostanoic acid (1), its site of action is at the cyclooxygenase level. Results with the unstable hydrazone derivative 3 indicate it to be a potent and time-dependent inhibitor of AA-induced human platelet aggregation, with its site of action also at the cyclooxygenase level.

Arachidonic Acid↗
PubMed1983

Human platelet phenol sulfotransferase: partial purification and detection of two forms of the enzyme.

To begin to study the usefulness of platelet phenol sulfotransferase (PST) as a possible measure of the enzyme activity in other organs such as the brain, we purified human platelet PST 36-120-fold. Activity toward 3-methoxy-4-hydroxyphenylglycol (MHPG), dopamine, 5-hydroxytryptamine (5-HT), and phenol eluted in the same Sephadex G-100 and Affi-Gel Blue column fractions. Specific activities of the enzyme with MHPG, dopamine, 5-HT, and phenol as substrates were 1198, 1068, 401, and 408 units/mg protein, respectively. Optimal assay conditions were established for each substrate. Apparent Km values were 598 microM, 21 microM, 19 microM, and 500 microM for MHPG, dopamine, phenol, and 5-HT, respectively. Apparent Km values for 3'-phosphoadenosine-5'-phosphosulfate (PAPS) with the same four substrates ranged from 0.11 to 0.25 microM. The pH optima were 6.3 for phenol, 6.8 for dopamine, and 7.0 for MHPG and 5-HT. An additional pH optimum at 8.6 was present for 5-HT. A thermolabile form of the enzyme measured with dopamine and 5-HT, as well as a thermostable form measured with phenol, were present. Dichloronitrophenol (10(-5) M) noncompetitively inhibited the thermostable enzyme activity by 96% but decreased the thermolabile activity by only 36%. These studies provide the basis for a more accurate comparison of human platelet PST with the enzyme in the human brain and in other tissues.

Arylsulfotransferase↗
PubMed1982

Prostacyclin potentiates 13-azaprostanoic acid-induced platelet deaggregation.

The specific thromboxane A2/prostaglandin H2 (TXA2/PGH2) antagonist 13-azaprostanoic acid (13-APA) reverses platelet aggregation stimulated by TXA2/PGH2 and the prostaglandin endoperoxide analog U46619. The present report demonstrates that the deaggregatory properties of 13-APA are potentiated by prostacyclin (PGI2). Human platelet-rich plasma was aggregated with U46619. Deaggregation was induced 2 min subsequent to the addition of the aggregating agent. Concentrations of 13-APA or PGI2 which induced 20 percent deaggregation were determined. Simultaneous addition of half of these concentrations resulted in 60 percent deaggregation, demonstrating that the observed response was supraadditive. Measurement of cyclic adenosine 3':5' monophosphate (cAMP) in resting or deaggregating platelets demonstrated that 13-APA itself did not stimulate cAMP production nor did 13-APA facilitate PGI2-induced increases in cAMP. In separate studies PGI2 and 13-APA were added to PRP prior to the induction of aggregation by U46619. Under these conditions, additive inhibition of aggregation was observed. Thus, it is clear that the pharmacological interaction between PGI2 and 13-APA depends upon the relative state of platelet activation.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1982

Prostaglandin F2 alpha antagonizes thromboxane A2-induced human platelet aggregation.

The effects of prostaglandin F2 alpha on human blood platelet function were investigated. PGF2 alpha at 15 muM completely blocked platelet aggregation induced by 500 muM arachidonic acid or 3 muM U46619 but had no effect on aggregation induced by 7.5 muM ADP. A similar specificity of action was not obtained with either PGI2 or PGE2. Thus concentrations of PGI2 (3 nM) or PGE2 (20 muM) which inhibited U46619- induced aggregation by 100% also blocked ADP-stimulated aggregation. The inhibitory properties of PGF2 alpha were not related to increases in platelet cAMP, since direct measurement of intracellular cAMP revealed that 15 muM PGF2 alpha produced no substantial change in cAMP levels. This finding was in direct contrast to results obtained using induced significant increases in platelet cAMP levels. The possibility that PGF2 alpha directly interacts at the platelet TXA2/PGH2 receptor was investigated by measuring [3H]PGF2 alpha binding to isolated platelet membranes. It was found that [3H] PGF2 alpha binding reached equilibrium within 30 min at room temperature and could be 90% displaced by addition of 1000 fold excess of unlabelled PGF2 alpha. Furthermore, when 1000 fold excess of either the TXA2/PGH2 "mimetic' U46619 or the TXA2/PGH2 antagonist displaced by 95% and 85% respectively. In contrast, the same molar excess of 6-keto-PFG1 alpha, azo analog 2, or TXB2, caused displacement of only 15%, 20% or 25% of the [3H] PHF2 alpha binding. Scatchard analysis indicated that [3H] PGF2 alpha has two binding sites; i.e., a high affinity binding site with an apparent Kd of 50 nM and a low affinity binding site with apparent Kd of 320 nM. These results suggest that the selective inhibition by PGF2 alpha of AA or U46619- induced aggregation may be mediated through interaction at the platelet TXA2/PGH2 receptor.

Adenosine Diphosphate↗
PubMed1982

Ability of implants of polymer-entrapped antiprogesterone antiserum to absorb and deplete progesterone from serum of the pregnant rat.

A highly specific antiprogesterone antiserum (APA) produced by immunization of sheep with an 11 alpha-hydroxyprogesterone hemisuccinate-thyroglobulin conjugate was purified, and the IgG fraction was entrapped within a polysiloxane matrix. The matrix immobilized APA but allowed penetration and binding of progesterone (P) to the APA. In this entrapped form APA implanted intraperitoneally in rats on the tenth day of pregnancy resulted in a decline in serum P from 50 to 12 ng/ml within 12 hours and to less than 2 ng/ml within 36 hours. Free serum P measured by equilibrium dialysis fell to less than 0.2 ng/ml at 36 hours. Concomitant with the decline in serum P was a rise in both serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) and eventual fetal resorption.

Animals↗
PubMed1982

Thromboxane A2/prostaglandin H2 directly stimulates platelet shape change independent of secreted ADP.

The relative contribution of thromboxane (TX)A2/prostaglandin (PG)H2 and ADP to platelet shape change was determined using the specific TXA2/PGH2 antagonist, 13-azaprostanoic acid (13-APA) and the ADP antagonist, ATP. Shape change was induced in human platelet-rich plasma with doses of arachidonic acid (AA) or the PG endoperoxide analog U46619, which did not cause measurable ATP/ADP release. Pretreatment of platelet-rich plasma with 13-APA completely inhibited shape change to AA or U46619 but did not inhibit ADP-induced shape change. In contrast, ATP completely blocked shape change to ADP but not to AA or U46619. In addition, 13-APA and ATP also selectively reversed shape change. Thus, 13-APA added 1.5 min subsequent to AA or U46619 resulted in almost complete reversal of the shape change response. However, 13-APA did not reverse ADP-induced shape change. A similar selectivity was observed with ATP which reversed shape change to ADP but not to AA or U46619. These findings provide evidence that the interaction of TXA2/PGH2 with its receptor results in the direct stimulation of shape change independent of secreted ADP. Furthermore, maintenance of this shape change response appears to require continued occupation of the TXA2/PGH2 receptor.

15-Hydroxy-11 alpha,9 alpha-(epoxymethano)prosta-5↗
PubMed1979

Azaprostanoic acid derivatives. Inhibitors of arachidonic acid induced platelet aggregation.

A series of 13-azaprostanoic acids (4a-h) and a 15-azaprostanoic acid (11a) have been prepared. Synthesis of the 15-aza derivative is based on a novel transformation of a ketone to an N-substituted ethylenamine using a formylmethylimino phosphate derivative. Several of the azaprostanoic acid derivatives were found to be potent inhibitors of platelet aggregation induced by arachidonic acid, whereas no effect was observed on ADP-induced primary aggregation, indicating blockade of the platelet arachidonic acid cascade. The compounds do not inhibit bovine cyclooxygenase activity and are postulated as acting beyond the synthesis of the prostaglandin endoperoxides. The inhibitory effect of the 13-aza series is highly sensitive to both stereochemistry and length of the amino side chain. Any deviation from the natural prostaglandin skeletal arrangement results in decreased biological activity.

Adenosine Diphosphate↗
PubMed1979

13-Azaprostanoic acid: a specific antagonist of the human blood platelet thromboxane/endoperoxide receptor.

A newly synthesized 13-aza derivative of prostanoic acid (13-APA) specifically inhibited human platelet aggregation induced by arachidonic acid, prostaglandin H2, or the stable endoperoxide analog (15S)-hydroxy-9 alpha,11 alpha-)epoxymethano)-prosta-5Z,13E-dienoic acid. 13-APA also inhibited [14C]serotonin release in response to arachidonic acid, ADP, or thrombin, but did not inhibit primary aggregation induced by ADP or thrombin. 13-APA completely blocked prostaglandin H2-induced aggregation in indomethacin-treated resuspended platelets but did not inhibit thromboxane synthesis. We therefore conclude that 13-APA acts as a direct antagonist of the platelet thromboxane/endoperoxide receptor.

Adenosine Diphosphate↗
PubMed1978

Biochemistry of the amatoxins: preparation and characterization of a stably iodinated alpha-amanitin.

Iodination of alpha-amanitin at the 7-position in the 6-hydroxy-2-sulfoxytryptophan moiety is effected with 1 equiv of iodine monochloride in methanol. The isolated product shows a lambdamax in methanol at 301 nm, compared with 305 nm for the parent alpha-amanitin; in methanolic 0.01 M NaOH the lambdamax are 330 and 332 nm for the product and parent, respectively. Spectrophotometric titration of the phenolic hydroxyl shows a decrease in pKa from 9.72 (alpha-amanitin) to 7.94 (7 iodo-alpha-amanitin). Appropriate spectrophotometric examination therefore distinguishes between parent and product. Proton magnetic resonance shows two aromatic protons (v4H = 7.57; V5H = 6.90 ppm; j4,5 = 9) in the 7-iodo-alpha-amanitin and three aromatic protons (v4H = 7.64; V5H = 6.78; V7H = 6.94 ppm; j4,5 = 9; J5,7 = 2) in alpha amanitin thus establishing the extent and position of iodine substitution. The 7-iodo-alpha-amanitin effectively inhibits RNA polymerase activity with half-maximal inhibition at 2 X 10(-9) M and 10(-4) M for the sea urchin RNA polymerases II and III, respectively. Addition of [125I]-7-iodo-alpha-amanitin (200 Ci/mmol) to crude extracts from sea urchin blastula, MOPC 315 plasmacytoma, and adult Oregon R Drosophila melanogaster followed by resolution on DEAE-Sephadex demonstrates that the radioactive ligand binds stably and specifically with RNA polymerase II in each of these extracts.

Amanitins↗
PubMed1975

Carbocyclic prostaglandin analogs. 1. Steroid carboxylic acids.

Certain structural similarities between prostaglandins with close-packed side chains and the perhydrocyclopentanophenanthrene nucleus of steroids prompted the synthesis and biological evaluation of 6beta, 17 beta-dihydroxy-5alpha-androstane-2alpha-carboxylic acid (30), its 6-deoxy derivative 28, and the corresponding 6-deoxy-2beta derivative 29 in an attempt to evaluate carbocyclic acids as potential prostaglandin analogs. Preliminary in vitro studies on isolated guinea pig ileum have shown weakly specific, prostaglandin-stimulated smooth muscle antagonism for 28 when compared with antagonism of bradykinin- and acetylcholine-induced contractions. Complete dose-response curves for 28 on prostaglandin-stimulated guinea pig ileum have shown a reduction in the maxium response and a decrease in the slope of the curve, indicating a noncompetitive type of inhibition for this type of derivative.

Acetylcholine↗
PubMedDate not supplied

A mass spectrometry screening method for antiaggregatory activity of proteins covalently modified by combinatorial library members: application to sickle hemoglobin.

A homogeneous assay, based on electrospray mass spectrometry, is described for identifying compounds in a combinatorial library that covalently modify a protein and thereby enhance its solubility. The technique is based on measuring the distribution of modified proteins in the supernatant versus aggregate. Compounds having the greatest anti-aggregatory activity are those with the highest supernatant/aggregate ratio. Mass is used as a marker to identify which covalent modifier in the library is involved. An exploratory study is presented which demonstrates that the antisickling activity of a family of isothiocyanates, as measured by the standard C(sat) assay, correlates well (r(2) = 0.98) with the mass spectrometry analysis of the supernatant/aggregate distribution. The technique has potential for screening libraries capable of covalently modifying other proteins of clinical interest, e.g., Alzheimer's, Huntington's, and various prion related diseases.

Antisickling Agents↗
PubMedDate not supplied

Pseudosemiglabrin, a platelet aggregation inhibitor from tephrosia semiglabra.

Following bioassay-directed fractionation procedures, two 7-oxygenated-8-prenylflavones, (-)-pseudosemiglabrin [1] and (-)-semiglabrin [2], were isolated from an MeOH extract of Tephrosia semiglabra. (-)-Pseudosemiglabrin [1] displayed in vitro inhibitory effects on human platelet aggregation.

Flavonoids↗
PubMedDate not supplied

Antagonism of prostanoid-induced vascular contraction by 13-azaprostanoic acid (13-APA).

Isometric contractions in vitro of helically cut strips of canine mesenteric arteries (O.D. = 0.6-1 mm) were recorded in the presence of 10 microM indomethacin. PGF2 alpha PGE2, U-46619 (TXA2 mimetic), norepinephrine, 5-hydroxytryptamine, and KCl produced dose-related contractions. The EC50 values of the prostanoids in the control period were: PGF2 alpha, 7.3 +/- 0.7 X 10(-7) M; PGE2, 2.1 +/- 0.2 X 10(-6) M; and U-46619, 4.1 +/- 1.0 X 10(-10) M. Exposure to 13-azaprostanoic acid (13-APA), 5 X 10(-5) M and 2 X 10(-4) M, for 20 min caused parallel and dose-related shifts to the right of the dose-response curves generated by all three prostanoids without affecting the contractile responses to KCl, norepinephrine, or 5-hydroxytryptamine or relaxation induced by PGI2. 13-APA, at the concentrations used, had no agonist activity. Small contractions (10-15%) seen on the addition of 13-APA to the baths were found to be related to the alcohol content of the solvent. Dose ratios (with/without antagonist) at the EC50 level were found to be: in the presence of 5 X 10(-5) M 13-APA PGF2 alpha, 2.7 +/- 0.3; PGE2, 3.5 +/- 0.9; U-46619, 5.2 +/- 0.9; in the presence of 2 X 10(-4) M 13-APA PGF2 alpha, 17.1 +/- 3; PGE2, greater than 50; and U-46619, 23.3 +/- 5.7. Thus, 13-APA is a specific antagonist of these prostanoids with no agonist activity of its own.

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