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Biomedical subjects

S T Crooke

Publications and source records attributed to S T Crooke.

At least 199 records · Page 11Linked to original sources
PubMed1986

Vascular vasopressin receptors mediate inhibition of beta adrenergic receptor-induced cyclic AMP accumulation.

Beta adrenergic receptor agonists and forskolin stimulated cyclic AMP (cAMP) accumulation in cultured rat aortic smooth muscle cells (A-10). Furthermore, these cells display a high density of vasopressin receptors of the vascular (V1) subtype. Addition of vasopressin to these cells inhibited beta adrenergic agonist- and forskolin-stimulated cAMP accumulation by 30 to 40% and by 25 to 35%, respectively. The extent of inhibition was dependent on the concentration of vasopressin used. Half-maximal inhibition of cAMP accumulation by isoproterenol occurred at 8 X 10(-10) M vasopressin. Basal cAMP levels were not affected. The inhibition by arginine vasopressin was mediated by V1 receptors because the V2 renal receptor subtype selective agonists (1-deamino, 8-D-arginine)vasopressin and (1-deamino,4-valine,8-D-arginine)vasopressin were ineffective. Of the antagonists tested, the V1-selective antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),2-(O-methyl)tyrosine,8-arginine]vasopressin was more potent than the mixed V1/V2 antagonist [1-beta-mercapto--beta, beta-cyclopentamethylenepropionic acid), 2-D-(O-ethyl)tyrosine,4-valine 8-arginine]vasopressin. The V2-selective antagonist [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid),2-D-isoleucine,4-valine,8-arginine]vasopressin displayed minimal ability to block the vasopressin-mediated inhibitory effect. These data demonstrate that in rat aortic smooth muscle cells V1 receptors are negatively coupled to adenylate cyclase. The studies presented suggest that the vasoconstrictor activity of vasopressin might involve inhibition of beta adrenergic receptor-mediated vascular relaxation through inhibition of cAMP accumulation.

Animals↗
PubMed1986

Leukotriene B4 induces formation of inositol phosphates in rat peritoneal polymorphonuclear leukocytes.

Leukotriene B4 (LTB4) induced rapid breakdown of prelabeled inositol phospholipids in rat peritoneal polymorphonuclear leukocytes (PMNs). Formation of [3H]inositol triphosphate ([3H]IP3) was rapid, with a peak of 250-300% of the control level, after 5-15 sec of exposure to LTB4. Accumulation of [3H]inositol bisphosphate was rapid, peaking after 30 sec of treatment. Accumulation of [3H]inositol monophosphate was also rapid in the presence of LiCl. The kinetics of [3H]IP3, [3H]inositol bisphosphate, and [3H]inositol monophosphate accumulation suggest that LTB4 may interact with receptors in PMNs and activate phospholipase C which in turn induces hydrolysis of inositol-phospholipids. The agonist activities of several LTB4 analogs were employed to investigate the structure-activity relationships of LTB4 receptor-mediated activation of phosphatidylinositol hydrolysis. Increases in [3H]IP3 formation were dependent upon the concentration of LTB4 and the agonist analogs. The rank order potency of these analogs was equivalent to that of the pharmacological activity of LTB4 agonists in the PMN chemotaxis assay. Furthermore, the islet activation protein isolated from Bordetella pertussis inhibited LTB4-induced [3H]IP3 formation. The tumor-promoting phorbol myristate acetate also inhibited LTB4-induced [3H]IP3 formation. The LTB4 receptors on a partially purified PMN membrane were characterized. LTB4 binding to the receptors was stereoselective and specific. The binding affinity (Kd) of [3H] LTB4 to the receptors was 1.3 +/- 0.2 nM. The maximum density of binding was 5.5 +/- 1.8 pmol/mg of protein. The rank order potency of binding affinities of several LTB4 analogs was equivalent to that of the induction of IP3 response induced by LTB4 and analogs. These results suggest that LTB4 may interact with receptors in rat PMNs, activate G protein-regulated phospholipase C, and induce [3H]IP3 formation.

Animals↗
PubMed1986

Leukotriene D4 receptor-mediated synthesis and release of arachidonic acid metabolites in guinea pig lung: induction of thromboxane and prostacyclin biosynthesis by leukotriene D4.

The effects of the peptidoleukotrienes C4 (LTC4), D4 (LTD4), E4 (LTE4) and a series agonists and antagonists on arachidonic acid metabolism were characterized in minced guinea pig lung. In response to LTD4, guinea pig lung utilized and converted the endogenous arachidonic acid into a variety of cyclooxygenase metabolites [prostaglandins (PGs) E2, F2 alpha, 6-keto-F1 alpha and thromboxane (Tx) B2] and lipoxygenase metabolites (5,12-dihydroxy-6,8,11,14-eicosatetraneoic acid and 5,15-dihydroxy-5,9,11,13-eicosatetraneoic acid). Using radioimmunoassays, the stable, pharmacologically important metabolites of the cyclooxygenase pathway, 6-keto-PGF1 alpha and TxB2, were quantitated. LTD4, LTE4 and several synthetic agonists induced dose-dependent synthesis and release of TxB2 and 6-keto-PGF1 alpha. Agonist-induced synthesis and release of 6-keto-PGF1 alpha and TxB2 was time-dependent and was maximal after 10 to 12 min of incubation. The slow-reacting substance of anaphylaxis antagonist, FPL 55712, and the newly reported dithioacetal LTD4 receptor antagonists (SKF 102922 and SKF 102081) did not induce synthesis and release of TxB2 and 6-keto-PGF1 alpha in concentrations that blocked the agonist-induced smooth muscle contraction. Preincubation with these antagonists inhibited the synthesis and release of prostanoids induced by LTD4 in the guinea pig lung. Islet activating protein, which inactivates the inhibitory guanine nucleotide binding protein (Gi protein), partially inhibited the agonist-induced synthesis and release of prostanoids. Furthermore, the receptor binding affinities and/or the myotonic activities of the LTD4 agonists correlated linearly with the agonist-induced prostanoid synthesis and release effect.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1986

Regulation of metallothionein gene expression in mammalian cells by gold compounds.

Metallothioneins are a class of low molecular weight, cysteine-rich proteins. Metallothioneins bind heavy metals and are thought to play a role in metal metabolism. Auranofin, an antiarthritic gold compound, is a potent inducer of metallothionein in Chinese hamster ovary cells. The induction of metallothionein by auranofin was mediated by active transcription of the gene and new mRNA was accumulated within 30 min after the exposure of Chinese hamster ovary cells to the drug. The extent of metallothionein induction was related to the concentration of the compound and was affected by the nature of the ligand attached to the gold molecule. A subline of these Chinese hamster ovary cells was established by growing them in the presence of normally cytotoxic concentrations of auranofin. In this auranofin-resistant cell line, the metallothionein genes were actively transcribed in the presence of auranofin, suggesting a relationship between cytotoxic action of auranofin and metallothionein gene transcription. Regulation of metallothionein gene transcription may play an important role in the molecular mechanism(s) of action auranofin and resistance to it.

Animals↗
PubMed1986

Cellular pharmacology of mu-[1,2-bis(diphenylphosphino)ethane]bis[(1-thio-beta-D-gluco pyranosato-S)gold(I)]: a novel antitumor agent.

SK&F 102912 (mu-[1,2-bis(diphenylphosphino)ethane]bis[(1-thio-beta-D- glucopyranosato-S)gold(I)], [(Autg)2(dppe)]) has shown reproducible and significant activity in transplantable murine tumor models and represents a structurally unique class of antineoplastic agents. A number of in vitro studies were performed to elucidate the cellular pharmacology of this gold-containing complex. [(Autg)2(dppe)] is a potent cytotoxic agent in vitro as demonstrated by its ability to inhibit the clonogenic capacity of a variety of tumor cell lines following a brief exposure to the drug. Cell-cycle analysis using HL-60 cells showed that low concentrations (2 microM) of [(Autg)2(dppe)] induced an S-phase block and higher concentrations induced a secondary block at the G1/S boundary. [(Autg)2(dppe)] had several effects on DNA metabolism and structure including preferential inhibition in cells of DNA synthesis (relative to RNA and protein synthesis) and the production of DNA single- and double-strand breaks as measured by alkaline elution. The cytoxic mechanism of this gold complex appears to be distinct from that of the monophosphine-gold complex auranofin.

Antineoplastic Agents↗
PubMed1986

The cellular and molecular pharmacology of auranofin and related gold complexes.

Investigations of the molecular pharmacology of auranofin (AF) and related gold compounds reveal that these gold complexes interact with proteins primarily via sulfhydryl reactions. Moreover, cell association, distribution and efflux of auranofin and related gold complexes can be explained by sequential sulfhydryl exchanges. The rate of the reactions and potential interactions with sulfhydryl groups in different environments vary according to the ligands associated with the gold. Secondary interactions of AF, such as the formation of triethylphosphine oxide and products of lipid oxidation, may also depend upon characteristics of the ligands. The mechanisms of cytotoxicity by which auranofin and closely related compounds affect cells probably include interactions with key membrane structural proteins, protein crosslinks, and effects on key membrane localized enzymes, e.g., phospholipase C. Other cellular effects may include inhibition of DNA polymerase and other enzymatic processes. Resistance to auranofin is mediated by induction of metallothionein in the cells studied. Gold-loaded metallothionein is less stable to proteolysis than cadmium-bound metallothionein, which probably explains the relatively ephemeral nature of resistance to auranofin.

Animals↗
PubMed1986

Modulation of the antitumor and biochemical properties of bis(diphenylphosphine)ethane with metals.

Bis(diphenylphosphine)ethane (DPPE) and its bis[chlorogold(I)] [DPPE(Au2Cl2)], and bis[trichlorogold(III)] [DPPE(Au2Cl6)], complexes have in vivo antitumor activity. To determine if interaction with metals in situ can play a role in the antitumor activity of DPPE, we have studied the effects of DPPE, DPPE(Au2Cl2), DPPE(Au2Cl6) and mixtures of DPPE with metal salts on in vitro and in vivo biological systems. The in vitro cytotoxic potencies of the two DPPE-gold complexes were approximately 10-fold greater than that of DPPE. In addition, the cytotoxic potency of DPPE was increased when incubated with cells in the presence of Au(III) and Cu(II) salts, whereas Mg(II), Zn(II), Mn(II), Fe(II), Co(II), and Cd(II) had no effect. The effects of DPPE, DPPE(Au2Cl2) and mixtures of DPPE and metal salts on the activity of a model enzyme system, DNA polymerase alpha were measured. While DPPE did not inhibit the activity of DNA polymerase alpha, the DPPE(Au2Cl2) complex and mixtures of DPPE and Cu(II) salts inhibited the activity of the enzyme. Consistent with the effects observed in vitro, coadministration of Cu(II) or Au(III) increased the in vivo potency of DPPE in mice bearing i.p. P388 leukemia. Fifteen other DPPE analogues were evaluated for in vivo antitumor activity and for the effect of Cu(II) on their in vitro cytotoxic potency; there was a relationship between the ability of Cu(II) to potentiate the cytotoxic activities of DPPE analogues and their having in vivo antitumor activity.

Animals↗
PubMed1986

In vivo antitumor activity and in vitro cytotoxic properties of bis[1,2-bis(diphenylphosphino)ethane]gold(I) chloride.

We have previously reported the cytotoxicity and antitumor activity of bis(diphenylphosphino)ethane (DPPE) and a variety of its transition metal complexes. During studies of the chemistry of a gold complex of this group [(AuCl)2(DPPE)], it was observed that this complex readily underwent ring closure on reaction with DPPE to form the tetrahedral complex [Au(DPPE)2]+. Various counterion forms (e.g., Cl-) of this cation were isolated and were found to exhibit a remarkably high stability in solution. Evaluation of [Au(DPPE)2]Cl in mice bearing i.p. P388 leukemia demonstrated that the compound produced an average of 87% increase in life span at its maximally tolerated dose (2-3 mumol/kg/day for 5 days). Activity was also seen in i.p. M5076 reticulum cell sarcoma (60% increase in life span) and s.c. mammary adenocarcinoma 16/c. Modest activity was evident in i.p. B16 melanoma and L1210 leukemia. A subline of P388 leukemia resistant to cisplatin was not cross-resistant to [Au(DPPE)2]Cl. In addition, combination therapy of [Au(DPPE)2]Cl and cisplatin against i.p. P388 demonstrated an advantage over single-agent therapy. In vitro studies of [Au(DPPE)2]Cl showed that the compound: is cytotoxic to tumor cell lines; is only minimally inhibited in its cytotoxic activity by the presence of serum; produces DNA protein cross-links and DNA strand breaks in cells; and inhibits macromolecular synthesis with a preferential inhibitory effect on protein synthesis relative to DNA and RNA synthesis. 31P nuclear magnetic resonance spectroscopy indicated that the compound is stable in the presence of serum proteins, thiols, or disulfides and that it reacts with Cu(II) resulting in the formation of a Cu(I)DPPE complex. The results of these in vivo and in vitro experiments suggest that the contrasting pharmacological profile of [Au(DPPE)2]Cl with respect to other gold(I) phosphine complexes may be related to both the kinetic stability of the complex and its stability in the presence of thiols.

Animals↗
PubMed1986

Purification, characterization, and structural properties of a single protein from rat basophilic leukemia (RBL-1) cells possessing 5-lipoxygenase and leukotriene A4 synthetase activities.

Arachidonate 5-lipoxygenase of rat basophilic leukemia (RBL-1) cells was purified more than 1000-fold by gel filtration and anion exchange protein-high performance liquid chromatography (HPLC). Physical properties of the purified 5-lipoxygenase such as molecular weight (74,000-76,000), N-terminal sequence (30 amino acids), and amino acid composition were determined. The purified enzyme converted [14C]arachidonic acid at 20 degrees to [14C] 5-hydroperoxyeicosatetraenoic acid (5-HPETE) and to [14C]dihydroxyeicosatetraenoic acids (diHETEs). Utilizing [14C] 5(S)HPETE as substrate, the purified enzyme also converted the hydroperoxy acid to [14C]diHETES. The [14C]diHETE reaction products were identified primarily (greater than 80% of recovered radioactivity) as the nonenzymatic hydrolysis products of leukotriene A4 (i.e., 6-trans-leukotriene B4 and 12-epi-6-trans-leukotriene B4) by reverse phase HPLC, scanning spectrophotometry, and gas chromatography-mass spectrometry. The bioconversion of [14C] arachidonate and [14C]5(S)HPETE to reaction products by the purified enzyme was dependent on the presence of both Ca2+ and ATP. The enzymatic activities were inhibited in a similar manner by the lipoxygenase inhibitors nordihydroguaiaretic acid, diphenyldisulfide, and SK&F 86002. The data provide evidence that RBL-1 cell 5-lipoxygenase and leukotriene A4 synthetase activities reside on a single monomeric protein with a free N-terminus and that they possess similar biochemical characteristics.

Amino Acids↗
PubMed1985

Identification and characterization of leukotriene D4 receptors in adult and fetal human lung.

Leukotriene D4 (LTD4) receptors were identified and characterized in adult and fetal human lung membranes. Macroscopically normal adult lung tissue was selected from seventeen surgical biopsy specimens, and twenty-seven fetal lung samples were obtained from therapeutic abortions. Binding assays were performed using pooled adult or fetal human lung membranes at 30 degrees under conditions which prevented metabolism of [3H]LTD4. Specific binding reached equilibrium within 30 min, remained constant for 60 min, was enhanced by Mg2+, and was inhibited by Na+ and guanyl-5'-yl-imidodiphosphate. Computer-assisted analyses of saturation binding data showed a single class of binding sites with similar apparent Kd (0.15 +/- 0.09 and 0.12 +/- 0.003 nM) and Bmax (68 +/- 29 and 62 +/- 14 fmoles/mg protein) values for adult and fetal samples respectively. Competition binding studies with [3H]LTD4 showed the same rank order potency for adult and fetal lung receptors (5S, 6R-LTD4 greater than 5S, 6R-LTD1 greater than 5R, 6S-LTD4 greater than 5S,6R-LTE4 greater than FPL 55712). A comparison of the receptor binding affinities of these compounds with their smooth muscle contractile agonist (pD2) and antagonist (-log[KB]) activities in guinea pig lung and trachea showed a good correlation (r = 0.88), suggesting that the saturable, high-affinity, stereoselective [3H]LTD4 specific binding sites identified in human lung may be physiologically relevant receptor moieties.

Adult↗
PubMed1985

Molecular structure of the beta-adrenergic receptor.

The beta-adrenergic receptor from several tissues has been purified to homogeneity or photoaffinity radiolabeled and its subunit molecular weight determined by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis. In this study we have examined the oligomeric structure of nondenatured beta 1- and beta 2-adrenergic receptor proteins, as solubilized with the detergent digitonin. Model systems used were frog and turkey red blood cell as well as rat, rabbit, and bovine lung plasma membrane preparations. To correct for the effects of detergent binding, sedimentation equilibrium analysis in various solvents, as adapted for the air-driven ultracentrifuge, was used. With this approach an estimate of 6 g of digitonin/g of protein binding was determined, corresponding to a ratio of 180 mol of digitonin/mol of protein. Protein molecular weights estimated by this method were 43 500 for the turkey red blood cell beta 1 receptor and 54 000 for the frog red blood cell beta 2 receptor. Molecular weights of 60 000-65 000 were estimated for beta 1 and beta 2 receptors present in mammalian lungs. These values agree with estimates of subunit molecular weight obtained by SDS gel electrophoresis of purified or photoradiolabeled preparations and suggest beta-adrenergic receptors to be digitonin solubilized from the membrane as single polypeptide chains.

Amino Acids↗
PubMed1985

The binding of leukotriene C4 and leukotriene D4 to membranes of a smooth muscle cell line (BC3H1) and evidence that leukotriene induced contraction in these cells is mediated by thromboxane, protein and RNA syntheses.

Leukotriene C4 (LTC4) and leukotriene D4 (LTD4) are important mediators of anaphylaxis and induced thromboxane (TxA2) synthesis in vivo and in vitro. The mechanism by which this occurs is not known and the cellular source of leukotriene (LT) induced TxA2 has not been identified. To obtain insights into this problem we have established an in vitro system using the BC3H1 murine smooth muscle cell line. A membrane fraction obtained from these cells contained binding sites for [3H]LTC4 having high specificity and affinity. Binding of [3H]LTC4 was saturable, specific and reversible with a dissociation constant (KD) of 33 +/- 16 nM and a maximum number of binding sites (Bmax) of 25 +/- 6 pmol/mg membrane protein. However, the amount of [3H]LTD4 specifically bound was considerably less than that of [3H]LTC4. LTC4 and LTD4 induced these cells to contract, a process which was blocked by inhibitors of cyclooxygenase and thromboxane synthetase. Using a radioimmunoassay, we have shown that the level of TxB2 (a stable metabolite of TxA2) was increased in response to LTC4 and LTD4 treatment in a dose-dependent manner. Cycloheximide, a protein synthesis inhibitor, and actinomycin D, an inhibitor of RNA synthesis, were found to inhibit both LTC4- and LTD4-induced TxB2 synthesis and cellular contraction. Arachidonic acid, in the absence of LT, increased the levels of TxB2 synthesis and contraction even in the presence of cycloheximide and actinomycin D. These data are consistent with the hypothesis that the rate-limiting step in LT-induced TxB2 synthesis is the formation of free arachidonic acid, a process which requires RNA and protein synthesis.

Animals↗
PubMed1985

Effects of coordinated gold compounds on in vitro and in situ DNA replication.

Auranofin, a coordinated gold compound, inhibits in vitro DNA synthesis and displays in vivo antitumor activity. To understand the mechanisms of inhibition of DNA replication, we have examined the effects of auranofin and other gold complexes on the activities of purified cellular and herpesvirus-induced DNA polymerases, and on in situ DNA replication in permeabilized S phase KB cells. Evaluation of the data suggests the following conclusions. (1) The gold compounds varied in their abilities to inhibit DNA polymerase activities. DNA polymerase alpha was more sensitive to inhibition by gold compounds than DNA polymerase beta; (2) Inhibition of purified DNA polymerases by gold (I) compounds was noncompetitive with both DNA template and triphosphate substrates. Inhibition by SKF 101675, a gold (III) complex was competitive with DNA. (3) None of the gold compounds tested preferentially inhibited herpesvirus-induced DNA polymerases. (4) The gold complexes that inhibited in vitro DNA replication also inhibited in situ DNA synthesis. However, the potency and order of potency of the compounds varied between the in vitro and in situ systems. (5) Auranofin and other gold compounds inhibited the clonogenic capacity of KB cells in a concentration-dependent manner. The IC50 values measured in the clonogenic assay were significantly lower than those obtained from the in vitro and in situ DNA replication assays.

Anti-Inflammatory Agents↗
PubMed1985

Studies on the fluorescence labeling of human red blood cell membrane ghosts with 4'-(9-acridinylamino)methanesulfon-m-anisidide.

4'-(9-Acridinylamino)methanesulfon-m-anisidide (mAMSA) interacts with red cell membranes, resulting in the formation of fluorescent protein adducts. The mAMSA-membrane protein adducts exhibited an emission fluorescence maximum at 445 nm, with two shoulders at approximately 425 and 470 nm. The major labeled proteins were identified as spectrins 1 and 2 and bands 3, 4.1, 4.2 and 5. The fluorescence intensity increased with increasing mAMSA concentrations (0.03 to 1.5 mM), time (15-120 min), and temperature of the reaction. Results from sodium dodecyl sulfate gel electrophoresis show that mAMSA caused no detectable change in the molecular weight of membrane proteins. This indicates that mAMSA is a monofunctional, noncrosslinking agent. Other acridine analogs, 9-aminoacridine and acridine, did not fluorescently label membrane proteins, suggesting that the presence of the acridine nucleus is not sufficient for labeling. Addition of 2-mercaptoethanol to the mAMSA-membrane reaction mixtures reversed the fluorescence labeling. Furthermore, pretreatment of membrane proteins with N-ethylmaleimide or iodoacetamide prevented the formation of fluorescent mAMSA-membrane protein adducts. These data suggest that mAMSA interacts with sulfhydryl groups of the membrane proteins. When the membrane sulfhydryl groups were assayed by labeling with N-[ethyl-2-3H]ethylmaleimide, it was shown that the accessible membrane sulfhydryl groups were reduced after the mAMSA treatment. The above results suggest that mAMSA covalently binds to the sulfhydryl groups in the red cell membrane, with the production of fluorescent mAMSA-protein adducts.

Aminoacridines↗
PubMed1985

Binding of a novel dopaminergic agonist radioligand [3H]-fenoldopam (SKF 82526) to D-1 receptors in rat striatum.

Fenoldopam (SKF 82526), a dopamine agonist which exhibits D-1 receptor subtype selectivity, was evaluated as a radioligand for this receptor subtype. In saturation studies in rat striatal membrane preparations, [3H]-fenoldopam appeared to label a single binding site with a KD of 2.3 +/- 0.1 nM and a Bmax of 590 +/- 40 fmoles/mg protein. In competition binding experiments, binding was shown to be stereoselective, and rank ordering of affinities of dopaminergic and non-dopaminergic compounds closely correlated with potencies of these compounds in stimulating or inhibiting dopamine-sensitive adenylate cyclase (D-1) and in binding to D-1 sites labelled with the antagonist [3H]-cis-flupenthixol. The most potent competitors were the recently identified D-1 selective antagonists, SCH 23390 and SKF R-83566. [3H]-Fenoldopam was also used to assess agonist/D-1 receptor interactions. The results suggest that [3H]-fenoldopam is a useful and selective agonist radioligand for the D-1 receptor.

Adenylyl Cyclase Inhibitors↗
PubMed1985

Leukotriene E4 binds specifically to LTD4 receptors in guinea pig lung membranes.

High affinity, stereoselective binding sites for [3H]leukotriene E4 ([3H]LTE4) have been identified and characterized in guinea pig lung membranes. [3H]LTE4 bound to these membranes with a pharmacological specificity identical to that previously observed for the [3H]LTD4 receptor in guinea pig lung. [3H]LTE4 specific binding was selectively inhibited by Na+, enhanced by Ca2+, Mg2+ and Mn2+ and modulated by guanine nucleotides. Scatchard analysis of saturation binding data showed a single class of high affinity and saturable binding sites, with a dissociation constant (Kd) of 0.4 +/- 0.2 nM and a density (Bmax) of 430 +/- 50 fmol/mg membrane protein, similar to values observed for the LTD4 receptor in guinea pig lung. The rank order potency of agonist binding to the [3H]LTE4 binding sites was LTD4 greater than LTE4 much greater than LTC4. These results indicate that [3H]LTE4 binds to [3H]LTD4 receptors and suggests that induction of smooth muscle contraction by LTD4 and LTE4 may be mediated by identical mechanisms and receptors in the guinea pig lung.

Animals↗
PubMed1985

Quantitative measurement of single- and double-strand breakage of DNA in Escherichia coli by the antitumor antibiotics bleomycin and talisomycin.

We developed an assay in which single-strand breakage (ssb) and double-strand breakage (dsb) of intracellular DNA by chemical agents can be accurately quantitated and differentiated. Escherichia coli cells containing plasmid pBR322 DNA were incubated with the antitumor antibiotics bleomycin A2 (BLM A2) or talisomycin A (TLM A). The plasmid DNA was isolated and then analyzed by electrophoresis on 1% agarose gels to separate the following conformational forms of plasmid DNA: (i) native, covalently closed, super helical, form I; (ii) nicked, relaxed circular, form II; and (iii) double-strand broken, linear, form III. Quantitation by densitometric analysis of the gels showed that BLM A2 and TLM A were equally active in terms of the concentrations of drug necessary to reduce equivalent amounts of form I DNA in the cells, whereas in vitro (using isolated pBR322 DNA as a drug substrate) twofold more TLM A than BLM A2 was required to produce an equivalent amount of reduction in form I DNA. TLM A produced more intracellular dsb than did BLM A2. The intracellular dsb activities (dsb/ssb ratio) measured from BLM A2 and TLM A were equivalent to those measured for the respective agents when isolated pBR322 DNA was used as the substrate. In E. coli both ssb and dsb were repaired, but TLM A damage was repaired more slowly and to a lesser extent, which may reflect the relative frequency of dsb.

Antibiotics, Antineoplastic↗