Enhancement of endogenous production of 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid in aortic smooth muscle cells by platelet-derived growth factor

Platelet-derived growth factor (PDGF) has a chemotactic effect on smooth muscle cells, which is inhibited by lipoxygenase inhibitor caffeic acid. In order to study the role of endogenous lipoxygenase products of arachidonic acid on the chemotactic action of PDGF, effects of PDGF on the lipoxygenase pathway in smooth muscle cells were examined. Lipoxygenase products were analyzed by high-performance liquid chromatography. 15-, 5- and 12-lipoxygenase activities, in order of magnitude, were found in smooth muscle cell homogenate. However, when the lipoxygenase products were analyzed using intact cells prelabelled with [14C]arachidonic acid, only 12-L-hydroxy-5,8,10,14-eicosatetraenoic acid (HETE) was found to be produced endogenously. In addition, 12-HETE was not released into the medium. Treatment of the cells with PDGF increased the endogenous production of 12-HETE. The amounts of intracellular 12-HETE in PDGF-treated cells were 126, 132 and 146% at 1, 3, and 10 hr's after the initiation of PDGF treatment, respectively, when control value at each time point was considered as 100%. Caffeic acid (10(-4) M) completely inhibited the PDGF effect on 12-HETE production. However, PDGF treatment did not significantly alter the 12-lipoxygenase activity. These results suggest that the stimulatory effect of PDGF on 12-HETE production was not mediated by the activation of 12-lipoxygenase activity. Since 12-HETE itself is a potent chemoattractant for smooth muscle cells, the present dat strongly suggest that 12-HETE could be an important intracellular mediator of the chemotactic action of PDGF on aortic smooth muscle cells.     

Metabolism of adrenic acid to vasodilatory 1alpha,1beta-dihomo-epoxyeicosatrienoic acids by bovine coronary arteries

Adrenic acid (docosatetraenoic acid), an abundant fatty acid in the vasculature, is produced by a two-carbon chain elongation of arachidonic acid. Despite its abundance and similarity to arachidonic acid, little is known about its role in the regulation of vascular tone. Gas chromatography/mass spectrometric analysis of bovine coronary artery and endothelial cell lysates revealed arachidonic acid concentrations of 2.06 +/- 0.01 and 6.18 +/- 0.60 microg/mg protein and adrenic acid concentrations of 0.29 +/- 0.01 and 1.56 +/- 0.16 microg/mg protein, respectively. In bovine coronary arterial rings preconstricted with the thromboxane mimetic U-46619, adrenic acid (10(-9)-10(-5) M) induced concentration-related relaxations (maximal relaxation = 83 +/- 4%) that were similar to arachidonic acid relaxations. Adrenic acid relaxations were blocked by endothelium removal and the K(+) channel inhibitor, iberiotoxin (100 nM), and inhibited by the cyclooxygenase inhibitor, indomethacin (10 microM, maximal relaxation = 53 +/- 4%), and the cytochrome P-450 inhibitor, miconazole (10 microM, maximal relaxation = 52 +/- 5%). Reverse-phase HPLC and liquid chromatography/mass spectrometry isolated and identified numerous adrenic acid metabolites from coronary arteries including dihomo (DH)-epoxyeicosatrienoic acids (EETs) and DH-prostaglandins. DH-EET [16,17-, 13,14-, 10,11-, and 7,8- (10(-9)-10(-5) M)] induced similar concentration-related relaxations (maximal relaxations averaged 83 +/- 3%). Adrenic acid (10(-6) M) and DH-16,17-EET (10(-6) M) hyperpolarized coronary arterial smooth muscle. DH-16,17-EET (10(-8)-10(-6) M) activated iberiotoxin-sensitive, whole cell K(+) currents of isolated smooth muscle cells. Thus, in bovine coronary arteries, adrenic acid causes endothelium-dependent relaxations that are mediated by cyclooxygenase and cytochrome P-450 metabolites. The adrenic acid metabolite, DH-16,17-EET, activates smooth muscle K(+) channels to cause hyperpolarization and relaxation. Our results suggest a role of adrenic acid metabolites, specifically, DH-EETs as endothelium-derived hyperpolarizing factors in the coronary circulation.     

Interactions of lectins with CHO cell surface membranes. I. Competition studies indicate concanavalin A and WGA bind to discrete populations of sites

Human platelet-derived growth factor (PDGF) stimulates release of arachidonic acid from cellular phospholipids, synthesis and release of prostaglandins from the cell, and initiation of DNA synthesis in cultures of 3T3 Swiss mouse fibroblasts at similar concentrations with four independent preparations representing a million-fold range of purification. Stimulation of archidonic acid and prostaglandin release is an early event (beginning within minutes) in the response to PDGF treatment. Incubating cells with PDGF at 4°C followed by washing leads to activation of archidonic acid release on warming the cells to 37°C, consistent with binding of the factor to the cell surface. PDGF-stimulated arachidonic acid release, prostaglandin release, and initiation of DNA synthesis are all inhibited by phenylglyoxal at similar concentrations. These results suggest that activation of arachidonic acid release from phospholipids plays an essential role in the mechanism by which PDGF stimulates the initiation of DNA synthesis in 3T3 cells. The stimulation of initiation of DNA synthesis by PDGF does not appear to be mediated by the synthesis of prostaglandins or other known arachidonic acid metabolites because neither indomethacin (a fatty acid cyclooxygenase inhibitor) nor phenidone (a lipoxygenase inhibitor) inhibit initiation of DNA synthesis at concentrations which inhibit arachidonic acid metabolism. Although the activation of arachidonic acid release by PDGF is a calcium-dependent process, a simple calcium flux appears unimportant to the mechanism of activation. Evidence was also obtained against an involvement of sodium fluxes or proteolytic activity in the mechanism of stimulating arachidonic acid release by PDGF or serum.     

Modulation of voltage-dependent Ca channel current by arachidonic acid and other long-chain fatty acids in rabbit intestinal smooth muscle.

The effects of arachidonic acid (AA) and other long-chain fatty acids on voltage-dependent Ca channel current (ICa) were investigated, with the whole cell patch clamp method, in longitudinal smooth muscle cells of rabbit ileum. 10-30 microM AA caused a gradual depression of ICa. The inhibitory effect of AA was not prevented by indomethacin (10 microM) (an inhibitor of cyclooxygenase) or nordihydroguaiaretic acid (10 microM) (an inhibitor of lipoxygenase). 1-(5-Isoquinolinesulfonyl)-2-methylpiperazine (H7; 25-50 microM) or staurosporine (2 microM) (inhibitors of protein kinase C) did not block the AA-induced inhibition of ICa, and application of phorbol ester (a protein kinase C activator) (phorbol-12,13-dibutyrate, 0.2 microM) did not mimic the AA action. Some other cis-unsaturated fatty acids (palmitoleic, linoleic, and oleic acids) were also found to depress ICa, while a trans-unsaturated fatty acid (linolelaidic acid) and saturated fatty acids (capric, lauric, myristic, and palmitic acids) had no inhibitory effects on ICa. Myristic acid consistently increased the amplitude of ICa at negative membrane potentials. The present results suggest the possible role of AA, and perhaps other fatty acids, in the physiological and/or pathological modulation of ICa in smooth muscle.     

Arachidonic acid metabolism of the murine eosinophil. II. Involvement of the lipoxygenase pathway in the response to the lymphokine eosinophil stimulation promoter

Eosinophil stimulation promoter (ESP) is a murine lymphokine that enhances the migration of eosinophils. Exogenous arachidonic acid between 0.5 and 2 micrograms/ml potentiated the activity of ESP on murine eosinophil migration, whereas such concentrations did not affect migration in the absence of ESP. Among the lipoxygenase products identified from an enriched population of murine eosinophils, leukotriene B4 (optimal activity at 100 ng/ml) and 12-HETE (optimal activity at 2 micrograms/ml) stimulated migration of these cells. Another lipoxygenase product from these cells 15-HETE inhibited ESP-induced migration; between 5 and 10 micrograms/ml 15-HETE decreased by one-half both stimulated migration and 12-HETE biosynthesis. Structurally diverse drugs at concentrations that inhibited HETE biosynthesis inhibited ESP-induced migration. The concentrations that decreased migration activity by one-half were 5 microM NDGA, 10 microM ETYA, and 150 microM BW755C. Aspirin and indomethacin at concentrations reported to inhibit prostaglandin biosynthesis did not substantially inhibit ESP activity, but concentrations of indomethacin above 20 microM caused concentration-dependent inhibition of migration. The selective lipoxygenases inhibitor 134,7,10,13-eicosatetraynoic acid was more potent than ETYA in inhibition of ESP-induced migration, and the selective cyclooxygenase inhibitor 6,9,12-octadecatriynoic acid did not effect inhibition. These results are consistent with the hypothesis that stimulation of eosinophils by the lymphokine ESP involves the generation of lipoxygenase products from arachidonic acid, which positively and negatively regulate the migratory activities of these cells.     

Formation of monohydroxyeicosatetraenoic acids from arachidonic acid by cultured rabbit aortic smooth muscle cells

In addition to the well established cyclooxygenase pathway, cultured aortic smooth muscle cells convert arachidonic acid to several polar metabolites identified by high performance liquid chromatography and gaz chromatography — mass spectrometry. 15-Hydroxyeicosatetraenoic acid, 12-Hydroxyeicosatetraenoic acid and 5-Hydroxyeicosatetraenoic acid are the major products formed. These observations indicate that the rabbit aortic smooth muscle cells are a potential source of lipoxygenase products and raise the possibility that this pathway of arachidonic acid metabolism can influence the biological functions of arterial myocytes under normal and pathological conditions.     

Mitochondria are direct targets of the lipoxygenase inhibitor MK886. A strategy for cell killing by combined treatment with MK886 and cyclooxygenase inhibitors

We have investigated the mitochondrial and cellular effects of the lipoxygenase inhibitor MK886. Low concentrations (1 microM) of MK886 selectively sensitized the permeability transition pore (PTP) to opening, whereas higher concentrations of MK886 (10 microM) caused depolarization through combination of an ionophoretic effect with inhibition of respiration. MK886 killed prostate cancer PC3 cells only at the higher, toxic concentration (10 microM), whereas the lower concentration (1 microM) had no major effect on cell survival. However, 1 microM MK886 alone demonstrably induced PTP-dependent mitochondrial dysfunction; and it caused cell death through the mitochondrial pathway when it was used in combination with the cyclooxygenase inhibitor, indomethacin, which had no effects per se. Treatment with 1 microM MK886 plus indomethacin sensitized cells to killing by exogenous arachidonic acid, which induces PTP opening and cytochrome c release (Scorrano, L., Penzo, D., Petronilli, V., Pagano, F., and Bernardi, P. (2001) J. Biol. Chem. 276, 12035-12040). Combination of MK886 and cyclooxygenase inhibitors may represent a viable therapeutic strategy to force cell death through the mitochondrial pathway. This approach should be specifically useful to kill cells possessing a high flux of arachidonic acid and its metabolites like prostate and colon cancer cells.     

A formyl peptide contracts guinea pig lung: role of arachidonic acid metabolites

We studied the role of cyclooxygenase and lipoxygenase products of arachidonic acid metabolism in mediating N-formyl-methionyl-leucyl-phenylalanine- (FMLP) induced contractions of guinea pig lung parenchymal strips. The cyclooxygenase inhibitors indomethacin (10(-5) M) and aspirin (3 X 10(-5) to 10(-4) M), the lipoxygenase inhibitor nordihydroguaiaretic acid (10(-5) to 3 X 10(-5) M), and the combined cyclooxygenase/lipoxygenase inhibitors 1-phenyl-3-pyrazolidinone (Phenidone) (3 X 10(-5) to 3 X 10(-4) M) and BW 755C (10(-5) to 10(-4) M) each caused a decrease in the maximum force induced by FMLP (Fmax) and an increase in the concentration of FMLP required to produce 50% of Fmax (EC50). The thromboxane synthesis inhibitor imidazole (3 X 10(-3) M) also decreased Fmax. The leukotriene D4 receptor antagonist FPL 55712 (5.7 X 10(-6) to 1.9 X 10(-5) M) increased the EC50 for FMLP, whereas desensitization of lung parenchymal strips to leukotriene B4 by pretreatment with this leukotriene (10(-7) M) had no effect on FMLP-induced contraction. After exposure to FMLP (10(-6) M), guinea pig lung produced (as determined by high-performance liquid chromatography and radioimmunoassay) leukotrienes C4 and B4, thromboxane A2 (as measured by its stable degradation product thromboxane B2), and prostaglandin F2 alpha. Lung strips not exposed to FMLP showed no evidence of leukotriene production. We conclude that thromboxane A2 and leukotriene C4 generated in response to FMLP mediate a substantial fraction of the force induced by this peptide in guinea pig lung parenchymal strips.     

Arachidonic acid and its acyclic derivatives regulate the short-term plasticity of the cholinoreceptors of the neurons in the edible snail]

On identified Helix neurones RPa3 and LPa3 using the method of double-electrode clamp technique on the membrane the influence was shown of eicosanoids on the dynamics of inward current extinction caused by the repeated ionophoretic applications of acetylcholine to soma. Extracellular influence of arachidonic acid (50-100 microM) increased the extinction. Phospholipase A2 inhibitor quinacrine hydrochloride (100-600 microM) decreasing the content of arachidonic acid in the cell acted differently. Inhibitor of lipoxygenase oxidation of arachidonic acid (nordihydraquiaretic acid) (3-10 microM) weakened the extinction. Blockader of cyclooxygenase oxidation of arachidonic acid--indomethacin (10-50 microM) did not influence the extinction. All the studied composition decreased the amplitude of input current caused by acetylcholine. The obtained results allowed to suppose that arachidonic acid and its acyclic metabolites formed as a result of lipoxygenase oxidation regulated short-term plasticity of snail neurones cholinoreceptors. Cyclic eicosanoids formed at cyclooxygenase oxidation of arachidonic acid had no regulating influence on cholinoreceptors plasticity.     

Arachidonic acid-induced chemiluminescence of human polymorphonuclear leukocytes

When human polymorphonuclear leukocytes were incubated with arachidonic acid, a rapid light emission was observed which reached a maximum within 2 min. The magnitude of chemiluminescence depended on the number of polymorphonuclear leukocytes and the concentration of arachidonic acid. The light emission was inhibited by about 40% or 70% by 100 μM 3-amino-1-(m-(trifluromethyl)-phenyl)-2-pyrazoline (BW755C) or 100 μM nordihydroguaiaretic acid as lipoxygenase inhibitors. In contrast, 100 μM indomethacin, a cyclooxygenase inhibitor, had no effect. These results suggested a pivotal role of the lipoxygenase pathway rather than the cyclooxygenase pathway in the light emission.     

Leukotrienes stimulate phosphatidylcholine secretion in cultured type II pneumocytes

We previously reported that arachidonic acid stimulates secretion of phosphatidylcholine in cultures of type II pneumocytes and, based on studies with cyclooxygenase and lipoxygenase inhibitors, suggested that this effect was mediated by lipoxygenase products of arachidonic acid metabolism (Gilfillan, A.M. and Rooney, S.A. (1985) Biochim. Biophys. Acta 833, 336-341). We have now examined the effect of leukotrienes on phosphatidylcholine secretion in type II cells as well as the effect of a leukotriene antagonist, FPL55712, on the stimulatory effect of arachidonic acid. Leukotrienes C4, D4 and E4 stimulated phosphatidylcholine secretion and this effect was dependent on concentration in the range 10(-12)-10(-6) M. Leukotriene E4 was the most stimulatory, followed by D4 and C4. Leukotriene B4 had no effect. Incubation of the cells with 10(-7) M leukotriene E4 for 90 min resulted in a 107% increase in the rate of phosphatidylcholine secretion. Incubation with 10(-6) M leukotrienes D4 and C4 for the same period resulted in 81% and 63% stimulation, respectively. The leukotrienes had no effect on cellular phosphatidylcholine synthesis or on lactate dehydrogenase release. The stimulatory effects of leukotrienes E4 and D4 were abolished by FPL55712. Similarly, the stimulatory effect of 6 X 10(-6) M arachidonic acid on phosphatidylcholine secretion was reduced from 74% to 25% by 10(-5) M FPL55712. Thus, the stimulatory effect of arachidonic acid on surfactant phospholipid secretion in type II cells is mediated at least in part by leukotrienes.     

12-Hydroperoxyeicosatetraenoic acid (12-HPETE) and 15-HPETE stimulate melatonin synthesis in rat pineals

The role of arachidonic acid metabolites in norepinephrine (NE)-induced N-acetyltransferase (NAT) activity and melatonin release was examined from 6 h-incubations of rat pineal glands. A cyclooxygenase inhibitor, indomethacin (5 x 10(-8) - 5 x 10(-6) M) was ineffective on melatonin release, in the presence of absence of NE (5 x 10(-6) M) while a lipoxygenase inhibitor, nordihydroguaiaretic acid (5 x 10(-7) -5 x 10(-5) M) had an inhibitory effect. Among the lipoxygenase metabolites, 12-hydroperoxyeicosatetraenoic acid (12-HPETE) and 15-HPETE stimulated both NAT activity and melatonin release in a dose-dependent manner, with a maximal effect occurring at 10(-6) M, while 5-HPETE or hydroxy derivatives of these compounds (12-HETE, 15-HETE and 5-HETE) were ineffective. These results indicate that 12-HPETE and 15-HPETE can be involved in NE-induced melatonin release.     

Reactive oxygen production associated with arachidonic acid metabolism by peritoneal macrophages

The nature of the calcium-dependent chemiluminescence observed in peritoneal macrophages after exposure to the calcium ionophore A23187 or during the phagocytosis of zymosan has been investigated. Eicosatetraynoic acid, an inhibitor of the lipoxygenase and cyclooxygenase pathways of arachidonic acid metabolism, inhibited the calcium-dependent chemiluminescence whereas indomethacin, a selective inhibitor of the cyclooxygenase pathway, did not. Arachidonic acid induced chemiluminescence only in phagocytosing cells, whilst 15-HPETE, an intermediate of the lipoxygenase pathway, generated a similar, transient chemiluminescent response in either unstimulated or phagocytosing cells. The results suggest that the lipoxygenase pathway may be a significant source of the reactive species of oxygen that give rise to chemiluminescence. Prostaglandin E₁ inhibited the chemiluminescence induced by zymosan and A23187, but did not affect that generated in response to 15-HPETE or arachidonic acid, suggesting that the inhibition is directed at a step either connected with or occurring prior to the release of free arachidonic acid by the cells.     

Lipoxygenase inhibitors enhance the proliferation of human B cells

The addition of drugs which inhibit the lipoxygenase pathways of arachidonic acid metabolism to 5 day cultures of mitogen-stimulated human B cells enhanced the proliferative response more than 10-fold. Several chemically dissimilar lipoxygenase inhibitors increased proliferation in this system, whereas the specific cyclooxygenase inhibitor indomethacin had no effect. A lipoxygenase inhibitor could be added as late as 48 to 72 h after the initiation of culture and still cause a significant increase in B cell proliferation. These drugs increased the proliferation of both peripheral blood B cells and tonsillar B cells activated by Staphylococcus aureus Cowan I or anti-Ig M antibodies, in combination with a crude T cell supernate, a commercial B cell growth factor preparation, or recombinant lymphotoxin. A similar effect was observed in tonsillar B cells purified by counterflow centrifugal elutriation to remove esterase positive accessory cells, suggesting this is a direct effect on the B cell. Lipoxygenase blockade also caused a greater than twofold increase in polyclonal Ig production. The enhanced proliferation caused by lipoxygenase blockade could not be reversed by adding back exogenous leukotrienes or hydroxyeicosatetraenoic acids to the cultures. Furthermore, B cells prelabeled with [3H]arachidonic acid did not produce radiolabeled lipoxygenase metabolites of arachidonic acid under the same culture conditions in which the addition of lipoxygenase inhibitors had a profound effect on proliferation. Thus, lipoxygenase inhibitors markedly stimulate B cell proliferation under a variety of experimental conditions, although the mechanism responsible for this action has not yet been elucidated.     

Comparative effects of inhibitors of arachidonic acid metabolism on erythropoiesis

The effects of a variety of inhibitors of the arachidonic acid metabolic pathway have been tested on the growth of early erythroid progenitor cell-derived colonies (CFU-E and BFU-E) in an attempt to discern whether products of the cyclo-oxygenase pathway or lipoxygenase pathway are essential for erythropoiesis. Murine erythroid progenitor cells obtained from fetal livers were cultured in the presence of erythropoietin for CFU-E and of interleukin 3 for BFU-E colony formation in response to the cyclo-oxygenase inhibitors, aspirin or sodium meclofenamate, and the lipoxygenase inhibitors, BW755C, nordihydroguiaretic acid (NDGA), phenidone, and butylated hydroxyanisole (BHA). The most potent inhibitor of colony formation (both CFU-E and BFU-E) was the selective lipoxygenase inhibitor, BW755C, followed by NDGA, phenidone and BHA. Neither aspirin nor sodium meclofenamate (10(-4) - 10(-6)M) significantly (p less than 0.05) inhibited CFU-E or BFU-E formation. These results support the hypothesis that lipoxygenase products of arachidonic acid metabolism may be essential for erythroid cell proliferation/differentiation.     

Abl regulates smooth muscle cell proliferation by modulating actin dynamics and ERK1/2 activation

Abl is a nonreceptor tyrosine kinase that has a role in regulating migration and adhesion of nonmuscle cells as well as smooth muscle contraction. The role of Abl in smooth muscle cell proliferation has not been investigated. In this study, treatment with endothelin-1 (ET-1) and platelet-derived growth factor (PDGF) increased Abl phosphorylation at Tyr(412) (an indication of Abl activation) in vascular smooth muscle cells. To assess the role of Abl in smooth muscle cell proliferation, we generated stable Abl knockdown cells by using lentivirus-mediated RNA interference. ET-1- and PDGF-induced cell proliferation was attenuated in Abl knockdown cells compared with cells expressing control shRNA and uninfected cells. Abl silencing also arrested cell cycle progression from G(0)/G(1) to S phase. Furthermore, activation of smooth muscle cells with ET-1 and PDGF induced phosphorylation of ERK1/2 and Akt. Abl knockdown attenuated ERK1/2 phosphorylation in smooth muscle cells stimulated with ET-1 and PDGF. However, Akt phosphorylation upon stimulation with ET-1 and PDGF was not reduced. Because Abl is known to regulate actin polymerization in smooth muscle, we also evaluated the effects of inhibition of actin polymerization on phosphorylation of ERK1/2. Pretreatment with the actin polymerization inhibitor latrunculin-A also blocked ERK1/2 phosphorylation during activation with ET-1 and PDGF. The results suggest that Abl may regulate smooth muscle cell proliferation by modulating actin dynamics and ERK1/2 phosphorylation during mitogenic activation.     

In vitro study of frog adrenal function--IX. Evidence against the involvement of lipoxygenase metabolites in the control of steroid production

The possible role of arachidonic acid metabolites of the lipoxygenase pathway in the regulation of steroidogenesis was studied in vitro using perifused frog interrenal (adrenal) glands. Graded doses of arachidonic acid (10(-6)-10(-4)M) increased the production of corticosterone and aldosterone in a dose-dependent manner. In the presence of indomethacin (5 X 10(-6)M), the effect of arachidonic acid on steroid secretion was totally abolished. Nordihydroguaiaretic acid (NDGA: 10(-6)M), a lipoxygenase inhibitor, did not alter the spontaneous secretion of corticosteroids and did not impair the stimulatory effect of arachidonic acid. In the presence of NDGA, both ACTH and angiotensin II were still able to stimulate corticosteroid production. Our data support the view that arachidonic acid metabolites play an important role in the regulation of amphibian steroidogenesis. Moreover, the results show that the lipoxygenase pathway is not involved in the spontaneous secretion of corticosteroids and in angiotensin II- or ACTH-induced steroidogenesis.     

非磷酸化肌球蛋白在血小板衍生生长因子诱导的血管平滑肌细胞迁移中的作用

为了阐明非磷酸化肌球蛋白在平滑肌细胞迁移中的作用,研究探讨了非磷酸化肌球蛋白是否介导了血小板衍生生长因子(PDGF)诱导豚鼠脑基底动脉平滑肌细胞(GbaSM-4)的迁移。研究结果显示,20ng/ml以下剂量的PDGF可诱导GbaSM-4细胞发生迁移,此时肌球蛋白轻链(MLC20)磷酸化水平无变化。该迁移作用可被肌球蛋白特异性抑制剂blebbistatin所拮抗。应用RNA干扰技术抑制肌球蛋白轻链激酶表达,经免疫印迹检测经果显示,MLC20的磷酸化水平发生了显著下降;但对PDGF诱导的迁移作用无影响;在RNA干扰后blebbistatin也可抑制其迁移作用。体外ATP酶活性测定结果显示,blebbistatin对从平滑肌中提取的非磷酸化肌球蛋白的ATP酶活性有明显的抑制作用,其主要作用位点位于肌球蛋白头的头部S1。上述结果提示,非磷酸化的肌球蛋白参与了PDGF诱导的平滑肌细胞迁移。     

The effects of somatostatin on the arachidonate cascade of platelets

Somatostatin (10(-9) M) significantly elevated the synthesis of thromboxane B2 in rat platelets. The transformation of arachidonic acid to active lipoxygenase metabolites was suppressed by somatostatin (10(-9) and 10(-8) M). The ratio of the lipoxygenase/cyclooxygenase products was significantly reduced by the polypeptide (10(-9) and 10(-8) M) in rat platelets. Higher concentrations (10(-7), 10(-6) and 10(-5) M) of somatostatin did not modify the lipoxygenase pathway of the platelets. The synthesis of the vasoconstrictor - proaggregatory cyclooxygenase products was stimulated by the polypeptide (10(-9) and 10(-8) M), while the formation of vasodilatator - antiaggregatory cyclooxygenase metabolites was induced by higher concentrations of somatostatin (10(-7) and 10(-6) M). Somatostatin might act on the deacylation process of phospholipids, reducing the free arachidonic acid substrate level, resulting in a lower lipoxygenation rate in the platelets, which could be responsible for the increased formation of thromboxane. The contradictory results reported by others concerning the action of somatostatin on the platelet function might be explained by our results that the effect of somatostatin depends on the applied dose.     

The effect of selected arachidonic acid metabolites on natural killer cell activity

The effect of arachidonic acid (AA) metabolites of lipoxygenase(s) was evaluated on natural killer (NK) cell activity in Fischer F344 rat splenic lymphocytes and compared with prostaglandin E2 (PGE2), a known inhibitor of NK cell lytic activity. It was observed that 5(S),12(S)-dihydroxy-6,10-trans-8,14-cis-eicosatetraenoic acid (5(S),12(S)-diHETE, EZEZ) inhibited NK cell activity to a degree comparable to the inhibitory effects of PGE2. This compound maximally inhibited NK cell activity at concentrations of 10(-6) and 10(-8) M. PGE2 and 5(S),12(S)-diHETE (EZEZ) inhibited NK activity to an identical degree at all concentrations and effector:target (E:T) cell ratios tested. Of the other lipoxygenase pathway metabolites screened, 8(S),15(S)-all trans-diHETE and 8(S),15(S)-diHETE (EZEZ) also inhibited NK activity, but only at 10(-6) M and a 50:1 E:T cell ratio. These findings provide further evidence that the lipoxygenase and cyclooxygenase pathways produce metabolites which can modulate NK cell function, and that 5(S),12(S)-diHETE (EZEZ), which has not been previously tested for effects on NK cells, may have a significant immunoregulatory role.