sq-23377 and 5-hydroxy-6-8-11-14-eicosatetraenoic-acid

14C arachidonic acid incorporation and 14C radioactivity release as well as prostaglandin (PG) and 5-hydroxyeicosatetraenoic acid (5-HETE) synthesis were measured in the pair of murine lymphoma L5178Y (LY) cell sublines differing in radiation sensitivity. Both LY sublines, LY-R (resistant) and LY-S (sensitive), incorporated exogenous arachidonic acid and released it from membrane phospholipids. Ca2+ ionophores (ionomycin and A23187) but not PMA stimulated the liberation of 14C arachidonic acid in LY cells. PMA did not potentiate the 14C arachidonic acid release both in the presence or in the absence of A23187; this observation suggests that protein kinase C activation is not essential for the regulation of arachidonic acid release by LY-R and LY-S cells. X-irradiation (5 Gy) did not change the uptake of 14C arachidonic acid into LY-R and LY-S cells and did not potentiate the release of its total radioactivity from the cells. PG synthesis was stimulated in irradiated LY-R cells but not in LY-S cells. The susceptibility of eicosanoid metabolism to A23187 and H2O2 was altered in irradiated LY-R cells. A23187 stimulated only PG and 5-HETE synthesis in irradiated LY-R cells. H2O2 did not stimulate the synthesis of PG from exogenous arachidonic acid in irradiated LY-R and LY-S cells and 5-HETE synthesis in LY-R cells. An implication of the increased PG synthesis in LY-R cells in the protection against radiation is discussed.

Topics: Animals; Arachidonic Acid; Calcimycin; Cell Line; Hydrogen Peroxide; Hydroxyeicosatetraenoic Acids; Ionomycin; Lymphoma; Mice; Phospholipids; Prostaglandins; Radiation Tolerance; Staurosporine; Tetradecanoylphorbol Acetate; Tumor Cells, Cultured; X-Rays

Products of arachidonic acid (AA) metabolism via the lipoxygenase pathways may have key roles in the maintenance of pregnancy and the onset of labor. We have determined whether calcium ionophores can modulate the rate of biosynthesis within the uterus of five important arachidonate lipoxygenase metabolites, i.e. leukotriene B4 (LTB4), LTC4, 5-hydroxyeicosatetraenoic acid (5-HETE), 12-HETE, and 15-HETE. Amnion, chorion, and decidual cells were isolated, grown to confluence and incubated with ionomycin. The production of LTB4, LTC4, 5-HETE, 12-HETE, and 15-HETE was determined using specific radioimmunoassays. Cell-specific, concentration-related stimulatory actions of ionomycin on 5-HETE, 12-HETE, 15-HETE, and LTC4 but not LTB4 production were found. A23187 had effects similar to ionomycin. Hence elevation of intracellular calcium levels can result in enhanced intrauterine production of arachidonate lipoxygenase metabolites that may affect pregnancy outcome.

Topics: 12-Hydroxy-5,8,10,14-eicosatetraenoic Acid; Amnion; Arachidonic Acid; Calcimycin; Chorion; Decidua; Female; Humans; Hydroxyeicosatetraenoic Acids; Ionomycin; Leukotriene B4; Leukotriene C4; Lipoxygenase; Pregnancy; Uterus

Mammalian 5-lipoxygenase systems exist in inactive or cryptic states and have to be stimulated in order to metabolize exogenous [14C]arachidonic acid to 5-HETE and leukotrienes. In most cells, both the activation process and the 5-lipoxygenase activity are calcium-dependent. However, the cryptic 5-lipoxygenase system in the murine PT-18 mast/basophil cell line, which can be stimulated by 15-hydroxyeicosatetraenoic acid (15-HETE), is unusual. Studies with fura-2 loaded PT-18 cells indicate that increases in cytosolic calcium do not appear to correlate with enhanced 5-lipoxygenase product formation. Thus, both the calcium ionophore ionomycin and arachidonic acid increase cytosolic calcium levels but have very little effect on [14C]5-HETE formation, whereas 15-HETE induces large increases in [14C]5-HETE production but no concomitant enhancement in cytosolic calcium is observed. Chelation of extracellular calcium by 3 mM EGTA resulted in a 30-40% inhibition of [14C]5-HETE formation induced by 15 HETE, whereas 3 mM EGTA has no appreciable effect on a crude PT-18 5-lipoxygenase homogenate. These results indicate that in PT-18 cells, calcium does not appear to play an important role in either the 15-HETE-induced activation process, or the enzymatic activity of the cryptic 5-lipoxygenase system.

Topics: Animals; Arachidonate 5-Lipoxygenase; Arachidonate Lipoxygenases; Arachidonic Acid; Arachidonic Acids; Basophils; Calcium; Calcium Channel Blockers; Cell Line; Cytosol; Egtazic Acid; Gallic Acid; Hydroxyeicosatetraenoic Acids; Ionomycin; Mast Cells; Mice