PubMed · 382403
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L O Carreras Vescio. 1979. [Prostaglandins and platelet function].. https://pubmed.ncbi.nlm.nih.gov/382403/
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Platelet suspensions, that secreted about 50% of their dense granule contents upon stimulation with alpha-thrombin, showed a dose-dependent increase in secretion after 30 min preincubation with 0.5-3.0 g low density lipoprotein (LDL) protein/1. A 1-5 min preincubation had no effect. The enhancement by LDL only occurred at about 20% secretion or more, indicating that a minimal degree of activation was required for LDL to become effective. Lysine-modified LDL was equally effective as native LDL. The effect of LDL on secretion was accompanied by enhanced thromboxane B2 formation caused by stimulation of the liberation of arachidonate from phosphatidylcholine and/or phosphatidylinositol. However, when thromboxane formation was inhibited or the prostaglandin H2-thromboxane A2-receptor was blocked, LDL remained a potent stimulator of the secretion response. Thus, LDL enhances platelet secretion by a thromboxane A2-dependent and a thromboxane A2-independent mechanism via an effect that is independent of specific binding sites on the platelet.
The molecular species composition of red blood cell diacyl-phosphatidylcholine (PC), diacyl-phosphatidylethanolamine (PE) and alkenylacyl-PE (plasmalogen PE) has been analyzed in normolipidemic and hyperlipidemic donors. In all three phospholipid subclasses the percentages of the species 16:0/20:4 were increased in hyperlipidemic patients. In diacyl-PE, 18:1/20:4 was also elevated. No changes were observed in the other quantitatively important molecular species containing arachidonic acid at sn-2, namely 18:0/20:4. The rise in 16:0/20:4 in diacyl-PC and diacyl-PE of hyperlipidemic donors was accompanied by a fall in molecular species with linoleic acid (18:2) at sn-2 (in particular 18:1/18:2). In alkenylacyl-PE the elevation of 16:0/20:4 was compensated by a decrease in species with docosatetraenoic acid (22:4) at sn-2 in particular by a fall in 16:0/22:4. Among all donors, the percentages of 16:0/20:4 in diacyl-PC and PE were positively associated with plasma total cholesterol levels. The changes in molecular species composition of PC and PE in hyperlipidemia are expected to alter the function of erythrocyte membrane transport proteins and--if present also in other cell types--to affect eicosanoid metabolism.
Human D3 dopamine receptor DNA was stably transfected into GH4C1 pituitary cells. Displacement of iodosulpiride binding in hD3 transfected cells (Kd = 0.3 nM, Bmax = 89 fmol/mg protein) by dopaminergic ligands was indistinguishable from that of hD3 receptors in CHO cells. Only two clonal cell lines exhibited weak GppNHp-dependent shifts in [3H]N-0437 binding, and these were used for functional assays. Neither arachidonic acid metabolism, cAMP levels, inositol phosphate turnover, intracellular calcium, or potassium currents were consistently affected by dopamine (1-10 microM). The paucity of responses indicates that human D3 receptors do not couple efficiently to these second messengers in GH4C1 cells.