Comparison of vasodilatory prostaglandins with respect to cAMP-mediated phosphorylation of a target substrate in intact human platelets.
The recent purification of a vasodilator-stimulated phosphoprotein (VASP) from human platelets and the development of a specific antiserum against VASP made it possible to study the quantitative effects of cAMP-elevating prostaglandins on cAMP-mediated phosphorylation of VASP in intact human platelets. Prostacyclin (PG-I2), prostaglandin-E1 (PG-E1) and the stable prostacyclinanalog Iloprost, all agents used for the treatment of peripheral vascular disease, induced rapid, stoichiometric and reversible phosphorylation of VASP in human platelets mediated by the cAMP-dependent protein kinase. However, there were substantial differences between these three cAMP-elevating prostaglandins with respect to their effects on extent, duration and reversibility of VASP phosphorylation. Maximal VASP phosphorylation was induced both by PG-I2 and Iloprost, but the PG-I2 effect was only of short duration in comparison to that of Iloprost. The extent of PG-E1-induced VASP phosphorylation was less than that observed with PG-I2 and Iloprost. In endothelial cell-platelet coincubations, an endothelial cell-derived, indomethacin-sensitive factor caused a rapid elevation of platelet cAMP level and VASP phosphorylation. These results provided direct evidence that human endothelial cells are capable of producing biologically active quantities of cAMP-elevating prostaglandins sufficient to induce stoichiometric cAMP-mediated protein phosphorylation in human platelets. VASP-phosphorylation induced by PG-I2 and PG-E1 was completely reversible after removal of the prostaglandins whereas this was only partially the case with Iloprost. In addition, evidence is presented that the prostaglandin-regulated adenylate cyclase system but not the cAMP-mediated protein phosphorylation desensitizes in human platelets after prolonged treatment with cAMP-elevating prostaglandins. VASP phosphorylation is proposed as a marker for quantitating aspects of vessel wall-platelet interaction.
Nolte
C
C
Medizinische Universitätsklinik, Klinische Forschergruppe, Würzburg, Federal Republic of Germany.
Eigenthaler
M
M
Schanzenbächer
P
P
Walter
U
U
D000527:Alprostadil / Q000494:pharmacology; D001792:Blood Platelets / Q000187:drug effects* / Q000378:metabolism; D001798:Blood Proteins / Q000378:metabolism*; D002478:Cells, Cultured / Q000187:drug effects; D000242:Cyclic AMP / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D004730:Endothelium, Vascular / Q000187:drug effects; D011464:Epoprostenol / Q000494:pharmacology; D006801:Humans; D016285:Iloprost / Q000494:pharmacology; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011453:Prostaglandins / Q000494:pharmacology*; D014665:Vasodilator Agents / Q000494:pharmacology*
D001798:Blood Proteins; D010750:Phosphoproteins; D011453:Prostaglandins; D014665:Vasodilator Agents; D011464:Epoprostenol; D000242:Cyclic AMP; D000527:Alprostadil; D016285:Iloprost