title: The effect of pyridoxal-5-phosphate on the inhibition of platelet aggregation and adenosine-3'-5'-cyclic monophosphate accumulation in human platelets.
abstract: Platelet adenosine-3'-5'-cyclic monophosphate (c-AMP) was determined in platelet rich plasma and washed platelets by a modification of the c-AMP protein binding assay. Studies were performed in the presence and absence of platelet aggregation inducers (adenosine diphosphate and thrombin) and inhibitors (pyridoxal-5-phosphate (PALP), prostaglandin E1 (PGE1), theophylline and papaverine). At 70% inhibitory concentration of platelet aggregation (PA) induced by papaverine or theophylline, a small but significant increase in platelet c-AMP level was found. With PALP however the inhibition of PA was not associated with a significant increase in the c-AMP level. PALP or theophylline potentiated greatly both the inhibition of PA and c-AMP accumulation induced by PGE1. Yet PALP potentiated the inhibition of PA induced by theophylline without increasing platelet c-AMP level. Our results indicate that the inhibition of PA by PALP is not mediated by c-AMP accumulation. However in the presence of PGE1, the increment in PA inhibition, is mediated by further indirect activation of the adenyl-cyclase.
mesh_terms: D000527:Alprostadil; D001792:Blood Platelets / Q000187:drug effects / Q000502:physiology*; D000242:Cyclic AMP / Q000097:blood*; D006801:Humans; D010208:Papaverine / Q000494:pharmacology; D010974:Platelet Aggregation / Q000187:drug effects*; D011458:Prostaglandins E / Q000494:pharmacology; D011732:Pyridoxal Phosphate / Q000494:pharmacology*; D013806:Theophylline / Q000494:pharmacology; D013917:Thrombin / Q000502:physiology
chemical_list: D011458:Prostaglandins E; D011732:Pyridoxal Phosphate; D013806:Theophylline; D010208:Papaverine; D000242:Cyclic AMP; D013917:Thrombin; D000527:Alprostadil