title: Receptor (norepinephrine), P-site (2',5'-dideoxyadenosine), and calcium-mediated inhibition of prostaglandin and forskolin-activated cyclic AMP-generating systems in human platelets.
abstract: Prostaglandin D2, 2-chloroadenosine, forskolin and combinations of these agents increase cyclic AMP-levels in intact human platelets. The inhibition of activated cyclic AMP-generating systems by 1) alpha2-adrenergic receptor-mediated hormonal input (norepinephrine), 2) a P-site agent (2',5'-dideoxyadenosine) and 3) a divalent cation (calcium) were examined: 1) Norepinephrine produces non-competitive inhibition of both forskolin and prostaglandin D2(PGD2)-stimulated cyclic AMP-accumulation in intact human platelets. The Ki values for norepinephrine versus forskolin, PGD2 and 2-chloroadenosine are similar in magnitude, while the Ki versus a forskolin-PGD2 combination is approximately 10-fold greater. Onset of inhibition by norepinephrine of the PGD2-response is several fold faster than for the forskolin-response. When platelets stimulated by the forskolin and PGD2 combination are exposed to norepinephrine, there is a transient increase in levels of cyclic AMP due to the potentiation of a minor beta-adrenergic component. This stimulation is followed by inhibition. 2) 2',5'-Dideoxyadenosine produces a non-competitive inhibition of the forskolin-response with a Ki of 110 microM. The inhibition of the PGD2-response by 2',5'-dideoxyadenosine is competitive with a Ki of 6-13 microM, while inhibition of the forskolin-PGD2 response has a Ki of 30 microM. Onset of inhibition by 2',5'-dideoxyadenosine is identical for forskolin or PGD2-stimulated platelets. There is a lag period for inhibition of platelets stimulated with the forskolin-PGD2 combination. The PGD2-forskolin combination appears to stabilize the cyclic AMP-generating system of platelets against inhibition by either norepinephrine or 2',5'-dideoxyadenosine. 3) Calcium ions cause a similar inhibition of cyclic AMP-generation in intact platelets, regardless of the type of stimulation.
authors.forename: A M
authors.initials: AM
authors.lastname: Siegl
authors.forename: J W
authors.initials: JW
authors.lastname: Daly
mesh_terms: D000067956:Adenylyl Cyclase Inhibitors; D001792:Blood Platelets / Q000378:metabolism*; D002118:Calcium / Q000502:physiology; D005576:Colforsin; D000242:Cyclic AMP / Q000096:biosynthesis* / Q000097:blood; D003839:Deoxyadenosines / Q000031:analogs & derivatives* / Q000494:pharmacology; D016048:Dideoxyadenosine / Q000031:analogs & derivatives*; D004224:Diterpenes / Q000494:pharmacology*; D006801:Humans; D066298:In Vitro Techniques; D007700:Kinetics; D011433:Propranolol / Q000494:pharmacology; D011448:Prostaglandin Antagonists / Q000494:pharmacology*; D015230:Prostaglandin D2; D011457:Prostaglandins D / Q000097:blood / Q000494:pharmacology; D011941:Receptors, Adrenergic / Q000378:metabolism*; D013997:Time Factors
chemical_list: D000067956:Adenylyl Cyclase Inhibitors; D003839:Deoxyadenosines; D004224:Diterpenes; D011448:Prostaglandin Antagonists; D011457:Prostaglandins D; D011941:Receptors, Adrenergic; D005576:Colforsin; D016048:Dideoxyadenosine; C021008:2',5'-dideoxyadenosine; D011433:Propranolol; D000242:Cyclic AMP; D015230:Prostaglandin D2; D002118:Calcium