Jr. Glenn et S. Heptinstall, EVIDENCE THAT ADENOSINE-DIPHOSPHATE CAN ACTIVATE ADENYLATE-CYCLASE VIA CONVERSION TO ADENOSINE IN PLATELET-RICH PLASMA CONTAINING MAGNESIUM, Thrombosis and haemostasis, 80(2), 1998, pp. 321-325
When adenosine diphosphate (ADP) is added to hirudinized platelet-rich
plasma (PRP) in which the level of platelet cAMP has been pharmacolog
ically elevated, there is an initial rapid fall in the level of cAMP b
rought about by inhibition of adenylate cyclase. This may be followed
by a subsequent activation of adenylate cyclase that does not occur wh
en citrated PRP is used in place of hirudinized PRP, and is more prono
unced in the presence of added Mg2+. Here we provide evidence that a)
the Mg2+-dependent activation of adenylate cyclase seen in hirudinized
PRP is mediated by adenosine, b) the adenosine produced synergizes wi
th forskolin and with DN9693 to raise the level of cAMP in platelets,
but not with iloprost, c) Mg2+ does not influence directly the rate or
extent of cAMP production and so is more likely to influence the rate
of adenosine production, and d) activation of adenylate cyclase by ad
enosine can lead to inhibition of platelet aggregation. ARL 66096, a P
-2T purinoceptor antagonist which inhibits ADP induced platelet aggreg
ation, prevented inhibition of adenylate cyclase by ADP. Conversely, A
RL 66096 did not appear to inhibit conversion of ADP to adenosine and
subsequent activation of adenylate cyclase.