MAGNESIUM MODIFIES THE RESPONSES OF PLATELETS TO INHIBITORY AGENTS WHICH ACT VIA CAMP

This study has investigated the interaction of raised extracellular ma gnesium and agents which act via cAMP with respect to inhibition of pl atelet aggregation and effects on platelet cAMP accumulation. Iloprost (3 ng/ml) and PGD2 (0.2 mu g/ml) each caused time dependent increases in platelet cAMP which were significantly greater in the presence of 3 mM added MgSO4 (p <0.01). Addition of ADP (5 mu M) resulted in a fal l in cAMP which remained higher in the presence of MgSO4 (p <0.01). Fo rskolin (5 mu g/gl) and DN9693 (100 mu M) also caused increments in pl atelet cAMP but these responses were not influenced by added MgSO4. Ad dition of ADP resulted in a further increase in cAMP which was augment ed by MgSO4 (p <0.03). This increase was abolished by adenosine deamin ase (1.2 U/ml). These experiments show that MgSO4 can modify the cAMP responses produced by iloprost and PGD(4) and by forskolin and DN9693 when ADP is present. It appears that as well as inhibiting, ADP can al so stimulate cAMP production under certain experimental conditions. Th is appears to be due to breakdown of ADP to adenosine.