Magnesium Modifies the Responses of Platelets to Inhibitory Agents which Act Via cAMP

Summary

This study has investigated the interaction of raised extracellular magnesium and agents which act via cAMP with respect to inhibition of platelet aggregation and effects on platelet cAMP accumulation.

Iloprost (3 ng/ml) and PGD2 (0.2 μg/ml) each caused time dependent increases in platelet cAMP which were significantly greater in the presence of 3 mM added MgS0₄ (p <0.01). Addition of ADP (5 μM) resulted in a fall in cAMP which remained higher in the presence of MgS0₄ (p <0.01).

Forskolin (5 μg/ml) and DN9693 (100 μM) also caused increments in platelet cAMP but these responses were not influenced by added MgS0₄. Addition of ADP resulted in a further increase in cAMP which was augmented by MgS0₄ (p <0.03). This increase was abolished by adenosine deaminase (1.2 U/ml).

These experiments show that MgS0₄ can modify the cAMP responses produced by iloprost and PGD₂ and by forskolin and DN9693 when ADP is present. It appears that as well as inhibiting, ADP can also stimulate cAMP production under certain experimental conditions. This appears to be due to breakdown of ADP to adenosine.

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