Magnesium and arachidonic acid metabolism.

The arachidonic acid content of plasma lipoproteins is altered during dietary magnesium deficiency, although the tissue arachidonic acid content seems to be unchanged. The primary event triggering these changes is probably the loss of extracellular Mg2+, as it is not clear whether dietary magnesium deficiency produces loss of intracellular Mg2+. In the isolated rabbit heart, in vitro perfusion conditions which produce loss of intracellular Mg2+ also result in disturbances of arachidonic acid metabolism. The metabolism of exogenous arachidonic acid to prostaglandins is increased without changing the Km or Vmax of cyclo-oxygenase. The incorporation of arachidonic acid into tissue phospholipids is significantly reduced, although the incorporation of oleate, stearate, and linolenate is either increased or unchanged. These data indicate that the activity of the enzymes (CoA synthetases and acyl transferases) which mediate arachidonate incorporation is reduced during Mg2+ depletion. Since protein-kinase-C-mediated phosphorylation of both CoA synthetase and acyl transferase reduces their activity, and since protein kinase C has an Mg2+ binding site, it is possible to speculate that loss of intracellular Mg2+ may lead to the activation of protein kinase C, with the consequent reduction of arachidonic acid reacylation enzyme activity.