Lipoxygenase and calcium entry in vascular smooth muscle

In the canine saphenous vein, inhibitors of cyclo-oxygenase augment contractile responses to acetylcholine, potassium chloride and partial alpha-adrenergic activation. This augmentation is prevented by inhibitors of lipoxygenase, and abolished by calcium entry blockers. These observations suggest that when Ca2+ enters the smooth muscle cells it activates the metabolism of arachidonic acid. If cyclo-oxygenase is inhibited, end-products of lipoxygenase exert a positive feedback on calcium entry. A similar mechanism may explain the hypoxic contractions observed in various blood vessels, including coronary arteries.