Biological activities of lipoxin A include lung strip contraction and dilation of arterioles in vivo.

Lipoxin A ([5S,6R,15S]-5,6,15-trihydroxy-7,9,13-trans-11-cis-eicosatetraenoic acid), a recently characterized lipoxygenation product of arachidonic acid, in submicromolar concentrations elicited long-lasting contractions of the guinea-pig lung strip. The response to lipoxin A was not due to release of acetylcholine, histamine, noradrenaline or cyclo-oxygenase products. 15-hydroperoxyeicosatetraenoic acid (15-HPETE), one precursor of lipoxin A, also contracted the lung strip, but 15-HPETE was less potent on the guinea-pig trachea whereas 15-HPETE relaxed this preparation. Lipoxin A was also inactive on the guinea-pig ileum. Intravital microscopy of the hamster cheek pouch disclosed that lipoxin A, as well as 15-HPETE, induced arteriolar dilation but had no effects on microvascular permeability or leucocyte adherence to venular endothelium. Taken together, the leucocyte product lipoxin A displayed a pattern of activity in spasmogenic assays and on the microvasculature that was distinct from those known for prostaglandins, thromboxanes and leukotrienes. The findings indicate that lipoxin A is an additional arachidonic acid derived autacoid with biological actions on smooth muscle in vitro and in vivo.