Butenoyl PAF is a PAF receptor agonist [1].

Platelet activating factor (PAF), a phospholipid mediator of inflammation, is secreted by several cell types including arterial endothelial cells, and can activate polymorphonuclear leucocytes and monocytes via specific cell surface receptors. PAF also stimulates the production of active oxygen species by human monocyte - derived macrophages. PAF play important roles in a variety of pathophysiological states including acute allergy, inflammation, asthma, gastrointestinal ulceration, and toxic shock [1][2].

Butanoyl-PAF and Butenoyl PAF are both products of the oxidative decomposition of 2-arachidonoyl phospholipids. Although Butenoyl PAF is 10-fold less potent than PAF as a PAF receptor agonist and ligand, it is 100-fold more abundant in oxidized LDL than PAF. Therefore, oxidation products of LDL phospholipids were physiologically relevant bioactive PAF-like molecules [1].

References:
[1].  Marathe GK, Davies SS, Harrison KA, et al. Inflammatory platelet-activating factor-like phospholipids in oxidized low density lipoproteins are fragmented alkyl phosphatidylcholines. J Biol Chem. 1999 Oct 1;274(40):28395-404.
[2].  Davies SS, Pontsler AV, Marathe GK, et al. Oxidized alkyl phospholipids are specific, high affinity peroxisome proliferator-activated receptor gamma ligands and agonists. J Biol Chem. 2001 May 11;276(19):16015-23.