Prostaglandin B1 (PGB1) is a metabolite of PGE1. PGE1 is a prostanoid. Prostanoids is a term that collectively describes prostaglandins, prostacyclines and thromboxanes. Prostanoids are a subclass of the lipid mediator group known as eicosanoids. They derive from C-20 polyunsaturated fatty acids, mainly dihomo-gamma-linoleic (20:3n-6), arachidonic (20:4n-6), and eicosapentaenoic (20:5n-3) acids, through the action of cyclooxygenases-1 and -2 (COX-1 and COX-2). PGB1does not inhibit phospholipase activity, but oligomers of PGB1 (PGBx) extracted from human neutrophils inhibit human phospholipases A2 in vitro and in situ in a dose-dependent manner; these oligomers inhibit arachidonic acid mobilization in human neutrophils and endothelial cells. One mechanism for the pharmacological effects of PGBx may be inhibition of cell-associated and extracellular phospholipase A2. PGB1 has the ability to enhance peripheral vascular resistance and elevate blood pressure. The effect is not central in origin and apparently is not the result of changes in cholinergic or alpha-adrenoceptor sensitivity or changes in vascular smooth muscle susceptibility per se. PGB1 blocks S-phase DNA synthesis; inhibition of DNA synthesis does not appear to require elevated levels of cAMP. (PMID: 7667505, 1477202, 2129000, 2597672, 6635328). Prostaglandins are eicosanoids. The eicosanoids consist of the prostaglandins (PGs), thromboxanes (TXs), leukotrienes (LTs), and lipoxins (LXs). The PGs and TXs are collectively identified as prostanoids. Prostaglandins were originally shown to be synthesized in the prostate gland, thromboxanes from platelets (thrombocytes), and leukotrienes from leukocytes, hence the derivation of their names. All mammalian cells except erythrocytes synthesize eicosanoids. These molecules are extremely potent, able to cause profound physiological effects at very dilute concentrations. All eicosanoids function locally at the site of synthesis, through receptor-mediated G-protein linked signalling pathways.