6-keto-Prostaglandin F1a is the physiologically active and stable metabolite of prostacyclin. (A prostaglandin found in nearly all mammalian tissue that is a powerful vasodilator and inhibits platelet aggregation; it is biosynthesized enzymatically from prostaglandin endoperoxides in human vascular tissue; the sodium salt has been also used to treat primary pulmonary hypertension (Hypertension, Pulmonary). A delayed and prolonged increase in 6-keto-PGF1 alpha is reported in animals with septic shock, i.e., those with fecal peritonitis or cecal ligation. 6-keto-Prostaglandin F1a plasma levels has been found increased in patients with epidemic hemorrhagic fever, in patients with acute obstructive suppurative cholangitis, in patients with gynecologic cancer and has significant correlation with the level of high density lipoprotein cholesterol in plasma. 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.