M embers of the family of prostanoids, made up of prostaglandins and thromboxanes, are generated via COX-mediated metabolism of arachidonic acid. These lipid mediators exhibit wide-ranging biological actions that include regulating both vasomotor tone and renal sodium excretion. As COX inhibition is often associated with sodium retention leading to edema and hypertension, prostanoids appear to have a role in preventing the development of high blood pressure. On the other hand, prostaglandin E₂ (PGE₂) and PGI₂ have also been implicated as determinants of renin secretion. A new study suggests that PGI₂ plays a critical role in stimulating renin release and promoting hypertension following renal artery stenosis.