The nomenclature 'prostanoids' encompasses both prostaglandins and thromboxane. These substances are produced by partial oxygenation of arachidonic acid, a natural ubiquitous constituent of the phospholipid in cell membranes. The liberation of arachidonate from the cell membranes is catalyzed by phospholipase A 2. This is the rate-limiting step of prostanoid synthesis.
Prostanoids can be formed by virtually every cell in the cyclo-oxygenase pathway, with minute amounts producing a vast array of potent effects. Thromboxane A 2 (TXA2) is the main cyclo-oxygenase product of the platelets. Epoprostenol (prostacyclin, PGI2) is primarily synthesized by endothelial cells. The main biological effects of the most common prostanoids are summarized in Table !.. The letters PG denote the word prostaglandin, and the third letter signifies the structure of the cyclopentane ring. The subscript that follows the third letter indicates the number of double bounds in the structure as well as the fatty acid precursor ( Vane and O'Grady... 1,993).
Table 1 The main biological effects of prostanoids
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