Thromboxanes table

Rats fed a purified nonlipid diet containing vitamins A and D exhibit a reduced growth rate and reproductive deficiency which may be cured by the addition of linoleic, a-linolenic, and arachidonic acids to the diet. These fatty acids are found in high concentrations in vegetable oils (Table 14-2) and in small amounts in animal carcasses. These essential fatty acids are required for prostaglandin, thromboxane, leukotriene, and lipoxin formation (see below), and they also have various other functions which are less well defined. Essential fatty acids are found in the stmctural lipids of the cell, often in the 2 position of phospholipids, and are concerned with the structural integrity of the mitochondrial membrane. 

Table 1 Selected PGF2cl derivatives evaluated as thromboxane A2 agonists. Very limited characterization data were supplied by author...

Each eicosanoid is associated with specific types of biological activity (Table 29.4). In some cases, the effects oppose one another. For example, thromboxanes are vasoconstrictors that trigger blood platelet aggregation, whereas prostacyclins are vasodilators that inhibit platelet aggregation. The levels of these two eicosanoids must be in the right balance for cells to function properly. 

Based on several randomized trials, aspirin has become the preferred antiplatelet agent in the treatment of aU ACSs. Early aspirin administration to all patients without contraindications within the first 24 hours of hospital admission is a quality care indicator (see Table 16-3). The antiplatelet effects of aspirin are mediated by inhibiting the synthesis of thromboxane A2 through an irreversible inhibition of platelet cyclooxygenase-1. Following the administration of a non-enteric-coated formulation, aspirin rapidly (<10 minutes) inhibits thromboxane A2 production in the platelets. Aspirin also has anti-inflammatory actions, which decrease C-reactive protein and also may contribute to its effectiveness in ACS. In patients undergoing PCI, aspirin prevents acute thrombotic occlusion during the procedure. 

Some of the unsaturated fatty acids containing more than one double bond cannot be synthesized by the body For many years it has been known that linolenic acid and linoleic acid, called the essential fatty acids, are necessary for specific biochemical functions and must be supplied in the diet (see Table 18.1). The fimction of linoleic acid became clear in the 1960s when it was discovered that linoleic acid is required for the bios)mthesis of arachidonic acid, the precursor of a class of hormonelike molecules known as eicosanoids. The name is derived from the Greek word eikos, meaning "twenty," because they are all derivatives of twenty-carbon fatty acids. The eicosanoids include three groups of structurally related compounds the prostaglandins, the leukotrienes, and the thromboxanes. 

Table 36.2. Pharmacological Properties of Prostaglandins, Thromboxane, and Prostacyclin...

---