Eicosanoids local action

Eicosanoid Biosynthesis Eicosanoids Exert Their Action Locally... 

Eicosanoid receptors are G protein-coupled receptors known effector mechanisms include activation or inhibition of adenylate cyclase and activation of phospholipase C. Duration of action is usually short inactivation occurs by oxidative metabolism either locally or in the lung, which is strategically placed for complete clearance of the circulating blood volume. 

All eicosanoids are very potent compounds present in low concentration in cells. They are local mediators, meaning that they perform their function in the environment in which they are synthesized. This distinguishes them from hormones, which are first synthesized and then transported in the bloodstream to their site of action. Eicosanoids are not stored in cells rather, they are synthesized from arachidonic acid in response to an external stimulus. 

The modulatory effect of n-3 PUFAs on eicosanoid production could also be achieved at the enzyme level. The action of n-3 fatty acids that decreases the production of PGE2 could be an effect of down-regulation of COX-2 activity in local tissues (129, 130). In a study with rats, dietary n-6 PUFA up-regulated COX-2 and, to some extent, COX-1 expression leading to a concomitant increase in COX enzyme activity and prostaglandin synthesis, but fats containing added menhaden oil (high in n-3 PUFAs) had an opposite effect (131). 

The distinctive feature of a modulator is that it originates from nonsynaptic sites, yet influences the excitability of nerve cells. Substances such as CO2 and ammonia, arising from active neurons or glia, are potential modulators through nonsynaptic actions. Similarly, circulating steroid hormones, steroids produced in the nervous system (i.e., neurosteroids, locally released adenosine, other purines, eicosanoids, and NO are regarded as modulators (see below). 

Localized tissue anemia due to obstruction of arterial blood White or colorless nucleated blood cell Eicosanoid formed by the action of lipoxygenase on arachidonic acid (Figure 13.11)... 

The two series of eicosanoids are illustrated in Table 1.2. The products, depending on their local serum concentrations or amoimts secreted, have elfects on ndgh-boring cells and tissues. It is the actions of these eicosanoids of one type or anotha-that may have important effects on athletic performance, almost exclusively in the highly trained competitive athletes (see below). 

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