Structure des Eicosanoïdes

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I- DEFINITION DES EICOSANOÏDES :

Your Eicosanoids are very small diffusible molecules, are derived from polyunsaturated fatty acids 20C (These are enzymatic peroxidation products of PUFA C20), Most often it s’is the arachidonic acid most often released from phosphatidylcholine following’action d’une phospholipase A2.

Very low concentration, eicosanoids play the role of’local hormones and are involved in many physiological and pathological processes (painful inflammatory processes). They are divided into three main families of compounds :

  • Leucotrienes (LT : A, B, C, D)
  • prostaglandins (PG : Until’to H)
  • Thromboxanes (TX : A.B)

There are d’other compounds still poorly known (lipoxine.hepoxvline…)

II- Role of eicosanoids :

Play a related role to the hormones :

  • Regulators physiological functions (smooth muscle contraction, coagulation, reproduction, inflammation)
  • Regulators multiple metabolic pathways : intracellular signaling, target gene expression,

lll- STRUCTURE DES EICOSANOÏDES :

1- THE PROSTAGLANDINS :

A-structure :

prostaglandins(Pg) are present in many peripheral tissues in minute doses. Pg are cyclical (cycle pentagonal) between C8 and 02 ; oxygenated substituents (ketones or hydroxyl) found mostly on C9et surCll,which conferred on Pg hydrophilicity. All Pg have a double C1B-C14 bond and an hydroxyl function on leC15.cn are several subgroups PGA to PGH.

B-Roles :

Prostaglandins have several actions :

-mediators during’inflammation - a contraction of smooth muscles (uterus

-regulation of motility of the bronchioles, and diameter

-sleep regulation, pain, of the temperature (fever) and immune system. Pg are very active molecules and have a very short lifespan.

2- LES leukotrienes :

A- structure :

These are linear molecules cyclized not derived from AG 20 C and especially l’arachidonic acid.

They present 3 conjugated double bonds.

Arachidonic acid

B- Roles leukotriene :

-A role in bronchoconstriction in response to allergens (Asthma) : they cause smooth muscle contraction primarily bronchial level.

– The most important property of leukotrienes is the ability of this substance to’attract d’other polynuclear, monocytes and macrophages at the site of’inflammation. Celt property is called chemotaxis

-vasoconstrictor effect.

3- LES THROMBOXANES :

So called because’they are produced by thrombocytes; they are synthesized by the spleen, lung, brain and platelets : thromboxane contracture is a powerful vascular and bronchial smooth muscles and a powerful platelet aggregating.