Prostanoid Receptors

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Chapter: Essential pharmacology : Prostaglandins, Leukotrienes (Eicosanoids) and Platelet Activating Factor

PGs, TX and prostacyclin act on their own specific receptors located on cell membrane. Five major types of prostanoid receptors have been designated, each after the natural PG for which it has the greatest affinity.


PROSTANOID RECEPTORS

 

PGs, TX and prostacyclin act on their own specific receptors located on cell membrane. Five major types of prostanoid receptors have been designated, each after the natural PG for which it has the greatest affinity. This has been supported by receptor cloning. All prostanoid receptors are Gprotein coupled receptors which utilize the IP3/ DAG or cAMP transducer mechanisms. Some selective antagonists of prostanoid receptors have been produced. The prostanoid receptors are:

 

DP Has greatest affinity for PGD2, but PGE2 also acts on it; activation increases cAMP which inhibits platelet aggregation.

 

EP Has greatest affinity for PGE2; enprostil is a selective agonist. It has been subdivided into EP1 which causes smooth muscle contraction through IP3/DAG pathway and EP2 which mediates smooth muscle relaxation by increasing cAMP. Cloning studies have identified two more subtypes EP3 and EP4. PGE2 enhances Cl¯ and water secretion in intestinal mucosa also by increasing cAMP. However, in some tissues (adipocytes) PGE2 inhibits cAMP formation—responsible for its antilipolytic action. EP1 receptors are activated by PGF2α also.

 

FP Has greatest affinity for PGF2α; fluprostenol is a selective agonist. The most prominent effect of activation of this receptor is smooth muscle contraction mediated through IP3/DAG formation.

 

IP Has greatest affinity for PGI2; PGE also acts on it and cicaprost is a selective agonist. It functions by activating adenylyl cyclase in platelets (inhibiting aggregation) and smooth muscles (relaxation).

 

TP Has greatest affinity for TXA2; PGH2 also acts on it. It utilizes IP3/DAG as second messengers which mediate platelet aggregation and smooth muscle contraction.

 

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