prostaglandins

Prostaglandins (PG) are diffusible, physiologically active C20 signaling molecules with a 5-carbon ring, which belong to the prostanoid subclass of eicosanoid fatty acid derivatives (left - PGE1)

actions : autocrine : biosynthesis : classification : diversity : immune system (insect) : mediators : paracrine : PG-receptors (GPCRs) : prostacyclin : secretion : side-chain substitutions : structural differences : thromboxane : transporters

Prostaglandins occur in almost all tissues and act as lipid mediators affecting platelets, endothelial cells, mast cells, etc. Prostaglandins are potent but have a short half-life before being inactivated and excreted, so their effects are confined to paracrine (local) or autocrine (same cell) functions. Prostaglandins exhibit subtle differences in their chemical structures on the basis of different side-chain substitutions. Classification is based on these structural differences. PGA to PGE and PGJ rings have a keto group and are some have double bonds or hydroxyl groups in various positions. The PGF ring has two hydroxyl groups while PGK has two keto substituents on the ring. PGG and PGH are bicyclic endoperoxides. (diagram)

These small structural variations are considered responsible for the immense diversity of physiological effects characteristic of prostaglandins. Adding to their physiological diversity, the same prostaglandins can elicit different responses in different tissues. [] basic PG structure (Jmol) []

Prostaglandins, with their fellow eicosanoids, are synthesized from C20 fatty acids in response to hormonal signals. (diagram, diagram 2) Approximately a dozen different prostaglandins have been identified, each associated with different activities plus different effects on various tissues. Prostaglandin secretion is mediated by the multidrug resistance protein 4 (MRP4, ABCC4) transporter, which is a member of the ATP-binding cassette transporter superfamily. Various prostaglandins ligate members of the G-protein-coupled receptors (DP1-2, EP1-4, FP, IP, and TP) that can have opposing effects on cAMP, IP turnover, and Ca2+ levels. (diagram PGE2→EP)

Prostaglandins have a wide variety of actions:
● muscular contraction
● relaxation of vascular smooth muscle (vasodilation)
● mediation of inflammation (diagram PGE2)
calcium movement
● ion transport
● lipolysis
hormone regulation
cell growth control
● temperature regulation

Table  Eicosanoid Actions

Thromboxane is released by platelets and causes platelet aggregation and vascular constriction. Prostacyclin is secreted by vascular endothelial cells and is antagonistic to thromboxane.

 Eicosanoid Actions

Prostaglandins and other eicosanoids mediate cellular immune responses to bacterial infections in insects – eicosanoids mediate insect microaggregation and nodulation responses to bacterial infections.[s]

[] prostaglandin gallery []

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