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 ActionsThromboxane is released by
platelets and causes platelet aggregation and vascular constriction.
Prostacyclin is secreted by vascular endothelial cells and is antagonistic to thromboxane.
Eicosanoid ActionsProstaglandins 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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tags
[Biochemistry] [Molecular Biology] [eicosanoid] [prostaglandins]
Phospholipids are formed from four components: fatty acids, a negatively charged phosphate group, an alcohol and a backbone. Phospholipids with a glycerol backbone are known as glycerophospholipids or phosphoglycerides. (left - click to enlarge image)
