We will study Prostaglandins only in Eicosanoids . Prostaglandins are unsaturated fatty acids found in almost all mammals and have the activity very closely to the hormones such as controlling smooth muscle contraction, blood pressure, inflammation and body temperature.
They contain cyclic ring structure made with the help of 20 carbon atoms.
Prostaglandins act on the tissues in which they are synthesized and within no time metabolized to useless products at the site of action.
Synthesis of Prostaglandins and Leukotrienes:
Prostaglandins bind to various membrane receptors via G-proteins, subsequently resulting in the activation or inhibition of adenylyl cyclase or stimulate phospholipase C. This causes an enhanced formation of diacylglycerol and IP3.
PGF2α, leukotrienes and thromboxane A2 mediate certain actions by:
1. Activating phosphatidylinositol metabolism.
2. Causing an increase of intracellular Ca2+.
These are released in allergic and inflammatory processes. They act as local signals and very specifically. They functions vary widely among the tissues. For example, TXA2 triggers contraction in certain smooth muscles while their release from platelets triggers the recruitment of new platelets for aggregation.
1. Abortion (Dinoprost, dinoprostone, carboprost, misoprostol alongwith methotrexate in terminating pregnancy in the 1st trimester).
2. Peptic Ulcers (misoprostol, a synthetic PGE1, is used to inhibit the secretion of HCL in stomach).
3. Alprostadil (PGE1), A vasodilator used for palliative therapy (treating symptoms only) to temporarily maintain patency of the ductus arteriosus (a fetal vessel in the 1st two months after birth) in neonates with congenital heart defects.
4. Dinoprost (PGF2α), It is used as an oxytocic agent (A drug that speeds up the child birth).
5. Dinoprostone (PGE2), An oxytocic agent used as an abortifacient.
Prostaglandins are rapidly catabolized in the body by:
1. 15-Hydroxydehydrogenase pathway.
2. Cytochrome P450 system.