Functions of PGs (Prostaglandins)

FUNCTIONS OF PGs

There are varieties of physiological effects including the following:

1. Blood clots are formed when a blood vessel is damaged. A type of PGs called thromboxane (TxA₂) stimulates constriction and clotting of platelets. Conversely, PGI₂ have the opposite effect on the walls of blood vessels.

2. Certain PGs are involved in the induction of labour and other reproductive processes. PGE₂ causes uterine contractions and has been used to induce labour.

Nomenclature

PGs are considered as analogues of poly unsaturated fatty acids. It is a 20 carbon carboxylic acid containing a five-member ring. The PGs (Table 2.1) are classified according to the nature of:

A.          Cyclopentane ring.

B.          Two side chain.

C.          Configuration of newly introduced functional group.

Table 2.1 Various types of PGs.

The main classes are further subdivided according to the number of double bonds in the side chain. This is indicated by the subscripts 1, 2, or 3 and refers to the fatty acid precursor in most instances.

Examples: PGE₂ and PGF₂α.

Two side chains are attached to the cyclopentane ring at C-8 and C-12. The upper chain, having a carboxylic acid group at the terminal, is α -side chain and the lower chain, having OH group at C-15 position, is a β side chain. The α and β chains are in trans configuration in the prostanoic acid. The chiral centre C-15 is a δ nature (PGE). The OH group at C-11 in the E series has the α configuration, however, in unnatural configurations the 11-OH is called 11-epi PGs, having arms fused C to each other and are named as iso prostaglandins.