AUTOCOIDS AND ANTAGONISTS-PART-2

AUTOCOIDS-AUTOCOIDS ANTAGONISTS-Contd...

PROSTAGLANDINS

Chemically prostaglandins are derivatives of prostanoic acid a 20 carbon fatty acids contain a pentagonal carbon ring.

In general prostaglandins are synthesized by our body from fatty acid eicosatetraenoic acid or arachidonic acid. As being these are all eicosanoids they are considered as true hormones.

Prostaglandins are very important biologically active substances in our bodies identical to hormones. In the beginning they were extracted from the seminal secretions of prostate glands. But nowadays they are found to be present in almost all tissues of our body. Even a nanogram of the chemicals is biologically very active.

Classifications

Prostaglandins are classified as A, B, and E.

They are classically abbreviated as PGA, PGB, and PGE. These classifications are further differentiated and related to the presence or absence of keto or hydroxyl groups at positions 9 and 11.

Subscripts relate to the number and position of double bonds in the aliphatic chain.

Pharmacology

Endogenous prostaglandins are biological substances that affect many body functions.

Many external stimuli which may be chemical, mechanical insults are causing the release of prostaglandins which contributes to the signs and symptoms of the inflammatory processes such as reddening, edema, pain, and itching. 

Prostaglandin releases are responded by our body physiologically with vasodilation, in many vascular beds and vasoconstrictions in isolated areas.

Prostaglandin-Es inhibit platelet aggregation, relax bronchial and GI smooth muscle, contract uterine smooth muscle, and inhibit gastric acid secretion. The gastric acid secretion block is done along with Prostaglandin-I.

Alternatively the Prostaglandin-Ds and Fs are causing contractions of bronchial and gastric smooth muscle.

In general all prostaglandins are increasing renal blood flow, increase diuresis with loss of sodium, and potassium in urine but paradoxically increases renin secretion.

They also cause diverse endocrine and metabolic effects.

Clinical Indications

PG-E Analogues

Alprostadil (Prostin VR Pediatric):-It is used for temporary maintenance of a patent ductus arteriosus, in awaiting corrective surgery for congenital heart defects.

Alprostadil(Caverject) To treat impotence due to erectile dysfunction.

Misoprostol:-To prevent and treat NSAIDs induced gastric ulcers. To induce abortion.

Also the other PGE analogs such as Dinoprostone(Prostin-E2, Prepidil, Cervidil)and Carboprost(Hemabate) are used to induce safe abortion. Also they are used to ease the labor during pregnancy by inducing cervical ripening.

Side Effects

1.CNS effects:-

CNS irritability

Fever

Seizures

Headache

2.Cardiovascular effects:-

Hypotension

Dysrhythmias

Vasodilation

Flushing

Cardiac arrest

3.Respiratory depression

4.Hematologic:-

Anemia

Thrombocytopenia

Disseminated Intravascular Coagulation

5.Diarrhea

6.Renal dysfunction

7.Irregular spotty menses

8.Abortion

9.Pain at the penis