2.20.2 Prostaglandins

Definition: Prostaglandins exist in virtually every mammalian tissue, acting as local hormones.

Source: Prostaglandins are derived from arachidonic acid.

Functions:

• Their functions vary widely depending on the tissue.
• Some reduce blood pressure, whereas others raise it.
• In the immune system, various prostaglandins help to:
• Induce fever and inflammation
• Intensify the sensation of pain
• They also help to regulate the aggregation of platelets — an early step in the formation of blood clots.

Aspirin and Prostaglandins:

• The ability of aspirin to reduce fever and decrease pain depends on the inhibition of prostaglandin synthesis.
• Aspirin inhibits the enzyme cyclooxygenase (COX) which is needed for prostaglandin synthesis.

Science, Technology and Society Connections (from textbook):

Relate the role of prostaglandin in inflammation with the inhibition of prostaglandin synthesis through aspirin.

• Prostaglandins play a pivotal role in inflammation — a process characterized by:
• Redness (rubor)
• Heat (calor)
• Pain (dolor)
• Swelling (tumor)
• The changes associated with inflammation are due to dilation of local blood vessels that permits increased blood flow to the affected area.
• The blood vessels also become more permeable, leading to the escape of white blood cells (leukocytes) from the blood into the inflamed tissues.

Intermediate Level

Steroids in Detail

• 17 carbon atoms
• Four attached rings:
• Three six-carbon rings (A, B, C)
• One five-carbon ring (D)
• Side chains distinguish different steroids.

Synthesis: - Synthesized from isoprene units.

• Structural component of cell membrane.
• Precursor of:
• Bile acids
• Testosterone
• Progesterone
• Estrogen
• Vitamin D
• Cortisol
• Aldosterone

Functions of Steroids:

Prostaglandins in Detail

Source: Arachidonic acid.

Functions:

• Inhibits prostaglandin synthesis.
• Reduces fever and pain.
• Inhibits cyclooxygenase (COX) enzyme.

Inflammation

• Redness (rubor)
• Heat (calor)
• Pain (dolor)
• Swelling (tumor)

• Dilation of local blood vessels.
• Increased blood flow.
• Increased permeability of blood vessels.
• Escape of white blood cells into tissues.

Role of Prostaglandins: - Prostaglandins play a pivotal role in inflammation.

Important Points

• 1. Steroids are lipids of high molecular weight which can be crystalline.
• 2. A steroid nucleus consists of 17 carbon atoms arranged in four attached rings.
• 3. Three of the rings contain six carbon atoms, and the fourth contains five.
• 4. The length and structure of the side chains that extend from these rings distinguish one steroid from other steroids.
• 5. These structures are synthesized from isoprene units.
• 6. Cholesterol is a structural component of cell membrane.
• 7. Cholesterol is the precursor of a large number of equally important steroids which include:
• - Bile acids
• - Male sex hormone testosterone
• - Female sex hormone progesterone and estrogen
• - Bile salts which emulsify fats
• - Vitamin D, which helps to regulate calcium metabolism
• 8. Prostaglandins exist in virtually every mammalian tissue, acting as local hormones.
• 9. Prostaglandins are derived from arachidonic acid.
• 10. Their functions vary widely depending on the tissue.
• 11. Some reduce blood pressure, whereas others raise it.
• 12. In the immune system, various prostaglandins help to:
• - Induce fever and inflammation
• - Intensify the sensation of pain
• 13. They also help to regulate the aggregation of platelets — an early step in the formation of blood clots.
• 14. The ability of aspirin to reduce fever and decrease pain depends on the inhibition of prostaglandin synthesis.
• 15. Inflammation is characterized by:
• - Redness (rubor)
• - Heat (calor)
• - Pain (dolor)
• - Swelling (tumor)
• 16. The changes associated with inflammation are due to dilation of local blood vessels that permits increased blood flow to the affected area.
• 17. The blood vessels also become more permeable, leading to the escape of white blood cells (leukocytes) from the blood into the inflamed tissues.

Remember

• - Steroids = four-ring structure; 17 carbons
• - Rings: A, B, C (six carbons); D (five carbons)
• - Cholesterol = precursor of steroids
• - Steroids from cholesterol: Bile acids, testosterone, progesterone, estrogen, vitamin D
• - Prostaglandins = local hormones; derived from arachidonic acid
• - Functions: Blood pressure, fever, inflammation, pain, platelet aggregation
• - Aspirin = inhibits prostaglandin synthesis
• - Inflammation signs: Redness, heat, pain, swelling
• - Cause of inflammation: Vasodilation; increased permeability

Common Mistakes

• 1. Confusing steroids and prostaglandins – Steroids = four-ring structure; Prostaglandins = derived from arachidonic acid.
• 2. Thinking cholesterol is only harmful – Cholesterol is essential for cell membrane structure and is a precursor for many important steroids.
• 3. Forgetting the number of rings in a steroid nucleus – Four rings (three six-carbon, one five-carbon).
• 4. Confusing the functions of prostaglandins – Prostaglandins have many functions (blood pressure, fever, inflammation, pain, platelet aggregation).
• 5. Thinking prostaglandins are only involved in inflammation – Prostaglandins also regulate blood pressure and platelet aggregation.
• 6. Forgetting that aspirin inhibits prostaglandin synthesis – Aspirin reduces fever and pain by blocking prostaglandin synthesis.
• 7. Confusing the signs of inflammation – Redness, heat, pain, swelling.
• 8. Thinking steroids are only sex hormones – Steroids also include bile acids, vitamin D, cortisol, and aldosterone.
• 9. Forgetting that cholesterol is a steroid – Cholesterol is a steroid and a precursor for other steroids.
• 10. Confusing the source of prostaglandins – Prostaglandins are derived from arachidonic acid.
• 11. Thinking prostaglandins are stored in the body – Prostaglandins are synthesized on demand and act locally.
• 12. Forgetting the role of prostaglandins in platelet aggregation – Prostaglandins regulate the aggregation of platelets, an early step in blood clot formation.

Quick Revision

• Steroids are lipids of high molecular weight which can be crystalline.
• A steroid nucleus consists of 17 carbon atoms arranged in four attached rings, three of the rings contain six carbon atoms, and the fourth contains five.
• The length and structure of the side chains that extend from these rings distinguish one steroid from other steroids.
• These structures are synthesized from isoprene units.
• Cholesterol is a structural component of cell membrane.
• Cholesterol is the precursor of a large number of equally important steroids which include the bile acids, male sex hormone testosterone, female sex hormone progesterone and estrogen etc.
• Bile salts which emulsify fats and Vitamin D, which helps to regulate calcium metabolism are also steroid.
• Prostaglandins exist in virtually every mammalian tissue, acting as local hormones.
• Prostaglandins are derived from arachidonic acid.
• Their functions vary widely depending on the tissue.
• Some reduce blood pressure, whereas others raise it.
• In the immune system, various prostaglandins help to induce fever and inflammation and also intensify the sensation of pain.
• They also help to regulate the aggregation of platelets an early step in the formation of blood clots.
• In fact, the ability of aspirin to reduce fever and decrease pain depends on the inhibition of prostaglandin synthesis.
• Science, Technology and Society Connections: Relate the role of prostaglandin in inflammation with the inhibition of prostaglandin synthesis through aspirin.
• Prostaglandins play a pivotal role in inflammation a process characterized by redness (rubor), heat (calor), pain (dolor), and swelling (tumor).
• The changes associated with inflammation are due to dilation of local blood vessels that permits increased blood flow to the affected area.
• The blood vessels also become more permeable, leading to the escape of white blood cells (leukocytes) from the blood into the inflamed tissues.

60-Second Revision

• Steroids = four-ring structure; 17 carbons
• Rings: A, B, C (six carbons); D (five carbons)
• Cholesterol = precursor of steroids
• Steroids from cholesterol: Bile acids, testosterone, progesterone, estrogen, vitamin D
• Prostaglandins = local hormones; derived from arachidonic acid
• Functions: Blood pressure, fever, inflammation, pain, platelet aggregation
• Aspirin = inhibits prostaglandin synthesis
• Inflammation signs: Redness, heat, pain, swelling
• Cause of inflammation: Vasodilation; increased permeability
• Warning: Steroids and prostaglandins are not the same. Cholesterol is not only harmful. Prostaglandins are not only involved in inflammation. Aspirin inhibits prostaglandin synthesis. Inflammation has four signs: redness, heat, pain, swelling.