Autacoids (Prostanoids)

Question 1

Inflammation prostanoids and their physiological role

Answer 1

→ PGE2 & PGI2
* Vasodilation → Enhance leukocyte infiltration
* Increase capillary permeability → Enhance edema formation.
* Increase pain induced by bradykinin.

Question 2

Pain prostanoids and its physiological role

Answer 2

→ PGs (especially PGE2)
* Potentiate the pain perception (centrally) and increase the sensitivity of nociceptors (at the peripheral nerve endings) to painful stimuli.
* Sensitize nerve endings to the action of chemical mediators (ex: bradykinin, histamine) released locally by the inflammatory process.

Question 3

Fever prostanoids and their physiological role

Answer 3

→ PGE2
* Produce a pyretic effect (Increase body temprature) by raising the body temprature set point in the Hypothalamic Regulatory Center (HRC)
* Note: Endogenous pyrogens release IL-1 from the inflammatory cells → leading to increase the synthesis and release of PGE2

Question 4

Gastro-protective effects prostanoids and their physiological role

Answer 4

• PGE2:
  (1) Stimulate synthesis of protective mucus in both stomach & small intestine
  (2) reduce pepsin content
  (3) inhibit gastric acid secretion.
• PGI2: Inhibit gastric acid secretion

Question 5

GI Smooth Muscles prostanoids and their physiological role

Answer 5

→ PGE2
* Stimulate the contraction of the main longitudinal muscle from stomach to colon → Stimulate the movement of water and electrolytes into the intestinal lumen

Question 6

Uterus prostanoids and its physiological role

Answer 6

→ PGE2 & PGF2α
* Have potent oxytocic actions → increase smooth muscle contractions in uterine

Question 7

Penis prostanoids and its physiological role

Answer 7

→ PGE1
* Induce vasodilation & smooth muscle relaxation → ↑ penile erection & sperm motility by relaxing the smooth muscle of the corpus cavernosum

Question 8

Eyes prostanoids and their physiological role

Answer 8

→ PGF2α
* Increase outflow of aqueous humor from the anterior chamber via the uveoscleral pathway → decrease intraocular pressure (I.O.P).
* No change the size of the pupil.

Question 9

Ductus arteriosus prostanoids and their physiological role

Answer 9

→ PGE2
* Maintains the ductus arteriosus patent until birth (keeps it opened during fetal life)

Question 10

Blood vessels prostanoids and their physiological role

Answer 10

• PGI2: Synthsized by COX-2 in endothelial cells & smooth muscles →
  (1) Inhibits platelet aggregation
  (2) produces vasodilation
  (3) inhibits proliferation of smooth muscle cells (this action may be particularly relevant in pulmonary HTN).
• TXA2: Synthsized by COX-1 in platelets → Increases platelet aggregation & local
  vasoconstriction (TXA2 is a potent vasoconstrictor)

Question 11

Kidneys prostanoids and their physiological role

Answer 11

→ PGE2 & PGI2
* Responsible for maintaining renal blood flow → Maintain blood pressure & regulate renal function.
* They cause:
(1) Vasodilation in afferent renal arteries
(2) Increased glomerular filtration & decresed sodium and water retention
(3) Increased renal blood flow.
* Increase the release of renin