Which of the following statement about prostaglandins is true ?
|A||They are precursors to arachidonic acid|
|B||They release arachidonic acid from membranes through the action of phospholipase A|
|C||They were first observed to cause uterine contraction and lowering of blood pressure|
|D||They may be converted to leukotrienes by lipoxygenase|
a. Although prostaglandins were originally isolated from prostate glands, seminal vesicles and semen, their synthesis in other organs has been amply documented; indeed, few organs have failed to demonstrate prostaglandin release.
b. Prostaglandins cause platelet aggregation smooth muscle contraction, vasodilation, and uterine con traction. Prostaglandins are synthesized from arachidonic acid, a 20- carbon fatty acid with interspersed carbon double bonds Signals such as angiotensin II, bradykinin, epinephrine, and thrombin can activate phospholipase A and release arachidonic acid from membrane lipids.
c. The arachidonic acid is cyclized by cyclooxygenase to form prostaglandins. Arachidonic acid can also be oxidized to leukotrienes by the action of lipoxygenases. Zilcuton is an inhibitor of enzyme 5-lipoxygenase.