- Action:
- powerful vasodilator and inhibits platelet aggregation thru activation of adenylate
cyclase, which leads to an increase in intracellular cyclic adenosine
monophosphate;
- prostacyclin and
thromboxane A(sub 2) are formed from arachidonic
acid, w/ endoperoxides & prostaglandins G2 and H2 as intermediates;
- variety of drugs with diverse mechanisms of action are reputed to
increase prostacyclin production;
- include calcium antagonists, captopril, dipyridamole, diuretic
agents, nitrates, and streptokinase;
- fall in BP induced by several antihypertensive drugs, including
propranolol, is reduced by
Aspirin, suggesting that
prostacyclin may have a more general role in their activity;
- it causes relaxation of the underlying smooth muscle, and in the lumen
it prevents platelets and perhaps other blood cells from clumping
onto the endothelium;
- Steroids:
- inhibit prostacyclin synthesis in endothelial & other cells by
stimulating formation of lipocortin, endogenous inhibitor of
phospholipase A(sub 2) activity;
- inhibits phospholipase A(sub 2), &
Aspirin-like drugs, by inhibiting
cyclooxygenase, reduce synthesis of prostacyclin &
Thromboxane
