Hypertension-related coronary thrombosis: prothrombic role of angiotensin II.

Although hypertension is a major risk factor in acute myocardial infarction, concomitant hypercoagulability causing thrombosis leading to myocardial infarction remains unproven for lack of an appropriate coagulation test. This study was devised to determine whether a modified recalcification time (MRT) test can demonstrate that angiotensin II, a potent vasoconstrictor, also accelerates coagulation to promote thrombosis. The MRT incorporates blood cells and chemical coagulants for maximizing sensitivity. Four groups (A, B, C, and D) of aliquots of citrated human blood were incubated for 2 hours at 37 degrees C after adding to A--20 microL saline, to B--10 micrograms Escherichia coli endotoxin, to C--20 micrograms angiotensin II, and to D--a combination of E coli endotoxin and angiotensin II. The experiment was repeated with nonincubated aliquots. Modified recalcification time values +/- standard deviation in minutes were: A--5.5 +/- 1.5, B--4.6 +/- 1.1, C--4.9 +/- 1.0, and D--3.9 +/- 1.0. Significance (Student's t test) was as follows: B versus A P < .001; C versus A, P < .05; C versus D, P < .001; B versus C, P < .05; and B versus D, P < .001. No significant changes occurred in nonincubated blood. We conclude that angiotensin II has a hypercoagulable effect, as does endotoxin. The hypercoagulability in concert with vasospasm can explain the role of hypertension in acute myocardial infarction. This in vitro study excludes the role of other in vivo mechanisms in the development of angiotensin II-induced hypercoagulability.