Concerning regulation of arterial luminal area, the following is/are true:

b. Compensatory vasodilation occurs until more than 40% of area inside the internal elastic lamina is obstructed in coronary arteries

d. When endothelium is absent, thrombin causes vasoconstriction.

The major determinant of arterial diameter is blood velocity as demonstrated by post-stenotic dilation. This adaptation by wall relaxation is limited to 40% of the area inside the internal elastic lamina in coronary arteries. The predominant vasodilator, nitric oxide, is derived from arginine. When endothelium is absent, a number of vasodilators, including thrombin, produce vasoconstriction.