Which of the following is NOT typically associated with increased vasoconstriction?

Nitric oxide is a key molecule in the cardiovascular system, primarily recognized for its role as a vasodilator. It is produced by endothelial cells and promotes the relaxation of smooth muscles in blood vessels, leading to an increase in vessel diameter and a reduction in vascular resistance. This action results in enhanced blood flow and decreased blood pressure.

In contrast, the other substances listed, such as angiotensin II, adrenaline, and vasopressin, are all associated with vasoconstriction. Angiotensin II is a potent vasoconstrictor involved in regulating blood pressure and fluid balance. Adrenaline (epinephrine) can cause vasoconstriction, especially in non-essential vascular beds during a stress response. Vasopressin, also known as antidiuretic hormone, can promote vasoconstriction in addition to its role in kidney function and water retention.

Thus, while the other options increase vascular tone and constrict blood vessels, nitric oxide stands out as the molecule that facilitates vasodilation, making it the correct choice for the question about which substance is NOT typically associated with increased vasoconstriction.