Which of the following is NOT a major effect of thromboxane A2?

Thromboxane A2 (TXA2) is a potent eicosanoid produced primarily by activated platelets and plays a significant role in hemostasis and vascular function. Its major physiological effects include promoting platelet aggregation, causing vasoconstriction, and inducing bronchoconstriction.

The reason vasodilation is not a major effect of thromboxane A2 is that TXA2 functions primarily to constrict blood vessels, thereby increasing blood pressure, and to facilitate the aggregation of platelets, which is essential in the hemostatic response to vascular injury. In contrast, vasodilation is primarily mediated by other substances, such as prostacyclin (PGI2) and nitric oxide, which serve to relax blood vessels and lower blood pressure. Thus, identifying vasodilation as a non-major effect of thromboxane A2 aligns with the understanding of its biological roles within the context of vascular and platelet physiology.