Which of the following activities is associated with B2 receptor activation?

B2 receptor activation is primarily associated with smooth muscle relaxation and inhibition of contraction in various tissues, particularly in the uterus. When B2 adrenergic receptors are activated, they promote relaxation of the uterine muscles, making it easier for the uterus to accommodate a growing fetus during pregnancy. This mechanism is significant in managing premature labor by reducing uterine activity.

While increased heart rate and myocardial contractility are generally linked to B1 receptor activation, B2 receptors also have some influence on cardiovascular effects, but those are secondary compared to the primary action on smooth muscle relaxation. Hypokalemia is not a direct result of B2 receptor stimulation; rather, it may follow from conditions or treatments that influence potassium levels.

Therefore, the association of B2 receptor activation with uterine relaxation highlights its critical role in obstetric practice and is why this option is the most relevant.