Final answer:
Adenosine causes bronchoconstriction via A2 receptors.
Step-by-step explanation:
The correct answer is B. Adenosine causes bronchoconstriction via A2 receptors.
Adenosine is a naturally occurring nucleoside that acts as a neurotransmitter in the body. It has various effects on different tissues and organs. In the context of this question, adenosine acts on the A2 receptors to cause bronchoconstriction. When adenosine binds to these receptors, it triggers a signaling cascade that leads to the contraction of smooth muscles in the bronchioles. This constriction narrows the airways, making it more difficult to breathe.
It is important to note that adenosine has different effects on different receptor subtypes. While it can cause AV block via its action at A1 receptors, it does not have this effect on A2 receptors. Adenosine also does not cause renal vasodilation or profound depression of the SA node. Furthermore, it does not decrease SA node automaticity.