Final answer:
Adenosine pharmacologically slows conduction velocity and increases the refractory period in cardiac muscle, is metabolised in the plasma, and its effects can be inhibited by methylxanthines.
Step-by-step explanation:
The question pertains to the pharmacological effects of adenosine on cardiac physiology. Adenosine acts by slowing conduction velocity through the atrioventricular (AV) node and increasing the refractory period of cardiac muscle cells. It does this by opening A1 receptors which leads to hyperpolarization of cells and a decrease in action potential frequency. Adenosine can be quickly metabolised by adenosine deaminase or taken up by cells, thereby being metabolised in plasma.
While it has a potential role in decreasing urate levels due to increasing renal blood flow, this is not its primary pharmacological action. Methylxanthines, like caffeine and theophylline, are adenosine receptor antagonists, and thus they would inhibit rather than increase adenosine responses.