The investigators are trying to determine if a single dose of Ticagrelor will increase delivery of intraarterially-infused adenosine into the forearm interstitium, consistent with adenosine reuptake blockade.

The investigators will compare adenosine interstitial levels using a parallel design study with three groups of subjects. Forearm interstitial adenosine levels will be measured at baseline and after intrabrachial infusion of adenosine at two doses. Subjects will then randomly receive Ticagrelor 180 mg, Dipyridamole 200 mg, or placebo. Two hours later the investigators will repeat the dialysate collections at baseline and after adenosine infusions.

Inclusion Criteria:

1. Subjects will be healthy volunteers, without significant pulmonary, cardiovascular gastrointestinal, hematological or renal diseases
2. Not taking any regular medications
3. Able to provide signed consent prior to study participation.

Exclusion Criteria:

1. History of asthma
2. Pregnancy
3. Exposure to an investigational drug in the last 2 months.
4. Known hypersensitivity to study medications