Sentence: Ra ( rate of production ) was measured during infusion of variable doses of epinephrine with or without variable doses of propranolol , a competitive beta-adrenergic antagonist to isolate the alpha-adrenergic agonist effects .
Drug combination annotation:
[{'class': 'COMB', 'spans': ['epinephrine', 'propranolol'], 'is_context_needed': True}]