Exclusion Criteria:1) History of acute or chronic illness that contraindicate the use of propranolol, may hinder study procedures, or confuse interpretation of the data (e.g. cardiac, dermatological, neurological, psychiatric or addictive diseases) 2) Clinically significant cardiovascular, pulmonary, hepatic or renal diseases 3) Pregnant or breast-feeding 4) Intake of prescription drugs with anti/pro-inflammatory action 5) Intake of prescription drugs with anti/pro-analgesic action 6) Inability to abstain from any anti/pro-inflammatory, or analgesic drugs 48 hours before, or during the study session 7) Inability to obtain at least 6 hours of sleep during the night preceding the study session 8) Known sensitivity or allergy to propranolol or alfentanil 9) Any history of drug or alcohol abuse