This study will use myocardial contrast echocardiography performed during a continuous intravenous infusion of Definity microbubbles (Perflutren lipid microbubbles) to determine if dexmedetomidine (an intravenous central sympatholytic drug) can reverse all the cardiovascular effects of low-dose intranasal cocaine-including vasoconstriction in the coronary microcirculation-both in cocaine-naïve and non-treatment seeking cocaine-addicted subjects.

Each subject will be participating in three study visits: Screening Visit, Visit 1: a low-dose dobutamine visit and Visit 2: a low-dose cocaine visit. At the dobutamine visit, the subject will only receive low-dose dobutamine, which will be used as an internal inotropic/vasodilator control for cocaine. At the cocaine visit, the subject will receive low-dose intranasal cocaine followed by either the active study drug (dexmedetomidine) or an inactive placebo (saline). Both cocaine and dobutamine will increase myocardial contractility and oxygen demand, thereby stimulating metabolic vasodilation. If, as predicted, cocaine also causes α-adrenergic agonist in the coronary microcirculation, then myocardial blood flow should increase less with cocaine then with dobutamine for a given level of myocardial oxygen demand. We will study if dexmedetomidine, a central sympatholytic, can normalize this cocaine effect. We previously have used dobutamine as a comparator for cocaine in our research. At both visits, myocardial contrast echocardiography will be used to measure regional myocardial perfusion.

Inclusion Criteria:

• Healthy adult subjects ages of 18-65 years without any history of substance abuse (other than tobacco), including narcotics, abuse of prescription painkillers, cocaine or any other recreational drug

Exclusion Criteria:

• Known or suspected right-to-left, bi-directional, or transient right-to-left cardiac shunts or detected by screening echocardiogram performed prior to I.V. infusion of Definity microbubbles
• Hypersensitivity or prior reactions to Definity microbubbles
• Pregnant or nursing women
• Any evidence of cardiopulmonary disease by history or physical examination, including subjects who are taking any cardiovascular medications of any sort
• History of hypertension or BP at time of consent > 140/90 mm Hg
• Any history of substance abuse (other than tobacco), including narcotics, prescription painkillers, cocaine or any other recreational drug (any person that says they have EVER tried these drugs will be excluded from this study)
• Subjects reporting alcohol intake of more than 2 drinks/day
• Severe psychiatric illness (e.g., schizophrenia, suicidal depression) in addition to drug dependence, which may signify a high risk of addiction
• Diabetes mellitus or any other systemic illness
• Individuals with a history of pseudocholinesterase deficiency
• Hypersensitivity to dexmedetomidine or lorazepam
• The presence of alcohol by breathalyzer
• Subjects who have poor echocardiography images will be screen failed.
• Persons with mechanically, magnetically, or electrically activated implants, such as cardiac pacemakers, neurostimulators, and infusion pumps (MRI only).
• Persons with ferromagnetic implants and ferromagnetic foreign bodies, such as intracranial, aneurysm clips, shrapnel and intraocular metal chips as these could become dislodged (MRI only).
• Persons unable to tolerate MRI imaging secondary to an inability to lie supine or severe claustrophobia (MRI only).
• Persons whose renal function test does not meet CSMC standard of care MRI contrast protocol requirements (GFR <45ml/min).
• Persons with allergy to animal dander or animal-instigated asthma
• Persons with a history of kidney or liver disease.