A 58-year-old man with a 10-year history of type 2 diabetes mellitus presents to the emergency department with acute onset severe hypotension (BP 70/45 mmHg) and altered mental status following a bout of acute gastroenteritis with profuse diarrhea and vomiting. Physical examination reveals cold, clammy extremities, weak peripheral pulses, and poor capillary refill. Urine output has dropped to 0.3 mL/kg/hr. After rapid fluid resuscitation with 2 L of normal saline, BP remains 78/48 mmHg. Which of the following adrenergic agonists would be the most appropriate choice for this patient at this stage?