A 45-year-old man with community-acquired pneumonia presents to the ICU with septic shock: BP 85/52 mmHg, HR 118/min, lactate 4.2 mmol/L. After fluid resuscitation (30 mL/kg crystalloid), his MAP remains 58 mmHg. The structure marked **A** in the diagram is initiated as the first-line vasopressor. Which of the following BEST explains why this agent is preferred over dopamine in septic shock according to current Surviving Sepsis Campaign Guidelines?