A 35-year-old man was admitted to the hospital following a car accident, and a blood transfusion was started. A few minutes later, he complained of nausea and pruritus and developed dyspnea with audible wheezing. His skin was mottled and cold, heart rate was 120 bpm , and blood pressure fell to 80/40 m m Hg. An intramuscular injection of epinephrine was given. Which of the following actions of the drug most likely contributed to its therapeutic efficacy in this patient?