MS-2202

A 58-year-old patient is having a planned hysterectomy. While the surgery is ongoing, her blood pressure suddenly decreases to 60/40 mmHg and her heart rate increases to 102 bpm. The anaesthetist decides to give phenylephrine. After a few minutes, the patient’s blood pressure returns to 100/80 mmHg and her heart rate drops to 85 bpm.

What is the mechanism of action of phenylephrine in this scenario?