Which of the following is the most likely reason why fentanyl does not disturb cardiovascular stability as much as morphine?

Morphine releases histamine and can cause cardiovascular instability. Fentanyl does not release histamine, and causes only mild decreases in heart rate and blood pressure. Fentanyl, a lipid-soluble drug, has an elimination half-life between 3 and 4 hours. It is 100 times more potent than morphine.