Final answer:
Nifedipine would decrease a postpartum client's blood pressure by relaxing the muscles of the heart and blood vessels. Oxytocin, often associated with labor contractions, and methylergonovine typically increase blood pressure, whereas misoprostol is not primarily used for blood pressure control.
Step-by-step explanation:
The drug that would decrease a postpartum client's blood pressure among the options listed is c) Nifedipine. Nifedipine is a calcium channel blocker used to treat high blood pressure and angina, and it works by relaxing the muscles of the heart and blood vessels. In contrast, oxytocin (option a), which is primarily responsible for contractions during labor, and methylergonovine (option b) usually increase blood pressure, while misoprostol (option d) is used to prevent stomach ulcers and is not primarily intended for blood pressure control.
In terms of the given references, angiotensin II (option d) is known to be a vasoconstrictor, and the hormone primarily responsible for contractions during labor is oxytocin (option a). Before the baby and placenta are expelled, contractions increase, facilitated by oxytocin in a positive feedback loop. The decrease in progesterone at the last weeks of pregnancy reduces the inhibition of uterine contractility, thus helping to bring on labor.