Which of the following could inhibit the initiation of labor?: (A) Administration of an antagonist of the actions of progesterone, (B) Administration of LH, (C) Administration of an antagonist of PGE2 effects, (D) Mechanically dilating and stimulating the cervix
Answer is C. Antagonism of progesterone's effects, dilation of the cervix and oxytocin all increase uterine smooth muscle excitability and facilitate contractions and the onset of labor. LH would have no effect. Prostaglandin E2 strongly stimulates uterine smooth muscle contraction and is formed at an increasing rate by the placenta late in gestation.