This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Endocrinology, Subject name: Pharmacology
True about atosiban is? 
Select and explain. 
A. Is an oxytocin receptor antagonist, B. Is an progesterone receptor antagonist, C. Is least effective in inhibiting preterm uterine Contractions, D. Is a anti-tocolytic drug
A: Is an oxytocin receptor antagonist
Answer: A: Is an oxytocin receptor antagonist 
Explanation: Atosiban is a peptide analog of oxytocin that acts as an antagonist at the oxytocin receptors. It is a tocolytic. It suppress uterine contractions and postpones preterm delivery. (Ref.Essentials of medical pharmacology TD Tripathi 6th edition page no.333).