This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Male Reproductive System, Subject name: Physiology
Which hormones antagonize the effect of NO and cause the penis to become flaccid after orgasm? 
Select and explain. 
A. Endothelin and norepinephrine, B. Estrogen and progesterone, C. Luteinizing hormone (LH) and follicle-stimulating hormone (FSH), D. Progesterone and LH
A: Endothelin and norepinephrine
Answer: A: Endothelin and norepinephrine 
Explanation: Norepinephrine is released from the nerve terminals and endothelin is released from endothelial cells in the vasculature, causing vasoconstriction of the vasculature.