This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Urethra & Penis, Subject name: Surgery
In evaluating the role of the autonomic nervous system related to urinary incontinence that developed in a 67-year-old man after prostatectomy, it is determined that the sympathetic nerves are injured. What is the natural hormone in the catecholamine pathway? 
Select and explain. 
A. Norepinephrine, B. Dopamine, C. Vasoactive intestinal peptide (VIP), D. Isoproterenol
A: Norepinephrine
Answer: A: Norepinephrine 
Explanation: The metabolic pathway of catecholamines is initiated by conversion of tyrosine to dopa, which in turn, forms dopamine. Dopamine forms norepinephrine, which is the precursor of epinephrine. Epinephrine is the main amine secreted during life and is concerned with the "fight or flight" reaction.