This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Physiology
In a patient with a transplanted heart which of these are the reasons for increased cardiac output during exercise 
Select and explain. 
A. Reinnervation of transplanted heart by vagus, B. Intrinsic mechanism., C. Epinephrine from medulla, D. Bainbridge reflex
C: Epinephrine from medulla
Answer: C: Epinephrine from medulla 
Explanation: Cardiac transplantation results in total denervation of the donor's heart, including the donor sinus node, which usually controls heart rate after transplantation.
Denervation causes an increase in basal heart rate due to parasympathetic sectioning (normally parasympathetic tone is greater than sympathetic tone on the heart).

Further increase in heart rate during exercise is dependent primarily on increase in plasma catecholamine concentration, e.g. from the adrenal medulla.