This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: Nervous system, Subject name: Physiology
Substrate P, actions all except 
Select and explain. 
A. Vasoconstriction, B. Pain transmission, C. Axon reflex, D. Peristalsis
A: Vasoconstriction
Answer: A: Vasoconstriction 
Explanation: Substance P a peptide composed of 11 amino acids, present in nerve cells scattered throughout the body and in special endocrine cells in the gut; it increases the contractions of gastrointestinal smooth muscle and causes vasodilatation; it is one of the most potent vasoactive substances known, and it seems to be a sensory neurotransmitter involving pain, touch, and temperature.Ref: Ganong&;s review of medical physiology 23rd edition Page no: 143