25685
This led to the still controversial hypothesis that LRP5 influences bone formation indirectly by regulating the expression of thp1 and as a consequence influencing the production of serotonin in the gut .
 serotonin
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 serotonin