27508
Ethanol and melatonin exert opposite effects on E2 and P4 , and they differentially regulate the expression of sex steroid receptors in female reproductive tissues .
 Ethanol, melatonin, steroid
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 Ethanol, melatonin, steroid