21580
The time course of effects on ovarian steroid production , circulating 17 beta - estradiol ( E2 ) and vitellogenin ( VTG ) concentrations , and expression of steroidogenesis - related genes in the ovary was measured .
 17 beta - estradiol, vitellogenin, VTG
Please list all entity words in the text that fit the category. Output format is "word1, word2". 
Option: Chemical 
Text: {0} 
Answer:
 17 beta - estradiol, vitellogenin, VTG