2.5. Determination of serum estradiol, kisspeptin and
NKB concentrations
Serum estradiol concentrations were measured using commercial radioimmunoassay (RIA) kits (Beijing North Institute of Biological Technology, Beijing, China) according to the manufacturer’s instructions. The intra- and inter- assay coefficient of variations (CVs) were lower than 10% and 15%, respectively. The sensitivity was 0.002 pg/mL and the correlation coefficient for the standard curve was
0.99940.