Objective To observe the effect of electroacupuncture(EA) at different frequencies on serum estradiol(E2)

progesterone(P)

thromboxance B2(TXB2)

6-Keton-prostaglandin F 1 alpha(6-keto-PGF1α)contents in late pregnancy rats so as to study its mechanisms underlying labor promotion.Methods A total of 66 late-stage pregnant Wistar rats were randomly divided into 6 groups: normal control

late-pregnancy model(model)

2 Hz-EA

20 Hz-EA

50 Hz-EA and 100 Hz-EA groups

with 11 rats in each group.On the 19th day after pregnancy

EA(2 Hz

20 Hz

50 Hz

100 Hz

0.1 mA) was applied to bilateral "Hegu"(LI 4) for 20 min first and to bilateral "Sanyinjiao"(SP 6) for 5 min afterwards.Serum E2

P

TXB2 and 6-keto-PGF1α contents were assayed by radioimmunoassay

and the ratios of E2/P and TXB2/6-keto-PGF1αwere calculated.Results Compared to the normal control group

serum E2 contents in 2 Hz-EA

20 Hz-EA

50 Hz-EA and 100 Hz-EA groups were increased significantly(P<0.001

P<0.01

P<0.05).Compared to the model group

serum E2 levels in the 2 Hz-EA and 20 Hz-EA groups were up-regulated further significantly(P<0.05).Comparison among the four EA groups showed that serum P level in the 100 Hz-EA group was significantly higher than those in the 20 Hz-EA and 50 Hz-EA groups(P<0.05).Compared to the normal control group

the contents of serum TXB2 and the ratios of E2/P in both 2 Hz-EA and 50 Hz-EA groups were significantly higher(P<0.05

P<0.001

P<0.01).Conclusion Both 2 Hz and 20 Hz EA can effectively increase serum E2.content

and 2 Hz and 50 Hz EA can raise serum TXB2 and E2/P levels in late pregnancy rats

which may contribute to their effects in strengthening the uterine contractility to promote labor by regulating hormone secretion.