Objective: To select the most effective parameters of electroacupuncture (EA) at Hegu (LI4) and Sanyinjiao (SP6), a traditional acupuncture formula that induces labor, by comparing its effects on uterine contraction in late-stage pregnant rats, so as to improve the effects of acupuncture on induction of labor and its clinical maneuverability and provide the basis for further mechanism research.
Methods: One hundred and eight female healthy adult Wistar rats were randomly divided into eight groups including one non-pregnancy control group (normal control group) and seven pregnant groups. Pregnant rats were prepared by free mating and vaginal plugs observation method and were randomly divided into six EA groups and one no EA group (model group) according to the requirements of a 2×3 factorial design. EA parameters included 2 types of waves (continuous wave and sparse-dense wave) and 3 types of frequency (15, 30 and 50 Hz). Rats in treatment groups received EA on bilateral LI4 for 20 min and then bilateral SP6 for 5 min with certain parameters accordingly. Each acupoint and a nearby non-acupoint at the proximal end (2 to 3 mm from the acupoint) were connected with two leads of one EA line. The current intensity of EA was 0.2 to 0.3 mA. A muscle tension transducer and the BL-420 Biological Experimental System were placed on the lower uterine segment of rats for detecting contractility, frequency and lasting-time of contraction wave.
Results: Compared with non-pregnancy control group, the amplitude, frequency and lasting time of contraction waves of uterine contraction in all EA groups and model group were significantly increased. Compared with control group, amplitudes of contraction waves of uterine contraction of both EA1 group (15 Hz continuous wave) and EA6 group (2/50 Hz sparse-dense wave) were significantly increased (P<0.01 or P<0.05); frequency of contraction waves of uterine contraction of EA6 group was significantly increased (P<0.01 or P<0.05); lasting time of contraction waves of uterine contraction of EA1 group, EA5 group (2/30 Hz sparse-dense wave) and EA6 group were significantly increased (P<0.01 orP<0.05). Comparisons between EA6 group and the other EA groups showed that, EA6 group had significantly higher levels of amplitude and frequency of contraction waves of uterine contraction than the other EA groups (P<0.01 orP<0.05) except EA1 group, there was no significant difference between EA1 group and EA6 group (P>0.05), but the mean value of EA6 group was higher than that of EA1 group; EA6 group had significantly higher levels of lasting time of contraction waves of uterine contraction than the other EA groups (P<0.01 or P<0.05) except EA1 group and EA5 group, there was no significant difference between EA6 group and EA1 group or EA5 group (P>0.05), but the mean value of EA6 group was higher than EA1 group and EA5 group.
Conclusion: EA with sparse-dense wave (2 Hz sparse wave and 50 Hz dense wave, alternately) at LI4 and SP6 was more effective than other EA parameters for increasing uterine contraction amplitude, frequency, and lasting-time of contraction waves in late-stage pregnant rats. This combination of electric wave and frequency for EA at LI4 and SP6, a traditional acupuncture formula for inducing labor, is recommended to be applied in clinical practice for parturition as well as for treatment of uterine atony.

Key words: electroacupuncture, parturition, uterine contraction, Hegu (LI4), Sanyinjiao (SP6), rats