The effect of bilateral pelvic neurectomy on uterine and abdominal electrical and pressure activity, as measured by telemetry in conscious, unrestrained pregnant rats.

AIMS Bilateral pelvic neurectomy (BPN) interferes with delivery in rats. This work measures the effect of BPN on uterine and abdominal electromyography (EMG) and pressure during gestation and delivery. METHODS Uterine EMG and intra-uterine pressure (IUP), as well as abdominal muscle EMG and intra-abdominal pressure (IAP), were recorded on days 19-24 in rats. Mean values were determined for the peak frequency of the power density spectrum (PDS) of the uterine and abdominal EMG "bursts," the integral of the abdominal EMG power spectrum (IPS), and the area under the IUP and IAP curves (AUIUP and AUIAP). RESULTS Uterine EMG power density spectrum peak frequency and AUIUP were low during days 19-21 in all rats, and on days 22-23 increased sharply and significantly in both groups. Before delivery, sham rat recordings showed sudden sharp increases in AUIAP, AUIUP and IPS as "pushing" was observed. Pushing was not observed or recorded in laboring BPN rats and they did not deliver normally. CONCLUSIONS A functional pelvic nerve is required for normal labor and delivery in rats. BPN inhibits abdominal EMG and contractions necessary to expel the fetus.