Cervical diameter in relation to uterine and cervical EMG activity in early postpartum dairy cows with retained placentas after PGF2alpha induced calving

The cervix must regain its normal diameter after parturition. Until now, little has been known about the pattern of cervical closure and the possible influences of myometrial and cervical contractions in this process. We continuously measured the cervical diameter with ultrasound cervimetry during the first 48h after calving in six cows with retained fetal membranes, while uterine (n=6) and cervical outer muscular layer (n=4) electromyographic (EMG) activity was measured with bipolar EMG electrodes. We found that the cervical diameter which was 6.2cm (+/-0.7) at 1.4h after calving, initially increased to 9.0cm (+/-1.0) during the first 14.8h (+/-2.8) postpartum. After this time, the diameter decreased gradually to 5.3cm (+/-1.0) at 48h after calving. The overall EMG activity after parturition decreased by 59% (+/-6) and 35% (+/-17) for the uterus and cervix, respectively. The decrease in EMG activity was due to a 50% (+/-7) decrease in EMG amplitudes of the myometrium; the EMG amplitudes of the cervix decreased by only 8% (+/-21) (P>0.05). At the same time in the cervix, burst frequency decreased by 69% (+/-17), while the decrease in burst frequency of the myometrium was only 11% (+/-5) (P>0.05). Uterine myometrial and cervical EMG activity after parturition showed burst patterns. These contractions of the uterus and cervix were accompanied by and correlated with transient dilatations of the caudal cervix. This could have functional relevance in the evacuation of the uterus.

Treadmill but not wheel running improves fatigue resistance of isolated extensor digitorum longus muscle in mice

AIM

The present study is the first to compare the physiological impact of either forced treadmill or voluntary wheel running exercise on hindlimb muscle in mice.

METHODS

Male C57BL/6 mice were subjected to either 6 weeks of forced treadmill or voluntary wheel running exercise. Mice in the treadmill running exercise group (TRE; n = 8) ran 1.9 km day(-1) at a speed of 16 m min(-1) against an uphill incline of 11 degrees. In the running wheel exercise group (RWE; n = 8) animals ran 8.8 +/- 0.2 km per day (average speed 42 +/- 2 m min(-1)). After the experimental period, animals were killed and mechanical performance and oxygen consumption of isolated extensor digitorum longus (EDL) muscle were determined during serial electrical stimulation at 0.5, 1 and 2 Hz.

RESULTS

Steady-state half-width time (HWT) of twitch contraction at 0.5 Hz was significantly shorter in TRE and RWE than controls (CON) (41.3 +/- 0.2, 41.3 +/- 0.1 and 44.3 +/- 0.1 s respectively; P < 0.05). The rate of fatigue development and HWT lengthening at 2 Hz was the same in RWE and CON but lower in TRE (1.2-fold and twofold respectively; P < 0.05). EDL oxygen consumption, mitochondrial content and myosin heavy chain (MyHC) composition were not different between the groups.

CONCLUSION

These results indicate that both exercise modalities have an effect on a hindlimb fast-twitch muscle in mice, with the greatest impact seen with forced treadmill running.