Comparison of the activity of circular and longitudinal myometrium from pregnant rats: co-ordination between muscle layers.
1. Contractions and electrical activity were recorded from isolated segments of longitudinal (L) and circular (C) myometrium from rats on gestation days 16-17 and 21 before and during parturition. 2. The segments were arranged so that the activity of the two layers could be monitored simultaneously and independently. 3. Out of the 15 preparations from days 16-17, 13 showed no co-ordination of activity between the layers. In the other two preparations a large contraction of C occasionally initiated a contraction of L. Surgical separation of the layers disrupted the co-ordination and L then developed its independent rhythm. 4. On day 21 before delivery, eight of 10 preparations exhibited 1:1 co-ordination of activity between the two layers, but C did not consistently pace L. The pacing shifted from one layer to the other several times during an experiment. 5. During parturition there was a 1:1 co-ordination of activity in all 10 preparations examined. In nine of these L initiated the activity of the C. Surgical separation of the layers disrupted the co-ordination and C developed its independent rhythm. In one the pacing shifted from one layer to the other several times during the experiment. 6. In all cases where co-ordination between the layers was observed it was myogenic and apparently related to the spread of action potentials between the two muscles.
Tomiyasu
B A
BA
Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912.
Chen
C J
CJ
Marshall
J M
JM
D000818:Animals; D004553:Electric Conductivity; D005260:Female; D009215:Myometrium / Q000502:physiology*; D011247:Pregnancy; D051381:Rats; D014590:Uterine Contraction