| Abstrakt: |
Previous studies showed that circular (CM) and longitudinal myometrium (LM) have different physiological and pharmacological characteristics. To determine if such differences also exist with respect to the actions of oxytocin and prostaglandin F2-alpha (PGF2α), we compared the effects of these agents on the spontaneous contractions of CM and LM from rats on Days 15, 17, and 21 (term) of pregnancy. Both agents stimulated CM and LM on all gestation days, but the responses differed as follows: 1) the CM response to oxytocin was all-or-nothing on Days 15 and 17, to PGF2αon Day 15, and was graded to both agents only at term; 2) the LM response to both agents was always graded; 3) the maximum response to oxytocin was always less in CM than in LM, and to PGF2αwas less in CM except at term, when it was greater than in LM; 4) the EC50(effective concentration that produced 50% of the maximum response) for PGF2αin CM was greater than in LM, indicating a lesser sensitivity of CM for this agent. Therefore, the heterogeneity between CM and LM extends to the effects of oxytocin and PGF2α, further emphasizing the importance of distinguishing between the two muscle layers in studies of uterine activity. |
