TY - JOUR
T1 - Maturation of spontaneous and agonist-induced uterine contractions in the peripartum mouse uterus
AU - Mackler, Ari M.
AU - Ducsay, Charles A.
AU - Veldhuis, Johannes D.
AU - Yellon, Steven M.
PY - 1999
Y1 - 1999
N2 - This study tested the hypothesis that the uterus achieves maximum contractile capabilities before the onset of labor. Basal and agonist- stimulated contractions were assessed in uterine strips on Day 15 or 18 of pregnancy, the day of parturition, or I day postpartum (n = 4-13 per group). Spontaneous contractions were evident in all groups (n = 4-13 per gestational group); contraction frequency was greater in peripartum groups than in virgin controls (~4.6 versus 2.8/200 sec). Peak amplitude was nearly 9-fold higher on Days 15 and 18 and over 30-fold higher in the postpartum and I day postpartum groups than in nonpregnant mice. Maximum frequency and peak amplitude were achieved in response to 10-6 to 10-8 M oxytocin or arginine vasopressin (OT(max) or AVP(max). Frequency of contractions in response to OT(max) peaked on Day 18 and then declined. Contraction amplitude increased 5-fold on Day 15, declined on the day of birth (equivalent to nonpregnant level), then rebounded to peak on postpartum Day 1. AVP(max) similarly increased frequency and amplitude of contractions, except that maximum contraction amplitude occurred postpartum. Thus, an endogenous oscillator, residing in the uterus, sustains high basal and agonist-induced contraction frequency during pregnancy. Although acceleration of this pacemaker occurred before term, the data suggest that peripartum increases in contraction amplitude characterize the transition to the powerful synchronous contractions of parturition.
AB - This study tested the hypothesis that the uterus achieves maximum contractile capabilities before the onset of labor. Basal and agonist- stimulated contractions were assessed in uterine strips on Day 15 or 18 of pregnancy, the day of parturition, or I day postpartum (n = 4-13 per group). Spontaneous contractions were evident in all groups (n = 4-13 per gestational group); contraction frequency was greater in peripartum groups than in virgin controls (~4.6 versus 2.8/200 sec). Peak amplitude was nearly 9-fold higher on Days 15 and 18 and over 30-fold higher in the postpartum and I day postpartum groups than in nonpregnant mice. Maximum frequency and peak amplitude were achieved in response to 10-6 to 10-8 M oxytocin or arginine vasopressin (OT(max) or AVP(max). Frequency of contractions in response to OT(max) peaked on Day 18 and then declined. Contraction amplitude increased 5-fold on Day 15, declined on the day of birth (equivalent to nonpregnant level), then rebounded to peak on postpartum Day 1. AVP(max) similarly increased frequency and amplitude of contractions, except that maximum contraction amplitude occurred postpartum. Thus, an endogenous oscillator, residing in the uterus, sustains high basal and agonist-induced contraction frequency during pregnancy. Although acceleration of this pacemaker occurred before term, the data suggest that peripartum increases in contraction amplitude characterize the transition to the powerful synchronous contractions of parturition.
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U2 - 10.1095/biolreprod61.4.873
DO - 10.1095/biolreprod61.4.873
M3 - Article
C2 - 10491618
AN - SCOPUS:0032865323
SN - 0006-3363
VL - 61
SP - 873
EP - 878
JO - Biology of Reproduction
JF - Biology of Reproduction
IS - 4
ER -