Uterine contractile response to the graded infusion of oxytocin in guinea pigs near term.
OBJECTIVE
Myometrial oxytocin binding characteristics do not change near term in guinea pigs. We tested the hypothesis that the uterine contractile response to oxytocin does not change near term.


METHODS
Chronically instrumented guinea pigs were given graded infusions of oxytocin (n = 19 animals) or saline solution (n = 4 animals) on days 58, 60, and 62 and then daily until delivery (term, 68 days). Uterine contractile response was assessed by the area of the quasi-integrated electromyogram. Concentrations of 13,14-dihydro-15-keto-prostaglandin F(2)(alpha) were measured in maternal plasma.


RESULTS
The uterine contractile response to oxytocin increased with advancing gestation (P =.007, random coefficients model) and labor (P =.005). Plasma concentrations of 13,14-dihydro-15-keto-prostaglandin F(2)(alpha) increased during oxytocin infusion (P <.022 vs saline solution infusion).


CONCLUSIONS
The uterine contractile response to oxytocin increases during the 1 to 2 weeks before term in guinea pigs, despite stable myometrial oxytocin receptor density. Oxytocin stimulates the production of prostaglandin F(2)(alpha).
Schellenberg
Jean-Claude
JC
Research Centre for Reproductive Medicine at the Department of Obstetrics and Gynaecology, University of Auckland, Auckland, New Zealand. jeanclaudeschellenberg@hotmail.com
Stewart
Alistair W
AW
Pliska
Vladimir
V
D000818:Animals; D015237:Dinoprost / Q000031:analogs & derivatives* / Q000097:blood; D004305:Dose-Response Relationship, Drug; D004576:Electromyography; D005260:Female; D005865:Gestational Age; D006168:Guinea Pigs; D007743:Labor, Obstetric / Q000502:physiology*; D010121:Oxytocin / Q000008:administration & dosage*; D011247:Pregnancy; D014590:Uterine Contraction / Q000187:drug effects*
C008228:15-keto-13,14-dihydroprostaglandin F2alpha; D010121:Oxytocin; D015237:Dinoprost