Mechanical responses of the isolated cervix and uterine horn of pregnant rats near term to drugs.

1 The responses of circularly cut strips of cervix and uterine horn from rats on days 20 and 22 of pregnancy to drugs were compared in vitro. 2 The cervix exhibited similar responses and sensitivities to acetylcholine, bradykinin, prostaglandin (PG) F2alpha (day 20) and isoprenaline (day 20) as did the uterine horn but was less sensitive or responded less consistently to isoprenaline (day 22), oxytocin and PG1. PGE2 was more potent on the cervix (day 20). 3 Before term the relatively inextensible connective tissue of the cervix plus contractions of the smooth muscle would help to prevent foetal expulsion. At term the cervical smooth muscle is sufficiently unresponsive to allow cervical dilatation.