The timing and possible mechanisms of cervical opening in the oestrous rat

The time that the retention of luminal fluid begins and its release from the uterus in pro-oestrous rats was determined precisely using a dye injection technique. Oestradiol was found to cause dye retention in ovariectomized rats when provided continuously from an implant of 5 mg. Injections of 0.5 microgram/d X 4 were ineffective. Administration or progesterone to rats bearing implants of oestrogen interfered with the ability of the uterus to retain dye. Treatment with relaxin for 28 h prevented retention of eye in pro-oestrous rats whereas treatment at the time of dye injection was without effect. Mechanical stimulation of the cervix did not cause loss of injected dye. It is suggested that the mechanisms of opening of the cervix at coitus and at the end of oestrous may differ.