Premature labour induced by cortisol in the unrestrained pregnant rabbit

The relationship between electrical activity (EMG) of the uterus, progesterone levels and gap junctions was studied in pregnant rabbits delivering either prematurely (cortisol-induced) or spontaneously at term. Electrodes were implanted in the myometrium and a catheter was inserted into the jugular vein for continuous infusion of saline or cortisol from gestational age 25 days. A tether and swivel system was used to connect the electrodes and catheter to the recording unit thus allowing protection of the wires and catheters while enabling the rabbit to move freely. The EMG was recorded continuously from day 25 of pregnancy until animals either delivered or were sacrificed at predetermined days of gestation. Both rabbit groups showed a similarity in patterns of EMG, progesterone levels and gap junction formation. We conclude that preterm labour induced by cortisol mimics normal term labour.