This experiment was planned to determine conditions favourable to the development of leucocytic invasion and exudate formation in uterine horns bearing intrauterine devices (IUDs). Three groups of rats were examined: (A) pregnant in one uterine horn and bearing an IUD in the contralateral horn, (B) pseudopregnant after mating to vasectomized males and bearing unilateral IUDs, and (C) pseudopregnant following mating to intact males and bearing bilateral IUDs.
Nylon double S-shaped IUDs were inserted into one or both horns of 125 adult Wistar rats using the transcervical approach described previously (Wrenn, Wood & Bitman, 1968). Females were mated to intact or vasectomized males after IUDs had been in place for 1 month. The day on which a copulation plug was found was taken as Day 1 of pregnancy or pseudopregnancy. The animals were killed on Day 15 following mating. Each uterine horn having an IUD was flushed with 1·5 ml of physiological saline into a Bauer-Schenck graduated centrifuge tube. The tubes were centrifuged and the packed-cell volume from each uterine horn measured to the nearest 0·004 ml. Smear preparations of the uterine contents were made and stained with Wright's stain. Results were compared statistically by Student's t test.