The Effects of an Intrauterine Device Containing Norgestrel in the Rat

Abstract

The expulsion of blank and norgestrel-loaded Silastic capsules free in the lumen of 1 uterine horn was studied in the rat in relation to the uterine phase at the time of insertion; mating and subsequent implantation in the experimental horns were also observed. The results of the study demonstrated little of no correlation between expulsion of the blank device and the uterine phase. The expulsion rates for blank c apsules were 60% (18 of 30) of those inserted during the positive phase and 50% (5 of 10) of those inserted during the negative phase. 50% of the norgestrel devices inserted during the negative phase were absent at autopsy. However norgestrel effected a definite retention of devices inserted during the positive phase of the uterus. Of the 30 capsules inserted during this period 26 (86%) were retained. This retention rate was twice as high as that of the blank devices inserted during the same period. Although implantation was observed in 1 horn bearing a blank device both types of capsule (blank and norgestrel) were highly effective in preventing implantation in the experimental horn. Neither type of capsule appeared to affect implantation in the control horn. It is concluded that under the conditions of the study norgestrel was released in sufficient quantity to significantly inhibit the expulsion of the Silastic device inserted during the positive phase of the uterus yet in an insufficient amount to interfere with fertility in the control horn via the systemic circulation.(AUTHORS MODIFIED)