Effect of intrauterine devices on pituitary gonadotropins, ovulation and pseudopregnancy in rabbits.

Abstract

An experiment was planned to test the effects of IUD in rabbits who had a pseudopregnancy before the treatment. The effects of IUD were compared in animals having a treatment period of 4 days of estrus versus a long treatment of a pseudopregnancy plus 8 days of estrus. 80 rabbits in the first 24 hours of estrus following a pseudopregnancy were assigned to 8 groups of 10 each. The experiment was 2 by 2 by 2 factorial the factors being: 1) treatment with IUD in both the uterine horns; 2) duration of treatment; and 3) mating. The treatment with IUD caused a significant increase in variability of the length of pseudopregnancy. In the treated animals the proportion of large follicles that had ovulated by 11 hours after mating was significantly less than in the control groups. This effect was more pronounced when the IUD had its effect for a shorter period than for a longer period. There was no significant difference in the total number of follicles that had matured in the different groups. The relative potency of the pituitary gland was higher in the non-mated than in the mated animals but differences due to the IUD treatment were not significant either. The lesser proportion of follicles ovulating by 11 hours in the treated animals is suggestive of an interference with acute release of luteinizing hormone (LH). The less pronounced effects of the IUDs after they had been installed for the longer time appear to reflect some kind of adaptation in their presence.