Effects of the Progesterone Receptor Antagonist Aglepristone on Implantation Administered on Days 6 and 7 after Mating in Rabbits

Abstract

There is no safe and accurate method for early termination of pregnancy in the rabbit. So this study was carried out to determine the effect of aglepristone administration in preventing early pregnancy before implantation in this species. Twenty-two animals (10-12 months old, New Zealand White rabbits) were naturally mated and pregnancies were confirmed in all animals by ultrasonographic examinations on day 6 after mating (5-7.5 MHz linear array transducer Dynamic Imaging Sonostar, UK) and the animals were grouped randomly: Group I & Group III: Aglepristone (Alizin, Virbac; 10 mg/kg, subcutaneously) was injected twice, 24 h apart, on days 6 and 7 after mating (n = 5; n = 8). Group II & Group IV: The same volume of 0.9% NaCl solution was subcutaneously injected in the same interval and served as controls (n = 5; n = 3). Ultrasonographical examination of the uterus was performed daily from day 7 to day 11 post-mating to test aglepristone efficiency. Blood samples were collected between days 6 and 30, centrifuged at 3070 g for 10 min and stored at -20 degrees C. The does in aglepristone groups (Group I, III) were not pregnant whereas all animals in control groups were pregnant (Group II, IV). The does in group I & III were examined only clinically and ultrasonographically; however, does in groups III and IV were laparomized on days 6, 7, 9 and 11 post-mating to control countable implantation sites. No implantation sites were present in group III whereas they were seen obviously in group IV. Side effects were not observed. The mean serum progesterone (P4) concentrations were not significantly different between control and treated does (p > 0.05). The results indicate that aglepristone treatment on days 6 and 7 after mating could prevent pregnancy after unwanted matings without any side effects in the rabbit. Aglepristone treatments are possibly not affecting further fertilities before implantation.