Efficacious and safe unwanted pregnancy termination technologies are still required in dogs. GnRH antagonists competitively block GnRH receptors sites at the pituitary gland (1). Acyline is a new GnRH antagonist that has been found to be 4 times more effective at suppression and maintenance of suppression of gonadotrophins than previous antagonists in other species (2). It was, therefore, the aim of this study to test the efficacy and safety of acyline on pregnancy interruption in a randomized placebo controlled trial in domestic bitches.

Twelve echographically confirmed pregnant (> 30 < 35 days from mating) bitches, were randomly be allocated to one of the following pharmacological protocols: acyline (NICHHD, USA; ACY, n = 6) 110µg/kg SC or placebo (PLA, n = 6) which received the corresponding equal volume of bacteriostatic water SC. All the bitches were followed up daily by clinical examination for 15 days. Clinical suspicious of pregnancy interruption was considered when vaginal discharge first appeared or fetuses were expulsed. Within the 8 hours of clinical suspicion, bitches were ultrasonographically monitored to confirm resorption or abortion. If no clinical signs of interruption were externally visible, ultrasound examination was carried out on day 8 and if no abnormalities were found, it was repeated on day 12. Descriptive statistics and proportions were carried out to characterize results.

All ACY bitches presented vulvar discharge and/or abortion 2 to 12 days after treatment (mean 7 ± 1.9 days). Pregnancy termination either by resorption (n = 1) or abortion (n = 5) was diagnosed ultrasonographically in all the group. In PLA animals gestation progressed normally as shown by the absence of clinical signs up to the end of the study and physiological ultrasound findings at days 8 and 12. None of the bitches presented local nor systemic undesirable effects related with the treatment.

In line with a previous abstract, in which an earlier GnRH antagonist was used (3), in the present study pregnancy was terminated in all the treated bitches. It is concluded that the GnRH antagonist, acyline, was an efficacious and safe drug to terminate unwanted gestation in the domestic bitch.

References

1.  Hoffmann B, Schuler G. Receptors blockers-general aspects with respect to their use in domestic animal reproduction. 2000 Anim Reprod Sci 60-61:295-312.

2.  Herbst KL et al. , 2002 Acyline: The first study in humans of a potent, new gonadotropin releasing hormone antagonist J Clin Endocrinol Metab 87: 3215- 3220

3.  Vickery BH et al. 1987 Effect of detirelix, a long acting LHRH antagonist on luteal function and pregnancy in beagle bitches Biol Reprod 1, 45 (abstract)