Effect of the GnRH antagonist, acyline, on early estrous cycle and gestation in the domestic cat

A RISSO; P.E. DE LA SOTA; DIAZ J; A JIMÉNEZ; E JUAREZ; C GOBELLO

Congreso; Encuentro Bianual del European Veterinary Small Animal Asociation. (EVSSAR) 7th Congress; 2010

Introduction: Gonadotrophin releasing hormone  (GnRH) antagonists competitively block GnRH receptors sites at the pituitary gland exerting an immediate inhibitory action on the gonadal axis which make them particularly useful when a rapid effect is required. Two studies were conducted to investigate the effects of the GnRH antagonist, acyline, on follicular development, ovulation and pregnancy maintenance in domestic cats.  Materials & Methods: In the first study, 24 proestrous periods (seven queens) were randomly assigned to one group treated with acyline (330 µg/kg sc;  ACY; n=17) and another group given a placebo (PLC; n=7). All queens were mated with a fertile tomcat. Estrus duration of the treated proestrus, ovulation and pregnancy rates were recorded.  Time to the  next proestrus  was  compared  between groups  by the Student t test  and ovulation and pregnancy rates by Chi square.  In the second study,  14  pregnant queens were randomly allocated, according to their mating date, to one of the following groups: treatment with acyline  (330 µg/kg sc)  in early pregnancy (< 25 days; n=3), mid pregnancy (days 26 to 45; n=4), late pregnancy (>45 days; n=3) or sc injection of a placebo in early (n=1), mid (n=2) or late  (n=1) gestation. Ultrasound examination of the uterus was carried out every other day for two weeks and  serum  progesterone (P4) was analyzed before and 7 and 14 days  after treatment. Abortion rates were compared by Chi square and P4 by ANOVA for repeated measurements (SPSS, IL, USA). Results: In the first trial estrus finished 7± 1.3 and 7 ±1.7 (P > 0.1) d after ACY and PLC administration, respectively. After ACY treatment only two of the 17 estrous periods ended up with coitus induced ovulation, while ovulation occurred in all seven PLC estrous phases (P < 0.05). All seven females of the PLC group became pregnant, while only one queen conceived after ACY treatment (P < 0.05).  Intervals from treatment to  start of next proestrus were 18.4 ± 1.7 and 120± 17.2 d after ACY and PLC treatment, respectively. In the second study, no one pregnancy was terminated either by ACY or by PLC and post treatment  P4  concentrations did not differ among treatment groups (P>0.1).  Conclusion: In the domestic cat GnRH withdrawal by acyline  seemed to prevent  ovulation when given in early follicular phase (proestrus) but did not affect luteal function during pregnancy