Aglepristone Administration in Mid-Proestrus Reduces the LH Peak but Does Not Prevent Ovulation in the Bitch

SIMPLE SUMMARY: The role of preovulatory progesterone for LH release and ovulation in the bitch is not clear. The aim of the study was to evaluate the influence of administration of aglepristone in mid-proestrus on progesterone concentration, LH release, and occurrence of ovulation in the bitch. Experimental bitches (n = 7) were treated on days 4 and 5 of proestrus with aglepristone (Alizin(®), Virbac) at the dose of 10 mg/kg body weight s.c. (i.e., the two treatments were 24 h apart). The progesterone concentration showed a similar pattern in both groups. The LH peak value and area under the curve for LH in bitches treated with aglepristone were significantly lower than those in control bitches. The ovulation occurred in all animals in both groups. The presented study showed that withdrawal of progesterone by administration of aglepristone in the mid-proestrus significantly reduced the preovulatory LH surge, but it had no effect on periovulatory progesterone concentration or the occurrence of ovulation. ABSTRACT: The aim of the study was to evaluate the influence of administration of aglepristone in mid-proestrus on progesterone concentration, LH release, and occurrence of ovulation in the bitch. Experimental bitches (n = 7) were treated on days 4 and 5 of proestrus with aglepristone at the dose of 10 mg/kg body weight s.c. (i.e., the two treatments were 24 h apart). Control animals (n = 7) received s.c. injections of saline. For progesterone determination, blood was collected daily until the first day of cytological diestrus. For LH determination, blood was collected daily and in the periovulatory phase every 8 h. The progesterone concentration showed a similar pattern in both groups. The LH peak value in bitches treated with aglepristone was significantly lower (p < 0.05) than that in control bitches (4.83 ± 1.20 vs. 13.66 ± 1.21 ng/mL). The area under the curve (AUC) for LH was significantly (p < 0.05) lower in treated than in control animals (6.85 ± 1.21 ng/mL/d vs. 12.25 ± 1.35 ng/mL/d). The ovulation occurred in all animals in both groups. The study showed that administration of aglepristone in the mid-proestrus significantly reduced the preovulatory LH surge, but it had no effect on progesterone concentration and the occurrence of ovulation.