Free Access
Reprod. Nutr. Dev.
Volume 42, Number 3, May-June 2002
Page(s) 251 - 264

Reprod. Nutr. Dev. 42 (2002) 251-264
DOI: 10.1051/rnd:2002023

Comparison of the effects of two GnRH antagonists on LH and FSH secretion, follicular growth and ovulation in the mare

Daniel Guillaume, Bernard Bruneau and Christine Briant

Physiologie de la Reproduction et des Comportements, Institut National de la Recherche Agronomique (INRA), 37380 Nouzilly, France

(Received 11 December 2001; accepted 30 May 2002)

The effects of two GnRH antagonists were tested in order to delay and/or synchronise ovulation in mares. Five mares received Antarelix (0.01 mg $\cdot$kg -1), 5 mares received Cetrorelix (the same dose), 5 mares (control mares) received the vehicle intravenously, twice daily, for 8 days from the day the largest follicle reached 22 mm following prostaglandin administration. Ovulation was postponed in all mares injected with Antarelix (19.4 $\pm$ 1.2 days after the beginning of the treatment) and in 2/5 mares injected with Cetrorelix (20 $\pm$ 1 days) vs. 6.2 $\pm$ 0.4 days in control mares. During the treatment, LH concentrations were strongly depressed in Antarelix and in Cetrorelix mares (1.6 $\pm$ 0.1 and 3.8 $\pm$ 0.5 ng $\cdot$mL -1 respectively vs. 21 $\pm$ 2.5 ng $\cdot$mL -1 in control mares). In the 3 Cetrorelix mares which ovulated during the treatment, 2 initiated their LH surge at this moment. FSH concentrations were not affected in Antarelix or in Cetrorelix mares during the treatment (11.4 $\pm$ 1.3 and 7.9 $\pm$ 0.8 ng $\cdot$mL -1 respectively vs. 10.5 $\pm$ 0.8 ng.mL -1 in control mares). In conclusion, Antarelix seems more efficient than Cetrorelix for postponing ovulation in mares. The role of LH in antral follicular development before the preovulatory stage is confirmed.

Key words: mare / GnRH antagonist / ovulation / FSH / LH

Correspondence and reprints: Daniel Guillaume

© INRA, EDP Sciences 2002