This study was performed to investigate the expression of embryo-derived gonadotropin-releasing hormone (GnRH) and its receptor, and to determine the role of GnRH in porcine preimplantation embryos. In Experiment 1, porcine blastocysts derived from in vitro fertilization (IVF) and cultured in North Carolina State University (NCSU)-23 medium were subjected to reverse transcription polymerase chain reaction (RT-PCR) amplification with specific primers for GnRH and its receptor. The results showed that GnRH and its receptor were expressed in porcine IVF blastocysts. In order to investigate the role of GnRH in embryo development, porcine IVF embryos were cultured in NCSU-23 supplemented with different concentrations (0, 0.1, 1, or 10 microM) of a GnRH agonist (leuprolide, Experiment 2) or GnRH antagonist (antide, Experiment 3). Supplementing the culture medium with 0.1 or 1 microM leuprolide increased the rate of blastocyst formation (28.5 or 27.6% versus 20.2%) and mean total cell number (129 versus 104) compared to the control group. In contrast, antide significantly decreased the rate of blastocyst formation [12.6% (0.1 microM), 10.2% (1.0 microM), or 8.9% (10.0 microM) versus 22.8% (control)] and total cell number [69 (1 microM) or 68 (10 microM) versus 104 (control)]. In Experiment 4, porcine IVF embryos were cultured in NCSU-23 medium containing 1 microM antide plus 1 microM leuprolide. The embryotrophic effect of GnRH agonist was reversed by co-supplementing with GnRH antagonist. In conclusion, the present study demonstrated that supplementing a culture medium with GnRH agonist can improve blastocyst formation and the quality of porcine IVF embryos, and that this action was mediated through GnRH receptors.