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Because a direct effect of GnRH on spermatozoa has been implied in clinical studies with subfertile bulls and stallions, we added GnRH to in vitro fertilization media to study effects on cleavage rates of bovine oocytes obtained from slaughterhouse ovaries. Cleavage rates were higher (p &lt; 0.01) in media containing 0.8 microgram/ml GnRH (68%) than in controls (59%) and were consistent across three bulls. In a second experiment two GnRH agonists also increased cleavage rates. A dose response for GnRH was demonstrated in a third experiment with a low-fertility bull (p &lt; 0.09): cleavage rates were 37, 36, 43, 48, and 47% for 0, 0.16, 0.8, 4, and 20 micrograms/ml GnRH, respectively. A GnRH antagonist was also shown to abolish the enhancing effect of GnRH on cleavage rates. No significant (p &gt; 0.10) effect on percentage blastocysts per cleaved ovum was detected in any experiment. No specific binding of a GnRH analog to sperm was detected in radioreceptor assays. However, mRNA for the GnRH receptor was detected in matured cumulus-oocyte complexes by means of reverse transcription-polymerase chain reaction and was verified by Southern hybridization with cDNA for the ovine GnRH receptor. In summary, GnRH and GnRH agonists enhance bovine in vitro fertilization, and detection of mRNA for the GnRH receptor in cumulus-oocyte complexes is suggestive that GnRH may act through its receptor.

Gonadotropin-Releasing Hormone Increases Cleavage Rates of Bovine Oocytes Fertilized in Vitro1