Effect of a delta opioid receptor agonist [D-Pen2-Pen5]enkephalin (DPDPE) on equine sperm cells motility

Reproductive physiology is affected by endogenous opioid peptides (EOP) that act as a multimessenger system in the Central Nervous System, pituitary gland and testis with a direct role on spermatozoa.In humans, a reduced motility is the principal disease of opiate addicts with both normal and abnormal serum gonadotropin levels. Opioid receptors (OR) have been identified on human spermatozoa and also on equine sperm cells. The aim of this work is to elucidate the possible involvement of Delta Opioid Receptor in equine sperm motility by performing an in vitro motility test. This work reports for the first time a functional test on equine spermatozoa describing the involvement of DOR in the control of sperm cells motility and provides new insights to the concept of EOP as “local modulators” of reproductive activity