The mu-opioid receptor (MOR) is expressed in @entity291 , @entity1 , @entity1641 and @entity235 oocytes, and in seasonal breeders, it is expressed with higher intensity during the anoestrous phase. Supplementation of in vitro maturation (IVM) medium with opioid agents, agonists or antagonists, was shown to affect oocyte maturation in several species such as @entity35 , @entity291 and @entity1641 . This study reports the effects of supplementing IVM medium with @entity1510 (Nx), an opioid antagonist, on nuclear and cytoplasmic maturation rate of oocytes recovered from anoestrous bitches. Cytoplasmic maturation was examined in terms of mitochondrial (mt) distribution. In order to confirm the receptor-mediated action of Nx, in oocytes of anoestrous bitches, MOR expression was analyzed by Western blot. Cumulus-oocyte complexes, recovered from the ovaries of bitches in anoestrous, were cultured in vitro and Nx was added at the concentrations of 1 x 10(-6), 1 x 10(-8) and 1 x 10(-10) M. The rate of oocytes resuming meiosis after culture in presence of 1 x 10(-6) M Nx (29%) was significantly higher than that of oocytes of control group (12%; p < 0.05). However, treatment with Nx did not affect mt distribution pattern. In denuded oocytes and in corresponding cumulus cells, a doublet of 65 and 50 kDa was observed. We conclude that, in oocytes of anoestrous bitches, MOR is expressed and Nx significantly improves nuclear maturation rate. Further studies should be performed to elucidate the expression of other opioid receptors, such as delta and kappa, and possible interactive effects of their antagonists on @entity235 oocyte maturation.

Expression of the mu opioid receptor and effects of the opioid antagonist XXXX on in vitro maturation of oocytes recovered from anoestrous bitches.

@entity1 :: ('9606', 'Species') :: ['human'] @entity1641 :: ('9796', 'Species') :: ['equine'] @entity235 :: ('9615', 'Species') :: ['canine'] @entity1510 :: ('MESH:D009270', 'Chemical') :: ['naloxone'] @entity35 :: ('10116', 'Species') :: ['rat'] @entity291 :: ('9913', 'Species') :: ['bovine']
@entity1510 :: (MESH:D009270,Chemical) :: ['naloxone']
