Effects of beta-endorphin and Naloxone on in vitro maturation of bovine oocytes.
Bovine cumulus-oocyte complexes (COCs) and mural granulosa cells express the mRNA coding for the micro-opioid receptor. The addition of beta-endorphin (beta-end) to oocytes cultured in hormonally-supplemented in vitro maturation (IVM) medium had no effect on the rates of oocytes reaching the metaphase II (MII) stage, but significantly decreased the maturation rate (P < 0.05) and arrested oocytes at metaphase I (MI) after culture in hormone-free medium (P < 0.001). Naloxone (Nx) reverted this inhibitory effect of beta-end. Moreover, Nx "per se" showed a dose-dependent dual effect. When added at high concentration (10 x (-3) M), it significantly reduced the rate of oocytes in MII (P < 0.001), thus increasing the rate of oocytes arrested in MI. However, Nx added at low concentration (10 x (-8) M) significantly increased oocyte maturation (P < 0.001). High concentration of Nx induced an increase in both intracellular calcium concentration ([Ca(2+)](i)) and in the activity of the mitogen-activated protein kinase (MAPK) also called extracellular-regulated kinase (ERK) in cumulus cells of bovine COCs. Blocking the rise in [Ca(2+)](i) with the calcium chelator acetoxymethylester-derived form of bis (o-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid (BAPTA-AM) reversed the Nx-dependent inhibition of meiotic maturation observed at high Nx concentrations. Whereas blocking ERK with the MAPK/ERK kinase (MEK) inhibitor, PD98059, had no effect on this process. Therefore, we concluded that the mocro-opioid receptor, by inducing [Ca(2+)](i) increase, participates in the cumulus-oocyte coupled signaling associated with oocyte maturation.
Department of Animal Production, Section of Reproduction, University of Bari, Italy. e.dellaquila@veterinaria.uniba.it
M E
ME
Dell'Aquila
V
V
Casavola
S J
SJ
Reshkin
M
M
Albrizio
L
L
Guerra
F
F
Maritato
P
P
Minoia
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002417:Cattle; D002454:Cell Differentiation / Q000187:drug effects*; D002614:Chelating Agents / Q000494:pharmacology; D004533:Egtazic Acid / Q000031:analogs & derivatives* / Q000494:pharmacology; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005260:Female; D005419:Flavonoids / Q000494:pharmacology; D006107:Granulosa Cells / Q000187:drug effects; D066298:In Vitro Techniques; D008540:Meiosis / Q000187:drug effects; D020928:Mitogen-Activated Protein Kinases / Q000187:drug effects; D009270:Naloxone / Q000494:pharmacology*; D009292:Narcotic Antagonists / Q000494:pharmacology*; D009865:Oocytes / Q000187:drug effects* / Q000201:enzymology; D017450:Receptors, Opioid, mu / Q000096:biosynthesis / Q000235:genetics; D001615:beta-Endorphin / Q000494:pharmacology*
D002614:Chelating Agents; D004791:Enzyme Inhibitors; D005419:Flavonoids; D009292:Narcotic Antagonists; D017450:Receptors, Opioid, mu; C070379:1,2-bis(2-aminophenoxy)ethane N,N,N',N'-tetraacetic acid acetoxymethyl ester; D009270:Naloxone; D004533:Egtazic Acid; D001615:beta-Endorphin; D020928:Mitogen-Activated Protein Kinases; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one; D002118:Calcium