Effects of β-endorphin and Naloxone on in vitro maturation of bovine oocytes

• Published in: Molecular reproduction and development Vol. 63; no. 2; pp. 210 - 222
• Main Authors: Dell'Aquila, M.E., Casavola, V., Reshkin, S.J., Albrizio, M., Guerra, L., Maritato, F., Minoia, P.
• Format: Journal Article
• Language: English
• Published: New York Wiley Subscription Services, Inc., A Wiley Company 01.10.2002; Wiley-Liss
• Subjects: Animals; beta-Endorphin - pharmacology; Biological and medical sciences; bovine oocyte; Calcium - metabolism; Cattle; Cell Differentiation - drug effects; Chelating Agents - pharmacology; Egtazic Acid - analogs & derivatives; Egtazic Acid - pharmacology; Enzyme Activation - drug effects; Enzyme Inhibitors - pharmacology; Female; Flavonoids - pharmacology; Fundamental and applied biological sciences. Psychology; Granulosa Cells - drug effects; Hormone metabolism and regulation; in vitro maturation; In Vitro Techniques; intracellular calcium; Mammalian female genital system; MAP Kinase; Meiosis - drug effects; Mitogen-Activated Protein Kinases - drug effects; Naloxone; Naloxone - pharmacology; Narcotic Antagonists - pharmacology; Oocytes - drug effects; Oocytes - enzymology; Receptors, Opioid, mu - biosynthesis; Receptors, Opioid, mu - genetics; Vertebrates: reproduction; β-endorphin; Morphinan derivatives; Enzyme; μ Opioid receptor; Mitogen-activated protein kinase; Ox; Germinal cell; Gene expression; β-Endorphin; Ovary; Vertebrata; Mammalia; Naloxone; Female genital system; Female; Artiodactyla; Granulosa; Ovarian follicle; Ungulata; Oocyte; Calcium Cations; Oocyte maturation
• ISSN: 1040-452X; 1098-2795
• DOI: 10.1002/mrd.10163

Bovine cumulus‐oocyte complexes (COCs) and mural granulosa cells express the mRNA coding for the μ‐opioid receptor. The addition of β‐endorphin (β‐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 β‐end. Moreover, Nx “per se” showed a dose‐dependent dual effect. When added at high concentration (10−3 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 (10−8 M) significantly increased oocyte maturation (P < 0.001). High concentration of Nx induced an increase in both intracellular calcium concentration ([Ca2+]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 [Ca2+]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 μ‐opioid receptor, by inducing [Ca2+]i increase, participates in the cumulus‐oocyte coupled signaling associated with oocyte maturation. Mol. Reprod. Dev. 63: 210–222, © 2002 Wiley‐Liss, Inc.