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[³ H]Naloxone binding sites in porcine ovarian follicles and corpora lutea during the ovarian cycle

Hamada H, Kishioka S, Yamoto M, Nakano R. [³H]Naloxone binding sites in porcine ovarian follicles and corpora lutea during the ovarian cycle. Eur J Endocrinol 1995;132:622–6. ISSN 0804–4643

We demonstrated the presence of opioid receptors in the porcine ovary using [³ H]naloxone. We also examined the change in the number of opioid receptors during follicular maturation. In addition, we found specific binding of [³H]naloxone in the porcine ovary using naloxone, β-endorphin, methionine-enkephalin and dynorphin. The binding of [³H]naloxone to porcine granulosa cells and the 2000-g subcellular fraction of corpora lutea was examined to demonstrate the presence of specific [³H]naloxone binding in the porcine ovary. Binding of [³H]naloxone to porcine granulosa cells was displaced by cold naloxone and β-endorphin but not by dynorphin and methionine-enkephalin. A similar phenomenon was also demonstrated in the 2000 g subcellular fraction of porcine corpora lutea. However, Scatchard analyses revealed a single class of high-affinity (K_d = 28.5 x 10^–9 mol/l) and low-capacity binding sites (B_max = 30.5 fmol/5 x 10⁶ cells) in porcine granulosa cells. Similar binding parameters were obtained in the 2000-g subcellular fraction of porcine luteal tissue (K_d = 28.3 x 10^–9 mol/l, B_max = 59.3 nmol/kg protein). [³H]Naloxone binding sites in the porcine ovary showed binding characteristics similar to those of opioid receptors in other organs like brain, uterus and placenta. Furthermore, we demonstrated that the specific binding sites of [³H]naloxone in porcine granulosa cells decreased during follicular maturation. Opioid receptors have been detected in the uterus, placenta and Sertoli cell cultures in some species. However, there is no detailed study on opioid receptors in granulosa cells and luteal tissues in any species. Our data suggest a relationship between folliculogenesis and ovarian opioid peptides. The opioid system may participate in the regulation of follicular maturation.

Hiroko Hamada, Department of Obstetrics and Gynecology, Shichibancho 27, Wakayama 640, Japan