[H-3] NALOXONE BINDING-SITES IN PORCINE OVARIAN FOLLICLES AND CORPORA-LUTEA DURING THE OVARIAN CYCLE

We demonstrated the presence of opioid receptors in the porcine ovary using [H-3]naloxone. We also examined the change in the number of opio id receptors during follicular maturation. in addition, we found speci fic binding of [H-3]naloxone in the porcine ovary using naloxone, beta -endorphin, methionine-enkephalin and dynorphin. The binding of [H-3]n aloxone to porcine granulosa cells and the 2000-g subcellular fraction of corpora lutea was examined to demonstrate the presence of specific [H-3]naloxone binding in the porcine ovary. Binding of [H-3]naloxone td porcine granulosa cells was displaced by cold naloxone and beta-end orphin but not by dynorphin and methionine-enkephalin. A similar pheno menon was also demonstrated in the 2000 g subcellular fraction of porc ine 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 10(6) cells) in porcine granulosa cells. Similar binding parameters were obtained in the 2000-g subcellular fr action of porcine luteal tissue (K-d = 28.3 x 10(-9) mol/l, B-max = 59 .3 nmol/kg protein). [H-3]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 demonst rated that the specific binding sites of [H-3]naloxone in porcine gran ulosa cells decreased during follicular maturation. Opioid receptors h ave 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 sugges t a relationship between folliculogenesis and ovarian opioid peptides. The opioid system may participate in the regulation of follicular mat uration.