CARNEVALI, Oliana

FACCHINETTI F.

MOSCONI, Gilberto

NABISSI, MASSIMO

POLZONETTI, Alberta Maria

English

Archivio istituzionale della ricerca - Università di Camerino

Endocrine (1994), 2, 665-668 © Macmillan Press Ltd, 1994 The pro-opiomelanocortin-derived peptide, p-endorphin, regulates ovarian function in the reproductive lizard, Podarcis s. sicula Raf. A.M. Polzonetti-Magni1, O. Carnevali 1, G. Mosconi1, M. Nabissi1 & F. Facchinetti 2 10epartment of Biology (MCA)! University of Camerino! Camerino (MC)! Italy; 20epartment of Obstetrics and Gynecology! University of Modena! Modena! Italy By in vitro s'tudies, it was found that ~-endorphin (P-EP) stimulates estradiol-17~ and progesterone secre'tion in 'the ovary of reproductive lizard Podarcis s. sicula; these effects were reversed by naloxone. In the post-ovulatory follicles no significant changes were observed in the pro­gesterone titres, when the medium was supplemented by ~-EP and/or naloxone; conversely, estradiol-17~ was stimulated by ~-EP and this effect was abolished by nalox­one. The data reported here provide evidence for the tonic activity of an endogenous opioid system in the ovary of this lizard. The action exerted by homologous pituitary, moreover, has also been evaluated in order to compare the effects of ~-EP with these of pituitary gland, generally considered the physiological trigger of gonadal function. Introduction The reproductive eycle of the oviparous lizard, Podar­cis s. sicula Raf., living in Southern Italy, has been studied in detail by several authors (Filosa, 1973; Angelini et al., 1976, 1986). Recent1y, the changes in plasma sex steroids related to ovarian aetivity has been described in the wild population of this squamate liv­ing in the surroundings of Naples (Ciareia et al., 1986). Their findings show the female lizard has a welI-defined reproductive eycle, as do other reptiles living in temp­erate zones (Licht, 1984). In early spring, the ovary resumes its growth, and several oocytes become vitelIo­genie, to be ovulated in May-June. During the breed­ing season, two or more egg clutehes ean be laid by females (Filosa, 1973); the sex steroid seasonal ehanges are eonsistent with very high estradiol-17P in the plasma during oocyte growth, and higher progesterone levels during ovulation and for as long as eggs are eontained in the oviducts (Ciareia et al., 1986). As in the majority of reptiles, also in Podarcis the ovary develops post-ovulatory follieles, whose life-span is elosely correlated \vith egg retention in this oviparous species. Moreover, in sumn1er the reproduetive activity suddenly declines because a kind of ovarian refrac­toriness intervenes under stilI favorable environn1ental eonditions. In addition to the long loop feed-back meehanism exerted by high sex-steroid plasma levels on the pituitary, the gonadal funetion ean be modulated in autoerine/paraerine fashion. In this eontext, pro-Correspondence: Prof. Alberta M. Polzonetti-Magni Received 21 January 1994; accepted 12 ApriI 1994 opiomelanocortin-derived peptides (POMC) have been considered to exert a local control of both ovarian and testicular activity (Faechinetti et al., 1992, 1993). In faet, in the frog Rana esculenta, by immunocyto­ehemieal and biochemical methods, p-endorphin (~-EP) has been found to be present in the theea and in granulosa celIs of the ovary, as an endogenous opioid system independent of that found in the brain and pituitary. This opiate activity seems to play a pivotal role in the regulation of estradiol-17P synthesis and release in in vitro experiments. An ovarian opioid system has also been described in the lizard, Podarcis s. sicula, since ~-endorphin-like immunoreaetive celIs were observed within the granu­losa layer, which, as previously demonstrated by Chieffi and Pierantoni (1987) possess definite steroido­genic activity. HPLC folIowed by immunoassay showed seasonal changes in the ~-endorphin ovarian content, and this peptide has been found to regulate estradiol­17~ seeretion in the winter ovary and in that eontain­ing vitellogenie follicles (Polzonetti-Magni et al., 1994). In the present paper, we aimed to investigate through in vUro experiments, whether p-endorphin can be involved in the regulation of the steroidogenic pat­tern in the ovary of reproductive lizard, Podarcis s. sicula, containing post-ovulatory follicles. The effects of homologous pituitary homogenate (HPH), n10re­over, have also been evaluated in order to compare the effects of p-EP with those of pituitary gland, generalIy considered the physiological trigger of gonadal func­tion. Results Figure l (upper panel) shows the effects of p-EP and naloxone on estradiol-17~ (E2) production in the medium by ovary incubated without post-ovulatory follicies. The p-EP significant1y increased (P<O.OOI) the E2 titres in the medium, up to 5105 pg/ml; this aetion was significant1y (P < 0.00 l) antagonized by the opioid antagonist, naloxone. In addition, naloxone when added alone significant1y (P < 0.05) lowered the E2 titres with respect to baseline levels of controI. A very intense stimulatory action of HPH on E2 levels in the medium was also found. In the bottom panel of Figure l, a significant (P<O.OI) inhibitory aetion of HPH on progesterone (P) content in the n1edia (3.9 pg/ml) is depicted, compared with the basaI levels (50 pg/ml). On the contrary, ~-EP induced a very signifieant increase (P<O.OOI) of P content, being antagonized by naloxone, whereas naloxone alone did 

The pro-opiomelanocortin-derived peptide, ß-endorphin, regulates ovarian function in the reproductive  lizard, Podarcis s. sicula  Raf

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The pro-opiomelanocortin-derived peptide, ß-endorphin, regulates ovarian function in the reproductive lizard, Podarcis s. sicula Raf

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Archivio istituzionale della ricerca - Università di Camerino