Acetyl salmon endorphin-like and interrenal stress response in male gilthead sea bream, Sparus aurata

The present study investigates the role of melanotrope proopiomelanocortinderived peptide in the interrenal stress response to different stressors in male gilthead sea bream, Sparus aur ata. Plasma cortisol and acetyl salmon endorphin (acetyl s-EP), as well as pituitary acetyl s-EP contents, were measured during two stress paradigms: (a) long-term (l-month) confinement and crowding, and (b) short-term (60-min) confinement, crowding, and manipulation. In addition, naltrexone, a highly specific opioid receptor antagonist, was employed in some experimental groups to evaluate the adaptability of the opioid response to interrenal stress. In the long-term (I-month) confinement and crowding, higher plasma cortisol levels and acetyl s-EP concentrations than in the control group were found. However, although plasma cortisol levels significantly increased in both types of stress paradigm, a significant rise in plasma acetyl s-EP was observed only in the case of confinement plus crowding. These data seem to suggest a direct correlation of acetyl s-EP plasma levels exclusively in cases of specific stress, and support previous observations about the different nature of the pituitary-interrenal stress response in salmonids and in mammals. The results obtained in the short-term (60-min) experiments demonstrate the double activation of both the opioid and corticotrope systems when manipulation plus crowding was applied

Multihormonal control of vitellogenin mRNA expression in the liver of frog, Rana esculenta

In Rana esculenta in an in vitro system, hepatic vitellogenin synthesis can be induced by growth hormone in both sexes. In this study: (1) the ability of this hormone to induce transcription of the VTG gene was determined, and (2) this ability was compared with that of estradiol-17β. The results indicate that growth hormone stimulates VTG mRNA transcription both in vivo and in vitro, in both sexes. The levels of mRNA are related to protein levels in the medium. In addition, seasonal variation occurs in the VTG gene transcription under growth hormone and estradiol-17β; indeed the more active inducer was growth hormone during the reproductive period and estradiol-17β during the prereproductive phase

Presence and activity of compounds with GnRH-like activity in the ovary of seabream Sparus aurata.

The binding and activity of gonadotropin-releasing hormone (GnRH) were characterized in the mature gilthead seabream (Sparus aurata) ovary by use of an analogue of salmon GnRH([D-Arg6,Trp7,Leu8,Pro9-N(Et)]GnRH, sGnRH-A) as labeled ligand. The binding of 125I-sGnRH-A to the seabream ovarian membrane preparation was saturable, displaceable, reversible, and dependent on time, temperature and tissue concentration. Addition of unlabeled s-GnRH-A displaced the radio-ligand in a dose-related manner, indicating the presence of one class of high-affinity binding sites with an equilibrium dissociation constant of 45.5 +/- 6.2 nM. Addition of other GnRH peptides, including salmon GnRH ([Trp7,Leu8]GnRH) and chicken GnRH-II ([His5,Trp7,Tyr8]GnRH), also displaced 125I-sGnRH-A; all these peptides bound with lower affinities than sGnRH-A to the seabream ovarian binding site. In this study, we also demonstrated the presence of compounds with GnRH-like activity in the ovary of seabream. Seabream ovarian extract stimulated pituitary gonadotropin release from the goldfish pituitary and displaced 125I-sGnRH-A binding in the seabream ovary. Furthermore, addition of sGnRH-A to cultured seabream oocytes directly stimulated reinitiation of oocyte meiosis, as indicated by germinal vesicle breakdown. Overall, the present study characterizes GnRH-binding sites in the seabream ovary and supports the hypothesis that GnRH or compounds with GnRH-like activity play an autocrine/paracrine role in the regulation of ovarian function in the seabream ovary

PCR-ELISA detection of estrogen receptor mRNA expression and plasma vitellogenin induction in juvenile sole (Solea solea) exposed to waterborne 4-nonylphenol

In this study, the effect of 4-nonylphenol (4NP) on reproductive axis of sole (Solea solea) has been investigated by using selected biomarkers of estrogenic effects: vitellogenin (VTG) and estrogen receptor beta (ERb) mRNA. Furthermore, an enzyme linked immunosorbent assay (ELISA) detection system of reverse transcriptase-polymerase chain reaction (RT-PCR) products for the analysis of sole ERb mRNA expression was developed and validated. The proposed method allows large-scale analyses of different mRNAs in fast and not expensive way. Our results have demonstrated that the PCR–ELISA method developed shows high sensitivity, good reproducibility and also the potential for semi-quantitative analysis of hepatic ERb mRNAs. Both plasma VTG level and ERb mRNA expression were increased in tested animals following a short exposure to environmental relevant concentrations (10-6 M) of 4NP, confirming the functional role of ERb in the regulation of xenoestrogens-induced production of VTG. The methodology provided in the present study together with the preliminary results on the hepatic expression of ERb may be useful in environmental xenoestrogens monitoring studies, using flatfish as ‘‘sentinel’’ species