| Summary: | 博士 === 國立臺灣海洋大學 === 水產養殖學系 === 93 === The objectives were to investigate the regulation of mammalian gonadotropin-releasing hormone (mGnRH), pituitary gonadotropins (GtHs), gonadosomatic index (GSI), GtH receptors (FSHR, LHR) and cytochrome P450 aromatase (P450arom) using sex steroids and pituitary homogenates in aqua cultured Japanese eels, Anguilla japonica.
We investigated estradiol-17β (E2), testosterone (T), and 5��-dihydrotestosterone (DHT) did not stimulate brain mGnRH content. E2 significantly increased pituitary LH content and LH-β mRNA expression in a dose-dependent manner. T significantly increased pituitary LH content but could not stimulate LH-β mRNA expression in pituitary of female. The FSH-β mRNA expression in pituitary significantly decreased in female treated with E2 or T. E2 or T could not significantly stimulate FSHR and LHR mRNA expression in ovary.
Brain mGnRH and pituitary mGnRH, LH content, glycoprotein-�n���z�nLH-β mRNA expression were significantly increased in maturing eels (GSI > 20%) injected with salmon (or catfish) pituitary homogenates. In contrast, the FSH-β mRNA expression was decreased in maturing eels. Glycoprotein-��, LH-β, FSHR and LHR mRNA levels increased but FSH-β mRNA levels decreased after inducing maturation.
Eel brain aromatase exhibited a Km of 75nM and a Vmax of 1.14 fmole/min/mg. protein (91.5 fmole/h/mg. protein), indicating an enzymatic activity much lower than in other teleosts but similar to that in mammals. Aromatase inhibitors could significantly suppress brain and pituitary aromatase activity. Comparison with another teleost, black porgy, further confirmed the low activity of aromatase in the eel. The low activity of eel aromatase, may be related to the special life cycle of the eel, and the long delay of puberty before the reproductive oceanic migration.
Pituitary aromatase activity and P450arom mRNA expression increased with GSI at all stages. Brain (specially forebrain) aromatase activity significantly increased in early vitellogenic control eels (GSI > 0.8 %) and maturing eels. Ovarian aromatase activity still remained low in the vitellogenic gonad (GSI = 8%). The aromatase activity and P450arom mRNA levels were increased with ovarian development after induced maturation and would decreased after the GSI higher than 22%. E2 o r T could significantly increased aromatase activity and P450arom mRNA expression in brain and pituitary, but not in gonad.
Glycoprotein-�n���z�nFSH-β mRNA expression levels in pituitary and were not different in aquacultured and wild eels. The LH-β mRNA expression in pituitary was higher in wild female than in aquacultured female. FSHR mRNA expression levels in aquacultured eels was similar to wild eels. The LHR mRNA expression levels in wild eels were higher than aquacultured eels. The FSHR and LHR mRNA expression levels in testis were higher than in ovary.
|
|---|
