腦下垂體研磨液及性類固醇注射對日本鰻卵巢發育之影響

Abstract

本研究以外源性腦下垂體及性類固醇激素誘導濾胞發育過程中，對日本鰻卵巢發育的影響。實驗主要以組織學觀察卵巢經注射誘導催熟發育成熟效果，並從下視丘-腦下垂體-性腺軸觀察，檢視不同荷爾蒙對卵黃前質的誘導效果，評估激素對卵黃蓄積之效果。 實驗中採用之種鰻(體重648±14公克)經個別標識後，分成六個處理組，注射鮭魚腦下垂體研磨液(SPH)或其與性類固醇(Estradiol-17β或17α-methyltestosterone)併用之注射劑，其劑量SPH及性類固醇分別為每公斤魚重之20mg及3mg，在室內溫控(20±1℃)之水槽中，每週注射乙次。在12週之催熟過程中，僅秤取體重，而於結束時才檢視種鰻之卵巢發育狀況，其中包括卵巢重、卵徑頻度分佈、總卵數及組織學之觀察及同時檢測肝臟之卵黃前質之生合成。實驗結果以SPH及MT+SPH處理組其GSI分別為24.65±14.7％及33.75±15.63%，與對照組(GSI2.92±0.78%)有顯著差異(P<0.05)，卵巢內卵胞分別有43％及76%已進入GVBD階段。注射E2或E2+SPH處理組，其生殖腺指數(GSI分別為5.31±0.65％及10.64±1.61%)或卵徑大小與對照組無顯著差異，但在卵胞數目方面則有顯著減少之趨勢(P<0.05)。在誘發肝臟合成卵黃前質(Vg)mRNA 的表現上，注射E2或E2+SPH均與對照組及其他各組有顯著差異(P<0.05)。 綜合結果顯示注射外源性的SPH可促進卵巢從卵原細胞至成熟卵細胞一連串卵黃蓄積過程，甚至達吸水卵階段，顯示在催熟過程中SPH是必要的。但單獨使用SPH處理組卵胞卵徑頻度分佈廣，呈現雙峰且非同步化現象，單獨施打17MT或E2處理組則對卵黃蓄積效果不大。外源性性類固醇，尤其為MT併用SPH確實可促進日本鰻的卵巢發育至卵黃蓄積甚至達吸水卵之階段，卵徑頻度呈單峰之同步化現象。此外，初步以RT-PCR方式確定E2及MT皆可誘發肝臟卵黃前質的表現。而E2對於卵胞可能造成卵胞數目之減少，MT雖能夠維持卵胞的存活，但與E2同樣無法使卵胞進一步生長，故性類固醇與卵胞發育及卵胞數之相關性為何，有待進一步證明。

Treatment of Japanese eel with salmon pituitary homogenate (SPH) to induce gonadal development has been demonstrated, yet still not so effectively. This experiment was designed to examine the effects by exogenous sex steroid and the SPH treatment. Besides control group, silver eels were divided into five treatments of SPH group, and sex steroids (E2 or MT) with or without SPH groups. Eels received weekly intraperitoneal injections SPH and /or sex steroids at 20μg and 3mg per kg body weight, respectively. The gonadal development were examined by histological analysis. In addition, the extent of induction were examined by the gene expression of hepatic vitellogenin. As results, we observed significant differences in the extent of induction of ovarian development. The SPH is indispensable to induce breeding. Both of the SPH treatment alone and the cotreatment with SPH plus MT were the most effective hormone therapy for enhaning the maturation of ovarian follicles. About 46% of the most advanced oocyte appeared to be at a GVBD stage in the SPH treatment (GSI=24.65±14.7%), more than 76% of the most advanced oocyte to be the GVBD stage in SPH plus MT treatment (GSI=33.75±15.63%), but the oocyte composition just showed monomodel distribution. Serial injection of E2 alone or E2 plus SPH did not further stimulate ovarian development, although the effect of E2 on vitellogenin synthesis were obvious and a decrease in the numbers of ovarian follicles was observed, however the ovarian follicles could survive with MT and SPH plus MT treatment.