性腺激素及脂蛋白對鯉魚性腺類固醇合成之影響

Abstract

鯉魚一年的生殖週期可分為四個階段（l）生長發育期，從九月至十一月，（2）成熟排卵期，從十二月至二月，（3）排卵後期，從三月至五月，（4）退化靜止期，從六月至八月。 本實驗分別以Diethylstibestrol (DES)及17α-Methyltesto-sterone(MT）兩種性腺類固醇活體處理各階段性腺發育的鯉魚，兩週後觀察其性腺合成類固醇的情形。結果發現，不論鯉魚的性腺發育處於那一個階段，經由類固醇處理過的鯉魚，其性腺分泌睾固酮的量，皆少於未處理過的鯉魚。 本實驗又以鯉魚性腺離體的培養方式來觀察血漿脂蛋白對性腺合成類固醇的影響。當有促性腺激素存在時，血漿脂蛋白對發育期的性腺具有促進性腺合成類固醇的作用，而且其促進作用隨著脂蛋白劑量的增加而增加。但是對於退化期的性腺，則沒有促進作用的發生。

The annual reproductive cycle of carp can be divided into four major stages; (1) the growing and developing stage, from September to November; (2)the mature and ovulating stage, from December to February; (3) the post-spawning stage from March to May, and (4) the regressed stage. from June to August. The effects of in vivo sex steroid treatment on gonadal steroidogenesis were investigated in carps at various stages of gonadal development. Female and male carps were intraperitoneally injected with 30 mg/kg of estrogen agonist, diethylstilbestrol (DES), and 10 mg/kg of androgen . 17α-methyltestosterone(MT), respectively. After two-week treatment, the gonads were removed and used to assay the steroid production in Vitro. Xo matter what developmental stage of the gonad is the androgen production in vitro by the gonads of steroid-treated carps is less than that by the gonads of vehicle-injected carps in the presence and absence of carp gonadotropin. It therefore suggests that there exists a negative feedback control by steroids on the regulation of pituitary gonadotropin and gonadal steroidogenesis in carps. Plasma lipoprotein is the carrier protein of cholesterol which, in turn, is the essential precursor of steroidogenesis. The effect of plasma lipoprotein on the gonadal steroidogenesis was investigated in vitro in carps. Only in the presence of carp gonadotropin, lipoprotein fraction of carp plasma can exert a dose-dependent stimulatory effect on the in vitro testosterone production by cap gonads at maturate stage. However, no significant effect of lipoprotein on the antrogen production by carp gonads at regressed stage was found. Further studies are obviously needed to realize the regulation of steroidogenesis by lipoprotein during the reproductive cycle in fish.