Chemical Classification and Biological Activity of Fish Pituitary Glycoprotein Hormones

硬骨鱼促性腺激素（GTH）的双重性：从鲑鱼、鲤鱼和鲣的脑垂体中分离到两种化学性质不同、与哺乳动物的促性腺激素同源的促性腺激素，分别命名为GTH I和GTH II，并克隆了它们的cdna。它们由两个亚单位组成。序列研究表明，两个-亚基的同源性约为30%，表明GTH基因的分化时间早于硬骨鱼从进化主线分化为四足动物的时间。三文鱼的GTH I和GTH II在刺激雌二醇的产生方面是相同的，而GTH II在刺激17,20 -二羟戊二醇合成方面似乎更有效。在鲑科鱼类中，GTH的血浆水平和垂体含量的比值以及GnRH的分泌控制表明，GTH I在卵黄形成和精子发生的早期阶段是主要的GTH，而GTH II在精子形成和排卵时期是主要的。GTH I和GTH II存在于完全独立的细胞中。在鳟鱼中，GTH I…More首先在个体发育中表达，而GTH II细胞与精子发生和卵黄发生同时出现，并在最终生殖成熟时急剧增加。GTH作用机制：两种类固醇激素雌二醇-17和17,20 -diOHprog分别参与卵黄形成和排卵的调节。在卵黄形成过程中，GTH刺激鞘细胞产生睾酮，睾酮通过增强芳香酶活性在颗粒细胞中转化为雌二醇-17。在卵母细胞成熟之前，卵泡中发生明显的类固醇性转移。GTH刺激鞘细胞产生17 -OHprog， 17 -OHprog通过增强20 - oh类固醇脱氢酶活性在颗粒细胞中转化为17,20 -二ohprog。两种类固醇激素参与了男性生殖细胞发育的两个重要过程的调节：11-酮睾酮用于精子发生，17,20 -二羟孕酮用于精子受精。睾丸类固醇生物合成途径的分析显示，睾丸类固醇代谢酶活性在GTH的作用下发生了变化。在精子发生过程中，睾丸合成了11-酮睾酮，17,20 -二羟孕酮的产生是在精子形成之前，这一途径发生变化的结果。GTH通过腺苷酸环化酶- camp依赖的步骤刺激卵巢和睾丸中这些类固醇激素的产生。甲状腺激素：鲑鱼TSH的生物测定是建立在幼鱼彩虹鲑血浆甲状腺素水平增加的基础上的。甲状腺激素存在于所研究的所有硬骨鱼的未受精卵的蛋黄中。用甲状腺激素处理幼鲑会增加耗氧量和体银色，但对海水适应性没有一致的影响。大马哈鱼鱼苗的组织和血浆激素水平在向下游迁移前增加。在比目鱼幼虫的变质高潮阶段，组织中激素水平也有明显的增加，向比目鱼的远洋幼虫注射甲状腺素或羊TSH，加速了比目鱼向底栖幼虫的变质。少

Duality of teleost gonadotropins (GTHs): Two chemically distinct GTHs homologous to mammalian GTHs were isolated form salmon, carp and bonito pituitary glands, designated GTH I and GTH II and their cDNAs were cloned. They are composed of and subunits. Sequence studies show that two -subunits have approximately 30% homology and suggest that the divergence of the GTH gene took place earlier than the time of divergence of teleosts from the mainline of evolution leading to tetrapods. Salmon GTH I and GTH II were equipotent in stimulating estradiol production, whereas GTH II appears to be more potent in stimulating 17 , 20 -diohprog synthesis. In salmonids, the ratio of plasma levels and pituitary contents of GTHs and the secretory control by a GnRH suggest that GTH I is the predominant GTH during vitellogenesis and early stages of spermatogenesis, whereas GTH II is predominant at the time of spermiation and ovulation. GTH I and GTH II are found in distinctly separate cells. In trout, GTH I … More is expressed first in ontogeny, whereas GTH II cells appear coincident with the onset of spermatogenesis and vitellogenesis, and increase dramatically at the time of final reproductive maturation.Mechanism of GTH actions: Two steroid hormones, estradiol-17 and 17 , 20 -diOHprog are involved in the regulation of vitellogenesis and ovulation, respectively. During vitellogenesis, GTH stimulates the thecal cells to produce testosterone, which are converted to estradiol-17 in granulosa cells by enhancing aromatase enzyme activity. A distinct steroidogenic shift occurs in follicles just prior to oocyte maturation. GTH stimulate thecal cells to produce 17 -OHprog, which is converted to 17 ,20 -diOHprog in granulosa cells by enhancing 20 -OHsteroid dehydrogenase activity. Two steroid hormones are involved in the regulation of two important processes of male germ cell development: 11-ketotestosterone for spermatogenesis and 17 ,20 -diOHprog for spermiation. Analysis of steroid biosynthetic pathways of the testis showed a shift in testicular steroid metabolic enzyme activity in response to GTH. During spermatogenesis, the testis synthesized 11-ketotestosterone, 17 ,20 -diOHprog production results from a change in the pathway, immediately prior to spermiation. GTH stimulates the production of these steroid hormones in ovary and testis via an adenylate cyclase-cAMP-dependent step.Thyroid hormones: A bioassay of salmon TSH was established based on the increase in plasma thyroxine levels in juvenile rainbow throut. Thyroid hormones are found in the yolk of unfertilized eggs of all teleost studied. Treatment of juvenile salmonids with thyroid hormones caused an increase in oxygen consumption and body silvering, but no consistent effect was seen in seawater adaptability. The tissue and plasma levels of the hormones of chum salmon fry increased just before downstream migration. A marked increase in the tissue levels of the hormones was also observed during metamorphic climax of the flounder larvae, and injection of thyroxine or ovine TSH into pelagic larvae of the flounder accelerated the metamorphosis to benthic larvae. Less