Chemical Classification and Biological Activity of Fish Pituitary Glycoprotein Hormones

硬骨促性腺激素(GTHs)的两面性：从鲑鱼、鲤鱼和鳄鱼脑垂体中分离出两个与哺乳动物GTH同源的硬骨促性腺激素，命名为GTH I和GTH II，并克隆了它们的cDNAs。它们由和亚基组成。序列研究表明，两个亚基有大约30%的同源性，这表明GTH基因的分歧发生在硬骨鱼与导致四足动物进化主线的分歧时间之前。鲑鱼GTH I和GTH II在刺激雌二醇产生方面是相同的，而GTH II在刺激17，20-二氢孕酮合成方面似乎更有效。鲑鱼血浆和脑垂体中GTH含量的比值以及GnRH的分泌控制表明，在卵黄发生和精子发生的早期阶段，GTH I是主要的GTH，而在精子和排卵时GTH II是主要的GTH。GTH I和GTH II存在于明显分开的细胞中。在鲑鱼中，Gth I…GTH作用机制：雌激素17和17，20-diOHprog两种类固醇激素分别参与卵黄发生和排卵的调节。在卵黄发生过程中，GTH刺激卵泡膜细胞产生睾酮，通过增强芳香酶活性，在颗粒细胞中将睾酮转化为雌二醇-17。卵泡在卵母细胞成熟前发生明显的类固醇激素转化。GTH刺激膜细胞产生17-OHprog，在颗粒细胞中通过增强20-OHsterid脱氢酶活性转化为17，20-diOHprog。两种类固醇激素参与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和17，20-diOHprog用于精子生成。对睾丸类固醇生物合成途径的分析表明，睾丸类固醇代谢酶活性随着GTH的反应而发生变化。在精子发生过程中，睾丸合成了11-酮-睾酮，17，20-diOHprog的产生是在受精前的途径改变的结果。GTH通过腺苷环化酶依赖的cAMP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：基于彩虹幼鱼血浆甲状腺激素水平的增加，建立了三文鱼TSH的生物测定方法。在所有被研究的硬骨鱼的未受精卵的蛋黄中都发现了甲状腺激素。用甲状腺激素处理鲑鱼幼鱼可增加耗氧量和体内银化，但在海水适应性方面没有看到一致的效果。鲑鱼鱼苗的组织和血浆激素水平在向下游迁移之前都有所增加。在牙鲆幼体的变态高潮阶段，激素的组织水平也显著升高，注射甲状腺素或绵羊TSH可加速向底栖性幼体的变态。较少

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