Induction of ornithine-urea cycle enzymes and nitrogen metabolism and excretion in rainbow trout (Oncorhynchus mykiss) during early life stages
Induction of ornithine-urea cycle enzymes and nitrogen metabolism and excretion in rainbow trout (Oncorhynchus mykiss) during early life stages
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发表时间：
1995
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通讯作者：
P. A. Wright;Andrew K. Felskie;Paul M. Anderson
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作者：
P. A. Wright;Andrew K. Felskie;Paul M. Anderson
鸟氨酸-尿素循环（OUC）存在于板鳃类鱼类和许多陆生脊椎动物中。最近，一个功能性的OUC已被报道在一些硬骨鱼物种，这表明所有硬骨鱼有OUC的基因，但表达相对罕见。我们调查的可能性，OUC是在鳟鱼早期发育过程中表达的一种机制，用于解毒氨从卵黄蛋白catestrin产生。我们遵循氨和尿素排泄率，组织氨和尿素水平和OUC酶活性虹鳟鱼受精后93天。氨和尿素组织浓度增加了几倍，在受精后的第一个40天（胚胎阶段），峰值分别为1.7 mmol N l-1和2.5 mmol N l-1。氨排泄可以检测到在4日龄的胚胎，但尿素排泄直到孵化后（45天）才开始。幼鱼（第42 - 93天）的尿素排泄量增加了几倍，到第93天，尿素排泄量占总氮排泄量的14%，与成年鳟鱼相同。谷氨酰胺合成酶（GSase）和谷氨酰胺酶的活动检测在“整个动物”匀浆刚孵化后和活动水平显着增加到第93天。氨甲酰磷酸合成酶（CPSase）和鸟氨酸转氨甲酰酶（OTCase）首先在40日龄的胚胎中检测到;活动在第53天和第71天之间达到峰值，然后下降。成人肝酶活性GSase是几倍低于整个幼虫鳟鱼和OTCase和CPSase III（谷氨酰胺和N-乙酰谷氨酸盐依赖的CPSase催化的第一步的OUC）活动基本上不存在于成人肝脏。我们的结论是，胚胎和幼虫鳟鱼主要是解氨的。尿素在受精后立即合成，但直到胚胎孵化后才排出。结果提供了证据的OUC在虹鳟鱼幼体的存在下，因为四个OUC酶诱导孵化后和活性水平相对较高的成年肝组织相比。此外，我们认为所有硬骨鱼都保留了OUC基因，这些基因仅在发育的某些阶段（胚胎发生）表达，并且在少数稀有物种中，表达在整个生命周期中保持，以科普不寻常的环境条件（例如碱性水，空气暴露）。
The ornithineurea cycle (OUC) is present in elasmobranch fish and many terrestrial vertebrates. Recently, a functional OUC has been reported in a few teleost species, suggesting that all teleost fish have the genes for the OUC, but expression is relatively rare. We investigated the possibility that the OUC is expressed during early development in trout as a mechanism for detoxifying ammonia produced from the catabolism of yolk protein. We followed ammonia and urea excretion rates, tissue ammonia and urea levels and OUC enzyme activities in rainbow trout up to 93 days after fertilization. Both ammonia and urea tissue concentrations increased several-fold in the first 40 days after fertilization (embryo stage), peaking at 1.7 mmol N l-1 and 2.5 mmol N l-1, respectively. Ammonia excretion could be detected in 4-day-old embryos, but urea excretion was not initiated until after hatching (day 45). Urea excretion in larval fish (days 4293) increased several-fold and by day 93 was 14 % of total nitrogen excretion, as found in adult trout. Glutamine synthetase (GSase) and arginase activities were detected in 'whole animal' homogenates just after hatching and the levels of activity increased markedly to day 93. Carbamoyl phosphate synthetase (CPSase) and ornithine transcarbamylase (OTCase) were first detected in 40-day-old embryos; activities peaked between days 53 and 71 and then subsequently decreased. Adult liver enzyme activity for GSase was several-fold lower than in whole larval trout and OTCase and CPSase III (glutamine- and N-acetylglutamate-dependent CPSase catalysing the first step of the OUC) activities were essentially absent in adult liver. We conclude that embryonic and larval trout are primarily ammoniotelic. Urea is synthesized immediately after fertilization, but is not excreted until after the embryo is hatched. The results provide evidence for the presence of the OUC in larval rainbow trout, since four of the OUC enzymes are induced just after hatching and the levels of activity are relatively high compared with those in adult liver tissue. Furthermore, we suggest that all teleosts have retained the OUC genes, which are expressed only during certain stages of development (embryogenesis), and in a few rare species expression is maintained throughout the life cycle to cope with unusual environmental conditions (e.g. alkaline water, air exposure).