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首页> 外文期刊>The Journal of Experimental Biology >Mechanisms of urea tolerance in urea-adapted populations of Drosophilamelanogaster
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Mechanisms of urea tolerance in urea-adapted populations of Drosophilamelanogaster

机译：果蝇适应尿素的人群对尿素的耐受机制

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When behavioral avoidance cannot prevent an animal from being exposed to novel environmental toxins, physiological mechanisms must cope with the toxin and its effects. We are investigating the basis of urea tolerance in populations of Drosophila melanogaster that have been selected to survive and develop in food containing 300 mmol l(-1) urea. Previous research has demonstrated that the urea-selected larvae have lower levels of urea in their body than control larvae reared under the same conditions. The current series of experiments focuses on three possible ways of reducing urea levels in the body: urea metabolism, increased urea excretion and decreased urea uptake from the environment. We tested for urea metabolism directly, by assaying for activity of two urea-metabolizing enzymes, and indirectly, by looking for reduced urea content of their medium. To measure urea excretion rates in whole animals, we reared control and urea-selected larvae on urea-containing food (urea food), switched them to normal food and monitored the loss of urea from their hemolymph. We measured urea uptake by rearing control and selected larvae on normal food, switching them to urea food and monitoring the rate of urea appearance in the hemolymph. We found no evidence for urea metabolism by either direct or indirect methods. Control larvae excreted urea at a higher rate than selected, probably because they contained more urea than the selected larvae and thus had a greater gradient for urea loss. The rate of urea uptake in selected larvae was 2 mmol l(-1) h(-1) slower than the rate in control larvae, a difference that could account for the measured differences in body urea levels. Thus the selected larvae appear to have adapted to urea exposure primarily by decreasing the ability of urea to enter their body in the first place. The mechanism responsible for this reduction in uptake is uncertain.
机译：当避免行为不能阻止动物接触新型环境毒素时，生理机制必须应对该毒素及其作用。我们正在调查果蝇果蝇的尿素耐受性基础，这些果蝇已被选择在含有300 mmol l（-1）尿素的食物中生存和发展。先前的研究表明，与在相同条件下饲养的对照幼虫相比，选择尿素的幼虫体内尿素水平较低。当前的一系列实验着重于降低体内尿素水平的三种可能方式：尿素代谢，尿素排泄增加和环境中尿素吸收减少。我们通过测定两种尿素代谢酶的活性来直接测试尿素的代谢，并通过寻找其培养基中尿素含量的降低来间接测试尿素的代谢。为了测量整个动物的尿素排泄率，我们在含尿素的食物（尿素食物）上饲养了对照和尿素选择的幼虫，将它们改为正常食物，并监测了其血淋巴中尿素的损失。我们通过饲养对照和选择正常食物上的幼虫，将它们转换为尿素食物并监测血淋巴中尿素的出现率来测量尿素的吸收。我们没有发现直接或间接尿素代谢的证据。对照幼虫以比选定的幼虫更高的速率排泄尿素，可能是因为它们所含的尿素比选定的幼虫要多，因此尿素损失的梯度更大。所选幼虫中尿素的吸收速率比对照幼虫中的尿素吸收速率慢2 mmol l（-1）h（-1），这一差异可以解释体内尿素水平的测量差异。因此，首先通过降低尿素进入其体内的能力，所选幼虫似乎已适应尿素暴露。导致这种摄取减少的机制尚不确定。

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