Marine elasmobranchs are nitrogen-limited owing to the requirement of nitrogen for both somatic growth and urea-based osmoregulation, and due to the loss of urea across the gills and kidney as nitrogenous waste. In this study we used in vitro stomach and intestinal gut sacs to investigate the effects of consuming a urea-rich meal (700 mM within a 2% body-mass ration of food-slurry) on nitrogen movement across the gastrointestinal (GI) tract of North Pacific spiny dogfish (Squalus acanthias suckleyi). Plasma urea concentrations did not differ between fasted (359 ± 19 mM), urea-poor fed (340 ± 16 mM), and urea-rich fed (332 ± 24 mM) dogfish. Interestingly, in vitro gut sacs of urea-rich fed dogfish showed no net urea absorption from the lumen over 3 h incubation, which contrasts previously published data on urea-poor fed dogfish that absorb urea from the lumen. In addition, ammonium (NH₄⁺) concentration within the gut sac intestinal lumen significantly increased from 0.62 to 4.35 mM over 3 h. This is likely due to a combination of tissue production and microbial urease activity in the intestine. The overall results highlight the ability of S. a. suckleyi to regulate and maintain internal nitrogen concentrations despite the addition of excess dietary urea.

由于对体细胞生长和基于尿素的渗透调节都需要氮，并且由于穿过nitrogen和肾脏的尿素作为含氮废物的损失，海洋弹性分支受到氮的限制。在这项研究中，我们使用了体外胃和肠肠囊来研究食用富含尿素的餐（在2％的食物泥浆质量比中为700 mM）对氮通过胃肠道的影响。北太平洋多刺的fish鱼（Squalus acanthias suckleyi）。禁食（359±19 mM），饲喂低尿素（340±16 mM）和饲喂高尿素（332±24 mM）的fish鱼之间的血浆尿素浓度没有差异。有趣的是，体外富尿素喂养的狗鱼的肠囊在孵化3小时后没有显示出管腔的净尿素吸收，这与先前发表的关于贫尿素喂养的狗鱼从管腔吸收尿素的数据相反。此外，肠道囊肠腔内的铵（NH ₄ ⁺）浓度在3小时内从0.62 mM显着增加到4.35 mM。这可能是由于组织产生和肠中微生物脲酶活性的结合。总体结果突出了S. a。的能力。尽管添加了过量的日粮尿素，但吮吸菌仍可调节和维持内部氮浓度。