Stiffler D F, Hawk C T, Fowler B C
J Exp Zool. 1980 Aug;213(2):205-12. doi: 10.1002/jez.1402130207.
Renal excretion of urea was assessed in adult and larval Ambystoma tigrinum by comparing simultaneous clearances of urea and inulin. The mean adult urea clearance ratio (CU/CIn) was 0.70 +/- 0.08 indicating net urea absorption. Larvae yielded a mean CU/CIn of 0.92 +/- 0.04. Individual larvae were quite variable however as approximately 30% displayed CU/CIn > 1. There was a significant negative correlation between CU/CIn and fractional water reabsorption. Comparisons of larval kidney urea concentration (KU) and plasma urea concentration (PU) revealed a mean KU/PU of 1.43 +/- 0.15. Treatment with 2,4-dinitrophenol decreased larval CU/CIn to 0.80 +/- 0.05 and KU/PU to 0.91 +/- 0.08. Phloridzin also decreased CU/CIn (0.67 +/- 0.06) however para-aminohippuric acid had no effect. Hypophysectomy combined with cautery of the pituitary stalk resulted in CU/CIn of 1.71 +/- 0.33 as compared to 0.84 +/- 0.08 in shams. These results are consistent with the possibility of net urea secretion at some point in the A. tigrinum nephron, followed by passive reabsorption in the distal segments under the influence of antidiuretic hormone.
通过比较成年和幼年虎纹钝口螈尿素和菊粉的同时清除率，评估了尿素的肾脏排泄情况。成年个体的平均尿素清除率（CU/CIn）为0.70±0.08，表明存在尿素净吸收。幼体的平均CU/CIn为0.92±0.04。然而，个体幼体差异较大，约30%的幼体CU/CIn>1。CU/CIn与水分重吸收分数之间存在显著负相关。对幼体肾脏尿素浓度（KU）和血浆尿素浓度（PU）的比较显示，平均KU/PU为1.43±0.15。用2,4-二硝基苯酚处理可使幼体的CU/CIn降至0.80±0.05，KU/PU降至0.91±0.08。根皮苷也可降低CU/CIn（0.67±0.06），然而对氨基马尿酸则无影响。垂体切除联合垂体柄烧灼导致CU/CIn为1.71±0.33，而假手术组为0.84±0.08。这些结果与虎纹钝口螈肾单位在某些部位可能存在尿素净分泌，随后在抗利尿激素影响下在远端节段被动重吸收的可能性一致。
