Robin J P, Cherel Y, Girard H, Géloen A, Le Maho Y
Laboratoire d'Etude des Régulations Physiologiques, Centre National de la Recherche Scientifique, Strasbourg, France.
J Comp Physiol B. 1987;157(4):491-9. doi: 10.1007/BF00691834.
Five ganders were subjected to an experimental fast comparable to that which spontaneously occurs during breeding in domestic geese, and during migration and breeding in various wild birds. Plasma uric acid and urea concentrations, and their excretion as a proportion of total nitrogen excretion, were studied in relation to daily change in body mass per unit body mass, mg/mdt. This variable has previously been found to reflect changes in protein catabolism over the three phases of fast: I, dm/mdt and protein utilization both decrease; II, they are maintained at a low value; and III, they increase. In the fed state, daily total nitrogen excretion was 5 gN X 24 h-1; uric acid, ammonia and urea accounted for 51, 15 and 5% respectively. The high remaining proportion of excreted nitrogen (29%), after subtraction of uric acid-N, ammonia-N and urea-N to total nitrogen, accords with the literature. During fasting, the changes in daily excretion of uric acid, urea, ammonia and total nitrogen followed a pattern essentially similar to that for dm/mdt. Uric acid accounted for a progressively increasing fraction of total nitrogen, up to 76% at the end of phase III, while urea remained at a constant 5%. Plasma concentrations of both uric acid and urea followed similar trends during the fast, in particular both increasing during phase III, i.e. when there was a rise in nitrogen excretion. This suggests they could be used as an index in field investigations, to determine whether birds which naturally fast in connection with specific activities have entered into the situation where proteins are no longer spared.
对5只雄鹅进行了一项实验性禁食，其禁食情况类似于家鹅在繁殖期间以及各种野生鸟类在迁徙和繁殖期间自然发生的禁食。研究了血浆尿酸和尿素浓度及其排泄量占总氮排泄量的比例，同时考虑了单位体重每日体重变化（mg/mdt）。此前已发现该变量可反映禁食三个阶段蛋白质分解代谢的变化：第一阶段，dm/mdt和蛋白质利用率均下降；第二阶段，它们维持在较低水平；第三阶段，它们上升。在喂食状态下，每日总氮排泄量为5 gN×24 h⁻¹；尿酸、氨和尿素分别占51%、15%和5%。从总氮中减去尿酸氮、氨氮和尿素氮后，排泄氮的剩余比例较高（29%），这与文献报道相符。在禁食期间，尿酸、尿素、氨和总氮的每日排泄量变化模式与dm/mdt基本相似。尿酸占总氮的比例逐渐增加，在第三阶段结束时达到76%，而尿素则保持在5%的恒定水平。禁食期间，尿酸和尿素的血浆浓度呈现相似趋势，特别是在第三阶段均升高，即氮排泄增加时。这表明它们可作为野外调查的指标，以确定因特定活动而自然禁食的鸟类是否已进入不再节省蛋白质的状态。
