Liu S M, Lobley G E, MacLeod N A, Kyle D J, Chen X B, Orskov E R
Rowett Research Institute, Bucksburn, Aberdeen.
Br J Nutr. 1995 Jun;73(6):829-39. doi: 10.1079/bjn19950088.
The effect of long-term dietary protein excess and deficit on whole-body protein-N turnover (WBPNT) was examined in lambs nourished by intragastric infusions of nutrients. Ten sheep were given 500 mg N/kg metabolic weight (W0.75) per d from casein for 2 weeks and then either 50 (L), 500 (M) or 1500 (H) mg N/kgW0.75 per d for 6 weeks. Volatile fatty acids were infused at 500 kJ/kgW0.75 per d. Daily WBPNT was measured by continuous intravenous infusion of [1-13C]leucine 3 d before, and on days 2, 21 and 42 after the alteration in protein intake. Whole-body protein-N synthesis (WBPNS) was calculated as the difference between WBPNT and the protein-N losses as urinary NH3 and urea. Whole-body protein-N degradation (WBPND) was then estimated from WBPNS minus protein gain determined from N balance. Fractional rates of WBPNS and WBPND were calculated against fleece-free body N content. WBPNS rates at the L, M and H intakes were respectively 35.1, 41.5 and 63.7 g/d (P < 0.001) on average over the 6 weeks and WBPND rates were 39.5, 41.1 and 56.8 g/d (P < 0.001). The fractional rates of WBPNS were 5.01, 6.37 and 7.73% per d (P < 0.001) while those of WBPND were 5.64, 6.29 and 6.81% per d (P < 0.005) respectively. On days 2, 21 and 42, WBPNS rates at intake H were 54.0, 61.8 and 75.4 g/d (P = 0.03) respectively, and WBPND rates were 43.2, 56.4 and 70.9 g/d (P = 0.03); at intake L the amounts were 38.2, 34.2 and 32.8 g/d for WBPNS (P = 0.003) and for WBPND were 43.4, 38.0 and 36.9 g/d (P = 0.016) respectively. There were no significant (P > 0.05) differences in fractional rates of WBPNS and WBPND with time at either the L or H intake. We concluded that absolute protein turnover was affected both by dietary protein intake and body condition while the fractional rate of turnover was predominantly influenced by intake.
通过向羔羊胃内输注营养物质，研究了长期膳食蛋白质过量和不足对全身蛋白质氮周转（WBPNT）的影响。10只绵羊每天从酪蛋白中摄入500毫克氮/千克代谢体重（W0.75），持续2周，然后分别以每天50（低蛋白组，L）、500（中蛋白组，M）或1500（高蛋白组，H）毫克氮/千克W0.75的量摄入6周。每天以500千焦/千克W0.75的量输注挥发性脂肪酸。在蛋白质摄入量改变前3天以及改变后的第2、21和42天，通过持续静脉输注[1-13C]亮氨酸来测量每日WBPNT。全身蛋白质氮合成（WBPNS）通过WBPNT与作为尿氨和尿素的蛋白质氮损失之间的差值来计算。然后根据WBPNS减去由氮平衡确定的蛋白质增加量来估算全身蛋白质氮降解（WBPND）。WBPNS和WBPND的分数速率根据去毛身体氮含量计算。在6周期间，低蛋白组、中蛋白组和高蛋白组的WBPNS速率平均分别为35.1、41.5和63.7克/天（P < 0.001），WBPND速率分别为39.5、41.1和56.8克/天（P < 0.001）。WBPNS的分数速率分别为每天5.01%、6.37%和7.73%（P < 0.001），而WBPND的分数速率分别为每天5.64%、6.29%和6.81%（P < 0.005）。在第2、21和42天，高蛋白组的WBPNS速率分别为54.0、61.8和75.4克/天（P = 0.03），WBPND速率分别为43.2、56.4和70.9克/天（P = 0.03）；低蛋白组的WBPNS量分别为38.2、34.2和32.8克/天（P = 0.003），WBPND量分别为43.4、38.0和36.9克/天（P = 0.016）。在低蛋白组或高蛋白组中，WBPNS和WBPND的分数速率随时间均无显著（P > 0.05）差异。我们得出结论，绝对蛋白质周转受膳食蛋白质摄入量和身体状况的影响，而周转分数速率主要受摄入量的影响。
