Effect of Duodenal Soybean Small Peptides Infusion on Mammary Uptake of Amino Acid and Expression of APN in Lactating Goat

The aim of this study was to investigate the effect of duodenal infusion of soybean small peptides(SSP) on mammary uptake of amino acids(AA).Eight Chinese Saanen goats with duodenal fistulae and catheters were used in a crossover design trial.Goats were infused with 0,60,120,180 g/d SSP.The experimental period lasted for 14 d.The results showed:1) milk protein yield and content were increased,with the increment in milk protein yield being significant(P【0.05).Milk fat yield and content were decreased with the increased amount of SSP infused(P【0.05).2) Mammary plasma flow was not changed(P】0.05) by SSP infusion though the average was slightly higher.Mammary plasma flow/milk yield was decreased by SSP infusion and there was significant difference between the 120 g/d treatment and the control(P【0.05).3) Compared with the control treatment,uptakes of most free amino acids were increased in the 60 and 120 g/d treatments,but decreased by the 180 g/d treatment.The uptakes of all peptide-bound essential amino acids(PB-EAA) were increased except for PB-Ile.Uptake of PB-Val,PB-Leu, PB-Phe,PB-Thr,PB-Met and PB-Lys was highest in the 120 g/d treatment.Among the peptide-bound nonessential amino acids(PB-NEAA),uptake of PB-Ser,PB-Tyr,and PB-Pro was increased(P【0.05) while that of PB-Gly was decreased(P】0.05).4) With the exception of Lys,secretion of all essential AA(EAA) was increased by SSP infusion from 0-120 g/d(P【0.05),while in the 180 g/d treatment the increase was not significant and was lower than that in the 120 g/d treatment.5) The expression of APN was increased by SSP;in the 60,120,180 g/d treatments expression was 13.55-,18.69-,and 10.01-fold over that of the controls.Conclusion:SSP might be used as substrates for milk protein synthesis by mammary gland,and can increase synthesis and secretion of milk protein.There was reason to believe that uptake and use of AA was either saturated or inhibited at high levels of infusion of SSP.Increased APN expression with infusion of SSP related to mammary uptake of PBAA by mammary gland,which suggested that APN was one of the peptidases regulating use of AA from small peptides in mammary tissue.

十二指肠大豆小肽梯度灌注对山羊乳腺氨基酸吸收与氨肽酶N基因表达的影响

旨在研究乳腺对不同水平大豆小肽的吸收利用情况。试验选用8只带有十二指肠瘘管和颈动脉、乳静脉血插管的泌乳奶山羊（体质量38 kg±2 kg）,采用交叉设计,分别向十二指肠灌注大豆小肽0、60、120和180 g.d-1,连续灌注14 d。结果表明：通过小肽的灌注,（1）提高了乳蛋白产量与乳蛋白含量,而且乳蛋白产量显著提高（P〈0.05）。乳脂产量与乳脂含量随着灌注量的升高呈显著下降趋势（P〈0.05）。（2）乳腺血浆流量有轻微的提高,但不显著（P〉0.05）。与对照组相比,各处理组血浆流量/产奶量出现下降,但只有120 g.d-1灌注组下降显著（P〈0.05）。（3）与对照组相比,大部分游离氨基酸在60和120 g.d-1灌注组吸收量增加,而在180 g.d-1灌注组出现下降趋势。除了PB-Ile,大豆小肽的灌注增加了所有肽结合必需氨基酸的乳腺吸收。但PB-Val、PB-Leu、PB-Phe、PB-Thr、PB-Met和PB-Lys均在120 g.d-1灌注组吸收率最高。非必需氨基酸中,小肽的灌注提高了PB-Ser、PB-Tyr、PB-Pro的吸收（P〈0.05）,而PB-Gly的吸收却出现了下降（P〉0.05）。（4）除了Lys,处理组中所有必需氨基酸的乳中分泌量都高于对照组,从0~120 g.d-1试验组,这些氨基酸乳中分泌量随着小肽灌注量的升高而呈增加趋势（P〈0.05）;在180 g.d-1灌注组,大部分必需氨基酸的分泌量增加不显著（P〉0.05）,且低于120 g.d-1灌注组。（5）小肽的灌注明显促进了APN基因的表达。灌注60、120和180 g.d-1小肽后,氨肽酶N（APN）的表达分别是对照组的13.55、18.69和10.01倍。结论：乳腺组织能够吸收动脉血液中的小肽,大豆小肽的灌注提高了乳蛋白产量显示乳腺组织可以将吸收的小肽用于乳蛋白的合成。但当乳腺所需的氨基酸达到饱和以后,再增加氨基酸的浓度会出现吸收抑制。APN表达变化与乳腺小肽吸收增加相一致,这可能因为APN是调控小肽乳腺吸收利用的主要酶类之一。