膳食非淀粉多糖（NSP）水平和添加胆汁酸对虹鳟鱼营养素消化和胆汁酸代谢的影响

The effects of dietary bile acid supplementation (BAS) on apparent digestibility coefficients (ADC) and the bile  acid metabolism in rainbow trout (Oncorhynchus mykiss) were investigated for diets differing in non-starch  polysaccharide (NSP) level. Four experimental diets were formulated according to an 2 by 2 factorial design.  A low-NSP and High-NSP diet (0 vs. 160 g kg− 1 inclusion of an NSP-rich ingredient mixture) were first  formulated. The aim of this was to create differences in the amount of faecal waste produced, and consequently  as previously shown in rainbow, the amount of faecal bile acid loss (FBAL). Both NSP-level diets were tested with  0% and 0.3% BAS (0 vs. 3 g kg− 1 inclusion of a bile acid mixture). The bile acid mixture contained taurocholic  acid (T-CA) and glycocholic acid (G-CA) in a 2:1 ratio. Glycocholic acid does not naturally occur in trout and was  used as marker to see if supplemented bile acids are efficiently absorbed and enter enterohepatic circulation  (EHC). Fish were fed to apparent satiation for 42 days. Dietary NSP level did not enhance FBAL. BAS was  beneficial for fat ADC, but not for the ADC of protein and carbohydrates. BAS improved fat ADC regardless of  NSP level, which suggests that bile acids are a limiting factor for fat digestion in rainbow trout. Total bile acid  synthesis was a 4-fold lower in fish fed the 0.3% BAS diets compared to the 0% BAS diets. Lower bile acid  synthesis with BAS occurred alongside enlarged body and liver + gallbladder bile acid pools and a higher content  of bile acids in the chyme. These higher bile acid levels most likely caused a negative feedback inhibition of bile  acid synthesis. Negative synthesis rates of G-CA were found when feeding the 0.3% BAS diets, which suggests  that this bile acid is catabolised or converted into other bile acid types in rainbow trout. The enlarged pool of TCA, but especially of the body foreign G-CA, with BAS in both the body and liver + gallbladder shows that dietary  bile acids are effectively taking part in EHC. The relative absorption of T-CA and G-CA over the different intestinal compartments was comparable, which shows that EHC does not differentiate between T-CA and G-CA.  While relative absorption of bile acids was highest between the distal intestine and the faeces, the absolute  decrease in chyme bile acid content was highest between the pyloric region and the mid intestine. The latter  shows that significant bile acid absorption occurs more proximal in the intestine of rainbow trout than previously  thought.

研究了日粮补充胆酸(BAS)对虹鳟鱼（Oncorhynchusmykiss）表观消化系数(ADC)和胆酸代谢的影响，研究了日粮中非淀粉多糖(NSP)水平的差异。按照2乘2的工厂设计制定了四种实验饮食。首先制定了低NSP和高NSP饮食（0对160克公斤-1含有富含NSP的成分混合物）。这样做的目的是在产生的粪便废物的数量上产生差异，因此，正如前面在虹鳟鱼中所显示的，粪便酸度损失的数量(FBAL)。NSP水平的饮食都用0%和0.3%BAS（0对3克千克-1掺入半酸混合物）进行测试。胆汁酸混合物以2：1的比例含有牛磺胆酸（T-CA）和糖胆酸（G-CA）。糖胆酸在鳟鱼中不是自然发生的，被用作标志物，以了解补充的酸是否被有效吸收并进入肠肝循环(EHC)。鱼被喂食到明显的满足42天。饮食NSP水平并不能提高FBAL。BAS对脂肪ADC有益，但对蛋白质和碳水化合物ADC不有益。BAS提高了脂肪ADC，而不考虑NSP水平，这表明胆汁酸是虹鳟鱼脂肪消化的限制因素。与0%BAS相比，0.3%BAS饮食中的鱼的总氢氟酸合成量低4倍。较低的苯甲酸合成与BAS发生在扩大的身体和肝脏+胆囊苯甲酸池和较高含量的苯甲酸在乳糜。这些较高的苯甲酸水平最有可能导致苯甲酸合成的负反馈抑制。当喂食0.3%BAS饮食时，发现G-CA的负合成率，这表明这种双酸在虹鳟鱼中被分解或转化为其他类型的胆汁酸。增加的TCA池，但特别是身体外的G-CA，在身体和肝脏+胆囊中都有BAS，表明膳食中的胆汁酸在EHC中的作用是有效的。不同肠室对T-CA和G-CA的相对吸收是可比的，这表明EHC对T-CA和G-CA没有区别。虽然远端肠和粪便对胆酸的相对吸收最高，但幽门区和中端肠对胆酸含量的绝对减少最高。后来的研究表明，比以前想象的更接近虹鳟鱼肠道的部位发生了显著的氢酸吸收。