Effect of oral administration of a single bolus of six different protein sources on digestive physiology of red seabream Pagrus major juveniles

To reveal direct effects of various protein sources on digestive physiology of red seabream, Pagrus major (38.5 ± 0.4 g), six different protein sources of fishmeal (FM), soybean meal (SBM), corn gluten meal (CGM), soy protein concentrate (SPC), poultry by-product meal (PBM), and poultry-feather meal (PFM) were orally administered to fish (2 mg protein/g body weight) and sampled at 1.5 h and 3 h after administration. Gallbladder weight of fish administered FM, PBM, and PFM decreased after administration (p < 0.0001), while no difference was observed in the other ingredients compared to a non-protein sham control group, indicating that animal protein sources could more strongly stimulate bile secretion than plant protein sources in red seabream. Trypsin and chymotrypsin activity in the intestinal content markedly increased by the FM, SBM, and PFM administration (p < 0.0001). Lipase and amylase activity was also increased by FM and SBM but also by CGM for lipase and by PBM and PFM for amylase (p < 0.0001). These indicate that stimulation effect of the secretion of digestive enzymes is largely different among the protein sources. This might be due to the absorptive capacity of the protein source since intestinal absorption parameter genes (anpep, cpa, ggt1, and atp1a2) also increased by the FM, SBM, PBM or PFM (p < 0.05). In addition to the secretion levels of bile and digestive enzymes, gene expression levels of bile related genes (cyp7a1, cyp8b1, and shp) and digestion-regulating genes (casr and cck) were increased by the FM, SBM, PFM, and/or PBM administration, suggesting that animal proteins and SBM could be potent digestive stimulants compared to CGM and SPC. This study first revealed that single protein sources directly influence digestive enzyme secretion and bile secretion in fish. Information about the direct effect of each single source on digestive physiology could help to design feed formulation with less fishmeal.

Enterohepatic circulation kinetics of bile-active folate derivatives and folate homeostasis in rats

We examined the effect of enteric infusion of 5,10-methylenetetrahydrofolate (5,10-CH2-H4PteGlu), tetrahydrofolate (H4PteGlu), 10-formyltetrahydrofolate (10-HCO-H4PteGlu), and 5-methyltetrahydrofolate (5-CH3-H4PteGlu) on concentrations of plasma 5-CH3-H4PteGlu in rats. Concentrations of plasma 5-CH3-H4PteGlu rapidly decreased during continuous bile diversion, whereas initial levels of plasma 5-CH3-H4PteGlu were maintained by means of enteric infusion of 5-CH3-H4PteGlu at a dose of 3 nmol/h, which was approximately equal to total secretion of bile folates. Plasma 5-CH3-H4PteGlu levels were also maintained by the infusion of 5,10-CH2-H4PteGlu, H4PteGlu, or 10-HCO-H4PteGlu at the same dose as 5-CH3-H4PteGlu. The results indicate that folates secreted into the bile are reabsorbed through the intestine to regulate plasma concentrations of 5-CH3-H4PteGlu. We examined the secretion kinetics of bile folates after the intravenous injection of 5-CH3-H4PteGlu or folic acid (PteGlu) at 1 mg/kg body wt. When 5-CH3-H4PteGlu was injected, the bile secretion of folates other than 5-CH3-H4PteGlu increased by < 5 times the base level, whereas that of bile 5-CH3-H4PteGlu markedly increased by approximately 30 times. When PteGlu was given, the bile secretion of nonmethylated tetrahydrofolates markedly increased by 15-27 times, whereas that of 5-CH3-H4PteGlu increased by approximately 7 times. The results suggest that oxidized folates may be one of the sources for bile nonmethylated tetrahydrofolates. It is concluded that nonmethylated tetrahydrofolates in bile play an important role in folate homeostasis through enterohepatic circulation, together with 5-CH3-H4PteGlu.