Changes in glucose uptake by and phlorizin binding to brush-border membrane vesicles of small intestine from streptozotocin-induced diabetic rats

The changes in the intestinal glucose transport in streptozotocin-induced diabetic rats have been demonstrated with brush-border membrane vesicles. When Na+-dependent D-glucose uptake and phlorizin binding activities were compared, both significantly increased either in the jejunum or ileum of diabetic rats compared with those of control. Kinetic studies showed the increases in the Vmax of glucose transport and the maximum binding of phlorizin (Bmax), whereas the Kt and Kd remained unchanged, respectively. These results suggested that the increase in glucose transport in diabetic rat intestine was due to the increase in the number of the intact glucose transporters.     

稳定性同位素在大鼠移植小肠吸收功能研究中的应用

作者用改良的Ｍｏｎｃｈｉｋ和Ｒｕｓｓｅｌｌ法对大鼠行异体节段性异位小肠移植，在肠外营养支持１０ｄ后用稳定性同位素测定技术测定大鼠移植小肠对＾１５Ｎ标记甘氨酸的吸收功能。结果示１ｈ的吸为３６．１１％，而在２ｈ和３ｈ的吸收率分别达到５６．４８％和６５．５４％，呈持续吸收状态。作者认为本研究中所采用的方法，在实验及临床小肠收功能研究方面值得借鉴。     

Isoleucine, a blood glucose-lowering amino acid, increases glucose uptake in rat skeletal muscle in the absence of increases in AMP-activated protein kinase activity

Leucine and isoleucine were shown to stimulate insulin-independent glucose uptake in skeletal muscle cells in vitro. In this study, we examined the effects of leucine and isoleucine on blood glucose in food-deprived rats and on glucose metabolism in skeletal muscle in vivo. Furthermore, we investigated the possible involvement of the energy sensor, 5'-AMP-activated protein kinase (AMPK), in the modulation of glucose uptake in skeletal muscle, which is independent of insulin, and also in leucine- or isoleucine-stimulated glucose uptake. Oral administration of isoleucine, but not leucine, significantly decreased the plasma glucose concentration. An i.v. bolus of 2-[1,2-3H]-deoxyglucose (2-[3H]DG) was administered to calculate glucose uptake. Glucose uptake in the skeletal muscle did not differ after leucine administration, but glucose uptake in the muscles of rats administered isoleucine was 73% greater than in controls, suggesting that isoleucine increases skeletal muscle glucose uptake in vivo. On the contrary, in the skeletal muscles, administration of leucine but not isoleucine significantly increased [U-14C]-glucose incorporation into glycogen compared with controls. AMPK alpha1 activity in skeletal muscle was not affected by leucine or isoleucine administration. However, isoleucine, but not leucine, significantly decreased AMPK alpha2 activity. The decrease in AMPK alpha2 activity was thought to be due to decreases in AMP content and the AMP:ATP ratio, which were related to the isoleucine administration. This is the first report of isoleucine stimulating glucose uptake in rat skeletal muscle in vivo, and these results indicate that there might be a relation between the reduction in blood glucose and the increase in skeletal muscle glucose uptake that occur with isoleucine administration in rats. The alterations in glucose metabolism caused by isoleucine may result in an improvement of the availability of ATP in the absence of increases in AMP-activated protein kinase activity in skeletal muscle.     

Effect of the ratio of casein phosphopeptides to calcium (w/w) on passive calcium transport in the distal small intestine of rats

OBJECTIVE: We investigated the influence of different ratios between casein phosphopeptides and calcium (CPP/Ca) in intestinal lumen on passive Ca transport across the distal small intestine of rats in vitro. METHODS: We measured the amounts of passive Ca absorbed across the everted distal small intestine of rats with the use of radioactive 45Ca as tracer. Four CPP/Ca ratios (5, 10, 15, and 20 w/w) and three mineral concentrations (4, 8, and 12 mmol/L) were tested on groups of six rats. RESULTS: We found a significant effect of the CPP/Ca ratio on mineral absorption (P < 0.001). The amounts of Ca absorbed increased from a ratio of 5 to a ratio of 15 and decreased with a ratio of 20, with a similar trend for every concentration tested. The more evident effect was found with the concentration of 12 mmol/L of Ca (P < 0.001 to 0.05). CONCLUSION: The positive effect of CPPs on passive Ca absorption seems to depend on the relative amounts of both species in intestinal lumen. In this study, the ratio 15 was identified as the most efficient at increasing mineral transport. This evidence might be considered before suggesting CPP as a Ca dietary integrator, although more studies in vitro and in vivo are needed.     

Intestinal, hepatic, splanchnic and hindquarter amino acid and metabolite partitioning during an established Trichostrongylus colubriformis infection in the small intestine of lambs fed fresh Sulla (Hedysarum coronarium)

Increased partitioning of amino acids (AA) from skeletal muscle to the intestine and immune system during parasitic infection may be the cause of poor growth in parasitised animals. The effect of an established Trichostrongylus colubriformis infection (6000 L3 T. colubriformis larvae for 6 d (n 5) or kept as parasite-free controls (n 6)) on AA fluxes across the mesenteric-drained viscera, portal-drained viscera (PDV), liver, total splanchnic tissues (TSP) and hindquarters were determined in lambs fed fresh Sulla (Hedysarum coronarium; 800 g DM/d) 48 d post-infection. The lambs were infused with rho-aminohippuric acid (PAH; 723 mg/h) into the mesenteric vein for 8 h to measure TSP plasma flow. Concurrently, indocyanine green (ICG; 14.6 mg/h) was infused into the abdominal aorta to measure plasma flow across the hindquarters. Blood was continuously collected from the mesenteric, portal and hepatic veins, vena cava and the mesenteric artery and plasma harvested. PAH, ICG, AA, metabolite and insulin concentrations were measured. Intestinal worm burdens on day 48 post-infection were higher in the infected lambs (P 0.10). There was a 28 % reduction in the release of AA from the PDV of infected lambs (P < 0.05). The uptakes of most AA were similar in the liver; however, there was increased uptake (P < 0.10) of AA by the TSP of infected lambs. Despite this reduction in AA availability at the liver, there was no effect of parasitic infection on AA uptake across the hindquarters (P < 0.05).