Ontogeny of intestinal nutrient transport

Children born prematurely lack the ability to digest and to absorb nutrients at rates compatible with their nutritional needs. As a result, total parenteral nutrition may need to be given. While this nutritional support may be lifesaving, the baby who receives this therapy is exposed to the risks of possible sepsis, catheter dysfunction, and liver disease. The rodent model of postnatal development provides a useful framework to investigate some of the cellular features of human intestinal development. The up-regulation of intestinal gene expression and precocious development of intestinal nutrient absorption can be achieved by providing growth factor(s) or by modifying the composition of the maternal diet during pregnancy and nursing or the weaning diet of the infant. Accelerating the digestive and absorptive functions of the intestine would thereby allow for the maintenance of infant nutrition through oral food intake, and might possibly eliminate the need for, and risks of, total parenteral nutrition. Accordingly, this review was undertaken to focus on the adaptive processes available to the intestine, to identify what might be the signals for and mechanisms of the modified nutrient absorption, and to speculate on approaches that need to be studied as means to possibly accelerate the adaptive processes in ways which would be beneficial to the newborn young.     

Effect of DTNB on rat intestinal galactose transport in vivo

The effect of the non-penetrating reagent of -SH groups: acid 5,5'-dithiobis (2-nitrobenzoic), (DTNB), on 1 mM galactose absorption in rat intestine in vivo has been studied. DTNB inhibits sugar absorption in about 35%, which is due to an action on the mediated transport component, but without affecting the diffusional passive one. Consequently it does not modify galactose absorption in the presence of 0.5 mM phlorizin or that of the non-transportable sugar 2-deoxy-glucose. Galactose transport inhibition appears after a not longer than 5 min preexposure period and it remains constant at least up to 30 min. The inhibitory effect does not vary between 0.1 and 1 mM DTNB and it reverses completely with 0.5 mM dithioerythritol. Protection by excess of substrate has not been observed. Results show that DTNB affects sulfhydryl groups very probably located at the luminal side and related to the proteins of the cotransport system.     

Effect of calcium on transport of cations to the xylem exudate of tobacco

Summary Roots of detopped tobacco plants (Nicotiana tabacum var. Virginia Gold) were exposed to Na, K, and Ca salts or to water, and cation transfer to xylem vessels was measured. In some cases plants had been exposed to Na in addition to regular nutrient solutions before detopping. Calcium in the external medium greatly depressed the transport of Na from the external medium to the xylem vessels and it often stimulated the transfer of K from the external medium to the xylem vessels. The K/Na ratio in the exudate thus was dependent upon the Ca content of the external medium under these conditions. In contrast, externally applied Ca or Ca deficiency had very little effect on the transfer of preaccumulated K and Na from compartments within roots to the xylem vessels. The K/Na ratio in the exudate under these conditions was not related to Ca levels nor to mild Ca deficiency. The ratios decreased with time after detopping regardless of Ca level. Intact plants accumulated more Na than did root systems of detopped plants in a 6-day period.Riverside University of CaliforniaSoil Science and Agricultural Engineering     

Effect of experimental azotemia on intestinal transport of butyric acid

Earlier studies have revealed an impairment of jejunal absorption of long chain fatty acids in experimental uremia. We investigated the intestinal absorption of butyric acid which is a short chain fatty acid in experimental renal failure (RF). Sprague-Dawley rats were randomized into the RF group which had subtotal nephrectomy, a sham-operated control group, and a pair-fed group. In vivo recirculating perfusion (n = 5) and in vitro everted sac incubation (n = 8) were employed. The in vitro experiments were repeated substituting the serosal buffer by either predialysis or postdialysis sera from uremic individuals, or normal serum (n = 10). The rate of in vivo butyric acid absorption was significantly lower while the in vitro absorption was significantly higher in the RF group than those observed in the sham-operated and pair-fed groups which showed comparable values. The normality of butyric acid absorption in the pair-fed animals despite comparable weight loss with the RF group tends to exclude anorexia and weight loss as a cause of altered butyric acid transport in RF animals. The disparity between the in vivo and in vitro data is suggestive of an inhibitory influence of uremic environment which is present in vivo and absent in vitro. This viewpoint was corroborated by the observed fall in butyric acid absorption by sacs containing predialysis uremic serum as compared with those containing normal or postdialysis sera. The latter further suggests that the inhibitory factor(s) is dialyzable.     

Comparative study on metal homeostasis and detoxification in two Antarctic teleosts

The main characteristic of Antarctic seawater is its low constant temperature and its high concentration of O(2), which can increase the formation rate of reactive oxygen species (ROS), together with a natural occurrence of elevated cadmium and copper levels. In the present paper, we studied the presence of cadmium, copper and zinc, metallothioneins (MTs) and glutathione (GSH), and antioxidant enzyme activities in the Antarctic teleosts Trematomus bernacchii and Trematomus newnesi, in order to determine the influence of the peculiar physico-chemical features of the Antarctic marine environment on these physiological defence systems in two species of teleosts. In both of them, cadmium and copper accumulation occurs mostly in the liver. T. bernacchii accumulates zinc mostly in the hepatic tissue, whereas T. newnesi does not show a preferential accumulation site. In addition to the intra-specific analysis, we decided to compare the two species of the Trematomus genus in order to verify if the different feeding habits and motility of these fish affects metal accumulation. Our results show that the liver of T. bernacchii accumulates cadmium and zinc at a higher extent with respect to T. newnesi. Glutathione (GSH) and metallothioneins (MTs) are present in great quantity in the liver of both species. Moreover liver is the tissue which generally showed the highest antioxidant enzyme levels. The results provide further insights in the physiological mechanisms evolved by animals living in this extreme environment.     

Ion transport systems in the kidney and urinary bladder of two Antarctic teleosts, Chionodraco hamatus and Trematomus bernacchii

Na⁺-K⁺-Cl^- cotransport and Na⁺/K⁺ATPase were studied by immunohistochemistry in the kidney and urinary bladder of Trematomus bernacchii and Chionodraco hamatus. The activity was correlated to the density of mitochondria. The first segment of the renal proximal tubule was more active than the second one. In T. bernacchii and the temperate marine teleost Pagellus bogaraveo, the immunoreactivity for the antibody to cotransporters and to the !-subunit of the sodium pump was stronger than in the icefish. This difference indicates in the kidney of the icefish, a weaker secretory activity, a consequent lower osmolarity in the lumen and lower water loss, which correlates well with the need for a greater blood volume in the icefish. The epithelium of the urinary bladder in T. bernacchii, where intense immunostaining was observed, was composed of columnar cells. In C. hamatus the columnar cells, where the immunostaining was weaker, lined only a portion of the urinary bladder, the other region being composed of cuboidal cells.     

Effect of human milk folate binding protein on folate intestinal transport

The present study examined the effect of human milk folate binding protein (FBP) on the intestinal transport of 5-methyltetrahydrofolate (5-CH3H4PteGlu). This was performed by examining the transport of radiolabeled 5-CH3H4PteGlu bound to FBP using everted sacs of rat intestine. In the jejunum at pH 6, transport of 27 nM bound 5-CH3H4PteGlu was linear with time for 30 min of incubation. Transport of 13 nM bound 5-CH3H4PteGlu was higher in the jejunum than in the ileum at both pH 6 (2.1 +/- 0.3 and 0.36 +/- 0.03 pmol/g wet wt/25 min, respectively) and pH 8 (1.9 +/- 0.3 and 0.32 +/- 0.02 pmol/g wet wt/25 min, respectively). In the jejunum, transport of 13 nM bound 5-CH3H4PteGlu at pH 6 was less than transport of an equimolar concentration of free 5-CH3H4PteGlu (2.1 +/- 0.3 and 5.1 +/- 0.5 pmol/g wet wt/25 min, respectively) but was similar at pH 8 (1.9 +/- 0.3 and 2.47 +/- 0.3 pmol/g wet wt/25 min, respectively). In the ileum transport of bound and free 5-CH3H4PteGlu was similar at pH 6 (0.36 +/- 0.03) and 0.41 +/- 0.06 pmol/g wet wt/25 min, respectively) and pH 8 (0.32 +/- 0.02 and 0.43 +/- 0.1 pmol/g wet wt/25 min, respectively). The transport process of bound 5-CH3H4PteGlu in the jejunum was energy, temperature, and Na+ dependent, but not pH dependent, and was competitively inhibited by sulfasalazine. Ninety-two percent of the transport substrate that appeared in the serosal compartment following incubation with bound 5-CH3H4PteGlu was found to be free (unbound) 5-CH3H4PteGlu. These results show that human milk FBP decreases the rate of transport of 5-CH3H4PteGlu in the jejunum and suggest that FBP-bound 5-CH3H4PteGlu may utilize the same transport system as free 5-CH3H4PteGlu. The results also suggest a role for human milk FBP in regulating the nutritional bioavailability of folate.     

Effect of inorganic cations and metabolic inhibitors on putrescine transport in roots of intact maize seedlings

The specificity and regulation of putrescine transport was investigated in roots of intact maize (Zea mays L.) seedlings. In concentration-dependent transport studies, the kinetics for putrescine uptake could be resolved into a single saturable component that was noncompetitively inhibited by increasing concentrations of Ca²⁺ (50 micromolar to 5 millimolar). Similarly, other polyvalent cations, including Mg²⁺ (1.8 millimolar) and La³⁺ (200 micromolar), almost completely abolished the saturable component for putrescine uptake. This suggests that putrescine does not share a common transport system with other divalent or polyvalent inorganic cations. Further characterization of the putrescine transport system indicated that 0.3 millimolar N-ethyl-maleimide had no effect on putrescine uptake, and 2 millimolar p-chloromercuribenzene sulfonic acid only partially inhibited transport of the diamine (39% inhibition). Metabolic inhibitors, including carbonylcyanide-m-chlorphenylhydrazone (20 micromolar) and KCN (0.5 millimolar), also partially inhibited the saturable component for putrescine uptake (V_max reduced 48-60%). Increasing the time of exposure to carbonylcyanide-m-chlorphenylhydrazone from 30 minutes to 2 hours did not significantly increase the inhibition of putrescine uptake. Electrophysiological evidence indicates that the inhibitory effect on putrescine uptake by these inhibitors is correlated to a depolarization of the membrane potential, suggesting that the driving force for putrescine uptake is the transmembrane electrical potential across the plasmalemma.