Enhancement of Ca++ uptake by lactose in the rat small intestine

In previous experiments, lactose was shown to increase the absorption of Ca++ by the small intestine of the rat and other mammals. To further investigate the mechanism of the lactose effect, Ca++ uptake was studied in everted gut sac preparations. Gut sacs from the rat ileum were preincubated with or without lactose for 45 minutes, and then the tissue uptake of 45Ca over the first 3 minutes was measured in the presence or absence of lactose. The presence of 160 mM lactose increased the initial rate of Ca++ uptake in the first minute by 64% compared to the NaCl control. The lactose effect was dependent on the presence of lactose in the preincubation medium only and not on the presence of lactose during the measurement of Ca++ uptake. Lactose increased Ca++ absorption when the Ca++ concentrations ranged from 0.1 to 10 mM. However, the magnitude of the enhancement was dependent on the lactose concentration and was reduced below 160 mM lactose. When Ca++ and lactose uptake during a 45 minute period was measured in parallel experiments, no evidence for the co-transport of lactose and Ca++ into the tissue was found. These and other data indicated that lactose is not interacting directly with Ca++ in solution but is interacting with the absorptive cells of the intestine to increase their permeability to Ca++.     

Intestinal transplantation. The first Swedish transplantation of the small intestine in an adult patient with pseudoobstruction

Recent advances, first and foremost the development of new immunosuppressive agents, have markedly improved the outcome of intestinal transplantation, which is a treatment option for patients with serious intestinal diseases who have become dependent on total parenteral nutrition. The first small bowel transplantation in Sweden was performed at Huddinge Hospital in 1997, in the adult patient with intestinal pseudo-obstruction. The article reports the course of this patient and an update of international progress in intestinal transplantation.     

Action of levorin on glucose transport in the rat small intestine

The technique of accumulating preparation of the mucosa and "turned out sac" was used to show that levorin, a polyenic antibiotic in a concentration of 10(-6) M, lowered the transport rate and accumulation of glucose by the epithelial cells of the rat thin intestine under conditions of oxygenation. Suppression of the glucose transport in the first stages resulted in partial inhibition of the transmembrane transfer. It is suggested that levorin suppression of the glucose transport through the erythrocyte apical membrane in the thin intestine is associated with a decrease in the electrochemical gradient of Na+.     

Mechanism of nitric oxide-induced contraction in the rat isolated small intestine

1. The contractile response to nitric oxide (NO) in ral ileal myenteric plexus-longitudinal muscle strips was pharmacologically analysed. 2. NO (10(-7) M) induced only contraction while 10(-6) M NO induced contraction followed by relaxation. Methylene blue (up to 10(-4) M) did not affect the NO-induced contractions but significantly reduced the relaxation evoked by 10(-6) M NO. Administration of 8-bromo-cyclic GMP (10(-6)-10(-4) M) only induced relaxation. 3. Sodium nitroprusside (SNP; 10(-7)-10(-5) M) induced concentration-dependent contractions per se; the contractile response to NO, administered within 10 min after SNP, was concentration-dependently reduced. The guanosine 3':5'-cyclic monophosphate (cyclic GMP) content of the tissues was not increased during contractions with 10(-8) M NO and 10(-6) M SNP; it was increased by a factor of 2 during contraction with 10(-7) M NO, and by a factor of 12 during relaxation with 3 x 10(-6) M NO. 4. The NO-induced contractions were not affected by ryanodine (3 x 10(-5) M) but were concentration-dependently reduced by nifedipine (10(-8)-10(-7) M) and apamin (3 x 10(-9)-3 x 10(-8) M). 5. These results suggest that cyclic GMP is not involved in the NO-induced contraction in the rat small intestine. The NO-induced contraction is related to extracellular Ca2+ influx through L-type Ca2+ channels, that might be activated in response to the closure of Ca(2+)-dependent K+ channels.     

First-pass metabolism of 5-fluorouracil in the perfused rat small intestine

The first-pass intestinal metabolism of 5-fluorouracil (5-FU) was investigated by single-pass perfusion of the rat small intestine. At the low concentration of 0.06 mg/ml, the fraction of 5-FU absorbed into (i.e., appeared in) the mesenteric venous blood (Fa,b) was about 50% smaller than the fraction absorbed (disappeared) from the intestinal lumen (Fa), indicating the first-pass extraction of 5-FU in the intestinal mucosa. By addition of uracil (6 mg/ml), the Fa of 5-FU was reduced presumably by competition for the pyrimidine carrier at the process of intestinal uptake (entry into the mucosa). The Fa,b was also reduced, but to a lesser extent, resulting in insignificant first-pass extraction. These results suggest that the extraction of 5-FU in the absence of uracil is caused by metabolism and that uracil is a competitor for this pathway. When 5-FU concentration was raised from 0.06 to 0.6 mg/ml in the absence of uracil, the Fa was reduced by about 50%, consistent with the suggestion of the involvement of saturable uptake by the pyrimidine carrier, and thereafter remained unchanged at 6 mg/ml. However, since Fa,b was also reduced by a similar extent, the intestinal availability (FI=Fa,b/Fa) was unchanged at about 0.5, indicating that the intestinal first-pass extraction of 5-FU is independent of concentration with the extraction ratio (difference between unity and FI) of about 0.5 over the wide range of concentration from 0.06 to 6 mg/ml. Thus, the present study demonstrates that the significant first-pass metabolic extraction of 5-FU occurs in the mucosa of the small intestine, supporting our previous suggestion that 5-FU undergoes first-pass metabolism not only in the liver but also in the small intestine after oral administration. Considering that the oral bioavailability of 5-FU in the human (28%) is reportedly comparable with that in the rat (28%), it is likely that intestinal first-pass metabolism may be significant also in the human. Intestinal first-pass metabolism should be taken into account to explore more efficient and controlled oral 5-FU therapy.     

A diurnal rhythm in the absorption of glucose and water by isolated rat small intestine

1. Glucose and water absorption by isolated small intestine from rats which have had unrestricted access to food is 50-60% higher at night than during the daytime. 2. When the feeding time is restricted to 06.00-09.00 hr G.M.T. glucose and water absorption rates in the period from 3 to 7 hr after withdrawal of food are almost as high as the rates observed at night-time in the animals with unrestricted feeding. 3. These changes in absorption rates appear to be associated with feeding time and not with the pattern of illumination.     

Inhibition of antigen-induced muscle contractions by inhibitors of thromboxane pathway in rat small intestine

The cell cycle is driven by the sequential activation of a family of cyclin-dependent kinases (CDK) in association with cyclins. In mammalian cells the timing of activation of cyclin A-associated kinase activity coincides with the onset of DNA synthesis in S-phase. Using in vitro replication of SV40 origin-containing DNA as a model system, we have analyzed the proteins associated with DNA during initiation of DNA replication in S-phase cell extracts. This analysis reveals that, in addition to replication initiation proteins, cyclin A and cdk2 are also specifically associated with DNA. The association of cyclin A and cdk2 with DNA during initiation is cell cycle regulated and occurs specifically in the presence of SV40 origin-containing plasmid and SV40 T antigen (the viral replication initiator protein). The interactions among proteins involved in initiation play an important role in DNA replication. We therefore investigated the ability of cyclin A and cdk2 to associate with replication initiation proteins. Under replication initiation conditions, cyclin A and cdk2 from S-phase extracts specifically associate with SV40 T antigen. Further, the interaction of cyclin A-cdk2 with SV40 T antigen is mediated via cyclin A, and purified recombinant cyclin A associates directly with SV40 T antigen. Taken together, our results suggest that cyclin A and cdk2 are components of the SV40 replication initiation complex, and that protein-protein interactions between cyclin A-cdk2 and T antigen may facilitate the association of cyclin A-cdk2 with the complex.     

Developmental study of alpha-methyl-D-glucoside and L-proline uptake in the small intestine of the White Leghorn chicken

Development changes in alpha-methyl-D-glucoside and L-proline accumulation were studied using everted sleeves from the duodenum, jejunum, and ileum of chickens. Six age groups of chickens were used: 1 d and 1, 2, 3, 5 to 6, and 12 to 14 wk. Our results showed the presence of a Na+-dependent mechanism of sugar and amino acid uptake that is already fully developed at hatch. The intestinal transport activity undergoes substantial changes with age and region studied. Intracellular accumulation of alpha-methyl-D-glucoside and L-proline was greater in newly hatched chicks and then declined with age in the three regions of the small intestine, except for L-proline transport in ileum, which remained constant during the period studied. The transport mechanisms for each nutrient followed separate developmental patterns along the small intestine during the period studied.     

High uptake of myo-inositol by rat pancreatic tissue in vitro stimulates secretion

A recent study by Hokin-Neaverson, M., Sadeghian, K., Majumder, A.L., and Eisenberg, F. (1975) Biochem. Biophys. Res. Commun. 67, 1537-1544, demonstrates that free myo-inositol in the pancreas is significantly increased during intense cholinergic stimulation of secretion. Incubation of rat pancreatic tissue in medium with 100 mM myo-inositol increases 10-fold the endogenous content of free myo-inositol and elicits a prompt and sustained 50% increase in the rate of release of amylase activity. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis reveals that the electrophoretic pattern of the protein mixture released in the presence of 100 mM myo-inositol is the same as that of the secretory output released in the presence of 10 muM carbamylcholine. Microscopic examination of tissue pieces indicates that there is no significant decrease in zymogen granule content of the pancreatic acinar cells during incubation in medium with 100 mM myo-inositol. Jamieson, J.D., and Palade, G.E. (1967) J. Cell Biol. 34, 597-615, have shown that pulse-labeled secretory proteins in guinea pig pancreas first appear in zymogen granules 1 hour postpulse, becoming maximally accumulated in these storage sites by 2 hours postpulse. myo-Inositol (100 mM) stimulates release of pulse-labeled secretory proteins only if incubation in medium with 100 mM myo-inositol is initiated anytime during the first 80 min postpulse. The findings thus indicate that a high uptake of myo-inositol by rat pancreatic tissue in vitro selectively stimulates the release of just those secretory proteins being packaged in newly forming zymogen granules.     

Intestinal absorption of azetirelin, a new thyrotropin-releasing hormone (TRH) analogue. II. In situ and in vitro absorption characteristics of azetirelin from the rat intestine

Intestinal absorption characteristics of azetirelin, a new thyrotropin-releasing hormone (TRH) analogue, were studied in rats by means of in situ closed loop and in vitro everted sac experiments. Plasma concentrations of azetirelin obtained in the in situ closed loop experiments were not significantly different among the intestinal segments. Area under the plasma concentration-time curve (AUC) of azetirelin following administration into the duodenal loop increased in proportion to the dose. The serosal to mucosal concentration ratio of the analogue in the everted sac experiment was constant over the mucosal drug concentration range of 0.01-10 mM. There was no directional difference in the transfer rate of azetirelin across the everted and non-everted sacs of the duodenum. Furthermore, its transport across the duodenum was not influenced by low incubation temperature (25 degrees C), addition of dipeptide (Gly-Gly), or pretreatment of the mucosal surface with 2,4-dinitrophenol, while that of TRH was inhibited under these conditions. These results suggest that the intestinal absorption mechanism of azetirelin is different from that of TRH, and that azetirelin is predominantly transported via a passive diffusion.     

The effect of Escherichia coli heat-stable (STA) enterotoxin on in vitro uptake of amino acids by small intestine of sucking rats during fluid accumulation

In vitro uptake of 14C-labelled amino acids by segments of small intestine was determined in sucking (2-4-d-old) Wistar rats. Intragastric injections of heat-stable (ST) toxin of enterotoxigenic Escherichia coli (ETEC) were given to produce fluid accumulation, defined as a gut weight: carcass weight value of > 0.085. Continued active uptake of the prototypic amino acids, leucine (by active transport system 1 for monoamino monocarboxylic (neutral) amino acids), lysine (by active transport system 2 for dibasic amino acids), and proline (by active transport system 3 for N-substituted amino acids), persisted during the active fluid accumulation response to ETEC ST toxin. The mean Kt and mean Vmax of the amino acid transport systems were similar in control (non-injected) and ST toxin-injected rats. The present study provides a scientific basis for the use of amino acids in oral rehydration solutions utilizing amino acid transport systems which are linked to absorption of Na (and water) so that reduction in diarrhoeal stools can be achieved, and emphasizes the importance of maintaining feeding during acute diarrhoea to prevent development of malnutrition.     

Effect of alcohol ingestion on the epithelial cell population in rat small intestine

Chronic administration of alcohol to well-nourished rats led to striking changes in the small intestinal cell population. The present experiments corroborate the view that alcohol is directly toxic to the small intestine.     

Circadian rhythms of digestive enzymes in the small intestine of the rat. II. Effects of fasting and refeeding

The effects of fasting were examined on the rhythmic changes in the activities of maltase [EC 3.2.1.20] and leucine aminopeptidase [EC 3.4.11.1] in the small intestine of rats which has been kept under scheduled feeding conditions. Irrespective of whether the rats had been kept on a daytime or nighttime feeding schedule, the rhythms of maltase and leucine aminopeptidase persisted when the animals were starved. However, the amplitude of the leucine aminopeptidase rhythm began to decrease from the first day of fasting, while that of maltase did not. Conspicuous rhythms persisted for at least 2 days during fasting, but they gradually became vague and disappeared after 5 days. When rats were refed after fasting, the leucine aminopeptidase activity increased within a few hours, but the maltose activity did not. It is suggested that the rhythms of the digestive enzymes in the small intestine of rats are not a direct consequence of food intake, but are triggered off by the anticipatory mechanism which operates when rats expect to be fed. The rhythmic change of leucine aminopeptidase seemed to be intensified by food intake.     

Effect of atrial natriuretic peptide on sodium-glucose cotransport in the rat small intestine

Atrial natriuretic peptide (ANP) decreases sodium absorption in small intestine of rats in vitro under sodium concentration-gradient conditions (SCG) and this effect may be mediated by the inhibition of the sodium/glucose cotransporter (SGLT). In order to assess this hypothesis, the effects of ANP, phloridzine (Phlz) and methylene blue (MB), added alone or together, using a voltage clamp technique in Ussing's chamber with SCG were studied. ANP and Phlz significantly decreased potential difference and short circuit current. Effects of Phlz and ANP were not additive. The addition of MB alone did not affect ion transport, whereas it abolished ANP effects. These data suggest that ANP blocks the SGLT through mechanisms mediated by cGMP and/or NO.     

Intestinal hypertrophy after small intestinal bypass in the rat. Studies on methods and reversibility of changes

This study assessed sex differences in spontaneous wheel running and maze performance in relation to puberal status in rats. No sex differences were found prepuberally in either task whereas, postpuberally, females exceeded males in wheel running and males made fewer maze errors than females. Postpuberal males and females were less active than independent groups of prepuberal males and females, respectively. Although mature females made more errors than prepuberal females, no differences were found between independent groups of pre- and postpuberal males.     

1-O-acyl derivatives of glucose as non-penetrating inhibitors of glucose transport by hamster small intestine in vitro

1-O-acyl derivatives of glucose are not transported by the hamster small intestine in vitro. These derivatives, however, are potent inhibitors of the glucose transport system. 1-O-Decanoyl glucose is a competitive inhibitor of beta-methyl glucoside transport.     

Ontogenic regulation of phospholipase C-gamma 1 activity and expression in the rat small intestine

The accumulation of low density lipoprotein (LDL) in the arterial intima is an important characteristic of atherosclerosis. We investigated the mechanisms by which LDL binds to different types of collagen. The binding activities of 125I-labeled human native LDL (nLDL) and copper-oxidized LDL (oxLDL) with different collagen gels prepared in type I collagen-based mixtures with types I, III, IV and V (I+I, I+III, I+IV and I+V, respectively) were examined. A concentration of 20 micrograms LDL protein/150 micrograms collagen/well was used. The diffusion of both nLDL and oxLDL into the collagen gels reached an equilibrium after 48 h. All of the collagen gels showed the same rates of diffusion with both LDLs. The binding activities of oxLDL were significantly greater than those of nLDL (P < 0.001%), while the binding activities for both LDLs followed the order I+I and I+III > I+V > I+IV. However, the increased binding rate of oxLDL compared to nLDL was 1.66 for I+IV, 1.50 for I+V, 1.33 for I+I and 1.19 for I+III. When a 10-fold higher dose of NaCl (1 M) was added to the oxLDL medium, the binding rate of oxLDL was reduced (rate of reduction: 52% (I+I), 48% (I+III), 35% (I+IV), 13% (I+V)). These results suggest that oxLDL binds more to type I and III collagens by negative charge-dependent mechanisms than to type IV and V collagens. Therefore, types I and III collagens may play an important role in trapping LDL, especially oxLDL. Therefore, oxidatively modified LDL may contribute to atherogenesis due to its longer retention in the arterial wall.     

Relationship between antigen and antibody-induced suppression of IgE antibody formation in the rat

Formation of specific IgE antibodies as elicited in Sprague-Dawley rats against Ascaris antigen could be suppressed by intravenous administration both of antigen and of specific antiserum. The suppressive agent in the antiserum was shown to be antibodies of the IgG class, whereas a suppressive effect of cytophilic activity and of IgE antibodies could be outruled. Suppression of IgE response lasted the longer the more antibodies were transferred. An antibody-induced suppression was achieved when antibodies were transferred during an early period (day -3 to day +8), whereas an antigen-induced suppression took place when the antigen was intravenously administered following the antibody-sensitive period (day +8 until day +14). This is consistent with the fact that an antigen-induced suppression of IgE formation requires the presence of a certain amount of antibodies. A strictly peripheric suppression could be outruled, since with elapse of time a decreasing dose of antigen was required to induce a suppression. The results are discussed on the basis of an antigen-antibody complex-induced suppression in the IgE system and its possible central site of action.