Assessing and influencing the fractional contribution of erythrocyte-bound 59Fe to individual 59Fe tissue content in murine 59Fe distribution studies.

BACKGROUND: Murine proteins of iron homoeostasis are frequently manipulated to investigate the mechanisms of iron-distribution and their toxicological consequences. Beyond subtracting erythrocyte-bound 59Fe of the residual blood content determined for each tissue (subtraction method), procedures are needed to determine 59Fe distribution in murine models of, e.g. inflammation or diabetes that cause local hyperaemia and changes in microcirculation. AIM: Two new methods were developed to correct total 59Fe tissue content individually for erythrocyte-bound 59Fe-labelled haem iron. METHODS: Iron-deficiency and iron-overload was induced in male C57BL6 mice by feeding of respective diets. Distribution of 59Fe between different tissues was determined 24h, 14, and 28 days after intravenous injection of 59Fe trace amounts. Haem-bound 59Fe was separated from non-haem 59Fe in homogenates from all tissues by dispersion in a mix of lipophilic cyclohexanone and hydrophilic H3PO4 (separation method). Moreover, the reduction of 59Fe-labelled tissue blood content was determined in all organs after in vivo saline perfusion via the left ventricle (perfusion method). RESULTS AND DISCUSSION: 59Fe-labelled non-haem iron determined by the separation method was not significantly different from values determined by the subtraction method, except for the iron-deficient spleen 14 and 28 days after 59Fe injection when the separation method yielded approximately 20% higher values. Approximately 20% of 59Fe-labelled haem iron spilled over into the hydrophilic phase. The impact of this error decreases in parallel to 59Fe radioactivity in the residual tissue blood content: thus, it is higher in iron-deficient mice which accumulate more 59Fe in their erythrocytes than iron-adequate and iron-rich mice. For the same reason this type of error is more marked after long distribution periods and in organs with high residual blood content. Saline perfusion via the left ventricle reduced total blood content in mice to less than 10%. Liver (95%) and duodenum (94%) showed the highest removal of blood while it is lowest in spleen (66%) and lungs (69%). CONCLUSIONS: The separation and the perfusion method can be used to correct the impact of erythrocyte-bound haem iron individually. A margin of error below 10% was determined for all organs except for spleen, lungs, and fat. Both methods can be applied sequentially to obtain satisfactory results in spleen, lungs, and fat.

Increased intestinal iron absorption in rats with normal hepatic iron stores. Kinetic aspects of the adaptative response to parenteral iron repletion in dietary iron deficiency.

Male Sprague-Dawley rats were fed an iron-deficient diet for 8 days. After this period, iron stores were repleted in three groups of animals by intravenous administration of iron dextran. In a second set of experiments, iron was administered in the same dose as Fe nitrilotriacetic acid complex. 12 h, 24 h and 48 h thereafter, the intestinal iron transfer in vitro and in vivo as well as the non-heme iron and ferritin content were determined in both the liver and the jejunal mucosa. In iron deficiency, intestinal iron transfer is increased to 230% of untreated controls, while non-heme iron and ferritin decreased to 20% and 10% in the liver and to 55% and 25% in the mucosa, respectively. 12 h and 24 h after parenteral administration of 0.1 mmol Fe/kg body weight iron transfer was as high as in iron deficiency, while liver iron stores were not significantly different from the untreated controls. In this situation, the close link between decreases in body iron stores and increases in iron transfer was temporarily dissociated. This can be related to the time lag between the incorporation of parenterally applied iron in the liver and in the jejunal mucosa. The data provide evidence for the hypothesis that the hepatic iron stores have no means of neural or hormonal communication with the small intestine in order to adapt iron transfer to their state of repletion on short notice. Intestinal iron transfer returned to control levels after 48 h.

A new class of inhibitors for in vitro small intestinal transport of sugars and amino acids in the rat.

Polycationic compounds like polylysine, protamine or polyethylenimine may interfere with a cation-related membrane transport system depending on superficially accessible binding sites for particular cations. In vitro experiments were performed using either everted segments of rat small intestine to measure tissue accumulation or everted sacs to determine mucosal-to-serosal transport. The effect of polycations was also tested using brush-border membrane vesicles of rat jejunum. Polycations inhibited the tissue accumulation of methyl alpha-D-glucoside as well as binding of phlorizin. Inhibition of accumulation was increased by raising the polycation concentration and by preincubation of the tissue with the polycations. Kinetic experiments revealed a competitive type of inhibition for the uptake of neutral amino acids and actively transported sugars. Using everted sacs to compare the monomeric cations with their corresponding polymeric forms for their inhibitory effect, it was found that only polymers applied to the mucosal compartment impaired active transport. The passive diffusion of solutes, e.g. 2-deoxy-D-glucose or mannitol, was slightly increased by polycations. With some intermediate oligomers of lysine it could be shown that more than 20 cationic groups are required for approximate complete inhibition. That membrane-related events are responsible for the observed inhibition is suggested by the reduced uptake of D-glucose by brush-border membrane vesicles in the presence of polycations. Therefore an interaction with transport-related cation binding sites, i.e. anionic residues, at the mucosal surface may be assumed.

In vitro inhibition of rat small intestinal absorption by lipophilic organic cations.

Cationic, lipid-soluble organic compounds may interfere with cation-mediated membrane transport processes. Thus, small intestinal absorption may be influenced by lipophilic organic cations. Therefore a series of arylalkylamines was studied in the concentration range from 0.5 to 20 mmol/l for their effect on the transport of various monosaccharides and leucine in the rat small intestine in vitro by means of the tissue accumulation technique. Whereas the monophenyl substituted monoamines (e.g. benzylamine, 2-phenylethylamine, 3-phenylpropylamine) did not show a significant effect on the active transport, the corresponding omega,omega-diphenyl derivatives exhibited a strong inhibition of the active transport of the sugars and the amino acid. These monoamines and drugs of similar structure (e.g. benzoctamine, diphenydramine) exhibited a mixed or non-competitive type of inhibition which correlated quite well with their octanol-water partition coefficients. In contrast, di- or triamines (e.g. harmaline, imipramine, pyrilamine) revealed a rather pure competitive type of inhibition. These findings tentatively suggest a different mode of action on the active transport by lipid-soluble organic amines according to the molecular charge distribution. In addition, membrane vesicles were used to examine the effect of the different amines on the sucrase activity. Regarding the cation-dependent hydrolysis of sucrose, however, no distinct pattern developed.

Long-term feeding of unavailable carbohydrate gelling agents. Influence of dietary concentration and microbiological degradation on adaptive responses in the rat.

Guaran, tragacanth, gum arabic, carrageenan, gum karaya, and methylcellulose were used in a long-term feeding study to evaluate their effects upon adaptive responses of nutritionally controlled parameters in rats by feeding a fiber-free diet containing increasing additions of polysaccharides. In general, supplements reduced weight increases due to lower energy intakes. Only in the case of microbiologically inert polysaccharides the dilution of the the energy density was partially compensated by an increased food intake. Neither of the polysaccharides fed, however, decreased energy utilization. All polysaccharides similarily increased small intestinal length up to about 30% without grossly altering mucosal protein and DNA per unit of length. Concerning their effects on the colon and the cecum, polysaccharides behaved differentially according to their accessibility to microbiological degradation. Inert polysaccharides exerted a more pronounced effect on the colon whereas the others mainly increased cecum weight. Degree and locus of the observed changes are determined mainly by the dietary concentration of the polysaccharides and their accessibility to bacterial degradation within the intestinal tract.

In-vivo inhibition by polycations of small intestinal absorption of methyl alpha-D-glucoside and leucine in the rat.

Polycations are able to inhibit active transport processes in rat small intestine in vitro. Whether this effect can also be confirmed in vivo is the concern of this study. Therefore, the effect of various polycations, e.g., protamine and polylysine, on the absorption of methyl alpha-D-glucoside and leucine was investigated in vivo by single-pass perfusion of rat jejunum. The inhibition of absorption of methyl alpha-D-glucoside and leucine by the polycations was strongly dose dependent. At a substrate concentration of 1 mmol/l a 50% inhibition was achieved with a protamine concentration of 3.2 mg/ml. The inhibition increased as the chain length of the polycation increased. In the presence of protamine the concentration-dependent leucine absorption was reduced at leucine concentrations below 60 mmol/l, but was increased at 100 mmol/l. Absorption of mannitol and 2-deoxy-D-glucose was significantly enhanced by the polycations. These results demonstrate that polycations inhibit active transport and increase passive diffusion processes in the rat small intestine in vivo. In addition, pretreatment of rats with a polycation added to the drinking water impaired the small intestinal absorption of methyl alpha-D-glucoside as subsequently measured by the tissue accumulation technique in vitro. Since polycations are hardly absorbed in the intestine, but do attach to negatively charged groups at the mucosal surface, polycations may be useful to study the influence of these negative groups on the absorption of nutrients and drugs.

Active transport inhibition in rat small intestine by amphiphilic amines: an in vitro study with various local anaesthetics.

In the present investigation with rings of everted rat small intestine, amphiphilic amines such as local anaesthetics (e.g. lidocaine, procaine, tolycaine) were employed to study their effects on intestinal absorption of methyl alpha-D-glucoside, L-leucine, D-fructose, and 2-deoxy-D-glucose. All the amphiphilic amines tested, except for benzocaine, significantly inhibited Na(+)-dependent active uptake of methyl alpha-D-glucoside and L-leucine while leaving uptake of D-fructose (facilitated diffusion) and 2-deoxy-D-glucose (passive diffusion) unaffected. Increasing concentrations of lidocaine in the incubation medium inhibited the uptake of methyl alpha-D-glucoside (IC(50) approximately 3.5 mmol/L) and L-leucine (IC(50) approximately 6 mmol/L) in a dose-dependent manner. Complete reversibility of the inhibitory effect could only be achieved at short-term incubations (

Comparison of the effect of two different hypoglycemic agents, glibenclamide and HB 699, on the rat small intestinal absorption of sugars and amino acids.

4-(2-[5-Chloro-2-methoxy-benzamido]-ethyl)-benzoic acid (HB 699) belongs to the group of hypoglycemic benzoic acid derivatives. Although lacking the sulfonylurea group, the structure of HB 699 partly resembles that of glibenclamide which is known to impair small-intestinal glucose absorption in vitro at high concentrations. Whereas this intestinal effect of glibenclamide is unlikely to contribute to its blood-glucose lowering properties, extrapancreatic and particularly intestinal effects may be important for the antidiabetic action of HB 699. Thus, HB 699 was compared with glibenclamide for the effect on the small-intestinal absorption of sugars and amino acids in vitro (everted-sac and tissue-accumulation technique) and in vivo (single-pass perfusion of the jejunum). In vitro both drugs inhibited the active transport of sugars and amino acids in a dose dependent manner. At equieffective doses (HB 699, 4.5 mmol/l and glibenclamide, 1 mmol/l) the mode of inhibition by the two drugs was similar. A 30-min incubation period reduced the uptake of methyl alpha-D-glucoside by about 75%. The degree of inhibition depended on the time of exposure of the tissue to the drugs. In vitro kinetic studies revealed a mixed type of inhibition. The in vivo effect of the drugs was in accordance with the in vitro findings. Inhibition, as in vitro, was not reversible and even increased further after reinfusion of a drug-free perfusate. In vivo, the drugs inhibited the absorption of methyl alpha-D-glucoside and leucine only at low (less than 20 mmol/l) but not at high (greater than 30 mmol/l) solute concentrations. These results indicate that hypoglycemic benzoic acid derivatives may exert their blood-glucose lowering properties in part by impairing the small-intestinal active transport of glucose.

109Cd accumulation in the calcified parts of rat bones.

A recent epidemiological study showed an increased risk for bone fractures after chronic low-level cadmium exposure. This finding agrees with those of cadmium accumulation in rat bones after chronic oral exposure which reduced the mechanical strength of the bones. There are indications that ossicular cadmium uptake may be higher during growth and may contribute over proportion to life long cadmium accumulation in the skeleton. The present study investigates this hypothesis in 59 male Sprague-Dawley rats. 109Cd distribution showed no differences after intravenous (i.v.) administration of different doses (0.02-2.00 micromol 109Cd/kg body weight) and at different time points after injection (3 and 10 days). Iron-deficiency had no impact on 109Cd distribution, neither during growth nor in adult animals. Age, however, showed an impact on cadmium distribution. Hepatic 109Cd accumulation was significantly higher in adult rats while 109Cd distribution in the bones as well as 109Cd concentration in cortical and trabecular bone tissue was significantly higher during growth. No difference in 109Cd uptake was found between femur epiphysis and diaphysis after one-dose i.v. application, which is in contrast to earlier results after chronic oral cadmium administration to rats. This difference may be explained by a different saturation for cadmium uptake in these two bone sections. Cadmium exposure during growth, thus, seems to contribute considerably to cumulative ossicular cadmium accumulation over a lifetime and possibly to cadmium-derived bone fragility in advanced age.

Use of gamma-spectrometry for simultaneous determination of 210Pb, 73As, 109Cd, 203Hg and 59Fe distribution and excretion in rats at low doses.

gamma-Spectrometry permits the identification and quantification of different gamma-isotopes in the same aliquot. To estimate the sensitivity and discriminative power of a comparably small and inexpensive 8% germanium detector, we determined the detection limits for simultaneously applied 210Pb, 73As, 109Cd, 203Hg and 59Fe. The concentration of Fe and of each of the four potential environmental contaminants was determined in aliquots from all organs and tissues 10 days after simultaneous i.v. administration (2 micromol/kg body weight) to adult and growing iron-deficient and iron-adequate rats. Relating these values to the total size of each organ permitted to derive a whole body distribution pattern for all five isotopes in each individual animal. Cumulative renal and faecal excretion values were determined during the 10 day distribution period to calculate the half-lives for both excretory pathways for all five isotopes simultaneously. Distribution and excretion values corresponded well to literature data. Extrapolation of the results showed that the detector would be sensitive enough to discriminate and quantify the five metals at human dietary exposure levels. The results recommend to use gamma-spectrometry to investigate kinetic aspects of interactions between toxic and essential trace metals, because the method reduces the number of required animals drastically.

Different behaviour of 63Ni and 59Fe during absorption in iron-deficient and iron-adequate jejunal rat segments ex vivo.

Nickel exhibits low oral toxicity. It shares the absorptive pathways for iron, though there are substantial quantitative differences in handling of both metals. To analyse these differences more closely, jejunal segments from iron-deficient and iron-adequate rats were luminally perfused ex vivo with 59Fe and 63Ni at six different concentrations (1-500 micromo1/l) under steady state conditions. 59Fe over-all absorption increased 2.0-4.6-fold in iron-deficiency at luminal concentrations between 1 and 100 micromol/l, while 63Ni absorption increased to a much lower extent (2.6-fold at 1 micromol/l and 1.5-fold at higher luminal concentrations). Moreover, there was a 5-7-fold higher concentration for 63Ni in the jejunal tissue than in the absorbate at luminal concentrations above 50 micromol/l which was not observed at 1 micromol 63Ni/l and not for 59Fe. 63Ni tissue load showed a linear and a saturable fraction. In iron-deficiency the saturable 63Ni fraction increased 4-fold as compared to only 1.5-fold increments for 59Fe. Moreover, a substantially higher share of 63Ni was retained in the jejunal tissue at high as compare to low luminal concentrations after perfusion had been continued without luminal radioactivity. This was not found for 59Fe and suggests a concentration-dependent block of 63Ni export across the enterocytes' basolateral membrane. To explain these results one may speculate that 63Ni may bind more tightly to tissue ligands than 59Fe due to the higher thermodynamic and kinetic stability of nickel complexes. In particular, nickel may bind to a basolateral population of metal carriers and block its own basolateral transfer in a concentration-dependent manner. Tight 63Ni binding to non-specific jejunal ligands is responsible for the unaltered high linear fraction of jejunal 63Ni load in iron-deficient and iron-adequate segments. Binding of 63Ni to food and tissue ligands in the small intestine may, thus, be a likely explanation for the low oral nickel toxicity.

Iron supplementation.

Iron deficiency affects approx. 20% of the world population. Due to predominantly vegetarian diets that reduce the bioavailability of food iron drastically, deficiency states are most widely distributed in developing countries. In addition, iron demand is increased by blood losses and by fast growth which increases the risk of iron deficiency in infants, young adolescents, and in menstruating and pregnant women. The symptoms of iron deficiency include impaired physical and intellectual performance. Iron supplementation may help to break the vicious cycle between inadequate nutrition and poverty. Fortification programs have to consider social and health aspects, including provision against iron overload. Excess iron stores may promote cancer and increase the cardiovascular risk, though the latter is a subject of current debate. The best approach to control such risks is individual iron supplementation geared to the demand by adequate laboratory controls. However, this approach is too costly for general application in developing countries. Food-iron fortification has successfully reduced iron deficiency in many trials and, in comparison, is much cheaper. As iron deficiency is widely distributed in most developing countries, the risk of inducing iron overload in the general population is low. Genetically determined diseases that may lead to siderosis, such as hereditary haemochromatosis or thalassaemia major, show a limited geographic and ethnic distribution. Such subgroups can be largely avoided by targeting food-iron fortification to infants, young adolescents, or pregnant women. Food vehicle and iron compound have to be matched in order to optimise iron bioavailability and to avoid rancidity in food, spoiling its taste and odour. The fortification of salt, sugar and spice mixtures or of bakery products with a short shelf-life are valid approaches to this end. Alternatively, haem iron can be used to fortify cereal-based food staples in developing countries such as tortillas or chappaties. Thus, a variety of options is available to solve the technical problems of food iron fortification. However, optimal solutions have to be tailored to the individual situation in each country.

Time course of arsenite-induced copper accumulation in rat kidney.

Oral administration of inorganic arsenic has been shown to lead to an accumulation of copper in the kidneys of rats and guinea pigs. However, nothing is known about the characteristics and mechanisms of this organ-specific renal copper accumulation. Many heavy metals accumulate in the kidney, either after environmental or occupational exposure. An additional accumulation of any other trace metals, even essential ones, may therefore be critical for that organ. This prompted us to follow the course of the renal copper accumulation. Rats were given daily subcutaneous doses of sodium arsenite for 12 d. Each second day, three rats were killed by exsanguination and the liver, kidneys, and blood removed and analysed for As, Cu, and other trace elements by atomic emission spectrometry. Results indicate that arsenic and copper accumulate in the kidney cortex synchroneously over time. Arsenic also accumulated in the liver and red blood cells (RBC). Copper levels in the RBC and liver as well as copper excretion into the urine were unaffected. After terminating arsenite administration, there was a slow decline in tissue levels of both arsenic and copper, a phenomenon which was parallel for both metals. Because the copper level in the liver was not affected, it is concluded from this study that renal processes and not hepatic or biliary mechanisms might be responsible for the renal copper accumulation. Furthermore, the strong linear correlation (r = 0.85) between arsenic and copper levels in the kidney during and after arsenite administration suggests a functional relationship between arsenic and copper with respect to their retention in the kidney.

Oral and subcutaneous administration of cadmium chloride and the distribution of metallothionein and cadmium along the villus-crypt axis in rat jejunum.

The route of Cd uptake influences the distribution of Cd, other metals, and metallothionein (MT). Although intestinal MT levels related to the tissue mass did not show proximodistal gradients after sc administration of CdCl2, orally administered high doses of CdCl2 increased mucosal MT levels longitudinally from the duodenum to the ileum. The gradient abolished when the mucosal MT level was related to the intestinal length. To further elucidate this finding, three groups of rats were studied: a control group, a group receiving dietary CdCl2, and a group receiving sc injections of CdCl2. The small intestine was removed after a 14-d treatment. Midjejunal segments were mounted in a cryomicrotome and cut transversally into five layers along the villus-crypt axis. Mucosal enzymes were measured to control these sections. Cd was measured by AAS and MT by RIA. Alkaline phosphatase and lactase activities exhibited the typical villus-crypt gradient. Mucosal MT levels paralleled those of Cd. Although Cd and MT concentrations were high at the tip of the villi and low in the crypts after oral administration, sc treatment reversed that profile. A molar Cd-MT ratio of approx 10 or 1 was reached after po or sc treatment, respectively. This demonstrates that only oral Cd may lead to an accumulation of Cd in the mucosal tissue fairly exceeding the binding capacity of small intestinal MT. The results show that different routes of Cd intake lead to a different MT-induction pattern in the intestinal wall and that longitudinal Cd and MT concentration gradients in the small intestine observed after high oral doses are a result of their high levels at the villus tips.

The longitudinal distribution of cadmium, zinc, copper, iron, and metallothionein in the small-intestinal mucosa of rats after administration of cadmium chloride.

Different routes of Cd intake may influence the intestinal distribution of Cd, metallothionein (MT), and trace metals differently. Therefore, we compared the effects of parenteral and enteral administration of Cd on the distribution of trace metals and MT along the small intestine. In a first experiment three groups of rats were employed: a control, one receiving CdCl2 within the drinking water, and another receiving sc injections of CdCl2. In a second experiment, rats were fed three different diets with either 0, 0.3, or 1 mmol CdCl2/kg for one and two weeks to study the time- and dose-dependent effects of orally administered Cd. Metal concentrations (Cd, Zn, Cu, Fe) were measured by atomic emission spectrometry and MT was determined by radioimmunoassay. Intestinal MT levels did not show proximodistal gradients in controls or after sc administration of Cd, but orally administered Cd increased mucosal MT levels longitudinally from the duodenum to the ileum. Cd levels paralleled those of MT. Compared with the metal concentrations in the controls, sc administration of Cd did not change intestinal Zn, Cu, and Fe levels. Oral administration of Cd, however, increased Cu and decreased Fe levels in the intestinal mucosa significantly. The second experiment revealed that only high dietary concentrations of Cd increase intestinal Cd and MT levels longitudinally toward the distal parts, whereas at lower dietary concentration the longitudinal distribution was reversed. This shows that different routes and doses of Cd intake lead to a different trace metal and MT distribution and emphasizes the role of dietary Cd in the local induction of small-intestinal MT.

Arsenic-copper interaction in the kidney of the rat.

1. The interaction between As and three toxic metals (Cd, Ni and Pb) and Cu (an essential trace metal) in the kidney was investigated in the rat by feeding diets containing various concentrations of As whilst maintaining constant concentrations of the other elements. After 1, 3, 7 and 15 weeks of feeding, metal contents in the renal cortex and medulla, red blood cells and plasma were determined by atomic emission spectrometry (ICP-AES). 2. As accumulated in the whole kidney, whereas Cu accumulated only in the cortex. Accumulation of Cu was found to depend on the feeding period and dietary As concentration. 3. As was also accumulated in red blood cells, where saturation was found at 550 micrograms As g-1 cells. 4. Although Cd was also accumulated in the cortex, its accumulation was independent of the dietary As concentration. Ni and Pb were not detected by ICP-AES. 5. Chromatography of the supernatants from cortical homogenates of control and As-treated rat kidney suggested that Cu accumulated in renal metallothionein (MT). Its accumulation in this fraction was independent of that of Cd, indicating that the As-Cu interaction was not a result of MT induction, but rather that it might result from altered renal handling of Cu with subsequent incorporation into MT.

Small-intestinal absorption of cadmium and the significance of mucosal metallothionein.

1 Although food intake is among the most important routes of Cd exposure, not many details are known about the intestinal absorption mechanisms of Cd. In this respect Cd is representative of most other nonessential, merely toxic metals. 2 Based on a concept of two distinguishable steps, intestinal absorption of Cd is characterized by high accumulation within the intestinal mucosa and a low rate of diffusive transfer into the organism. 3 After uptake into the mammalian organism, Cd is sequestered into hepatic metallothionein (MT). It is assumed that hepatic Cd-MT then gradually redistributes Cd to the kidney, which is the main target organ for chronic Cd toxicity. 4 When feeding low levels of dietary CdCl2, however, Cd accumulates preferentially in the kidney and to a lesser degree in the liver, a distribution pattern also found after intravenous and peroral administration of the Cd-MT complex itself. As dietary Cd induces intestinal MT, intestinal Cd-MT complexes could be at least partly responsible for the renal accumulation of dietary Cd. 5 For this mechanism, however, serosal release of mucosal Cd-MT is required. In fact, in vitro findings in rats reveal a concentration-dependent release of intestinal MT to the serosal side of the small intestine. These results indicate that endogenous intestinal MT may deliver Cd-MT to other inner organs, thus contributing to the preferential renal accumulation of ingested Cd.

Species differences in arsenic-mediated renal copper accumulation: a comparison between rats, mice and guinea pigs.

1. Administration of arsenite leads to an accumulation of copper in the rat kidney. Owing to the high retention of arsenic in the erythrocytes, however, the rat is considered to possess special toxicokinetics of arsenic and is therefore considered less comparable with other species in this respect. 2. Therefore, we compared the effect of dietary arsenite in mice and guinea pigs with that in rats. Each species was divided into four groups of animals according to the diets fed which contained increasing concentrations of sodium arsenite (NaAsO2; 0, 10, 30 and 60 mg As/kg of diet). Animals were killed after 1, 2 and 3 weeks. Tissues were sampled and analyzed for arsenic and other trace metals (Cu, Fe, Zn and Mn). 3. Compared to controls with copper levels of about 10 microg Cu/g wet wt. in the renal cortex, dietary administration of arsenite up to 60 mg As/kg of diet for 3 weeks to rats increased cortical levels to 65 microg Cu/g wet wt. An increase of renal copper levels similar to that in rats, was only observed in guinea pigs but not in mice. Renal copper accumulation in guinea pigs was time- and concentration-dependent as in rats. Feeding a diet with 60 mg As/kg for 3 weeks increased cortical copper levels from about 6 - 40 microg Cu/g wet wt. Renal copper levels in mice as well as other trace metal levels in guinea pigs and mice were not essentially altered by dietary arsenite. 4. The study shows that the renal copper-arsenic interaction is not restricted to the rat. Since in rats and guinea pigs, but not in mice, arsenic accumulated in the kidney rather similarly, a common mechanism is suggestive. As it was previously shown in rats that only inorganic arsenic is involved in this interaction, a rapid conversion of the inorganic form into methylated metabolites as in mice may diminish the extent of the renal copper accumulation whereas the lack of, or a less efficient, methylation as in guinea pigs or rats increases it.

Small-intestinal transfer mechanism of prunasin, the primary metabolite of the cyanogenic glycoside amygdalin.

1. The small-intestinal transfer of prunasin (D-mandelo-nitrile-beta-D-glucoside), the primary metabolite of amygdalin which is not absorbed in the small intestine as such, was studied in rat jejunum and ileum in vitro. 2. As shown by high pressure liquid chromatography, prunasin is transferred essentially intact across the intestinal wall, without cleavage of the glycosidic bond and thus no formation of benzaldehyde or cyanide during the mucosal passage. 3. Only the jejunal transfer of prunasin followed saturation kinetics (vmax = 1.6 mumol cm-1 min-1; KT = 460 mumol l-1) and exhibited a clearsodium-ion dependence. As indicated by the temperature dependence, only the jejunal mucosa-to-serosa transfer and the corresponding tissue uptake of prunasin required apparently high activation energies. Transfer in the terminal ileum showed diffusion characteristics. 4. Jejunal methyl alpha-D-glucoside transfer was inhibited by the presence of prunasin. Furthermore, the tissue uptake of methyl alpha-D-glucoside in rat jejunum was competitively inhibited by prunasin. 5. The results indicate that prunasin is absorbed unmetabolised in the jejunum of the rat via the transport system of glucose.

Adaptation of the small intestine to induced maldigestion in rats. Experimental pancreatic atrophy and acarbose feeding.

Intestinal adaptation has been studied in rats with pancreatic atrophy induced by feeding a copper-deficient diet and penicillamine and in rats with carbohydrate maldigestion induced by feeding of an alpha-glucosidase inhibitor (acarbose). Pancreatic atrophy led to a significant increase of weight, protein, and DNA content as well as specific activities and total amounts of the enzymes sucrase and maltase in the distal but not in the proximal part of the small intestine. Plasma levels of CCK and GIP were significantly higher in rats with pancreatic atrophy, whereas plasma levels of gastrin and insulin were lower. Tissue concentrations of gastrin in the antrum and GIP in duodenum and jejunum were unchanged. Duodenal CCK and jejunal substance P, somatostatin, and VIP and ileal substance P and somatostatin were significantly decreased in rats with acinar atrophy. Glucosidase inhibition by acarbose feeding led to weight increase of the small intestine and cecum. This was more marked when acarbose was fed together with a fiber-free diet. Under these conditions the protein and DNA content also increased significantly in both gut segments and maltase and sucrase content predominantly in the distal part. Insulin plasma concentration decreased significantly in the acarbose-fed groups, whereas GIP, gastrin, and CCK plasma concentrations remained unchanged. After fiber-rich diet tissue concentrations of gastrin in the antrum and insulin in the pancreas were significantly higher and GIP concentrations in the duodenum and jejunum significantly lower than after fiber-free diet. Acarbose increased the pancreatic insulin concentration only in the fiber-free group and did not influence gastrin and GIP concentrations.(ABSTRACT TRUNCATED AT 250 WORDS)