Cell differentiation and L-ornithine decarboxylase activity in the small intestine of rats fed low and high protein diets

Ornithine decarboxylase activity in muscle, liver, and intestinal tissue of turkeys during a short-term feed withdrawal and following refeeding

The activity of ornithine decarboxylase (ODC), an enzyme associated with cellular growth and protein synthesis, was examined in breast muscle, liver, and intestinal tissues of turkeys during a short-term period of feed withdrawal (FW) and following refeeding. Turkeys from a randombred control line were reared under standard management practices to 3 wk of age in battery brooders. Feed was then withdrawn from FW birds for a 48-h period, after which feed was consumed ad libitum. Control birds consumed feed ad libitum throughout the test period. Tissues were collected from 12 birds per treatment following 24 and 48 h of FW and at 6, 12, 24, and 48 h following refeeding for later determination of tissue ODC activity. Activity of ODC was greater in tissue from the small intestine than in liver tissue and both had greater activity than that exhibited by breast muscle. Short-term FW and refeeding produced differential responses in ODC activity of the three tissues examined. Feed withdrawal resulted in a reduction of ODC activity in intestinal tissue, whereas activity was unaffected for liver or breast muscle tissues. Compensatory increases in ODC activity were observed in liver and intestinal tissues; however, the increase was both more rapid and transitory in small intestine than in liver tissue. The ODC activity in breast muscle was largely unaffected by short-term FW and refeeding. Patterns of ODC activity in liver during FW and refeeding closely resembled patterns observed for absolute and relative liver weight. Thus, the results of the present experiment demonstrate that short-term FW and refeeding influence underlying growth mechanisms of supply organs, such as hepatic and intestinal tissue, in addition to affecting overall growth and muscle development.

Activation of intestinal mitochondrial phospholipase D by polyamines and monoamines

Intestinal mitochondria have a phospholipase D (PLD) activity which was stimulated by polyamines and monoamines resulting in the formation of phosphatidic acid (PA) from endogenous phospholipids. When stimulated by polyamines, mitochondrial PLD utilized endogenous phosphatidylethanolamine (PE) as substrate whereas stimulated by monoamines, both PE and phosphatidylcholine (PC) were hydrolysed. Stimulation of PA formation by spermine was enhanced by the presence of calcium. Since polyamines are known to alter the calcium transport by mitochondria and PA is known to possess an ionophore effect, stimulation of PA formation in mitochondria by polyamines suggests that polyamine-induced alteration in calcium homeostasis might involve a PA related mechanism.

Immunocytochemical localization of polyamines in the gastrointestinal tracts of rats and mice

An immunocytochemical method using a recently produced monoclonal antibody (ASPM-29) with an antibody specificity to spermine (Spm) and spermidine (Spd) fixed in situ, was used to demonstrate an immunocytochemical localization of polyamine (PA) pools in the gastrointestinal tracts of rats and mice. High PA immunoreactivity was always found in the cytoplasm of cells not only at the cell proliferative zone or the precursor cell zone but also at the neighboring non-proliferative premature cell zone of the epithelium, and a gradient of decreasing PA levels was noticed from these cells to the fully mature differentiated gastric surface mucous cells and absorptive cells of the small and large intestines. Also, strong staining for PAs was seen in the cytoplasm of fully differentiated gastric chief cells and neurons of both the myenteric and submucous plexuses, whereas the nuclei of the cells remained virtually unstained. These results may suggest that PAs are closely associated with the high biosynthetic activity in the cells of the gastrointestinal mucosa of normal rats and mice. This seems to be consistent with the PA immunocytochemical results previously obtained for neoplastic cells and active protein- or peptide-secreting cells, including exocrine or endocrine cell types.

Peroxisomes and peroxisomal enzymes along the crypt-villus axis of the rat intestine

The development of peroxisomes and expression of their enzymes were investigated in differentiating intestinal epithelial cells during their migration along the crypt-villus axis. Sequential cell populations harvested by a low-temperature method were identified by microscopy, determination of alkaline phosphatase and sucrase activities and incorporation of [3H]-thymidine into DNA. Ultrastructural cytochemistry after staining for catalase activity, revealed the presence of peroxisomes in undifferentiated stem cells located in the crypt region. Morphometry indicated that the number of these organelles increased as intestinal epithelial cells differentiate. Catalase activity was higher in the crypt cells than in the mature enterocytes harvested from villus tips. On the other hand, an increasing gradient of activity was observed from crypts to villus tips for peroxisomal oxidases, i.e. fatty acyl coA oxidase, D-amino acid oxidase and polyamine oxidase. These findings indicate that biogenesis of peroxisomes occurs during migration of intestinal epithelial cells along the crypt-villus axis and that peroxisomal oxidases contribute substantially to the biochemical maturation of enterocytes.

Polyamine metabolism in enterocytes isolated from newborn pigs

In the pig, the growth of intestinal mucosa is very intense after birth. Since the polyamines are key elements affecting cell proliferation and differentiation, the present work was undertaken in order to know whether this hypertrophy is associated with an adaptation of polyamine metabolism. Villus enterocytes isolated from pig immediately after birth or 2 days later were found to contain similar amounts of putrescine, spermidine and spermine, i.e., 0.23; 0.41 and 1.24 nmol/10(6) cells, respectively. At birth, despite a relatively high ODC activity, putrescine synthesis from 1 mM L-arginine or 2 mM L-glutamine was very low in isolated enterocytes (6.4 +/- 3.8 pmol/10(6) cells per 30 min), while spermidine and spermine production were not detectable. This could be explained by a very low L-ornithine generation from both amino acids and to an inhibitory effect of polyamines on ODC activity. Two days later, polyamine synthesis from L-arginine remained undetectable despite a higher L-ornithine generation. This was concomitant with a dramatic fall in ODC activity. At both stages, enterocytes were able to take up polyamines from the extracellular medium in a temperature-dependent manner. It is concluded that de-novo synthesis of polyamines from L-arginine or L-glutamine does not play a significant role in the control of polyamine content of pig enterocytes during the postnatal period. In contrast, polyamine uptake by enterocytes would contribute to maintain a steady-state polyamine content during this period.

Protein oxidation associated with aging is reduced by dietary restriction of protein or calories

The accumulation of unrepaired oxidative damage products may be a major factor in cellular aging. Both oxidative lesions in DNA and oxidatively damaged proteins have been shown to accumulate during aging. The accumulation of oxidized proteins in Fischer 344 rats was compared for animals consuming protein-restricted and calorically restricted diets--both of which have been shown to extend lifespan. Rats were fed diets restricted in either protein (5% or 10% of the diet as compared with the normal 20% casein), or calories (25% or 40% less than normal), or total diet (40% less than normal). In addition, some of the rats fed a diet providing 5% or 20% protein were irradiated twice weekly (125 rads per exposure; 1 rad = 0.01 Gy). The level of oxidative damage to proteins (protein carbonyls) was determined in rats sacrificed at various times. The oxidative damage to proteins increased with aging and with radiation. Either protein or calorie restriction markedly inhibited the accumulation of oxidatively damaged proteins. Protein restriction reduced the accumulation of oxidatively damaged proteins during the oxidative stress of chronic irradiation.

Adaptive response of ileal mucosa to malnutrition in the rat: role of polyamines

Mucosal disaccharidases and ornithine decarboxylase activities were measured in malnourished, preweaning (19 days), post weaning (24 days) and young adult (37 days) rats. Malnutrition resulted in decreased body weight, intestinal weight, DNA and protein content. Mucosal Prot/DNA ratios were elevated in the ileal segments of the 24 and 37 day rats. Preweaned malnourished rats had significantly enhanced lactase specific activity in both jejunal and ileal segments. Adult malnourished rats showed enhanced jejunal lactase and sucrase activities which were not accompanied by elevated ornithine decarboxylase values. Mucosal sucrase and ornithine decarboxylase specific activities were significantly elevated in the ileal segment of the 24 and 37 day old malnourished rats. Studies of adult rats showed that these increased specific activities were located in the mature enterocytes at the villus tip, and persisted during a 24 h diurnal cycle. DFMO administration for 4 days completely inhibited mucosal ornithine decarboxylase and abolished the rise of ileal sucrase activity. We concluded that the intestinal response to reduced food intake is age related and differs in the jejunum and ileum: ornithine decarboxylase and polyamines are involved in ileal adaptation to malnutrition in postweaned and adult rats.

Subcellular localization of recently-absorbed iron in mouse duodenal enterocytes: identification of a basolateral membrane iron-binding site

The subcellular distribution of newly absorbed iron in isolated mouse duodenal enterocytes was investigated by analytical subcellular fractionation using sucrose density gradient centifugation. Two major peaks of mucosal 59Fe activity were observed: one soluble and one particulate (density 1.18-1.20 g ml-1). The latter was increased following prior exposure of animals to chronic hypoxia. The particulate 59Fe was localized to the basolateral membranes using the marker enzyme Na+, K+ activated, Mg2+ dependent, ATPase and by washing intact enterocytes with the selective plasma membrane perturbant digitonin. The basolateral membrane can be selectively labelled by in vitro incubation of intact enterocytes at 0 degrees C with 59Fe(III)-nitrilotriacetate complex, confirming the presence of a 59Fe binding site on this membrane. No significant difference in in vitro iron binding to this site was observed between normal and chronically hypoxic animals. Iron binding to the basolateral membrane was significantly higher in disrupted, compared to intact enterocytes, indicating that this site is present on both sides of the basolateral membrane. It is therefore suggested that the increased labelling of this site in hypoxia, in vivo, is a consequence of an increase in a mucosal Fe pool which is available for binding to a membrane receptor.

Effects of dietary amines on the small intestine in calves fed soybean protein

An experiment was conducted using 16 Holstein male calves from 4 to 21 d of age to compare 1) the effects of an all-milk protein milk replacer (MPR) and a milk replacer with 20% of the protein from soy protein concentrate (SPC) on morphological and enzymic small intestinal variables, and 2) the effects of SPC plus putrescine (SPP) or SPC plus ethylamine (SPE) on intestinal variables. Small intestinal absorption, based on xylose absorption tests, was greater in calves fed MPR than in those fed SPC (P less than 0.01) and was intermediate in SPP- and SPE-fed calves. Small intestinal segments were surgically excised from the proximal and distal jejunum of all calves at 7, 14 and 21 d of age. Villus length tended to be greatest in calves fed MPR, and mitotic index was least in SPC-fed calves (P less than 0.05). Mucosal protein concentration was 46, 41, 44 and 44 micrograms/mg mucosa for calves fed MPR, SPC, SPP and SPE, respectively. The ratio of mucosal protein:RNA was greatest in calves fed MPR, least in those fed SPC at d 7 (P less than 0.01) and d 14 (P less than 0.05), and intermediate in calves fed SPP and SPE. In proximal jejunum, activity of mucosal ornithine decarboxylase (ODC, EC 4.1.1.17; the rate-limiting enzyme in polyamine biosynthesis) in calves fed SPP was less than 50% of that in calves fed MPR, SPC or SPE. The activity of lactase (EC 3.2.1.108) and ODC in distal jejunum was 50% less in calves fed soybean protein than in those fed MPR.(ABSTRACT TRUNCATED AT 250 WORDS)

Stability of enterocytes and certain enzymatic activities in suspensions of cells from the villous tip to the crypt of Lieberkühn of the mouse small intestine

A series of studies in this laboratory have focused on how an indigenous microbiota influences the activities of alkaline phosphatase, phosphodiesterase I, and thymidine kinase in the enterocytes of the upper small intestine of mice. To draw conclusions about the role of the microflora in determining levels of enzymatic activity, we found it necessary to develop a procedure by which cell suspensions could be obtained containing enterocytes isolated sequentially from the villous tip to the crypt of Lieberkühn. The procedure was modified from the one developed for rats by Weiser (J. Biol. Chem. 248:2536-2541, 1973), involved a minimum number of interfering factors (e.g., proteolytic enzymes and mechanical agitation), and worked reproducibly for mice. During development of the procedure, some variables affecting the assays of the enzymes known to be present in enterocytes were also explored. Rods to which were tied everted segments of gut were incubated in a series of tubes containing a solution of EDTA the concentration of which was changed from 1.5 to 5.0 mM, thus giving a greater yield of enterocytes at every step. The cells incubating in the chelating solution were most stable when 0.23 M sucrose was included in the EDTA solutions. Success in assaying enzymatic activities in the cell suspensions depended on (i) how the cells were isolated, (ii) the assay procedure for thymidine kinase, and (iii) whether cellular suspensions or extracts were assayed.

Influence of level of dietary protein on tryptophan-induced promotional activity in induction of gamma-glutamyl transpeptidase-positive foci of rat liver

The influence of varying the dietary protein content on the emergence of gamma-glutamyl transpeptidase (GGT)-positive foci in the livers of male rats fed elevated (2%) L-tryptophan (TRP) after being exposed to a hepatocarcinogen was investigated. Subtotal hepatectomies were performed, and 18 hr later the rats were treated with diethylnitrosamine (30 mg/kg). Ten days later four dietary groups were followed for 10 weeks: (1) control diet containing 21% protein (C); (2) control diet containing 5.3% protein (C-LP); (3) C + TRP; and (4) C-LP + TRP. Rats fed the C-LP diet developed heavier livers but fewer and smaller GGT + foci than did rats fed the C diet. Rats fed elevated TRP diets (C + TRP and C-LP + TRP) developed more and larger GGT + foci than did rats fed the regular control diets (C and C-LP), indicating that the promotional effect of elevated dietary TRP was similar at the two levels of dietary protein.

Biochemical and cytochemical comparison of intestinal bicarbonate-stimulated Mg2+ dependent ATPase and alkaline phosphatase activities in rat, rabbit and guinea pig

Bicarbonate-stimulated Mg2+ dependent ATPase activity was demonstrated both biochemically and cytochemically, in brush border membranes from rat, rabbit and guinea pig duodenum. There was no correlation between enzyme activity and basal HCO3- secretion rates in the different species. The concentration of HCO3- necessary for optimal stimulation of ATPase activity, degree of stimulation and total activity was higher in the rat than in other species. Activity was higher in rat duodenum than in the ileum. This is consistent with the proposed electrogenic HCO3- secretion in the duodenum. Distribution of activities of alkaline phosphatase and HCO3(-)-stimulated Mg2+-ATPase along the duodenal villus showed significant differences, suggesting that the two activities reflect, at least in part, distinct enzymes.

A bovine epithelial membrane protein that binds polymeric immunoglobulin and has a structure related to that of bovine secretory component

A protein of Mr 94000 was isolated from detergent-solubilized bovine intestinal, liver and mammary-gland membranes. It binds immunoglobulin M and also undergoes proteolytic fragmentation in a similar manner to bovine secretory component (Mr 74000). The affinity-purified membrane protein is therefore most likely to be the bovine epithelial receptor for polymeric immunoglobulin. A structural model is proposed.

Rat gastrointestinal transglutaminase: demonstration of enzyme activity and cell and tissue distributions

The properties, tissue and cellular distribution of intestinal transglutaminase have been investigated. Transglutaminase was assayed with dimethylcasein and [14C]putrescine as substrates. The enzyme has maximum activity at pH 10, although more reliable assays are made at pH 9. Transglutaminase showed an absolute requirement for Ca2+ and exhibited linear assay kinetics. The Km for putrescine was approx. 0.15 mmol/l. Tissue distribution studies suggest transglutaminase is more active in the more muscular segments of the gut. The cellular localization in jejunum was investigated by sequential cell release techniques. Approximately 2 per cent of the total activity was found in the enterocytes and crypt cells. Most of the activity was in the submucosa and serosa suggesting an interstitial cell localization. Acute hypoplastic enteropathy induced by methotrexate was accompanied by a striking decrease in mucosal transglutaminase but the activity returned to control values by 72 h. There was no significant increase in activity during the period of intense crypt cell hyperplasia and it is concluded that intestinal transglutaminase is not implicated in crypt cell proliferation.

The distribution of (Na+ + K+)-ATPase along the villus crypt-axis in the rabbit small intestine

The migration of intestinal epithelial cells from the crypts to the tips of villi is associated with progressive cell differentiation. The changes in Na+-pump levels during migration have been measured in epithelial cells isolated from rabbit small intestine. A significant proportion of ouabain-sensitive (Na+ + K+)-ATPase in the cell homogenates was latent but could be unmasked by detergent treatment. Highest detergent activation was observed in villus cells. The distribution of pumping sites was also assessed by measuring ouabain binding to intact cells. The kinetics of specific binding was consistent with the interaction of the cardiac glycoside with a single population of binding sites with an apparent Kd of around 10(-7) M. Both enzyme assay and ouabain-binding measurements suggest that a 2-3-fold increase in the number of Na+-pumping sites accompanies cell differentiation in rabbit jejunal epithelium. This increase in pumping capacity might be an adaptation of the cells to their absorptive function.

Cellular adaptation of amino acid transport following intestinal resection in the rat

1. The ability of rat ileal enterocytes to take up alanine and lysine before and after proximal resection of the small intestine has been assessed using both autoradiographic and dual-isotope methods of analysis. 2. The length of individual villi was approximately doubled after resection. Alanine uptake measured in the presence or absence of Na, represented per cm2 mucosal surface area, decreased following intestinal resection. 3. Alanine and lysine uptake were confined to villus tip enterocytes in both control and ileal remnants. The net effect of intestinal resection was to increase amino acid uptake calculated per individual villus or per unit length of intestine. 4. Adaptational changes occurring as a result of resection included a shortening of the time needed for enterocytes to reach the stage where they first began to absorb amino acids and a doubling of the rate at which absorption increased during the later stages of enterocyte differentiation. 5. It is suggested that the physiological response to intestinal resection can best be appreciated by studying events taking place within individual enterocytes. The way in which adaptational changes become organized within the mucosa remains to be elucidated.