Age-related changes in duodenal adaptation after distal small bowel resection in rat

Two groups of male Fisher 344 rats (young: 4 months old; aged: 25 months old) underwent either 70% distal small bowel resection or sham operation (small bowel transection). Rats from each treatment group of each age were sacrificed on the 10th (N=15: young rats;N=13: aged rats) or 20th (N=15: young;N=13: aged) postoperative day (POD), and the duodenal mucosa was weighed and assayed for DNA, RNA, and protein contents, as well as for specific activities of the disaccharidase, sucrase, maltase, and lactase. Compared to the sham operation, distal small bowel resection significantly increased DNA by 48%, RNA by 122%, and protein by 75% in young rats and DNA by 40%, RNA by 92%, and protein by 71% in aged rats on the 20th POD. Both young and aged rats showed similar adaptive hyperplasia on the 10th POD. On the 20th POD after distal small bowel resection, specific activities of all tested enzymes were significantly increased in young rats (sucrase +86%, maltase +110% and lactase +64%), but showed no significant changes in aged rats. These findings suggest that the duodenum of aged rats may have sufficient proliferative potential to respond to distal small bowel resection, but that the mechanisms governing return of function in response to distal small bowel resection are inhibited in aged rats, compared to those mechanisms in the young.Supported by grants from the National Institutes of Health (5R37 DK15241, P01 DK 35608).     

Age-related changes in polyamine biosynthesis after fasting and refeeding

The effect of aging on ornithine decarboxylase (ODC) activity and polyamine biosynthesis in the proximal small intestine was studied in two groups of male Fisher 344 rats (young [4-month old] and aged [26- to 27-month old]) using a fasting and refeeding model. In control (nonfasted) rats, levels of polyamines (putrescine, spermidine and spermine) and ODC activity were significantly higher in aged compared with young rats. In aged rats, fasting significantly reduced the levels of putrescine by 41%, spermidine by 23%, and spermine by 11%; however, fasting had no effect on polyamine levels in young rats. ODC activity was decreased 75% in young and 50% in aged rats after fasting compared with the respective age-matched controls. Conversely, 2 h after reinstituting a chow diet increased ODC activity by 17-fold in young rats but only 8-fold in aged rats. Putrescine levels were also increased in both age groups after refeeding; however, similar to ODC activity, these increases were much less in aged rats. In addition, spermidine and spermine levels remained significantly depressed in the aged groups even after 24 h of refeeding. These findings suggest that the normal rigid control of gut polyamine biosynthesis and proliferation noted in young rats is markedly altered with aging.     

Pancreatic growth after distal small bowel resection is altered with aging

We have examined age-related changes in the stimulatory effects of distal small bowel resection on the growth of the pancreas and on polyamine biosynthesis. Two groups of male Fischer 344 rats (young; 4-month-old, aged; 25-month-old) underwent either 70% distal small bowel resection or transection of distal small bowel (control). Rats from each treatment group of each age were sacrificed on the 10th or 20th postoperative day (POD), and pancreas was weighed and assayed for DNA, RNA, and protein contents as well as polyamines. We found that young rats with distal small bowel resection exhibited significant increases in pancreatic weight, RNA, protein, putrescine, and spermine contents on the 10th POD, but aged rats that had undergone resection, showed only increased spermine content. On the 20th POD distal small bowel resection increased pancreatic weight, DNA, RNA, and protein as well as spermidine and spermine contents in young rats; aged rats had increased pancreatic weight only. These findings suggest that the trophic responses of the pancreas to distal small bowel resection are altered in aged rats, and that the polyamine biosynthetic pathway appears to be involved in this impaired response.     

Pancreatic growth after distal small bowel resection is altered with aging

We have examined age-related changes in the stimulatory effects of distal small bowel resection on the growth of the pancreas and on polyamine biosynthesis. Two groups of male Fischer 344 rats (young; 4-month-old, aged; 25-month-old) underwent either 70% distal small bowel resection or transection of distal small bowel (control). Rats from each treatment group of each age were sacrificed on the 10th or 20th postoperative day (POD), and pancreas was weighed and assayed for DNA, RNA, and protein contents as well as polyamines. We found that young rats with distal small bowel resection exhibited significant increases in pancreatic weight, RNA, protein, putrescine, and spermine contents on the 10th POD, but aged rats that had undergone resection showed only increased spermine content. On the 20th POD distal small bowel resection increased pancreatic weight, DNA, RNA, and protein as well as spermidine and spermine contents in young rats; aged rats increased pancreatic weight only. These findings suggest that the trophic responses of the pancreas to distal small bowel resection are altered in aged rats, and that the polyamine metabolism might be associated with this impaired response.     

Aging and intestinal polyamine metabolism in the rat

Hyperproliferation and delayed expression of enzyme activity occur in small intestinal enterocytes of aging rats, and starvation and refeeding result in impaired control of these processes. Since altered polyamine metabolism may accompany changes in enterocyte proliferation, we studied the effects of nutrient manipulation upon cell numbers, ornithine decarboxylase (ODC) activity and polyamine content in jejunum and ileum of 4- to 5- and 26- to 27-month Fischer rats. In both groups, cell numbers fell during starvation and and increased during refeeding. Crypt cell hyperplasia was found in aging animals. Jejunal putrescine, spermine and spermidine content were greater in older rats, fell during starvation, and rose during refeeding. Ileal ODC activity was 66% greater in the aging rats, but jejunal ODC activity was modestly increased in young animals. Intestinal polyamine content correlates with proliferative changes and polyamine metabolism responds appropriately to nutrient manipulation during aging. Dissociation of ODC activity and polyamine content in aging jejunum probably occurred because enterocyte differentiation was delayed. Investigation of intestinal polyamine metabolism may be useful in elucidating deranged proliferative activities found in the intestine of aging rodents.     

Polyamine metabolism and cell-cycle-dependent gene expression in IMR-90 human diploid fibroblasts during senescence in culture

Aging of IMR-90 human diploid fibroblasts in culture is accompanied by specific changes of polyamine metabolism including: (a) a fivefold decrease of serum-induced activity of ornithine decarboxylase (ODC¹ EC 4.1.1.17); (b) a six to tenfold increase of polyamine catabolism; and (c) a reduction of putrescine uptake. These changes apparently led to a significant reduction of putrescine accumulation in senescent cells following serum stimulation. Since the induction of ODC is a mid-G₁ event, the change of polyamine metabolism may be related to changes of expression of other cell-cycle-dependent genes during cellular aging. In addition to ODC gene, we have examined the expression of two early G₁ genes, c-erbB and c-myc, and one late G₁/S gene thymidine kinase, at mRNA levels, in both young and old IMR-90 cells. We have also compared the enzyme activities of two late G₁/S genes, thymidine kinase and thymidylate synthetase, in young and old cells following serum stimulation. We did not observe significant changes of c-erbB, c-myc, and ODC mRNA levels during cellular senescence. However, we found that serum-induced mRNA level of thymidine kinase gene in old IMR-90 cells was significantly reduced compared to that in the young cells. Results also demonstrate that aging of IMR-90 cells was accompanied by significant decrease of both thymidine kinase and thymidylate synthetase activities. In view of the recognized importance of polyamines in growth regulation, it is possible that alteration of polyamine metabolism may contribute to the impairment of expression of some key G₁/S genes and such impairment may contribute to the ultimate loss of dividing potential in senescent cells.     

胰高血糖素样肽-2对短肠大鼠残留小肠吸收功能基因表达的影响

目的研究胰高血糖素样肽-2(GLP-2)对短肠大鼠残留小肠钠葡萄糖共同转运体(SGLT1)和二肽转运体(PEPT1)的mRNA表达影响。方法将75%小肠切除大鼠分为空白对照组(空白组)、生长激素对照组(GH组)和胰高血糖素样肽2组(GLP-2组),另设一组正常进食大鼠作空白组的对照组(正常组)。术后1d起进食标准大鼠饲料。术后6d取末端回肠黏膜,用逆转录多聚酶链反应方法半定量检测其SGLT1和PEPT1的mRNA表达情况。结果残留回肠SGLT1和PEPT1的mRNA表达,空白组显著高于正常组(P<0.05),空白组和GH组及GLP2组之间差异均无统计学意义(P>0.05)。结论GLP-2术后短期应用对短肠大鼠残留回肠SGLT1和PEPT1的mRNA表达可能无显著影响。     

Decreased ornithine decarboxylase activity in the kidneys of Dahl salt-sensitive rats.

To assess the roles of polyamines (putrescine, spermidine, and spermine) and ornithine decarboxylase (ODC), the rate-limiting enzyme of polyamine synthesis, in the development of salt-sensitive hypertension, we evaluated activity and expression of ODC, urinary polyamine excretion, and antizyme (endogenous ODC inhibitor protein) expression in Dahl salt-sensitive (SS) and salt-resistant (SR) rats after they were fed on a low (0.3%) or high (4%) salt diet for 4 weeks. We also examined the effects of spermidine and difluoromethylornithine (DFMO: a specific inhibitor of ODC) on the systolic blood pressure and ODC protein expression in SS rats fed a high salt diet. Renal ODC activity and urinary polyamine excretion in SS rats were lower than those in SR rats after 4 weeks treatment with a low or high salt diet. The renal ODC protein expression of SS rats was paradoxically increased as compared to the SR group. A high salt diet did not alter ODC activity but increased ODC protein only in SS rats. ODC mRNA and antizyme protein expressions were not significantly different among the four groups. Spermidine supplementation attenuated and DFMO exaggerated hypertension in SS rats fed a high salt diet. Spermidine down-regulated and DFMO up-regulated renal ODC protein in SS rats on a high salt diet. ODC activity was decreased but protein was paradoxically increased in kidneys of SS rats. ODC protein was suggested to increase in compensation for the inhibition of its activity. Impaired ODC activity and polyamine production in the kidney may exaggerate salt-sensitive hypertension in SS rats.     

The effect of age on small bowel adaptation and growth after proximal enterectomy.

We examined the effect of age on the adaptive capacity of small bowel mucosa following 60% enterectomy. Two groups of male Fischer 344 rats (3 mo old and 26 mo) underwent either a mid-small bowel transection and reanastomosis (control) or 60% proximal enterectomy beginning at the duodenojejunal junction. Rats were sacrificed at 5, 14, and 21 days after operation, and the mucosa was weighed and assayed for DNA, RNA, protein, and polyamine concentration and content. Ornithine decarboxylase activity was also measured in ileal mucosa at 5 days after surgery. Young rats had completed the adaptive hyperplastic response within 2 weeks after operation by all biochemical measurements; similar adaptation was not seen until 3 weeks after operation in the old rats. We conclude that although the capacity to achieve intestinal adaptation after enterectomy is preserved into old age in rats, this compensatory response is delayed.     

Nutrient-independent increases in proglucagon and ornithine decarboxylase messenger RNAs after jejunoileal resection.

To assess potential mediators of adaptive bowel growth, ileal proglucagon messenger RNA (mRNA) ornithine decarboxylase (ODC) mRNA, plasma enteroglucagons, and plasma glucagonlike peptide I (GLP-I) were analyzed in rats soon after jejunoileal resection or control transection. Analyses were performed before and after refeeding to establish whether responses are nutrient dependent. The elevation of ileal proglucagon and ODC mRNAs within 12 hours after resection and before refeeding shows a nutrient-independent component of the adaptive response. The onset of adaptive growth of the ileum required luminal nutrient but occurred very rapidly, within 4 hours of refeeding. The onset of adaptive growth was accompanied by transient elevation of ileal ODC mRNAs. Ileal proglucagon mRNA and plasma GLP-I levels were also elevated, and these increases were sustained up to 8 days after resection. These early and sustained increases in proglucagon mRNA and plasma GLP-I indicate that in addition to the enteroglucagons, other intestinal proglucagon-derived peptides must be considered as potential mediators of adaptive growth after jejunoileal resection.     

Ethanol's Effect on Tissue Polyamines and Ornithine Decarboxylase Activity: A Concise Review

An extraordinarily diverse literature describes the cellular/tissue systems in which the molecular effects of both acute and chronic alcohol exposure seem to be mediated by changes in polyamine levels and/or ornithine decarboxylase (ODC) activity. The single unifying factor that links most of these studies is that they all, in some way, involve tissues that are undergoing relatively rapid cell division. Non-dividing cells expressing the NMDA receptor are a notable exception in that ethanol and the polyamines seem to act via discrete regions of that receptor. Under most cellular conditions, ODC activity is a reflection of the relative tissue polyamine content, and an increase in ODC activity and polyamine content seems to be one of the early events in the progression of quiescent cells toward cell division. Thus, it is not surprising that ethanol, which has been widely reported to delay cell division, should be found to interact with the ODC/ polyamine pathway. Perhaps the most unique aspect of these studies is the fact that, with rare exception, both acute and chronic ethanol exposure have been found to slow growth and to lower tissue polyamine (putrescine) content. Furthermore, in most studies, the ethanol-induced suppression of cell division could be overcome by the administration of exogenous putrescine. These data suggest that the ethanol-induced suppression of cell division resulted from the loss of putrescine. In addition, because the cells were able to respond to the exogenous putrescine, the studies suggest that the signaling pathway remained intact beyond the polyamine synthesis step. Increased ODC activity (and polyamines?) has been reported during the perinatal and postnatal periods in fetal animals exposed to ethanol during early development. Although not examined in all models, the perinatal/postnatal increase in fetal ODC activity may be a compensatory response to an initial loss of ODC activity, as the organism attempted to overcome the alcohol-induced growth suppression.     

Ornithine decarboxylase activity during gastric ulcer healing in dogs

Ornithine decarboxylase (ODC) activity has been associated with mucosal growth and injury, yet, little information is available on ODC activity during gastric ulcer healing. We measured ODC activity in the ulcer base submucosa and the surrounding mucosa at 1 cm and 2 cm and assessed ulcer surface healing and a histologic score in experimentally induced ulcers (Quinton ulcer-maker) at 0 and 5 hr and at one, two, three, four, and seven days. A total of 26 dogs were studied, eight of which received 2% difluoromethylornithine (DFMO, a specific inhibitor of ODC) in drinking water. Ulcer healing was assessed by digitizing initial (plug size), and final ulcer surface area and was expressed as percent ulcer surface reduction. A histologic score was assessed by two independent pathologists unaware of the treatment. ODC induction was observed in the submucosa of the ulcer base but not in the surrounding mucosa. The baseline submucosal ODC activity was measured at 0.2±0.1 pmol (¹⁴CO₂)/mg protein/hr, and at one day the ODC activity increased to 4.0±0.7, at three days to 15.2±5.5, and at seven days to 2.6±1.0 (P<0.001). DFMO treatment delayed GU healing significantly up to three days, but no difference was noted at seven days. The assessed histologic parameters did not correlate with ODC activity, and DFMO treatment did not alter the histologic score. These data suggest that polyamine biosynthesis occurs in the ulcer base submucosa during the first seven days of experimentally placed gastric ulcers. Suppression of ODC activity with DFMO delays ulcer surface reduction during the first three days, but the significance of ODC induction and polyamine biosynthesis during early ulcer healing remains in question.     

Activity and modulation of ornithine decarboxylase and concentrations of polyamines in various tissues of rats as a function of age

The activities of ornithine decarboxylase (ODC) on the soluble and nuclear fractions of the cerebral cortex, heart and lungs of 4- (young), 38- (adult) and 85-week (old) male rats were studied. Also, the effects of aminophylline, histamine and estradiol on the activity of soluble ODC have been determined in vitro using slices of these tissues. The activity of ODC is significantly higher in the soluble fraction of all the tissues in comparison to that of nuclear fraction. Its activity in both the fractions is highest in the immature and decreases with increasing age in all the tissues except in the nuclear fraction of the lungs in which it increases with age. The ODC of the heart, lungs and cerebral cortex appear to be different as seen from the differences in their sensitivities to aminophylline, histamine and estradiol. In general, there is a decrease in its sensitivity to the three effectors with increasing age. This may be due to a decrease in the receptors and a concomitant decrease in ODC activity. A direct relationship between ODC activity and polyamine levels of the brain exists at various ages of the rat.     

Acute hypoxia increases ornithine decarboxylase activity and polyamine concentrations in fetal rat brain.

The cellular responses to hypoxia are poorly understood. To test the hypothesis that ornithine decarboxylase (ODC; L-ornithine carboxy-lyase; EC 4.1.1.17) activity and polyamine concentrations change in response to acute hypoxia, we performed the following studies. Pregnant Sprague-Dawley rats inspired various O2 concentrations (9-21%) for various time periods (0.5-48 h) from days 15 to 21 of gestation. In fetal brains we measured the activity of ODC, ODC mRNA, and polyamines. In response to 4-h acute mild hypoxia, ODC activity in fetal rat brain (cerebrum, cerebellum, and hippocampus) increased to 330-450% from control values (P < 0.001), after which it declined to control levels in 6-8 h. The 4-h ODC response varied inversely with inspired O2 concentration and was not mimicked by beta 2 agonist or blocked by beta 2-antagonist administration. The ODC response was associated with an increase in fetal brain putrescine concentration to 190% above control at 4-6 h (P < 0.01) and an increase in the polyamines spermidine and spermine to about 115% above control at 6-8 h. We also observed that ODC mRNA increased significantly after 2-4 h of hypoxia. ODC activity and polyamine concentrations appear to be useful enzymatic markers for fetal brain hypoxia. The magnitude and time course of the acute hypoxic ODC increase were similar to responses to extracellular signals that result in differentiation or cell growth. Thus, the well-defined and regulated ODC activity response may represent a protective mechanism in brain to hypoxia.     

Dietary lipids alter the effect of steroids on the uptake of lipids following intestinal resection in rats

Steroids alter the transport function of the intestine. This study was undertaken to assess the effect of glucocorticosteroids on lipid uptake in rats fed either a saturated (SFA) or a polyunsaturated fatty acid (PUFA) diet. Sprague-Dawley rats underwent transection or 50% resection of the small intestine. The steroids had no effect on the uptake of lipids. However, resection decreased the jejunal uptake of palmitic acid in animals fed SFA and increased the jejunal uptake of palmitic and linoleic acids in those fed PUFA. In animals undergoing intestinal resection, fed SFA, and given control vehicle, there was a reduction in jejunal proglucagon mRNA expression as compared to those fed chow or PUFA. Ornithine decarboxylase (ODC) mRNA expression in the jejunum of resected animals was reduced. In summary, dietary lipids modify the uptake of lipids in resected animals and ODC and proglucagon may be involved in this adaptive response.     

Chronic Lipid Hydroperoxide Stress Suppresses Mucosal Proliferation in Rat Intestine: Potentiation of Ornithine Decarboxylase Activity by Epidermal Growth Factor

We recently demonstrated that chronic exposure of rat intestine to sublethal levels of peroxidized lipids suppresses ornithine decarboxylase (ODC) activity, consistent with attenuated intestinal proliferation. The current study was designed to better understand the influence of exogenous epidermal growth factor (EGF) on intestinal proliferation in normal intestine and intestine that was challenged by oxidative stress induced by dietary consumption of peroxidized lipids. Male Sprague-Dawley rats (250-300 g) were fed standard chow (control) or peroxidized lipid chow for 4 weeks. EGF was injected intraperitoneally at a dose of 40 microg/kg. Intestinal proliferation was evaluated by ODC activity in fed or fasted states and at specified times during the circadian phase. Chronic peroxide consumption significantly attenuated ODC activities in association with increased tissue peroxide content. The suppressed ODC activities were restored to control values by EGF in the small intestine; in the colon, EGF increased ODC activity threefold over control rats given EGF. This elevated colonic ODC activity was correlated with decreased tissue GSSG and an increased GSH/GSSG ratio. These results show that EGF administration reverses the suppression of intestinal ODC activities induced by chronic peroxidized lipid intake. In contrast, EGF significantly elevates proliferative activity in the peroxide-stressed colon. This exaggerated proliferation may contribute to a better understanding of colonic susceptibility to oxidant-induced malignant transformation.     

Sex difference in gene expressions of cholecystokinin (CCK) and CCK receptor in young and old rats

The gene expressions of cholecystokinin (CCK) in the proximal small intestinal mucosa and CCK-A receptor in the pancreas were examined in male and female young (4-8 months old) and old (26-29 months old) rats. Their concentrations of CCK in the intestine were also compared. In males, but not in females, the mRNA levels of CCK in the intestine and those of the CCK-A receptor in the pancreas were significantly lower in old than young rats. In females, but not in males, the tissue content of CCK in the proximal intestinal mucosa was significantly higher in old rats. The pancreatic wet weight and trypsin activity in the proximal lumen were similar in young and old rats of both sexes. Therefore, changes in the regulations of gene expressions of CCK and the CCK receptor with age differ in male and female rats.     

The aging gut motility decay: may symbiotics be acting as "implantable" biologic pace-makers?

Motility recording of small and large intestine was performed in old Wistar rats divided into three groups: (a) standard diet, (b) standard diet plus a symbiotic preparation, and (c) standard diet plus a heat-inactivated symbiotic preparation. SCM-III. significantly increased the myoelectric activity of small intestine and colon (p < 0.01 versus [a] and [c]) paralleling "young" values of 4-month-old rats and increased the spike burst frequency in the proximal-distal colon (p < 0.05). SCM-III significantly increased the frequency and duration of spike bursts in the jejunum, transverse-distal colon, and defecation frequency, while decreasing the intervals of migrating motor complex in the colon (p < 0.01) to "young" values with an increased mRNA expression of VIP (p < 0.05). Gut flora manipulation aimed to modulate myoelectric activity can tentatively help reversing age-related motility decay.     

Enteral supplementation with ornithine alpha ketoglutarate improves the early adaptive response to resection.

BACKGROUND: Polyamine synthesis or uptake, or both, might be an important event that initiates the adaptive hyperplasia seen in the intestinal remnant after partial small bowel resection. AIM: The ability of an enteral diet supplemented with the ornithine salt: ornithine alpha ketoglutarate (OKG), a precursor for polyamine synthesis, to modulate the adaptive response of the remnant ileum after jejunectomy was evaluated. METHODS: Adult Wistar rats underwent a resection of the proximal 50% of the small intestine. Controls underwent a single transection. The rats were fed intragastrically with a nutritive mixture supplemented either with casein hydrolysate or with OKG (1 g/kg). The isoenergetic and isonitrogeneous diets was given continuously for seven days. RESULTS: Villus and crypt hyperplasia was observed in the remnant ileum compared with transfected controls. OKG supplementation started after resection a further increase in villus height. After resection, OKG supplementation increased significantly the putrescine content and the amount of ornithine decarboxylase mRNA. A twofold to threefold increase of sucrase activity was measured in the resected animals compared with the transected rats. In contrast, the amount of sucrase mRNA was significantly lower in the ileum of the resected rats and OKG supplementation initiated a further drop in the amount of sucrase mRNA without pronounced changes in enzyme activity. CONCLUSIONS: The adaptive hypertrophy seen after resection can be accelerated by supplementing the diet with ornithine (OKG) a precursor of polyamine synthesis. In the remnant ileum, the reduced amount of sucrase mRNA, despite the increased level of sucrase activity, suggests a post-translational control of sucrase expression.