Regulation of rat antral gastrin and somatostatin gene expression during starvation and after refeeding.

Antral gastrin and somatostatin gene expression during starvation and after refeeding with liquid meals of varying composition were studied. Northern and slot-blot hybridization analyses showed that starvation caused a marked decrease in antral gastrin messenger RNA (mRNA) level by 12 hours associated with an increase in somatostatin mRNA. After 48 hours of fasting, antral gastrin mRNA was 26% and somatostatin mRNA was 136% of their prefasting levels. Refeeding caused increased 2-hour integrated gastrin mRNA levels after liquid peptone (+45%), phenylalanine (+31%), and olive oil (+13%), but no changes were observed with glucose or saline solutions. Integrated 2-hour immunoreactive antral gastrin content was increased after peptone (+106%), phenylalanine (+68%), and olive oil (+32%) meals but was not increased after glucose (-11%) or saline (-10%). In some cases, both gastrin mRNA and peptide responses could be measured as early as 15 minutes. The same nutrients that increased gastrin mRNA levels caused decreased 2-hour integrated somatostatin mRNA levels; peptone (-30%), phenylalanine (-28%), and olive oil (-21%), but neither glucose nor saline, altered somatostatin mRNA levels. These results suggest that antral gastrin and somatostatin genes were regulated in opposite directions, in a coordinate manner, by specific gastric nutrients that stimulate gastrin release.     

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.     

Effect of aging on gastric acid secretion,serum gastrin,and antral gastrin content in rats

The purpose of this study was to characterize the effects of aging on gastric acid secretion and on serum and antral concentrations of gastrin in rats. Young and old Fischer 344 rats were prepared with gastric fistulas. Twenty-four hours after surgery, graded doses of human synthetic gastrin-17 (SHG-17) (2, 5, 10, 20, and 40 g/kg) were given intravenously in random order. Gastric secretions were collected for gastric acid measurement before and at 15-min intervals after each dose of gastrin. In a separate study, blood was collected and the stomachs were removed for antral gastrin extraction from fed young and old rats. Serum and antral gastrin was measured by radioimmunoassay. The basal and gastrin-stimulated acid secretions were significantly decreased in aged rats compared to the young rats. The basal acid output was 0.4±0.2 eq/15 min in the aged rats and 1.5±0.5 eq/15 min in the young. The maximal acid output stimulated by gastrin was 11.1±1.8 eq/15 min in the aged rats and 24.2±2.8 eq/15 min in the young. Both serum and antral concentrations of gastrin were significantly decreased in aged rats. Serum gastrin concentration was 114.8±7.4 pg/ml in the aged rats and 192.0±14.4 pg/ml in the young. Antral gastrin concentration was 3.9±0.5 g/g tissue in the aged rats, which was significantly less than the concentration in the young (6.5±0.4 g/g tissue). Antral gastrin content did not change with aging. Gastric acid secretion in aged rats is significantly decreased compared to the young in both the basal condition and in response to fixed doses of exogenous gastrin. Diminished concentrations of circulating gastrin may well be responsible, at least in part, for the diminished acid secretion in the aged rats.Part of this work was presented at the special session on aging during the Digestive Disease Week held by the American Gastroenterology Association (AGA) in New York, May 14, 1985, and has been published in abstract form (Gastroenterology 88:1445, 1985).Supported by grants from the National Institutes of Health (RO1 DK 15241, PO1 DK 35608, RCDA CA 00854, CA 38651) and a grant from the American Cancer Society (PDT-220).     

Adaptive changes of intestinal enzymes to nutritional intake in the aging rat

We previously have shown that aging alters the expression of several intestinal enzymes during cell migration from the crypt base to the villus tip. The activities of many mucosal enzymes are dramatically altered by starvation and refeeding. We compared the effects of starvation and refeeding on the activities of selected intestinal enzymes in young and aging Fischer 344 rats. Gut mass fell during starvation and rose during refeeding to a similar extent in both groups. Sucrase and maltase specific activities in control aging rats were lower than in young controls and, during starvation, enzyme activities declined at approximately similar rates in both groups. Total duodenal enzyme activities fell by about two-thirds in young animals and by greater than 80% in aged animals. Alkaline phosphatase and adenosine deaminase activities also were lower in aging than young animals. During refeeding, enzyme activities rose more in aging rats than in the young. In fact, the specific activities of sucrase and maltase in aging rats refed for 1 day exceeded the values found in fed aging controls. The adaptive responses of duodenal enzymes exceeded those in the jejunum. In conclusion, the aging intestine responds appropriately to starvation and refeeding. However, the fluctuations in brush-border enzyme activities are much greater in aging than in young rats. Such alterations may be an important influence of aging on gut differentiation and might have an adverse impact upon nutritional maintenance in aging animals.     

Colonic proliferation is increased in senescent rats

Our previous studies suggested that crypt size enlarged and that proliferation rate might be greater in the small intestine of rats during senescence. Crypt cell numbers and crypt cell proliferation rates, using the vincristine-induced metaphase arrest technique, now have been measured in the colon of aging and young Fischer 344 rats. The proximal colon of 26-28-mo-old unfasted rats had 10% more crypt cells and a higher proliferative rate than 3-4-mo-old young controls. In the distal colon, the crypt cell proliferation rate in aging rats was 56% greater than in the young. A 3-day fast reduced crypt cell proliferation about fourfold in young rats but only by 20% in aging rats. One-day refeeding abruptly increased the crypt cell population and proliferation rate in rats of both age groups. The crypt zone of proliferating cells from aging rats was broader than that seen in young rats. In addition, starvation lowered colonic crypt cell cycling rate much less in aging than in young animals. We conclude that the colons of aging rats demonstrate a hyperproliferative state and a failure to adapt appropriately to changes in food intake. These observations may be relevant to states of altered proliferation that occur in the premalignant colon.     

Altered controls of proliferation in proximal small intestine of the senescent rat.

The proximal small intestine responds to starvation by rapidly reducing crypt cell proliferation rate and villus cellularity and to resumption of food intake (refeeding) by abruptly increasing proliferation and the number of villus epithelial cells. We show that villus cellularity responds to starvation and refeeding similarly in young and aging animals. However, as compared to young animals, senescent rats showed increased basal DNA synthetic activity, starvation resulted in a smaller decrease in DNA labeling of crypt cells, and refeeding produced an abrupt broadening of the proliferative zone in older animals without concomitant increased numbers of villus cells. Such altered crypt proliferative responses resemble precancerous changes seen in the colon and the aberrant proliferation found in both small and large intestine after administration of the carcinogen dimethylhydrazine.     

Relationship between the changes in gastrin levels and intestinal properties in the starved rat

Intestinal DNA, RNA, and protein content were decreased to a greater extent than was body weight when rats were starved for 3 days. Specific lactase and maltase activity increased with progressively longer periods of starvation. Antral and serum gastrin concentration significantly decreased during the 3 days of starvation. Pentagastrin (250 μg/kg 3 times daily) was injected into a group of rats for the duration of a 3-day starvation period and caused a small but significant increase in the relative intestinal RNA and protein content and decreased lactase and maltase specific activities in comparison with the levels of 3-day starved controls. Pentagastrin thus partially reversed some of the starvation-induced changes toward fed levels. Thus, a deficiency in the trophic hormone gastrin may be partially responsible for the disproportionate changes in intestinal tissue during starvation.     

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.     

Age-dependent hepatic lipogenic enzyme activities in starved-refed rats

Food intake, plasma glucose, insulin (I) and triiodothyronine (T3) and liver glucose 6-phosphate dehydrogenase (G6P-DH), malic enzyme (ME). ATP-citrate lyase, acetyl-CoA carboxylase (AcCoACx) and fatty acid synthase (FAS) activities were measured in 2 and 22 months old rats before, after 3 d starvation and 2,4,6. 24 and 48 h refeeding a high carbohydrate (74% w/w) diet. Expressed per 100 g of body weight, the carbohydrate intake of old rats was 55% lower than that of young rats. Plasma insulin was higher in old than in young rats and decreased (-40%) after starvation and returned to control values 4 h after refeeding. In young rats plasma insulin fell after starvation (-85%) and returned to normal values 2 h after refeeding. No significant differences were observed in plasma [T3] between the two groups. During the first 6 h of refeeding, plasma glucose increased 2-fold and returned to control values after 24 h in young rats. In old rats, plasma glucose returned to its control value after 2 h. Compared to the starved level, 48 h after refeeding, G6P-DH, ME, ATP-citrate lyase, AcCoACx and FAS activities increased 5- to 6-fold in young rats, while in old rats the increase was much smaller and represented 35% of that observed in young rats. These results suggest, that the age-related reduction in inducibility of hepatic lipogenic enzymes of rats refed a high carbohydrate diet after starvation may be due to a spontaneous decrease in the carbohydrate intake and to a decrease effectiveness of insulin (insulin resistance).     

Age-dependent glycolysis and gluconeogenesis enzyme activities in starved-refed rats

Food intake, plasma glucose, insulin (I) and glucagon (G), hepatic glycogen and fructose 2,6-bisphosphate (F-2, 6-P2) and liver glucokinase, glucose 6-phosphatase (G6-Pase), 6-phosphofructo-2-kinase/fructose-2,6-bisphosphatase (6-PF-2 kinase/F-2, 6-P2ase), pyruvate kinase (PK-L) and phosphoenolpyruvate carboxykinase (PEPCK) activities were measured in 2 and 22-month-old rats before 3 d starvation and after 2, 4, 6, 24 and 48 h refeeding a high carbohydrate (HC, 74% w/w) diet. Expressed per 100 g of body weight, the food intake of old rats was 55% lower than that of young rats and the amount of carbohydrate absorbed hourly during the first 6 h of refeeding was 2.4-fold higher in young than in old rats. During the first 6 h of refeeding plasma glucose increased 2-fold and returned to normal values after 24 h in young rats, while plasma glucose did not change during refeeding in old rats. In young rats [I] fell by 85% after starvation and returned to normal values 2 h after refeeding. [I] was higher in old than in young rats; it decreased by 40% after starvation and returned to the basal value 4 h after refeeding. No marked changes were observed in plasma [G] in both groups. No difference was observed in hepatic glycogen in the two groups, while F-2, 6-P2 was higher in old than in young rats. In young rats, the opposite changes in liver glucokinase and G6-Pase activities occurring after starvation and during refeeding were     

Effects of somatostatin and acid on inhibition of gastrin release in newborn rats

Newborn dogs, humans, and rats have elevated gastric luminal pH values and significantly elevated serum gastrin levels compared to adults. In the adult, acidification of the antral mucosa to pH 3.0 or lower inhibits gastrin release. Somatostatin is released by acid and may mediate this effect. We examined the effects of gastric acidification and somatostatin injection in rats aged 10 days to adult. Gastric gavage with 0.15 M HCl significantly lowered serum gastrin in animals of all ages. Somatostatin injection (400 micrograms/kg) significantly decreased serum gastrin in rats aged 18 days or older, but not in 10- and 15-day-old animals. These data indicate that 1) the mechanism whereby antral acidification inhibits gastrin release is at least partially developed in unweaned rats, 2) somatostatin is not a necessary mediator of the inhibition of gastrin release, and 3) at least part of the hypergastrinemia found in newborn animals is of antral origin.     

Evidence for the effect of aging on tissue contents of gastrin, cholecystokinin and somatostatin in the rat

The changes associated with aging in the tissue concentrations of cholecystokinin, somatostatin and gastrin in young (7-month-old), middle-aged (13-month-old) and old (25-26-month-old) rats were investigated. The concentrations and total contents of somatostatin and gastrin significantly decreased in the antrum in 13- and 25-26-month-old rats compared with the young controls. The cholecystokinin concentration in the proximal intestine and its total content significantly increased in the old rats. Somatostatin concentrations in the intestine and cerebral cortex did not change with age. Cholecystokinin content in the cerebral cortex decreased in old rats because of the decrease of tissue wet weight. We conclude that the effects of aging on the changes of peptide concentrations in tissues vary depending on peptide specie and in different tissues studied.     

Alterations in serum and antral gastrin levels in genetically diabetic mice.

Many gastrointestinal structural and functional properties are known to be altered in diabetes. In this study, we investigated whether serum and tissue gastrin levels are abnormally altered in a strain of genetically diabetic mice (C57BL/KSJ). Both serum and antral gastrin concentration were found to be significantly increased 3.4- and 2-fold above normal values in diabetic mice fed ad libitum. The increase in tissue gastrin concentration is most probably due to an increase in both cellular gastrin content and G-cell number, since the latter property is increased 130% in diabetic animals. Pair feeding studies demonstrated that diabetes associated hyperphagia is not a major factor in inducing these endocrine changes, since antral and serum gastrin are still significantly elevated above normal in diabetic animals fed a restricted diet. G-cell number, however, is not significantly increased above normal values in pair fed diabetic mice. The peak serum gastrin concentration after a meal and the duration of postprandial hypergastrinemia are also significantly increased above normal in diabetic animals. Gel filtration chromatography studies indicate that the antral nucosae of normal and diabetic mice have identical molecular forms of the hormone. It is therefore concluded that antral and serum gastrin concentration are increased in genetically diabetic mice due to both dietary alterations and other, as yet undefined, factors specific for the disease, and that the resultant hypergastrinemia may contribute to some of the gastrointestinal alterations seen in diabetes.     

Helicobacter pylori alters gastric epithelial cell cycle events and gastrin secretion in Mongolian gerbils

BACKGROUND & AIMS: Human colonization with Helicobacter pylori increases the risk for distal gastric adenocarcinoma, possibly by altering gastric epithelial cell cycle events and/or gastrin secretion. This study aimed to determine whether H. pylori virulence-related characteristics affect apoptosis, proliferation, and gastrin levels in a rodent model of gastric adenocarcinoma. METHODS: Mongolian gerbils were challenged with H. pylori wild-type or isogenic cagA(-) and vacA(-) mutants, and apoptotic and proliferating cells were identified by terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick-end labeling and proliferating cell nuclear antigen immunohistochemistry, respectively. Serum gastrin levels were determined by radioimmunoassay. RESULTS: Gastric epithelial cell turnover was no different after infection with the wild-type, cagA(-), or vacA(-) strains. H. pylori infection significantly increased antral apoptosis 2-4 weeks after challenge, before apoptotic indices decreased to baseline. In contrast, antral proliferation rates were significantly higher 16-20 weeks after inoculation, but then decreased by 40 weeks. Antral proliferation was significantly related to serum gastrin levels, whereas antral apoptosis was inversely related to acute inflammation and lymphoid follicles. CONCLUSIONS: In H. pylori-infected gerbils, enhanced antral apoptosis is an early and transient cell cycle event. Epithelial cell proliferation peaks later and is significantly related to increased gastrin levels, suggesting that epithelial cell growth in H. pylori-colonized mucosa may be mediated by gastrin-dependent mechanisms.     

Antral gastrin cells and serum gastrin in achlorhydria.

Forty-five patients with achlorhydria due to severe atrophic corpus gastritis or gastric atrophy were studied by determination of serum gastrin, histological examination of multiple biopsy from the antrum, and quantitation of gastrin cells revealed by an indirect immunofluorescence technique. In a reference group of 12 persons with normal gastric secretion and without atrophic antral gastritis the mean number of gastrin cells per field of vision was 52 +/- 6.5 (S.E.M.). In a group of achlorhydric patients having normal antral mucosa (n = 24), the serum gastrin levels was 324 +/- 56 pmol/l and the number of gastrin cells was 79.6 +/- 7.5 cells/field of vision. The corresponding values for a group of achlorhydric patients with chronic superficial antral gastritis (n = 11) were 361 +/- 186 pmol/l and 88.0 +/- 14.4 cells/field of vision. In a group of achlorhydric patients with atrophic antral gastritis (n = 10) serum gastrin was 15.0 +/- 3.3 pmol/l, and the number of gastrin cells was 6.2 +/- 3.3 cells/field of vision. Compared to the subjects in the reference group, the number of gastrin cells was significantly higher in the groups of achlorhydric patients with normal or superficially inflamed antral mucosa and significantly lower in achlorhydric patients with atrophic antral gastritis. It is concluded that serum gastrin in general is a good indicator for the presence or absence of antral atrophic gastritis in achlorhydria.     

Small intestinal crypt cell proliferation rates are increased in senescent rats

Our previous studies implied that intestinal epithelial cell replication might be increased in senescent rats. Duodenal, jejunal, and ileal crypt cell production rates (CCPR) were measured in 3-4-mo and 26-28-mo female fed control, 3-day starved and 1-day refed, and in 4-5-mo and 26-28-mo male fed Fischer rats, using the vincristine-induced metaphase arrest technique. Fed aging rats had greater proximal intestinal crypt cell numbers which fell less during starvation than those of young controls. Metaphase accumulation also was higher in aging rat duodenum and jejunum, and CCPR were 30-100% more than in young rats. Starvation reduced CCPR by more than 40% in the duodenum of young, but only by 10% in older animals. Crypt proliferative patterns demonstrated a broadened proliferative zone in aging rats. These combined results directly demonstrate that small intestinal cell production is enhanced in senescent rats and that the nutritional controls of proliferation are blunted.     

Antral gastrin cell proliferation after vagotomy in rats.

The total number of antral gastrin cells, the antral surface area and the serum gastrin concentration were determined in two groups of rats. The animals had been submitted at random either to vagotomy and pyloroplasty or to pyloroplasty alone 3 weeks before. The indirect immunoperoxidase reaction and a direct quantitative histological method were used to count the gastrin cells. Radioimmunoassay was used to estimate the serum gastrin concentration. The total number of gastrin cells in the stomach was 52% (p less than 0.01) more elevated in the vagotomized animals. Both antral mucosal surface and calculated concentration of gastrin cells per square millimeter of mucosa were significantly higher (0.01 less than p less than 0.05) in this group of animals. The serum gastrin values were significantly (p less than 0.01) more elevated after vagotomy. These observations indicate that vagotomy may induce an antral gastrin cell hyperplasia which could explain in part the hypergastrinemia observed after this surgical procedure.     

Effects of carbachol on gastrin and somatostatin release in rat antral tissue culture

Recent studies have demonstrated that somatostatin-containing cells are in close anatomic proximity to gastrin-producing cells in antral mucosa, suggesting a potential local regulatory role for somatostatin. The purpose of this study was to examine further the relationships between gastrin and somatostatin and the effects of the cholinergic agonist carbachol on content and release of gastrin and somatostatin using rat antral mucosa in tissue culture. Antral mucosa was cultured at 37 degrees C in Krebs-Henseleit buffer, pH 7.4, gassed with 95% O2-5% CO2. After 1 h, the culture medium was decanted and the tissue was boiled to extract mucosal gastrin and somatostatin. Inclusion of carbachol 2.5 X 10(-6) M in the culture medium decreased medium somatostatin from 1.91 +/- 0.28 (SEM) ng/mg tissue protein to 0.62 +/- 0.12 ng/mg (p less than 0.01), extracted mucosal somatostatin from 2.60 +/- 0.30 to 1.52 +/- 0.16 ng/mg (p less than 0.001), and percentage of somatostatin released from 42% +/- 2.6% to 27% +/- 2.2% (p less than 0.01). Carbachol also increased culture media gastrin from 14 +/- 2.5 to 27 +/- 3.0 ng/mg protein (p less than 0.01). Tissue content and release of gastrin and somatostatin were also examined during culture of rat antral mucosa in culture media containing antibodies to somatostatin in the presence and in the absence of carbachol. Incubation with somatostatin antisera, both with and without carbachol, markedly increased culture media concentrations of somatostatin, all of which was effectively bound by antibodies present in the media. Antibody binding of somatostatin was accompanied by significant increases in culture media gastrin concentrations, both in the presence and in the absence of carbachol. Results of these studies support the hypothesis that antral somatostatin exerts a local regulatory effect on gastrin release and that cholinergic stimulation of gastrin release is mediated, at least in part, through inhibition of somatostatin synthesis and release.     

Regulatory mechanism of bombesin on gastrin release

Bombesin has been demonstrated to stimulate gastrin release by an atropine-resistant mechanism. In the present study, the effects of truncal vagotomy and chemical sympathectomy on the gastrin release by exogenous and endogenous bombesin using rat antral mucosa in tissue culture were studied. Exogenous bombesin 10^-8 mol/l significantly stimulated gastrin release. The stimulation of gastrin release by bombesin was abolished by truncal vagotomy, but not altered by chemical sympathectomy. Bombesin antiserum inhibited gastrin release by blocking the effect of endogenous bombesin. The inhibition of gastrin release by bombesin antiserum was abolished by truncal vagotomy, but not altered by chemical sympathectomy. In addition, the concentrations of bombesin-like immunoreactivity in antral mucosa were not altered by truncal vagotomy. These results suggest that the mechanism of gastrin release by bombesin is influenced by non-cholinergic local nerves under vagal control.     

Relationship between gastrin cell number, serum, antral mucosa and luminal gastrin concentration and gastric acidity in antral atrophic gastritis.

The aim of our study was to investigate the relationship between gastrin producing cell density with antral mucosa, luminal and serum gastrin concentration in antral atrophic gastritis. Our study group consisted of 17 patients: six with mild atrophic gastritis, seven with moderate atrophic gastritis and four with severe atrophic gastritis. None of the patients had type-A atrophic gastritis but the body mucosa was affected by superficial gastritis at various extent in some. A group of 15 healthy subjects served as control. All subjects underwent gastroscopic examination with multiple bioptic sampling. Radioimmunoassay was used for gastrin determination and photomicroscopy for gastrin producing cell density assessment. Electron microscopy was used to assess the gastrin producing granule density index. Patients with moderate and severe atrophic gastritis showed a lower gastric acidity and acid output as compared to control. Serum gastrin did not show significant differences among the groups. In moderate and severe atrophic gastritis, gastrin producing cell granule density index, gastrin producing cell density and antral mucosa gastrin concentration were significantly lower when compared with control and decreased with advancing of the severity of atrophic gastritis. In atrophic gastritis, however, the latter two measurements were not correlated. In moderate and severe atrophic gastritis luminal gastrin concentration significantly increased, compared with control, after the severity of atrophic gastritis. Gastrin producing cell granule density index and luminal gastrin concentration showed a significant correlation with gastric pH. These data suggest that in antral atrophic gastritis with reduced gastric acidity, the decrement of gastrin producing cells is followed by gastrin producing cell hyperfunction with increased luminal release of gastrin.