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Query: UMLS:C0038187 (starvation)
 24,951 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

We have compared the nucleosomal organization of c-Ha-rasVal 12 oncogene-transformed NIH-3T3 fibroblasts with that of normal fibroblasts by using micrococcal nuclease (MNase) as a probe for the chromatin structure. The bulk chromatin from asynchronously and exponentially growing ras-transformed cells was much more sensitive to MNase digestion than chromatin from the normal cells. Southern hybridization analyses of the MNase digests with probes specific for the ornithine decarboxylase (odc) and c-myc genes showed that the coding and/or 3' end regions of these growth-inducible genes carry a nucleosomal organization both in ras-transformed and normal cells. Studies with cells synchronized by serum starvation showed that in both cell lines the nucleosomal organization of chromatin is relatively condensed at the quiescent state, becomes highly decondensed during the late G1 phase of the cell cycle, and starts again to condense during the S phase. However, in ras-transformed cells the decondensation state stayed much longer than in normal cells. Moreover, irrespective of the phase of the cell cycle the bulk chromatin as well as that of the odc and c-myc genes was more sensitive to MNase digestion in the ras-transformed cell than in the normal fibroblast. Decondensation of the chromatin was also observed in the normal c-Ha-ras protooncogene-transfected cells, but to a lesser extent than in the mutant ras-transformed cells. Whether the increased degree of chromatin decondensation plays a regulatory role in the increased expression of many growth-related genes in the ras-transformed cells remains an interesting object of further study.
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PMID:c-Ha-rasVal 12 oncogene-transformed NIH-3T3 fibroblasts display more decondensed nucleosomal organization than normal fibroblasts. 219 41

Ornithine decarboxylase and thymidine kinase are enzymes that increase in activity in regenerating liver. We found that both activities and mRNA levels for these enzymes increase significantly after 70% partial hepatectomy in the rat. After sham hepatectomy (laparotomy) there were significant decreases in activity; however, mRNA content was unaltered. Similar decreases in enzyme activity, without changes in mRNA content, were found with pair-feeding, and additional decreases in activity after starvation. In contrast to previous reports of no change in ornithine decarboxylase and thymidine kinase after sham hepatectomy, the present results indicate that decreases occur. This may be mediated by the decrease in food intake after surgery. Dietary factors may be important in the physiologic regulation of these enzymes in the liver.
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PMID:Effects of partial and sham hepatectomy on ornithine decarboxylase and thymidine kinase activities and mRNA contents. 235 25

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.
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PMID:Aging and intestinal polyamine metabolism in the rat. 236 31

The signals which regulate the proliferation of astrocytes have relevance to both normal developmental processes and abnormal states of gliosis or glial tumor formation. We have extended studies of astrocyte proliferation and related responses in primary cultures of rat telencephalic cortical astrocytes as a result of treatment with epidermal growth factor. Epidermal growth factor stimulates the rate of DNA synthesis five fold and maintains the rate of protein synthesis. The stimulation occurs at a dose of 2 ng/ml and is greater in higher density cultures than in lower density cultures, perhaps representing a relative starvation for the growth factor. The astrocyte response is still present even after being cultured 3 1/2 weeks in serum-free and non-growth factor or hormone-supplemented media. Combined immunofluorescence and thymidine autoradiography disclose that glial fibrillary acidic protein containing cells are the cells synthesizing DNA in response to the growth factor, and combined rhodamine and fluorescein-linked stains disclose that epidermal growth factor is in the glial fibrillary acidic protein containing cells. Proliferation-related 2-deoxyglucose uptake is stimulated at approximately the same dose as DNA synthesis is stimulated, but the time course is relatively slow, maximizing at 48 hr. Ornithine decarboxylase is stimulated in 6 hr indicating more rapid nuclear stimulation by the signal. In conclusion, epidermal growth factor has a clear direct interaction with glial fibrillary acidic protein-containing cells which is greater in higher density cultures, is still present in long-quiescent cells, and includes DNA synthesis, cell cycle progression, hexose uptake, and polyamine synthesis.
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PMID:Proliferation-related responses in rat astrocytes to epidermal growth factor. 238 77

Evidence is accumulating that 1,25(OH)2D3 may stimulate calcium transport from the intestinal lumen extremely rapidly by a mechanism which appears independent of de novo protein synthesis. To investigate this rapid action of 1,25(OH)2D3, the rate of calcium uptake by isolated enterocytes from duodena of young rats was determined in vitro as the uptake of 45Ca from 1-15 min. Prior in vitro exposure of cells to 1,25(OH)2D3 (100 pM) for 20 min significantly increased the rate of calcium uptake (p less than 0.001), an effect unaltered by 50 microM cycloheximide. Incubation with 100 pM 1-alpha-hydroxyvitamin D3 produced the same effect (p less than 0.01). In contrast, exposure to 10 pM 1,25(OH)2D3, as well as to 100 pM or to 1,000 pM 25-hydroxyvitamin D3 induced no significant change. Because both 1,25(OH)2D3 and starvation may stimulate key enzymes in polyamine metabolism, we investigated the effects of (i) difluoromethyl-ornithine (CHF2-Orn), a specific irreversible inhibitor of ornithine decarboxylase and (ii) varying the timing of feeding prior to sacrifice. Both in vitro CHF2-Orn and feeding prior to sacrifice significantly decreased the baseline rate of calcium uptake (p less than 0.05) and reduced the effect of 1,25(OH)2D3. Increased duration of starvation significantly increased the baseline rate of calcium uptake (p less than 0.02) without changing the increment in rate of calcium uptake induced by 1,25(OH)2D3. The study suggests (i) that the early action of 1,25(OH)2D3 on the influx process of intestinal calcium transport may involve a different molecular specificity from that involved in the genomic action of 1,25(OH)2D3 and (ii) that changes in polyamine metabolism may play a part in this process.
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PMID:Rapid stimulation of calcium uptake by isolated rat enterocytes by 1,25(OH)2D3. 249 43

Tetrahymena thermophila cells grown in a synthetic nutrient medium for 9 h removed 97% of the free L-arginine but less than 50% of any of the other essential amino acids. The major portion of the arginine was degraded rapidly (76-92%) whereas 5-15% was conserved as intact and only 2.5-10% were incorporated into protein. However, if bovine serum albumin (BSA) was present in the medium as a macromolecular arginine source the incorporation of free arginine into protein was reduced to less than 1% but the degraded fraction was increased. Apparently, the uptake mode of arginine determines its fate: arginine taken up by phagocytosis is bound for protein biosynthesis, arginine taken up by membrane receptors is chanelled to degradation. Media without arginine did not support growth of Tetrahymena. Citrulline and ornithine, the precursors of arginine biosynthesis in yeast and vertebrates, were not able to substitute for arginine. Pronounced morphological changes, e.g. greatly reduced ribosome content, were observed in Tetrahymena cells after 24 h of arginine starvation in otherwise complete medium, but not in cells starved in water, salt solution, or buffer. Thus, arginine is an essential nutrient component for Tetrahymena and the rapid degradation of this compound involving the enzymes arginine deiminase (ADI) and citrulline hydrolase (CH) might be of regulatory importance for the unicellular, as it is the case with acetylcholine and catecholamines in mammalian organisms. Since the product of these enzymes, L-ornithine, is the substrate for the regulatory key enzyme of polyamine biosynthesis, ornithine decarboxylase (ODC), the effects of the presence of absence of arginine on the activities of each particular enzyme of the pathway were studied, including ODC and the enzyme ornithine-oxo-acid aminotransferase (O delta T), which is a competitor of ODC for the common substrate. The arginine-degradative pathway was stimulated by extracellular free but not by peptide-bound arginine and was modulated by extracellular protein which induced phagocytosis; O delta T was stimulated with a time lag. The stimulation of ODC was in a reciprocal relation to the arginine concentration and enhanced by phagocytosis and previous arginine starvation.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Stimulation of growth and polyamine biosynthesis of the ciliated protozoan Tetrahymena thermophila. Regulation by L-arginine. 261 Sep 29

Starvation followed by refeeding, which provides a model of intestinal adaptation characterised by proliferative and biochemical changes, was used to clarify the biological roles of ornithine decarboxylase (ODC) and diamine oxidase (DAO)--enzymes involved in polyamines metabolism. Ornithine decarboxylase and DAO were assayed in the proximal and distal small bowel mucosa of 55 rats, starved for four days and then refed. Rats (five per day) were killed after four days' starvation and at days 1, 2, 3, 4, 5, 6, 7, 8, 10 and 12 of refeeding. ODC, whose specific activity was similar in both intestinal segments, almost disappeared after starvation and showed a biphasic response during refeeding. High values were found on day 3 of refeeding in the proximal, and on day 4 in the distal small bowel; thereafter, they decreased gradually to be followed by a further significant increase during the last two days of the experiment. Diamine oxidase specific activity increased after starvation despite a very low total DAO activity in both intestinal segments. Refeeding induced a gradual recovery of DAO total activity. Diamine oxidase specific activity also reverted gradually to control values after five days of refeeding. These data confirm the prominence of ODC in the replication processes and suggest that intestinal DAO may not play a major role in enterocyte replication.
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PMID:Modifications in ornithine decarboxylase and diamine oxidase in small bowel mucosa of starved and refed rats. 312 54

The role of polyamines on growth and early development of D. discoideum has been investigated following the activity of ornithine decarboxylase (ODC) and the effects of difluoromethylornithine in vivo. Pretreatment of growing amoebae with difluoromethylornithine inhibited proliferation and markedly reduced the decarboxylase activity in the first hour after fasting without affecting the subsequent development. These results show the essentiality of ODC for proliferation but are inconsistent with the hypothesis atributing a developmental role to the transient increase in ODC shortly after D. discoideum starvation.
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PMID:Role of polyamines in proliferation and differentiation of Dictyostelium discoideum as ascertained by difluoromethylornithine treatment. 312 66

Some cultures of Escherichia coli BGA8, a mutant unable to synthesize putrescine, showed a change of behaviour and could grow almost equally well in either the absence or the presence of polyamines after repeated periods of polyamine starvation. Experiments in vivo with radioactive precursors showed that the bacteria which evaded the polyamine requirement had recovered their ability to synthesize putrescine from glucose or glutamic acid, but not from ornithine or arginine. These results are in agreement with the fact that the polyamine-independent cells were still deficient in the enzymes ornithine decarboxylase and agmatinase. Our findings seem to indicate the existence of a new pathway synthesize putrescine which does not involve ornithine or arginine as intermediates.
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PMID:A probable new pathway for the biosynthesis of putrescine in Escherichia coli. 352 93

The ability to respond to changes in the external and internal environments is a fundamental characteristic of intestinal structure and function. We compared the responses of the rat proximal and distal small intestine to the stresses of fasting and refeeding in the rat. In the duodenum, 3 days of starvation caused villus and crypt hypoplasia, reduced incorporation of [3H]thymidine into crypt cells, decreased cell migration rate on the villus, and lowered specific and total activities of several cellular enzymes. These changes were reversed by 1 day of refeeding. In contrast, mucosal hypoplasia did not occur in the ileum during fasting, and the specific activities of the disaccharidases were increased after 3 days of starvation. However, ileal [3H]thymidine incorporation, thymidine kinase activity, and ornithine decarboxylase activity decreased during starvation. These effects were also reversed by refeeding. The results of these studies illustrate differing responses for the proximal and distal small intestine and suggest the presence of distinctly differing mechanisms for the control of their mucosal mass and enzyme activities.
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PMID:Ileal hyperplastic response to starvation in the rat. 372 71


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