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

Degradation rates of muscle proteins were determined in young rats allowed access to standard rat chow 12 h/day. degradation was assessed by determination of 3-methylhistidine (3MH) excretion rates. 3MH is a nonreutilized amino acid produced almost exclusively within the actin and myosin of skeletal and cardiac muscle. Because plasma levels of 3MH are low and renal clearance is high, excretion reflects myofibrillar degradative rates. Excretion of 3MH was determined for 4-h periods beginning 12 and 20 h after initiation of feeding and after 24-and 48-h fasts. Excretion of 3MH per 4-h period increased with time after the last feeding. Because creatinine excretion is a function of muscle mass dividing 3MH excretion by creatinine excretion represents myofibrillar degradation per unit muscle mass, the fractional degradative rate. Degradation rates rose from 4.6 to 14.5%/day between 12 and 16 and 60 and 64 h after the beginning of the last meal. These results support the presence of a diurnal pattern of protein degradation as well as increased muscle degradation during starvation.
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PMID:Protein degradation in muscle: response to feeding and fasting in growing rats. 88 48

The effects of ageing and starvation on the rat myocardium were studied by morphometric methods. Since cardiac muscle is a tissue with a high level of anisotropy, methods based on the concept of vertical planes were used to describe quantitative alterations in the rat myocyte both at the cellular and ultrastructural level. During starvation rapid and important changes were noted, particularly in the transverse dimension of cells and organelles. The most striking change, however, was the immediate dilatation of the myocyte T-system, reflecting an adaptive interaction between the intra- and extracellular environment. At the same time exocytosis of intracellular components into the extracellular space of the T-system was observed. The ratio of mitochondria to myofibrils decreased progressively during starvation. Such a decrease, in general, may reach a point when cellular energy supply becomes compromised. A comparison between different regions of the heart showed no differences and it can be concluded that the morphological changes during starvation are the same, and equally distributed, in both ventricles. The changes described in the aged rat heart point in the direction of a hypertrophy of the aged myocyte. This leads to a lower ratio between surface and volume which finds its representation at the subcellular level in a more spherical shape of nuclei and mitochondria. Unlike what is seen in malnutrition, the mitochondrial/myofibril ratio is higher in the older rat. From the morphological point of view, the atrophy of malnutrition and the hypertrophy of ageing are opposed, but in both there is a change in the relationship of the myocyte to its environment which directly influences the substrate exchange capacity. This tends to protect the myocyte in starvation but jeopardizes the older cell.
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PMID:Effect of ageing and malnutrition on rat myocardium. I. The myocyte. 141 85

We have investigated the change of catalase activity in the homogenates of rat cardiac and skeletal muscles. After 7 days' starvation, the catalase activity of heart increased about 3-fold and that of soleus muscle enhanced 2-fold higher than that of control rats. Immunoblot analysis of catalase showed a single band in the homogenates of cardiac and soleus muscles and increase of catalase antigen after starvation. Light microscopic immunoenzyme staining showed that after starvation catalase positive granules markedly increased in both the cardiac and soleus muscle. Quantitative analysis of the staining showed that number of the granules per 100 microns 2 of tissue section was about 1.4-fold in the soleus muscle and 1.7-fold in the cardiac muscle after starvation. By electron microscopy of alkaline DAB staining, we confirmed that the granules were peroxisomes, which increased in both number and size. Furthermore, we stained the peroxisomes for catalase by a protein A-gold technique. Labeling density (gold particles/micron 2) of the cardiac and soleus muscles from the starved rat increased approximately 1.4 times as much as that of normal animal. When the numerical density is multiplied by the labeling density, the values are largely consistent with the enhancement of catalase activity. These results show that increase in the catalase activity of the muscle tissue after starvation is caused by increase in number and size of peroxisomes.
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PMID:Peroxisomes of the rat cardiac and soleus muscles increase after starvation. A biochemical and immunocytochemical study. 231 55

In an attempt to elucidate the effect of protein restriction and subsequent refeeding on cardiac muscle function, 133 rat hearts were studied on a Langendorff perfusion apparatus: 19 normal controls, 55 rats during 6 weeks of protein restriction, and 59 rats during 6 weeks of refeeding following starvation. During starvation animals lost 14.3% of body weight and 12.8% in heart weight, both to be gained upon refeeding. Both developed force and force velocity tended to decrease in starving rats compared to control or refeeding rats. This trend was present at time 0, but more so after 60 min of perfusion. Furthermore, these differences became even more obvious and significantly different at the higher heart rates of 300 and 400 beats/min, and less so at 100 or 200 beats/min. These protein malnutrition-associated cardiac function derangements reversed almost completely to normal upon refeeding.
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PMID:Cardiac function during protein malnutrition and refeeding in the isolated rat heart. 309 3

The continuous turnover of intracellular protein and other macromolecules is a basic cellular process that serves, among other functions, to regulate cytoplasmic content and provide amino acids for ongoing oxidative and biosynthetic reactions during nutrient deprivation. The intensity of breakdown and pattern of regulation, though, vary widely among cells. Rat hepatocytes, for example, exhibit high absolute rates of proteolysis and regulatory effects that diminish during starvation, while corresponding responses in skeletal and cardiac muscle move in the opposite direction. It is also becoming apparent that effects of insulin and other acute regulatory agents on muscle breakdown are limited to nonmyofibrillar components. The latter may be sequestered and degraded within autophagic vacuoles, whereas myofibrillar proteins require an initial attack by calcium-dependent proteases in the cytosol. By contrast, most if not all of the breakdown of resident (long-lived) proteins as well as RNA in the hepatocyte can be explained by lysosomal mechanisms. The uptake of cytoplasmic components by lysosomes can be divided into two major categories, macroautophagy and micro- or basal autophagy. The first is induced by amino acid or insulin/serum deprivation. In the hepatocyte, amino acids alone can regulate this process almost instantaneously over two thirds of the full range of proteolysis, 4.5% to 1.5% per hour. Glucagon, cyclic AMP, and beta-agonists also stimulate macroautophagy in hepatocytes but have opposite effects in skeletal and cardiac myocytes. Basal autophagy differs from the macro type in that the cytoplasmic "bite" is smaller and sequestration is not acutely regulated. It is, however, adaptively decreased during starvation in parallel with absolute rates of basal turnover. Since endoplasmic reticulum comprises an appreciable fraction of the vacuolar content, volume sequestration would be compatible with the known heterogeneity of individual protein turnover if some proteins (or altered proteins) selectively bind to membranes. The amino acid control of macroautophagy in the hepatocyte is accomplished by a small group of direct inhibitors (Leu, Tyr/Phe, Gln, Pro, Met, Trp, and His) and the permissive effect of alanine whereas only leucine is involved in myocytes and adipocytes. Of unusual interest is the fact that the inhibitory amino acid group alone evokes responses in perfused livers that are identical to those of a complete plasma mixture at 0.5 and 4 times normal plasma levels but loses effectiveness almost completely at normal concentrations.(ABSTRACT TRUNCATED AT 400 WORDS)
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PMID:Intracellular protein catabolism and its control during nutrient deprivation and supply. 330 Jul 46

Twenty-one dogs were chronically instrumented with ultrasonic left ventricular dimension transducers and micromanometers to elucidate the effects of acute protein-calorie malnutrition on cardiac function. Ten dogs received a regular diet for 3 wk, whereas 11 dogs received a protein-calorie-deficient diet designed to achieve a mean weight loss of 20-25% over a 3-wk period. Studies of cardiac function were performed in awake intact animals at base line (1 wk postoperatively) and after 3 wk. In the malnourished dogs, cardiac mass was lost in proportion to total body mass loss. Mean cardiac mass fell from 115 to 91 g. This was largely due to wall thinning in this group. Heart rate dropped from 125 to 79 beats/min with malnutrition and ejection fraction increased from 29.8 to 34.6%. Cardiac output fell from 2.98 to 2.38 l/min, but cardiac index normalized to body surface area was unchanged. No significant changes in hemodynamics were observed in the control group. In the malnutrition group, global ventricular contractility, as measured by the load-independent index of systolic function or the slope of linear relationship between end-systolic pressure and end-systolic volume (EmaxPV), decreased slightly from 3.56 to 2.81 mmHg/ml (P = 0.07). However, Emax calculated from circumferential stress and strain data was unchanged. This indicates that depressed contractility was due to loss of cardiac muscle mass rather than any change in the myocardium per se. Response to beta-adrenergic stimulation was unchanged with starvation. Acute protein-calorie malnutrition causes significant cardiac atrophy that is reflected in decreased cardiac output and slightly reduced contractility but not in intrinsic properties of the myocardium.
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PMID:Left ventricular function in malnutrition. 361 11

Glucagon is a vasodilator substance that reduces blood pressure via a decreased vascular resistance in the splanchnic and hepatic vasculature. Species differences in the response of various vascular beds to glucagon have been documented. In the kidney, glucagon in relatively large doses increased renal plasma flow, glomerular filtration, and electrolyte excretion. It has been shown that intraarterial injection of glucagon into the renal artery can produce an increase in electrolyte excretion on the side that received an injection with minimal or no changes in glomerular filtration. This indicated a direct tubular effect of this polypeptide. This effect may be related to the increased glomerular filtration observed in poorly controlled diabetics where insulin concentrations are low and glucagon concentrations are high. The tubular effects of glucagon are probably mediated via cAMP and prostaglandin formation in renal tubular cells, especially the ascending limbs of Henle and collecting ducts. Glucagon increases the RNA concentration in glomerular tissue, and this effect is probably independent of cAMP. The latter effect of glucagon has been related to the glomerular enlargement and membrane thickening observed in poorly controlled insulin-dependent diabetics. Starvation natriuresis has been related to increased concentrations of glucagon in blood. The likely mechanism is that glucagon increased the renal excretion of organic acids, possibly by inhibiting the renal tubular reabsorption of these acids. Little is known concerning the effects of glucagon on the cAMP content of vascular smooth muscle. Indirect evidence suggests that such effects may be mediated via the production of cAMP. If this can be established, it would be likely that the glucagon-induced vasodilation is due to a cAMP-dependent phosphorylation of the myosin light chain kinase. This kinase shows reduced sensitivity to the Ca++ calmodulin complex when it is phosphorylated by the cAMP-dependent kinase and thus may produce relaxation of smooth muscle. In cardiac muscle, glucagon produced positive inotropic and chronotropic effects. These effects show species differences and in some species activate only the auricle with minimal effects of ventricular muscle. The effects of glucagon in general resemble those of a beta-adrenergic agent; however, glucagon seems to be nonarrhythmogenic in a variety of cardiac preparations and its effects are not blocked by propranolol. In some of these experimental conditions the chronotropic effects of glucagon play an important role in the antiarrhythmogenic effects, although direct cardiac membrane effects have been postulated. Several factors can modify the
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PMID:Glucagon and the circulation. 631 31

Previous studies have established that older (16 wk) and more obese rats conserve body protein during prolonged starvation. This adaptation is due in part to a curtailment of muscle proteolysis. To determine whether this response occurs also in younger rats and whether protein is conserved at sites other than muscle, studies were conducted in young 6-wk-old rats previously fed either a chow or a high-fat diet before starvation. Fat feeding caused a marked increase in adipose mass and prolonged survival. Whereas chow-fed rats survived the fast for approximately 5 days, fat-fed rats lived for 10 days and diminished their excretion of nitrogen for at least 6 days, indicative of protein conservation. Despite the ability of fat-fed rats to survive the fast longer, protein was conserved in only a few organs. The timing and magnitude of protein loss from liver, kidney, intestine, and lung was similar to that in chow-fed rats, and little protein was lost during the fast from brain, stomach, skin, and soleus muscle in either group. In fat-fed rats, cardiac and skeletal muscle were the principle tissues in which protein was conserved, and this adaptation was lost when body fat stores were nearing exhaustion. In both groups nitrogen excreted in the urine early in the fast was derived mainly from protein lost from muscle, liver, and to a lesser extent intestine. Later in the fast, the principal source was muscle. These findings indicate that during starvation in the rat the conservation of protein occurs principally in skeletal and cardiac muscle. They also suggest that the ability of the rat to conserve protein is dependent on the size of its lipid stores.
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PMID:Sites of protein conservation and loss during starvation: influence of adiposity. 672 Sep 43

Oxidative-decarboxylation rates of branched-chain amino acids in rat hemidiaphragm and of branched-chain 2-oxo acids in hemidiaphragm, soleus muscle and heart slices of 110-120 g rats were increased considerably by 3-4 days of starvation, when they were calculated from the specific radioactivity in the medium. When the supply from endogenous protein degradation to the oxidation-precursor pool was severely limited by transaminase inhibitors, oxidative-decarboxylation rates of branched-chain 2-oxo acids rose significantly. Since this apparent increase was relatively larger in preparations from fed rats than from 3-days-starved rats, the differences in oxidation rates with nutritional state became less or even not significant. With rat heart the smaller dilution of the oxidation precursor pool after starvation is in accordance with the reported decrease in protein breakdown. Since protein degradation increases with starvation in skeletal muscles, we suggest that the amino acid pool arising from protein degradation is more segregated from the oxidation precursor pool in muscles from starved than from fed rats. We conclude that starvation increases branched-chain amino acid and 2-oxo acid oxidation in skeletal and cardiac muscle considerably less than has been suggested by previous studies.
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PMID:The effect of starvation on branched-chain 2-oxo acid oxidation in rat muscle. 672 54

Contact is a vital mechanism used by cells to interact with their environment. Contact with living and nonliving elements adjacent to a cell is the basis for many common biological events ranging from growth regulation to metastasis to embryonic pattern formation. We describe the cloning and characterization of a novel density-regulated protein (drp) whose expression is increased in cultured cells at high density compared with cells at low density. A drp cDNA was isolated from the human teratocarcinoma cell line PA-1. Northern analysis with a drp probe revealed transcripts of 2.8 and 3.2 kb. The drp RNA was expressed in a variety of tissues, with the highest amounts in skeletal and cardiac muscle. Using antipeptide antisera, increasing amounts of a 70-kDa protein were detected using several experimental approaches in several cells lines as cell density is increased. Conditioned medium from high-density cells was unable to induce expression of drp in cells growing at low density. Similarly, growth arrest by serum starvation or transforming growth factor-beta (TGF-beta) treatment failed to elicit drp expression. We conclude that drp is a novel protein whose expression is increased at high cell density but not growth arrest.
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PMID:drp, a novel protein expressed at high cell density but not during growth arrest. 962 87


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