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Biomedical subjects

V R Preedy

Publications and source records attributed to V R Preedy.

At least 181 records · Page 10Linked to original sources
PubMed1989

The effect of chronic ethanol ingestion on synthesis and degradation of soluble, contractile and stromal protein fractions of skeletal muscles from immature and mature rats.

1. An investigation was carried out into the response of soluble, myofibrillar and stromal protein fractions of skeletal muscle to chronic ethanol feeding. Groups of male Wistar rats, of approx. 85 or 280 g body wt., were pair-fed on a nutritionally complete liquid diet containing glucose or a diet in which 36% of the total energy was provided by ethanol. After 6 weeks, rates of protein synthesis were measured with a flooding dose of L-[4-3H]phenylalanine. 2. The protein contents of soluble, myofibrillar and stromal fractions in gastrocnemius muscle from small and large rats were decreased by ethanol feeding. Greater changes were observed in small than in large rats. 3. Fractional synthesis rates of soluble, myofibrillar and stromal proteins of gastrocnemius were all decreased by ethanol treatment. All fractions responded similarly, though percentage decreases in large rats were greater than in small rats. Absolute synthesis rates in gastrocnemius muscles were also decreased after ethanol treatment. All protein fractions responded similarly, and the magnitudes of the responses in large and small rats were also similar. 4. Fractional rates of breakdown, measured by the difference between fractional growth and synthesis rates, were apparently decreased, in both sets of rats, in all protein fractions. 5. It was concluded that chronic ethanol exposure causes perturbations in soluble, myofibrillar and stromal protein accretion by a mechanism involving unidirectional changes in protein synthesis and possibly breakdown.

Animals↗
PubMed1989

The effects of fasting or hypoxia on rates of protein synthesis in vivo in subcellular fractions of rat heart and gastrocnemius muscle.

We measured rates of protein synthesis in vivo in subcellular fractions (soluble, myofibrillar and stromal fractions) of the heart and the gastrocnemius from rats after fasting or under hypoxic conditions (i.e. atmospheres containing 5% or 10% O2). Such interventions are known to inhibit protein synthesis under some circumstances. The recovery of tissue protein after fractionation was 80-100%. The proportions of protein present in the soluble and stromal fractions were different in the two muscles. The rates of protein synthesis in the myofibrillar and stromal fractions were less than those for total mixed tissue protein, whereas the rate for soluble protein was greater. Both fasting and moderate hypoxia (10% O2 for 24 h) inhibited protein synthesis in the gastrocnemius. In this tissue, the synthesis of the myofibrillar fraction was apparently the most sensitive to inhibition, and this resulted in some significant increases in the soluble-fraction/myofibrillar-fraction protein-synthesis rate ratios. In the heart, fasting inhibited protein synthesis, but moderate hypoxia (10% O2 for 24 h) did not. The rate of protein synthesis in the cardiac myofibrillar fraction was again more sensitive to fasting than were the rates in the other fractions, but it was not as sensitive as that in the gastrocnemius. Under severely hypoxic conditions (5% O2 for 1 or 2 h), protein synthesis was decreased in all fractions in both tissues. These results suggest that the rates of protein synthesis in these relatively crude subcellular fractions vary.

Animals↗
PubMed1989

Protein metabolism in the small intestine of the ethanol-fed rat.

The effects of chronic ethanol feeding on the small intestine were investigated in young rats. Rats were fed a nutritionally-adequate liquid diet, containing 36 per cent of total energy as ethanol (treated, n = 7), or isovolumetric amounts of the same diet in which ethanol was substituted by isocaloric glucose (controls, n = 7). After six weeks the wet weight and total tissue contents of protein, RNA and DNA were significantly reduced by 21 per cent, 23 per cent, 16 per cent and 28 per cent respectively, (p less than 0.014). Rates of protein synthesis were measured with L[4(3H)]phenylalanine and fractional rates (defined as the percentage of constituent tissue protein synthesised each hour, i.e. ks, % h-1) were calculated from the specific radioactivity of free phenylalanine in both tissue homogenates and plasma. Ethanol-feeding reduced ks by approx 10 per cent (p less than 0.181). The amount of protein synthesized unit-1 RNA was also reduced by approx 15 per cent (p less than 0.059) but the amount of protein synthesis unit-1 DNA was unaffected by ethanol-feeding (p less than 1.000). In contrast, the absolute rates of protein synthesis were reduced by approximately 30 per cent (p less than 0.022). It was concluded that, as the small intestine contributes to approx. 20-25 per cent of whole body synthesis these results may have an important effect on whole body nitrogen homeostasis and may have implications for the gastrointestinal effects of ethanol seen during chronic alcoholic abuse.

Animals↗
PubMed1989

Effect of chronic ethanol ingestion on tissue RNA and blood flow in skeletal muscle with comparative reference to bone and tissues of the gastrointestinal tract of the rat.

1. The effects of feeding a diet containing ethanol as 36% of total calories for 4-5 weeks on muscle RNA content and blood flow was investigated in male rats weighing 150-250 g. Control animals were pair-fed the same diet in which ethanol was substituted by isocaloric glucose. 2. Chronic ethanol consumption reduced the capacity for type II (anaerobic, fast-twitch) fibre-rich skeletal muscles to synthesize protein as reflected by a decreased RNA/protein ratio. Type I (aerobic, slow-twitch) fibre-rich muscles were unaffected. 3. Ethanol feeding had no significant effect on cardiac output. Furthermore, the percentage of cardiac output to type I and type II fibre-rich muscles, bone and tissues of the gastrointestinal tract, i.e. stomach, small intestine and large intestine, was unaffected by ethanol consumption. Similarly, ethanol feeding had no effect on blood flow when it was calculated on the basis of tissue weight (ml min-1 g-1). 4. It was concluded that chronic ethanol feeding in the rat was associated with selective skeletal muscle dysfunction in the absence of changes in blood supply.

Alcoholism↗
PubMed1989

Synthesis of subcellular protein fractions in the rat heart in vivo in response to chronic ethanol feeding.

An investigation was made into the chronic effects of ethanol on the subcellular protein fractions in the hearts of young rats (80-100 g body weight). Rats were fed a nutritionally adequate liquid diet containing ethanol as 36% of total energy. Controls were fed the same diet in which ethanol was substituted by iso-energetic glucose. At the end of 6 weeks, rats were killed and hearts were fractionated into sarcoplasmic, myofibrillar and stromal protein fractions by differential solubilisation. The total myofibrillar protein content was significantly reduced by chronic ethanol feeding, though the contents of other fractions were relatively unaltered. The fractional and absolute rates of myofibrillar protein synthesis were significantly increased, but the synthesis rates of sarcoplasmic and stromal protein fractions were unaffected by ethanol feeding. This suggests independent regulation of myofibrillar protein content in the ethanol exposed heart. These changes may be responsible for alterations in myocardial function in alcoholic cardiomyopathy.

Alcoholism↗
PubMed1989

An investigation into the effects of chronic ethanol feeding on hepatic mixed protein synthesis in immature and mature rats.

1. The response of the liver to chronic ethanol feeding was investigated in sexually immature (85 g) and sexually mature (280 g) male Wistar rats. Rats received a nutritionally adequate liquid diet ad libitum, in which ethanol comprised 36% of total calories, for up to 6 weeks. Controls were pair-fed the same liquid diet in which ethanol was substituted by isocaloric glucose. 2. In immature rats, total hepatic protein, RNA and DNA contents were reduced by 12-23%. The amount of RNA, relative to protein or DNA, was also decreased by 11-12%, though the amount of protein relative to DNA was unaltered. In mature rats, no change in total hepatic protein and DNA contents were observed, though total RNA, RNA/protein ratio, RNA/DNA ratio and the amount of protein relative to DNA was reduced by 7-18%. 3. Rates of protein synthesis were measured with a flooding dose of L[4-3H]-phenylalanine without anaesthesia or surgical stress. In both immature and mature rats the fractional and absolute rates of hepatic protein synthesis and protein synthesis relative to DNA were reduced by approx 25%.

Animals↗
PubMed1989

Ethanol-induced skeletal muscle myopathy: biochemical and histochemical measurements on type I and type II fibre-rich muscles in the young rat.

Rats were pair-fed either a nutritionally complete liquid diet containing 36% of total calories as ethanol or isovolumetric amounts of the same diet in which ethanol was substituted by isocaloric glucose. Chronic ethanol feeding caused a preferential decline in the wet weight of the plantaris (predominantly Type II muscle fibres) which was accompanied by a reduction in the total DNA content. The soleus (a predominantly Type I fibre muscle) was relatively unaffected. Chronic ethanol exposure had no effect on the biochemical index of cell size (protein/DNA ratio) in either the plantaris or soleus. Quantitative histochemistry of Type II fibres in the plantaris demonstrated that ethanol caused an increase in the proportion of fibres with smaller diameters. Similar effects were observed for Type II fibres in the soleus. In contrast, ethanol exposure was associated with an increase in the relative proportion of Type I fibres with higher diameters, in both plantaris and soleus. Light microscopic examination of myopathic muscle sections demonstrated that lesions occurred without evidence of inflammation, fibrosis or other infiltration by non-muscle cells. It is concluded that chronic exposure of rats to ethanol is associated with skeletal muscle atrophy. The lesion appears to be specific for Type II fibres, irrespective of the predominant fibre type in the particular muscle.

Alcohol Drinking↗
PubMed1989

Use of the Lieber-DeCarli liquid feeding regime with specific reference to the effects of ethanol on rat skeletal muscle RNA.

This communication discusses the ways in which parameters of tissue injury in chronic ethanol-fed rats can be presented. These are: concentration (amount per unit wet weight), absolute amount (total quantity per organ or tissue) or relative to body weight (total quantity per unit body weight). Specific reference is made to the amount of RNA in skeletal muscles from rats fed the Lieber-DeCarli liquid diet containing ethanol for 6 weeks. Comparisons were made with data from rats which were pair-fed the same diet in which ethanol was substituted by iso-caloric glucose. Chronic ethanol-feeding had no statistically significant effect on the concentration of skeletal muscle RNA, though the absolute amount was reduced by 20%. When expressed relative to body weight the magnitude of this decline was reduced, to only 10%. Due to the nature of the liquid feeding regime the animals showed variable alterations in body weight. The amount of liquid diet consumed by control and ethanol-fed rats over a 24 hr period can comprise as much as 40% (w/w) of body weight. It is therefore suggested that data expressed relative to body mass may, on occasions, be erroneous. Episodic engorgement with food may also have an influence on other metabolic processes such as the kinetics of protein, fat or carbohydrate metabolism. These issues may have important implications for other studies using the Lieber-DeCarli liquid diet to examine the effects of ethanol on muscle or non-muscle tissues.

Animal Feed↗
PubMed1988

The effect of rejuvenation of aged erythrocytes on biochemical parameters in the perfused hind limb muscle preparation.

(1) A systematic investigation was carried out into the use of time-expired erythrocytes in an isolated perfused skeletal muscle preparation. Comparisons were made between erythrocytes subjected to a process of 'rejuvenation' (Rennie and Holloszy (1977), Biochem. J. 168, 161-170) and untreated erythrocytes (controls). (2) The use of rejuvenated erythrocytes had no significant effect on concentrations of muscle ATP, phosphocreatine and lactate, nor fractional rates of muscle protein synthesis. However, muscle water concentrations were reduced when compared to controls. (3) There was an influx of K+ from the plasma into rejuvenated erythrocytes. This was accompanied by a substantial loss (17%) of intramuscular K+. There was also loss of K+ from control preparations but this amounted to approx. 1% of muscle content. (4) Erythrocyte fragility was greater in the control perfusate (6%, haemolysis) when compared to the medium with rejuvenated cells (1%, haemolysis). As a consequence of either erythrocyte storage, rejuvenation or haemolysis, plasma concentrations of phosphate, magnesium, calcium and potassium were significantly different from starting values, by as much as 300% in both groups, and varied throughout the study. (5) It is concluded that the use of rejuvenated erythrocytes does not confer any advantage in unexercised perfused skeletal muscle preparations. However, both types of erythrocyte induce changes in perfusate composition relative to starting or in vivo profiles.

Animals↗
PubMed1988

The effect of chronic ethanol ingestion on protein metabolism in type-I- and type-II-fibre-rich skeletal muscles of the rat.

1. The effects of chronic ethanol feeding on muscles containing a predominance of either Type I (aerobic, slow-twitch) or Type II (anaerobic, fast-twitch) fibres were studied. Male Wistar rats, weighing approx. 90 g or 280 g, were pair-fed on a nutritionally complete liquid diet containing 36% of total energy as ethanol, or isovolumetric amounts of the same diet in which ethanol was replaced by isoenergetic glucose. After 6 weeks feeding, fractional rates of protein synthesis were measured with a flooding dose of L-[4-(3)H]-phenylalanine and muscles were analysed for protein, RNA and DNA. 2. Ethanol feeding decreased muscle weight, protein, RNA and DNA contents in both small and large rats. Type-II-fibre-rich muscles showed greater changes than did Type-I-fibre-rich muscles. Changes in protein paralleled decreases in DNA. 3. The capacity for protein synthesis (RNA/protein), fractional rates of protein synthesis and absolute rates of protein synthesis were decreased by ethanol feeding in both small and large rats. The amounts of protein synthesized relative to RNA and DNA were also decreased. Changes were less marked in Type-I than in Type-II-fibre-rich muscles. Loss of protein, RNA and DNA was greater in small rats, but protein synthesis was more markedly affected in large rats. 4. It was concluded that chronic ethanol feeding adversely affects protein metabolism in skeletal muscle. Fibre composition and animal size are also important factors in determining the pattern of response.

Age Factors↗
PubMed1988

Inhibition of protein synthesis by glucagon in different rat muscles and protein fractions in vivo and in the perfused rat hemicorpus.

The effect of glucagon on the rate of muscle protein synthesis was examined in vivo and in the isolated perfused rat hemicorpus. An inhibition of protein synthesis in skeletal muscles from overnight-fasted rats at various plasma concentrations of glucagon was demonstrated in vivo. The plantaris muscle (Type II, fibre-rich) was more sensitive than the soleus (Type I, fibre-rich). Myofibrillar and sarcoplasmic proteins were equally sensitive in vivo. However, protein synthesis in mixed protein and in sarcoplasmic and myofibrillar fractions of the heart was unresponsive to glucagon in vivo. In isolated perfused muscle preparations from fed animals, the addition of glucagon also decreased the synthesis of mixed muscle proteins in gastrocnemius (Type I and II fibres) and plantaris, but not in the soleus. The sarcoplasmic and myofibrillar fractions of the plantaris were also equally affected in vitro. Similar results were observed in vitro with 1-day-starved rats, but the changes were less marked.

Animals↗
PubMed1988

The influence of restraint and infusion on rates of muscle protein synthesis in the rat. Effect of altered respiratory function.

1. Male rats (110-140 g body wt.) were restrained by a standard laboratory technique, by wrapping in a linen towel, and subjected to a constant intravenous infusion of saline (0.15 M-NaCl) for periods of 1 or 6 h. Fractional rates of protein synthesis (ks, %/day) were estimated at the start and at the end of the infusion period, by injection of a large concentration of [3H]phenylalanine. 2. In fed and overnight-fasted rats, restraint and infusion of saline for 1 and 6 h decreased ks in skeletal muscle by 15-20% and 30-35% respectively. Plasma glucose, insulin, glucagon and corticosterone concentrations in restrained and infused rats were not characteristic of immobilization stress. 3. Restrained rats responded to nutrient administration; ks in skeletal muscle increased by 35-40% after infusion of a mixture of amino acids and glucose for 1 or 6 h, as compared with saline-infused rats. 4. Restraint and infusion for 1 or 6 h did not overtly decrease ks and kRNA (protein synthesis per unit of RNA) in hypoxaemia-sensitive tissues, such as heart and liver. Restraint and infusion in an open cage, or in a cloth of open weave, did not decrease ks in muscle after 1 h. Blood gas measurements showed that rats restrained in a linen cloth were hypercapnic and acidotic compared with rats in an open cage. 5. It was concluded that respiratory acidosis, rather than hypoxia, resulting from restraint in a linen cloth decreases muscle protein synthesis.

Animals↗
PubMed1988

The effects of surgical stress and short-term fasting on protein synthesis in vivo in diverse tissues of the mature rat.

1. We measured fractional rates of protein synthesis, capacities for protein synthesis (i.e. RNA/protein ratio) and efficiencies of protein synthesis (i.e. protein-synthesis rate relative to RNA content) in fasted (24 or 48 h) or fasted/surgically stressed female adult rats. 2. Of the 15 tissues studied, fasting caused decreases in protein content in the liver, gastrointestinal tract, heart, spleen and tibia. There was no detectable decrease in the protein content of the skeletal muscles studied. 3. Fractional rates of synthesis were not uniformly decreased by fasting. Rates in striated muscles, uterus, liver, spleen and tibia were consistently decreased, but decreases in other tissues (lung, gastrointestinal tract, kidney or brain) were inconsistent or not detectable, suggesting that, in many tissues in the mature rat, protein synthesis was not especially sensitive to fasting. 4. In fasting, the decreases in fractional synthesis rate resulted from changes in efficiency (liver and tibia) or from changes in efficiency and capacity (heart, diaphragm, plantaris and gastrocnemius). In the soleus, the main change was a decrease in capacity. 5. Surgical stress increased fractional rates of protein synthesis in diaphragm (where there were increases in both efficiency and capacity) by about 50%, in liver by about 20%, in spleen by about 40%, and possibly also in the heart. In liver and spleen, capacities were increased. In other tissues (including the skeletal muscles), the fractional rates of protein synthesis were unaffected by surgical stress.

Animals↗
PubMed1988

Acute effects of ethanol on protein synthesis in different muscles and muscle protein fractions of the rat.

1. The effects of a single dose of ethanol (75 mmol/kg body weight) on rates of muscle protein synthesis were examined in young rats. Fractional rates of protein synthesis were measured in the soleus, plantaris, gastrocnemius, diaphragm and stomach by the large 'flooding-dose' technique. 2. After 150 min, the fractional synthesis rates of all muscles were reduced by 15-35%. Skeletal muscles containing a predominance of anaerobic (fast-twitch, type II) fibres showed greater changes when compared with skeletal muscles with a predominance of aerobic (slow-twitch, type I) fibres. 3. Gastrocnemius muscles were separated into sarcoplasmic, stromal and myofibrillar protein fractions. Protein synthesis was reduced similarly in all fractions by ethanol treatment, by approximately 30%. 4. As skeletal muscle mass comprises 40% of body weight, the responses have important physiological implications and may also be responsible for the muscle atrophy observed in alcoholic patients.

Animals↗
PubMed1988

The biochemical actions of phentolamine and papaverine on rat perfused skeletal muscle.

The direct actions of the vasodilators, papaverine and phentolamine, on skeletal muscle metabolism were investigated in an isolated perfusion system. Eviscerated male rats were hemisected above the diaphragm and perfused, via the aorta, with a physiological perfusion medium containing erythrocytes. Papaverine, but not phentolamine, reduced vascular resistance throughout the 80 min study. Papaverine caused marked reductions in muscle concentrations of ATP and phosphocreatine, when compared with muscle from preparations without added vasodilators. This was accompanied by elevations in lactate concentrations. Water content of papaverine-treated muscle was also higher than values in unperfused muscle taken in-vivo. Phentolamine, in contrast, had no effect on muscle ATP, phosphocreatine, lactate or water content. The metabolism of the entire preparation was also investigated. Papaverine induced increases in lactate output while phentolamine treatment caused an initial uptake, followed by an increased output of lactate. There was no significant effect of either papaverine or phentolamine on the metabolism of K+ and glucose. Arteriovenous differences in oxygen-saturation of haemoglobin and pH were also unaltered. Investigations on aspects of protein metabolism demonstrated that papaverine and phentolamine caused significant reductions in muscle protein synthesis when compared with control perfusions or in-vivo values. The reductions in synthesis were not due to reductions in cAMP or limitations in branched-chain amino acid supply. However, there was the suggestion that phentolamine caused a decrease in protein breakdown. The overall data indicated that papaverine and phentolamine may cause impairment of skeletal muscle metabolism. This has important implications for their therapeutic or experimental use.

Animals↗
PubMed1988

Acute ethanol dosage reduces the synthesis of smooth muscle contractile proteins in the small intestine of the rat.

The effects of an acute dose of ethanol (75 mmol/kg body weight; ip) on protein synthesis were investigated in the small intestine of the rat (n = 6). Control rats (n = 6) were injected with isovolumetric 0.15 mol/l NaCl, ip. After 2.5 h, fractional rates of protein synthesis (defined as the percentage of tissue protein renewed each day by synthesis and RNA efficiencies (defined as the amount of protein synthesised per unit RNA) were measured with a large flooding dose (0.3 Ci/mol; 150 mmol/l; 150 mumol/100 g body weight; iv) of [4(3)H]-phenylalanine. Rats were killed 10 minutes after injection of the isotope and portions of the small intestine were rapidly dissected and frozen. Tissues and plasma were processed for phenylalanine specific radioactivities to obtain fractional rates of protein synthesis or protein synthesis rates relative to RNA. Rates of protein synthesis in mixed tissue proteins fell approximately 15-25% (p ranged from less than 0.005 to greater than 0.05), in response to acute ethanol dosage. The decrease in the synthesis rates of the cytoplasmic protein fraction was similar (p less than 0.025). Proteins extracted from the smooth muscle contractile apparatus, however, showed a greater response to ethanol--that is, 40-50% inhibition in protein synthesis (p less than 0.001). It is therefore possible that the functional disturbances in the ethanol-exposed gut may be because of changes in smooth muscle protein turnover with decreased amounts of contractile apparatus.

Animals↗