Effect of denervation on the synthesis of ribonucleic acid and deoxyribonucleic acid in rat diaphragm muscle

Differential response of protein metabolism in splanchnic organs and muscle to pectin feeding

The aim of the present study was to determine whether the addition of soluble fibre in the diet affected protein metabolism in the intestinal tissues, some visceral organs and in skeletal muscle. A diet supplemented with pectin (80 g/kg) was fed to young growing rats and the effect on organ mass and protein metabolism in liver, spleen, small and large intestines and gastrocnemius muscle was monitored and compared with the control group. Protein synthesis rates were determined by measuring [13C]valine incorporation in tissue protein. In the pectin-fed rats compared with the controls, DM intake and body weight gain were reduced (9 and 20 %, respectively) as well as gastrocnemius muscle, liver and spleen weights (6, 14 and 11 %, respectively), but the intestinal tissues were increased (64 %). In the intestinal tissues all protein metabolism parameters (protein and RNA content, protein synthesis rate and translational efficiency) were increased in the pectin group. In liver the translational efficiency was also increased, whereas its protein and RNA contents were reduced in the pectin group. In gastrocnemius muscle, protein content, fractional and absolute protein synthesis rates and translational efficiency were lower in the pectin group. The stimulation of protein turnover in intestines and liver by soluble fibre such as pectins could be one of the factors that explain the decrease in muscle turnover and whole-body growth rate.

Increased availability of leucine with leucine-rich whey proteins improves postprandial muscle protein synthesis in aging rats

OBJECTIVE

We previously found that aging was characterized by a decreased sensitivity of muscle protein synthesis to leucine and that a free leucine-supplemented diet corrected this defect in old rats and elderly humans. The present experiment was undertaken to evaluate the efficiency of selected leucine-rich proteins to stimulate postprandial muscle protein synthesis in old rats to optimize nutritional protein support in the elderly.

METHODS

Sixty rats (22 mo old) received an experimental meal for the first hour of feeding and a standard diet for the rest of the day for 30 d. Experimental meals contained milk proteins that differed in leucine content: beta-lactoglobulin (14.5% leucine), Prolacta (13.4%), alpha-lactalbumin (10.9%), and casein (10%). As a control, a fifth group was added that received herring flour protein (7.3% leucine). Muscle protein synthesis was determined in vivo in the postprandial state at the end of the 30-d nutritional period using the flooding dose method (1-(13)C phenylalanine).

RESULTS

Leucine intake and plasma leucine concentrations were significantly increased in rats fed meals containing the leucine-rich proteins (i.e., beta-lactoglobulin and Prolacta). As previously observed with free leucine-supplemented meals, postprandial muscle protein synthesis was significantly improved in rats fed the meals containing the leucine-rich proteins. Interestingly, the beneficial effect was maintained after the 30-d supplementation.

CONCLUSION

The results indicated that leucine-rich proteins were efficient in improving muscle protein synthesis in old rats. Thus, nutritional supplements containing such proteins may be efficient in preventing sarcopenia in the elderly and would represent a safe and optimized nutritional strategy. However, further experiments are necessary to determine the duration of such nutritional support to obtain a significant protein gain in muscle.

Dietary conjugated linoleic acid has limited effects on tissue protein anabolism in sedentary and exercising adult rats

The effects of conjugated linoleic acid isomers (CLA) and endurance training on lean body mass are expected to result from their action on tissue protein metabolism. The aim of this study was to analyze their effects on protein metabolism in 2 muscles, the small intestine and liver of adult rats. Four-month-old male Wistar rats were fed diets containing either no CLA, cis-9, trans-11 CLA isomer (1 g.100 g(-1)), trans-10, cis-12 CLA isomer (1 g.100 g(-1)) or both isomers (1 g.100 g(-1) each) for 6 weeks. Half of the rats were subjected to endurance training by running on a treadmill. At the end of this period, the rats were injected with a flooding dose of (13)C-valine to determine protein synthesis rates in the post-absorptive (experiment 1) and in the post-prandial (experiment 2) states. No effect of CLA or endurance training were detected in the small intestine. Training reduced food intake and protein synthesis rates in the liver but no effect was found on the protein synthesis rates in muscles. In the post-absorptive state, protein synthesis rate was increased by feeding the trans-10, cis-12 CLA isomer alone in the liver (+9%) or in combination with the cis-9, trans-11 isomer in the gastrocnemius (+30%), mostly in sedentary rats. In the post-prandial state, the cis-9, trans-11 CLA isomer tended to reduce the protein synthesis rate in the gastrocnemius muscle. However, no effect of CLA was found on muscle protein amounts. In conclusion, CLA isomers would have limited but differential effects on tissue protein metabolism in adult rats.

Differential Effects of Cooked Beans and Cooked Lentils on Protein Metabolism in Intestine and Muscle in Growing Rats

AIMS

The effect of diets based on cooked beans or lentils on protein metabolism in intestines and muscles was studied in rats.

METHOD

The cooked seeds were used as the unique protein source in balanced diets (containing 229 and 190 g of crude protein per kg dry matter) fed to young growing rats for 20 days. Their effects were compared with those of the control casein diet in pair-fed rats. Protein synthesis rates in small and large intestines and in gastrocnemius and soleus muscles were determined in vivo, in a fed state, by the flooding dose method, using 13C-valine.

RESULTS

In the small and large intestine tissues of the legume fed groups, protein, RNA relative masses (mg.100 g BM(-1)) and protein synthesis rates (FSR and ASR) were higher than in the control rats (p < 0.05). In gastrocnemius and soleus muscles,protein and RNA contents (in mg) and protein synthesis rates were significantly (p < 0.05) lower in the legume-fed groups than in the control rats.

CONCLUSION

The chronic intake of cooked legumes increased protein synthesis rates in intestinal tissues and decreased them in muscles. This effect was greater for beans than for lentils in the large intestine and in gastrocnemius muscle.

Differential effect of lentil feeding on proteosynthesis rates in the large intestine, liver and muscle of rats

The aim of this work was to test the hypothesis that the trophic effect of lentil feeding on large intestine results from a stimulation of protein synthesis and to determine whether it interferes with protein metabolism in other splanchnic or peripheral organs. Two groups of growing Sprague Dawley male rats were pair-fed iso-caloric iso-nitrogenous balanced diets containing either cooked lentils (Lens esculenta puyensis) or casein as unique protein source. Protein synthesis rates were measured in vivo, in large intestine, liver and gastrocnemius at the postprandial state. In large intestine, protein and ribonucleic acid contents were higher in the lentil-fed group than in the control group, and the amount of proteins synthesized was also higher (+57%). By contrast, liver protein and ribonucleic acid contents as well as protein synthesis rates were significantly lower in the lentil-fed group than in the control group. In the gastrocnemius muscle protein and ribonucleic acid contents were significantly lower and the amount of protein synthesized was also lower (-18%) in the lentil fed group than in the control group. This study suggests that stimulation of protein synthesis in the large intestine is compensated for by a decrease in liver and muscle.

Changes in diaphragm structure following prolonged mechanical ventilation in piglets

BACKGROUND

Prolonged mechanical ventilation and inactivity negatively affect muscle function. The mechanisms for this dysfunction are unclear and clinical studies of respiratory muscle are difficult to carry out. An animal model simulating the critical care environment was used to investigate the effects of 5 days' mechanical ventilation and diaphragm inactivity on diaphragm muscle morphology.

METHODS

Twelve 2-4-month-old piglets weighing 23-30 kg were studied. Seven animals received controlled mechanical ventilation and sedation such that spontaneous breathing efforts were inhibited over 5 days. Five control animals were ventilated for only 4-6 h following surgical preparation. Diaphragm biopsies were obtained from the left costal region at the end of all experiments.

RESULTS

Morphometric, morphologic, electron microscopic and enzyme histochemical examination of costal diaphragm biopsies was carried out. Contractile properties were studied over 5 days and the results have been previously reported. Cross-sectional area of alI fiber types was increased compared with controls. The proportion of type IIb/x fibers increased following inactivity (P < 0,05) and the proportion of type I and IIa fibers tended to decrease although not significantly. Focal areas of diaphragm fiber regeneration were found without signs of inflammation. Increased appearance of cytoplasmic vacuoles consisting of lipid accumulation was noted in type I fibers. Several study animals developed focal areas with weak myofibrillar ATPase activity and disrupted fiber organization. There were areas of myofibrillary destruction and loss of sarcomeric pattern, without evidence of selective thick filament loss or a change in the myosin to actin ratio.

CONCLUSION

Five days' mechanical ventilation with sedation and complete diaphragm inactivity resulted in changes in muscle fiber structure. A causal relationship can not be concluded but the acute changes in fiber type distribution and structure suggest that previously reported diaphragm contractile impairment occurs at the level of muscle fibers.

Chronic inflammation alters protein metabolism in several organs of adult rats

Despite the prevalence of chronic inflammatory diseases in developed countries, few studies have considered the metabolic alterations observed in these disorders. To determine which perturbations in protein metabolism occur during chronic inflammation, and the consequences they have on nutritional requirements, a model of ulcerative colitis was adapted for use in adult rats. Adult Sprague-Dawley male rats (9 mo old) received dextran sulfate sodium (DSS) in their drinking water at 50 g/L for 9 d, then at 20 g/L for 18 d. A group of control rats, matched for age and weight, was pair-fed to the treated rats. DSS induced body weight loss and chronic inflammation characterized by an increase of spleen, liver, ileum and colon weights, of blood leukocytes and acute-phase protein levels. The main inflammatory site was the colon, which presented characteristic histological alterations and increased myeloperoxydase activity. Inflammation was accompanied by oxidative stress, characterized by increased plasma protein carbonyl content and increased liver glutathione concentration, but decreased glutathione concentration in muscle. This DSS-induced colitis led to a stimulation of protein synthesis in spleen (+223%), ileum (+40%) and colon (+63%). By contrast, protein synthesis in muscle slowed down (-23%). In conclusion, like acute inflammation, chronic inflammation induced a stimulation of protein metabolism in several splanchnic organs. In muscle, both protein synthesis and degradation were reduced. Taken together, these data are consistent with inadequate amino acid supply to meet the increased requirement resulting from chronic inflammation.

Postprandial stimulation of muscle protein synthesis in old rats can be restored by a leucine-supplemented meal

Aging is characterized by a progressive loss of muscle mass. A decrease of muscle protein synthesis stimulation has been detected in the postprandial state and correlated to a decrease of muscle protein synthesis sensitivity to leucine in vitro. This study was undertaken to examine the effect of a leucine-supplemented meal on postprandial (PP) muscle protein synthesis during aging. Adult (8 mo old) and old (22 mo old) rats were fed a semiliquid 18.2% protein control diet for 1 mo. The day of the experiment, rats received no food (postabsorptive group) or either an alanine or leucine-supplemented meal for 1 h (postprandial groups: PP and PP + Leu groups, respectively). Muscle protein synthesis was assessed in vivo 90-120 min after the meal distribution using the flooding dose method (1-(13)C phenylalanine). Plasma leucine concentrations were significantly greater in the PP + Leu group compared with the PP group at both ages. Muscle protein synthesis was significantly greater in the adult PP group, whereas it was not stimulated in the old PP group. When supplemented with leucine, muscle protein synthesis in old rats was stimulated and similar to that observed in adults. We conclude that acute meal supplementation with leucine is sufficient to restore postprandial stimulation of muscle protein synthesis in old rats. Whether chronic leucine meal supplementation may limit muscle protein wasting during aging remains to be verified.

Expression of mRNA for plasminogen activators and protease nexin-1 in innervated and denervated mouse skeletal muscle

Plasminogen activators (urokinase-type, u-PA and tissue-type, t-PA) are serine proteases that have been suggested to play important roles in synaptic remodeling. The enzymatic activity of u-PA in particular has previously been shown to increase dramatically after denervation of skeletal muscle. Using (32)P-labeled riboprobes and Northern blots the expression of mRNA for u-PA, t-PA and the inhibitor protease nexin-1 (PN-1) has been studied in innervated and 1-10-days denervated hind-limb muscle from mouse. Using RNA extracted from innervated and 6-days-denervated mouse hemidiaphragm muscles the expression of these mRNAs has also been investigated in synaptic and extrasynaptic muscle regions. For both u-PA and t-PA the observed autoradiographic signals were similar for RNA extracted from innervated and denervated leg muscles. The signals were also similar for RNA extracted from perisynaptic and extrasynaptic regions of hemidiaphragm muscle but u-PA signals were lower in denervated than in innervated hemidiaphragm. No such difference was observed for t-PA. PN-1 mRNA levels were also found to decrease after denervation in the hemidiaphragm but no substantial decrease was observed in denervated hind-limb muscles. No difference was observed between PN-1 expression in perisynaptic and extrasynaptic regions. The effect of denervation on PA enzymatic activity in skeletal muscle is therefore likely to be mediated at some post-transcriptional level.

Evidence for an alteration of plasma and liver proteins response to dexamethasone in aging rats

The aim of this study was carried out to analyse the liver and plasma proteins response to dexamethasone in adult (6-8 months) and old (24 months) rats in order to ascertain the involvement of glucocorticoids in the aging process. The animals received dexamethasone (Dex) for 5 or 6 days. As Dex decreased food intake, all groups were pair fed to dexamethasone-treated old rats. The synthesis of mixed plasma and liver proteins (assessed by a flooding dose of [13C] valine) was similarly greatly improved in adult and old rats after Dex treatment. However, the level of mixed plasma proteins was only slightly increased. When specific plasma proteins were assessed, a similar increase in the concentration of albumin and alpha1 acid glycoprotein was observed in adult and old rats. By contrast, fibrinogen decreased to a greater extend in old rats and alpha2 macroglobulin became undetectable in old animals. It was concluded that the response of plasma and liver proteins to Dex was altered in old rats and may contribute to the pathogenesis of several diseases which occur during aging.

Diazoxide-induced insulin deficiency greatly reduced muscle protein synthesis in rats: involvement of eIF4E

We have investigated the effect of a postprandial acute insulin deficiency induced by diazoxide injection on rat skeletal muscle protein synthesis. Diazoxide administration lowered plasma insulin >85% within 3 h after injection, whereas other hormones (insulin-like growth factor I, glucagon, corticosterone) involved in the regulation of muscle protein synthesis were not altered significantly compared with control animals. The fractional rate of muscle protein synthesis, measured in vivo, was reduced significantly (P < 0.05) in epitrochlearis (-46%), gastrocnemius (-41%), and soleus (-35%). The reduction in protein synthesis did not result from a reduced total RNA content but was associated with diminished translation efficiency. Analysis of ribosomal subunits revealed that the decreased translation efficiency resulted from an impairment in the initiation phase of protein synthesis. Diazoxide-induced insulin deficiency was associated with a dramatic decrease in eukaryotic initiation factor (eIF) 4G bound to eIF4E and a 2.5-fold increase in the amount of the eIF4E. 4E-binding protein 1 (BP1) complex. In contrast, diazoxide injection did not change either the relative amount of eIF4E present in gastrocnemius or its phosphorylation state. These results indicate that an acute insulin deficiency significantly decreases postprandial muscle protein synthesis by modulating the interaction between 4E-BP1, eIF4G, and eIF4E to control translation initiation.

Effect of glucocorticoid excess on skeletal muscle and heart protein synthesis in adult and old rats

This study was carried out to analyse glucocorticoid-induced muscle wasting and subsequent recovery in adult (6-8 months) and old (18-24 months) rats because the increased incidence of various disease states results in hypersecretion of glucocorticoids in ageing. Adult and old rats received dexamethasone in their drinking water for 5 or 6 d and were then allowed to recover for 3 or 7 d. As dexamethasone decreased food intake, all groups were pair-fed to dexamethasone-treated old rats (i.e. the group that had the lowest food intake). At the end of the treatment, adult and old rats showed significant increases in blood glucose and plasma insulin concentrations. This increase disappeared during the recovery period. Protein synthesis of different muscles was assessed in vivo by a flooding dose of [13C]valine injected subcutaneously 50 min before slaughter. Dexamethasone induced a significant decrease in protein synthesis in fast-twitch glycolytic and oxidative glycolytic muscles (gastrocnemius, tibialis anterior, extensor digitorum longus). The treatment affected mostly ribosomal efficiency. Adult dexamethasone-treated rats showed an increase in protein synthesis compared with their pair-fed controls during the recovery period whereas old rats did not. Dexamethasone also significantly decreased protein synthesis in the predominantly oxidative soleus muscle but only in old rats, and increased protein synthesis in the heart of adult but not of old rats. Thus, in skeletal muscle, the catabolic effect of dexamethasone is maintained or amplified during ageing whereas the anabolic effect in heart is depressed. These results are consistent with muscle atrophy occurring with ageing.

Interactive effects of denervation and malnutrition on diaphragm structure and function

The purpose of this study was to examine the interactive effects of unilateral denervation (DN) and prolonged malnutrition (MN) on the structure and function of the diaphragm muscle (Dia). Four groups of rats were studied: control (Con), MN, DN, and DN-MN. MN began 2 wk after DN and lasted 4 wk. In both the DN and DN-MN groups, the relative loss in Dia weight exceeded the relative change in body weight. Compared with the Con group, Dia specific force was reduced by approximately 40% in both the DN and DN-MN groups but was unaffected in the MN group. Dia fatigue resistance improved in all experimental groups but to a greater extent in the DN and DN-MN groups. In both the DN and DN-MN groups, approximately 50% of Dia fibers were classified as type IIc, whereas fiber type proportions did not change in the MN group. In the DN group, only type IIb/x fibers atrophied, whereas all fiber types atrophied in the MN and DN-MN groups. We conclude that in the DN-MN group the reduction in specific force combined with the reduction in total cross-sectional area of the muscle significantly curtails Dia force-generating capacity.

Age-related changes in protein synthesis measured in vivo in rat liver and gastrocnemius muscle

This study analyses in detail the effects of ageing on gastrocnemius muscle and liver protein synthesis measured in vivo at three ages, 1.5 months (young), 12 months (adult) and 24 months (old) in Sprague-Dawley rats. Comparing adult and old rats, muscle protein synthesis was decreased in old rats when expressed per unit of RNA and per day (translational efficiency), was unchanged when expressed in absolute terms and increased when expressed in fractional terms as a result of protein loss due to muscle atrophy. In the liver, only translational efficiency tended to decrease in old rats compared to adult rats. It is concluded that the decline in protein turnover described in vitro is consistent with a decrease in translational efficiency, but that absolute synthesis rates are maintained during ageing. Muscle atrophy is unlikely to result from alterations in protein synthesis pathways.

The effect of sodium repletion on growth and protein turnover in sodium-depleted rats

This study examines the consequences of sodium chloride supplementation to young rats previously made salt deficient by feeding them a sodium-deficient, chloride-replete diet. Salt-deficient rats received the test diet and distilled water for 10 days. As in our previous studies, rats cared for in this manner grew more slowly than rats fed the identical diet but allowed to drink 37 mM sodium chloride. On day 11, half of the salt-depleted animals received 37 mM sodium chloride in their drinking water. Sodium-deficient and supplemented rats were studied 1,2,5-6 and 11-12 days later. Urinary sodium rapidly rose from undetectable of 46 mEq/l urine within 1 day of supplementation and there was no further increase the next day, suggesting that extracellular fluid volumes were rapidly repleted. Food intake increased in the supplemented rats compared with the deficient animals but the difference in food intake equalled only 2.25 g/day for the first 2 days of supplementation. Over the last 12 days of the study, the slopes of both weight and length gains were equal in both the supplemented and the control group and significantly higher than those in the deficient rats. Over the course of the study, full catchup was not obtained in either length or weight. In addition to total weight and length gains, liver and kidney weights increased proportionately and by 5-6 days of supplementation were equivalent to the weights seen in the control group.(ABSTRACT TRUNCATED AT 250 WORDS)

Mechanisms of differential growth of heart ventricles in newborn pigs

The left ventricular free wall (LVFW) grew approximately three times faster than the right ventricular free wall (RVFW) during the first 10 days of life in neonatal pigs. Faster growth was associated with proportional increases in total RNA and messenger RNA. These findings indicated that greater capacity for protein synthesis was a major factor in accelerated growth. Despite faster growth, heart content of ribosomal subunits was higher in piglets than in 60-day-old pigs or adult rats, suggesting a relatively slower rate of peptide chain initiation than elongation. When hearts from 5-day-old pigs were perfused in vitro, protein synthesis was more rapid in the LVFW than in the RVFW. In the absence of added insulin, the higher rate was due to both greater efficiency and greater capacity for protein synthesis. In the presence of the hormone, greater capacity was responsible for the increased rate of protein synthesis in the LVFW as compared with the RVFW.

Role of polyamines and intracellular pH change in the hypertrophy of the denervated rat hemidiaphragm

The transient hypertrophy of the denervated rat hemidiaphragm is associated with a rise in concentrations of putrescine and spermidine. Hypertrophy still occurs following denervation in rats injected with difluoromethylornithine which reduces the increase in spermidine and particularly putrescine levels. Administration of isobutylmethylxanthine tended to raise putrescine concentrations in the denervated but not innervated tissue. No evidence could be found that the enhanced protein synthesis rate in the denervated tissue is associated with an increase in intracellular pH.

Mitogenic response of rat lung to endotoxin exposure

Adult rats exposed to hyperoxia are protected from lung injury by treatment with bacterial endotoxin. Experiments were undertaken to determine whether endotoxin treatment produces a mitogenic effect on the lung. Endotoxin treatment caused a significant (P less than .05) loss of body weight (8%) in rats exposed to either air or greater than 95% O2 for 24 hr. Therefore, experiments were also undertaken in which both saline- and endotoxin-treated rats were starved for the duration of the experiments to make equal any nutritional imbalance. The rate of DNA synthesis in lung slices from fed rats treated with endotoxin did not differ from that of saline-treated controls. In contrast, lung DNA synthesis in starved rats treated with endotoxin increased 50%. The effect of endotoxin treatment was similar in rats breathing air or greater than 95% O2, and lung protein synthesis generally paralleled lung DNA synthesis. These results indicate that endotoxin does exert a mitogenic effect on the lung and this effect can be masked by the nutritional imbalance resulting from endotoxin administration.

Leupeptin's effect on organ weight, RNA, DNA, and protein content after long bone fracture in the rat

Long bone fracture in the rat is accompanied by enhanced urinary nitrogen loss reflecting changes in protein synthesis and breakdown. The effects of leupeptin, an inhibitor of lysosomal proteases, were assessed on organ weights, RNA, DNA, and protein content after injury in the rat. Two groups of 8-week-old rats were studied: The first group received left femoral fracture. Half of these received leupeptin (25 mumole ip/day), and the remainder received saline. The second group served as uninjured pair-fed controls, with half receiving leupeptin and half receiving saline. On Days 0, 1, 2, 4, and 7 after injury, animals were sacrificed and organs were removed for determination of weight, RNA, DNA, and protein content. All injured rats lost weight, with maximum loss occurring on Day 4. Food intake was also reduced. Pair-fed rats lost the same amount of weight as injured ones, and leupeptin could not prevent whole body weight loss. Expressed as percentage of total body weight, livers from leupeptin-treated injured rats weighed 10% greater than saline-treated ones on Days 2, 4, and 7 after injury (P less than 0.05). No differences occurred in RNA, DNA, or protein contents. Diaphragms similarly weighed 10, 20, and 30% greater on Days 2, 4, and 7 after injury, respectively, in leupeptin-treated rats (P less than 0.05). In addition, the RNA and DNA contents of diaphragms were 96 and 88% greater, respectively, in treated rats than in controls (P less than 0.05) on Day 4. It is concluded that leupeptin causes a relative increase in the weights of livers and diaphragms after injury, and causes a marked increase in the RNA and DNA contents of diaphragms.

Histochemical and biochemical characteristics of the transient hypertrophy of the denervated rat hemidiaphragm

A systematic study of the different fiber types of rat diaphragm muscle in the first 10 days after unilateral denervation showed approximately a 10% decrease in diameter of the white fibers, 25% increase in that of intermediate fibers, and 35% increase in that of red fibers together with diminished differential staining properties both for myosin ATPase and Sudan black. There was also a doubling of the amount of connective tissue. A reduction in total lipid concentration of the tissue included decreases in both triacylglycerol and phospholipid, but not cholesterol. Magnesium concentration in the tissue also declined, as did activity of Ca2+-activated, though not Mg2+-activated, myosin ATPase.

Vitamin D Deficiency, hypocalcemia, and increased skeletal muscle degradation in rats

The myopathy associated with vitamin D deficiency was examined in vitamin D-deficient and vitamin D-supplemented rats. When compared with either vitamin D-supplemented ad lib. or pair-fed rats, weight gain and muscle mass were decreased in vitamin D-deficient hypocalcemic animals. With the exception of a modest decrease in muscle creatine phosphate levels, muscle composition was unchanged by vitamin D deficiency. Muscle protein turnover rates were determined in both in vivo and in vitro studies and demonstrated that myofibrillar protein degradation was increased in vitamin D deficiency. Normal growth rates could be maintained be feeding the rats vitamin D-deficient diets containing 1.6% calcium, which maintained plasma calcium within the normal range. In addition to its role in maintaining plasma calcium, vitamin D-supplemented rats had significantly higher levels of the anabolic hormone insulin. Vitamin D supplementation may affect muscle protein turnover by preventing hypocalcemia, as well as directly stimulating insulin secretion, rather than by a direct effect within skeletal muscle.

A fluorescent microscopy study of biopsied muscles from infantile neuromuscular disorders

The Acridine Orange (AO) stain for muscle biopsies is particularly useful to identify regenerating and ongoing hypertrophic muscle fibers under fluorescent microscopy. This method was applied to muscle biopsies from 65 patients who suffered from various childhood neuromuscular disorders. While normal fibers showed dull green cytoplasm with small green-yellow nuclei, striking fluorescent fibers were observed in eight cases of congenital muscular dystrophy (CMD) and 12 cases of Duchenne muscular dystrophy (DMD); these fibers were characterized as follows: (1) small fibers with big oval or spherical nuclei which fluoresced strongly with a bright orange color; (2) fibers of various sizes and different degrees of orange fluorescence; and (3) opaque fibers with bright yellow cytoplasm. The small diameter fibers in Werdnig-Hoffmann (WH) disease, nemaline myopathy, and congenital fiber type disproportion failed to show apparent AO-RNA fluorescence. Although all the atrophic fibers in Kugelberg-Welander (KW) disease showed a vague orange fluorescent color, this was obviously different from that of regenerating fibers seen in CMD and DMD. In addition to these findings, the hypertrophic fibers in a case of unclassified myopathy also showed moderate orange fluorescence around the entire periphery of the cytoplasm.

Denervation modulated changes in mouse skeletal muscle RNA concentration

We have examined normal and denervated mouse skeletal muscle for histological evidence of changes in RNA concentration using acridine orange/nucleic acid fluorescence. In denervated muscle, cytoplasmic RNA concentration increases dramatically. The earliest increase is in the subsarcolemmal region, 7 days after denervation. By 28 days after denervation, the increase in RNA is distributed throughout the cytoplasm of the atrophic cells, non-atrophic cells show little or no increase. Prior to the increase in cytoplasmic RNA concentration, many myocyte nuclei exhibit enlarged nucleoli, indicative of active ribosomal RNA synthesis. Such active nucleoli are present throughout the 42 day study period. We conclude that both new RNA synthesis, and preferential accumulation of cytoplasmic RNA are prominent events in denervation atrophy. There is an ordered progression from nucleolar synthesis to subsarcolemmal accumulation to diffuse accumulation in atrophying cells. These observations complement biochemical findings of others which indicate an increase in both RNA and protein synthesis after denervation.

Cyclic nucleotides in the denervated rat diaphragm and the effect of cyclic AMP on ornithine and adenosylmethionine decarboxylases

The concentrations of cyclic AMP and cyclic GMP were measured in the denervated rat diaphragm at various times following unilateral phrenicectomy. Cyclic AMP concentration was raised by the second day after operation, reached a peak by the third day, followed by another increase at around 10 days. By contrast, cyclic GMP concentration was decreased within a day after denervation and remained below control levels at all subsequent times studied. Epinephrine in vitro produced a comparable increase in the concentration of cyclic AMP in both normal and denervated tissue. The concentration of adenosine appeared unchanged in the denervated diaphragm by comparison with its innervated control. Activity of ornithine decarboxylase was elevated in the diaphragms of rats treated with dibutyryl cyclic AMP, but this effect could also be achieved with sodium butyrate alone. Adenosylmethionine decarboxylase activity, was unaffected after treatment with either compound. These observations and others discussed are taken to indicate a lack of direct relationship between cyclic AMP concentrations and the activity of the rate-limiting enzymes of polyamine biosynthesis in the rat diaphragm.

The influence of nerve section on the metabolism of polyamines in rat diaphragm muscle

Concentrations of spermidine, spermine and putrescine have been measured in rat diaphragm muscle after unilateral nerve section. The concentration of putrescine increased approx. 10-fold 2 days after nerve section, that of spermidine about 3-fold by day 3, whereas an increase in the concentration of spermine was only observed after 7-10 days. It was not possible to show enhanced uptake of either exogenous putrescine or spermidine by the isolated tissue during the hypertrophy. Consistent with the accumulation of putrescine, activity of ornithine decarboxylase increased within 1 day of nerve section, was maximally elevated by the second day and then declined. Synthesis of spermidine from [14C]putrescine and either methionine or S-adenosylmethionine bt diaphragm cytosol rose within 1 day of nerve section, but by day 3 had returned to normal or below normal values. Activity of adenosylmethionine decarboxylase similarly increased within 1 day of nerve section, but by day 3 had declined to below normal values. Activity of methionine adenosyltransferase was elevated throughout the period studied. The concentration of S-adenosylmethionine was likewise enhanced during hypertrophy. Administration of methylglyoxal bis(guanylhydrazone) produced a marked increase in adenosylmethionine decarboxylase activity and a large increase in putrescine concentration, but did not prevent the rise in spermidine concentration produced by denervation. Possible regulatory mechanisms of polyamine metabolism consistent with the observations are discussed.

Protein synthesis and degradation in skeletal muscle of normal and dystrophic hamsters

Dystrophic hamsters (BIO 53.58) had lower body weights and gastrocnemius muscle weights than normal hamsters (BIO RB). Dystrophic muscle contained less protein than normal muscle. The proportion of collagenous to noncollagenous protein remained unchanged. Loss of protein in the dystrophic muscle was the result of an increase in the rate of protein degradation. This was accompanied by higher activities of two lysosomal proteases, cathepsins B and D. The net effect of the increase in protein degradation was blunted by an increase in the rate of synthesis of total protein and myosin. The faster rate of synthesis in dystrophic muscle was partially due to an increase in the concentration of cellular RNA. Rates of peptide-chain initiation and protein synthesis decreased in muscles of normal hamsters perfused in the absence of insulin. In the presence of insulin, these processes were maintained at higher rates. However, the rate of protein synthesis in dystrophic muscle appeared less insulin-dependent than normal muscle. Protein degradation was inhibited by insulin in both types of muscle.

Effects of glucocorticoids on muscle protein turnover in perfused rat hemicorpus

Normal and adrenalectomized rats treated with cortisone lost 2% of their initial body weight per day, whereas controls gained weight at a rate of 2%/day. Five days of treatment resulted in a 25% reduction in the weights of a number of mixed fiber type muscles, but did not affect the weights of heart or soleus, a muscle consisting of slow-twitch red fibers. Reductions in muscle weights were accompanied by a loss of protein and RNA. Perfused hemicorpus preparations from rats receiving 5 days of treatment released several amino acids in greater amounts than the controls. Protein synthesis in perfused gastrocnemius was reduced 50-60% after 3 or 5 days of steroid treatment. This reduction was due to a loss of RNA and to an inhibition of translation resulting from an impairment in peptide-chain initiation. In contrast, RNA content and initiation were not altered in heart and soleus. Protein degradation in perfused hemicorpus and cathepsin D activity in gastrocnemius were unaffected by cortisone treatment, suggesting that loss of muscle weight and protein content as well as increased amino acid release resulted from the reduction in protein synthesis.

Early changes in muscle glucose-6-phosphate dehydrogenase activity after denervation: locus and dependence on nerve stump length

Glucose-6-phosphate dehydrogenase (G6PD) activity of rat diaphragm muscle increased significantly 12 h after intrathoracic ('distal') denervation. Since this change represented one of the earliest known events after loss of innervation, the mechanism of neuronal regulation and the nature of the muscle response were further investigated. When, instead of distal denervation, the motor nerve was cut about 3.5 cm from the diaphragm, G6PD activity slightly decreased 12 h later. Denervations in which part of the same hemidiaphragm had a short nerve stump and another part, a long nerve stump, also showed a differential increase of G6PD activity dependent on length of nerve stump. In biochemical studies of the locus of the early post-denervation elevation of G6PD, enzyme activity was increased both in endplate and non-endplate regions of the muscle. Finally, the histochemical reaction for G6PD was more intense in both muscle fibers and interstitial elements, although the former made the major contribution to the biochemical results. In sum, muscle G6PD enzyme activity is closely regulated by a neurotrophic mechanism partly independent of nerve or muscle electrical activity.

Effects of starvation and diabetes on protein synthesis in lung

Metabolism of lung proteins was investigated in rats starved 3 days or made diabetic with streptozotocin. Body weight was below normal in both groups, but lung weight decreased only in starved animals. Total lung protein and RNA (mg/lung) decreased during starvation and diabetes. Protein concentration (mg/g) was unchanged in either group of animals; RNA concentration decreased only during starvation. Protein synthesis, estimated in lungs perfused in situ, was reduced 22% in starvation, but remained unchanged in diabetes. Inhibition of protein synthesis was accounted for by loss of RNA. Ribosomal profiles were unchanged by starvation, suggesting an unaltered relationship between rates of peptide-chain initiation and elongation in vivo. Activity of an eIF-2-like initiation factor decreased during starvation in proportion to the loss of RNA. In diabetes, factor activity remained normal. Thus, starvation but not streptozotocin-induced diabetes, reduced the capacity of the lung to synthesize protein. No evidence for reduced efficiency of synthesis was observed.

The influence of passive stretch on the growth and protein turnover of the denervated extensor digitorum longus muscle

At 7 days after cutting the sciatic nerve, the extensor digitorum longus muscle was smaller and contained less protein than its innervated control. Correlating with these changes was the finding of elevated rates of protein degradation (measured in vitro) in the denervated tissue. However, at this time, rates of protein synthesis (measured in vitro) and nucleic acid concentrations were also higher in the denervated tissue, changes more usually associated with an active muscle rather than a disused one. These anabolic trends have, at least in part, been explained by the possible greater exposure of the denervated extensor digitorum longus to passive stretch. When immobilized under a maintained influence of stretch the denervated muscle grew to a greater extent. Although this stretch-induced growth appeared to occur predominantly through a stimulation of protein synthesis, it was opposed by smaller increases in degradative rates. Nucleic acids increased at a similar rate to the increase in muscle mass when a continuous influence of stretch was imposed on the denervated tissue. In contrast, immobilization of the denervated extensor digitorum longus in a shortened unstretched state reversed most of the stretch-induced changes; that is, the muscle became even smaller, with protein synthesis decreasing to a greater extent than breakdown after the removal of passive stretch. The present investigation suggests that stretch will promote protein synthesis and hence growth of the extensor digitorum longus even in the absence of an intact nerve supply. However, some factor(s), in addition to passive stretch, must contribute to the anabolic trends in this denervated muscle.

Subcellular distribution of a factor inactivating tyrosine aminotransferase. Study of its mechanism and relationship to different forms of the enzyme

The subcellular distribution of a tyrosine aminotransferase inactivating factor in rat liver has been investigated. Most of its activity is associated with plasma membranes, with minor amounts in mitochondria and endoplasmatic reticulum. The factor is also found in kidney and inactivates the enzyme reversibly in presence of cysteine, most likely by modification of -SH groups. ATP counteracts this inactivation only, when crude enzyme extracts are inactivated by purified subcellular fractions or when the purified enzyme is inactivated in presence of liver or kidney cortex homogenates. The relationship of this inactivation to reported different forms of the enzyme has been investigated. Form I of three different forms, that can be obtained by hydroxyl-apatite chromatography, is readily inactivated, form III can be partly converted to form I by incubation in presence of purified plasma membranes. The relationship of these findings to a possible multistep mechanism in the turnover of the enzyme discussed.

The effects of denervation on protein turnover of the soleus and extensor digitorum longus muscles of adult mice

1. Changes in protein turnover of the soleus and EDL muscles of adult mice have been studied 1, 7 and 80 days after denervation. 2. Increased rates of protein degradation 7 and 80 days post-denervation correlated with the atrophy and loss of protein from these muscles. 3. Rates of protein synthesis in the EDL decreased 24 hr after nerve section. However, these synthetic rates increased again to become higher in the 7 day denervated muscles compared with their controls. These latter anabolic changes are inconsistent with the concept of a denervated muscle being inactive. 4. These findings have been compared with a similar study on muscles of growing rats. Any passive stretching of the denervated muscles by continued bone growth appears unlikely to be a crucial factor explaining the increased rates of protein synthesis 7 days after denervation.

Age-related changes in protein turnover and ribonucleic acid of the diaphragm muscle of normal and dystrophic hamsters

Diaphragm muscles of dystrophic hamsters were found to be larger than those of control animals at two of three ages studied. The additional growth of these afflicted muscles correlated with large increases in protein synthesis and concentrations of RNA. Protein breakdown was also increased in the dystrophic muscles, but to a smaller extent than synthesis.

The effects of denervation on protein turnover of rat skeletal muscle

The effects of denervation on muscle weight, rates of protein synthesis and breakdown, and RNA concentraitons were studied in the soleus and extensor digitorum longus muscle. Althrough the soleus underwent a true atrophy after section of the sciatic nerve, the extensor digitorum longus continued to grow, albeit at a lower rate than innervated controls. At 24h after nerve section protein breakdown was increased in both muscle types when compared with internal controls, and remained so throughout the 10 days studied. The possibility that this increased catabolism might arise from conformational changes of proteins after denervation was not substantiated, as myofibrillar or soluble proteins of denervated and control tissues were equally susceptible to degradation in vitro by three proteinases. Tyrosine uptake into the denervated extensor digitorum longus was decreased throughout the 10 days studied, whereas two phases of increased transport of the amino acid were found in the soleus. Significant decreases in rates of protein synthesis were found 1 and 2 days after denervation and results are presented that suggest that these changes may result from a decrease in ribosomal involvement in the translation process. These initial decreases were not maintained and the rate of protein synthesis was in fact increased when compared with controls, at 7 and 10 days. The increased synthetic rates of the 7-day denervated tissues were reflected as proportional increases in both myofibrillar and soluble proteins. It is suggested that the increase in synthesis at this time may result from an increase in both the abailability and active involvement of ribosomes, and that these anabolic trends may be caused by spontaneous fibrillation and/or the amount of passive stretching of the denervated muscles.

Effects of denervation on the glycogen content and on the activities of enzymes of glucose and glycogen metabolism in rat diaphragm muscle

1. Changes in the content and concentration of glycogen and in the activity of a number of enzymes involved in glucose and glycogen metabolism were studied in the rat hemidiaphragm after unilateral denervation. 2. After nerve section the tissue hypertrophies; this hypertrophy is said to be confined to the smaller red fibres and not to the white. 3. The total hexokinase activity increases, whereas that of total glycogen phosphorylase decreases. The specific activity of phosphorylase a, determined after Halothane anaesthesia, remains fairly constant. 4. In fed animals the denervated tissue stores less glycogen, but in the early stages its glycogen content does not fall on starvation. 5. The effect of denervation on the specific activities of several other characteristically white-fibre enzymes are not consistent with the response of glycogen phosphorylase; the increase in content of glyceraldehyde 3-phosphate dehydrogenase and lactate dehydrogenase is thought to be related to proliferation of the sarcoplasmic reticulum. 6. The ratio of lactate dehydrogenase M/H subunits increases at the height of the hypertrophy, but then declines as the mass of the tissue falls. 7. The chronology of these changes in enzyme activities suggests a multiplicity of distinct responses after nerve section not consistent with any one model, either specific fibre development or reversion to de-differentiated, foetal-type metabolism.

A comparison of the effects of diabetes induced with either alloxan or streptozotocin and of starvation on the activities in rat liver of the key enzymes of gluconeogenesis

1. Measurements of the activities in rat liver of the four key enzymes involved in gluconeogenesis, i.e. pyruvate carboxylase (EC 6.4.1.1), phosphoenolpyruvate carboxykinase (EC 4.1.1.32), fructose 1,6-diphosphatase (EC 3.1.3.11) and glucose 6-phosphatase (EC 3.1.3.9), have been carried out, all four enzymes being measured in the same liver sample. Changes in activities resulting from starvation and diabetes have been studied. Changes in concentration (activity/unit wet weight of tissue) were compared with changes in the hepatic cellular content (activity/unit of DNA). 2. Each enzyme was found to increase in concentration during starvation for up to 3 days, but only glucose 6-phosphatase and phosphoenolpyruvate carboxykinase showed a significant rise in content. Fructose 1,6-diphosphatase appeared to decrease in content somewhat during the early stages of starvation. 3. There was a marked increase in the concentration of all four enzymes in non-starved rats made diabetic with alloxan or streptozotocin, for the most part similar responses being found for the two diabetogenic agents. On starvation, however, the enzyme contents in the diabetic animals tended to fall, often with streptozotocin-treated animals to values no greater than for the normal overnight-starved rat. Deprivation of food during the period after induction of diabetes with streptozotocin lessened the rise in enzyme activity. 4. The results are compared with other published values and factors such as substrate and activator concentrations likely to influence activity in vivo are considered. 5. Lack of correlation of change in fructose 1,6-diphosphatase with the other enzymes questions whether it should be included in any postulation of control of gluconeogenic enzymes by a single gene unit.