Contrasting response of protein degradation to starvation and insulin as measured by release of N tau-methylhistidine or phenylalanine from the perfused rat heart.
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ABSTRACT:
SUBMITTER: Smith DM
PROVIDER: S-EPMC1146998 | biostudies-other | 1986 Jul
REPOSITORIES: biostudies-other
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Project description:Mice and rats were injected with tracer doses of radioactive N tau-[Me-14C]methylhistidine in order to determine the recovery of the injected radioactivity and the extent of the metabolism of N tau-methylhistidine. In the first 27 h after injection, 96.3, 78.0 and 97.5% of radioactivity was excreted by female mice, male mice and male rats respectively. Recovery after 5 days of collection was 98.4 and 92.8% for female and male mice respectively. However, radioactivity associated with N tau-methylhistidine or its acetylated derivative accounted for 44, 86.5 and 96.0% of the excreted radioactivity for female mice, male mice and rats respectively. In female mice the remaining excreted radioactivity was associated with four major peaks of activity when the metabolites were separated by cation-exchange chromatography. In male mice there were only three of these metabolites present. After chromatographic purification, one metabolite was identified by mass spectroscopy to be 1-methylimidazole-4-acetic acid. Examination of the possible sources of this metabolite indicates that, in mice, N tau-methylhistidine is decarboxylated and enters the chain of reactions common to histamine metabolism. Such extensive metabolism precludes the use of N tau-methylhistidine excretion as an index of myofibrillar protein breakdown in mice.
| S-EPMC1152894 | biostudies-other
Project description:The role of glucocorticoids in regulating the rate of muscle protein breakdown was evaluated by measuring excretion of N(tau)-methylhistidine during administration of various doses of corticosterone to adrenalectomized rats. Groups of rats received daily subcutaneous injections of 0, 0.2, 0.5, 1.0, 5.0 or 10.0mg of corticosterone/day per 100g body wt. for 7 days, followed by 3 days without hormone treatment, after which they were killed. A group with intact adrenal glands served as an additional control. All animals were pair-fed with the untreated adrenalectomized group. No significant differences were noted in growth rate or N(tau)-methylhistidine excretion between the intact or adrenalectomized control groups, or those given 0.2, 0.5 and 1.0mg of corticosterone, whereas growth ceased and N(tau)-methylhistidine excretion rose markedly in the groups receiving 5 and 10mg of corticosterone. After these two high doses of corticosterone, but not after lower doses, there was a loss of weight of the gastrocnemius muscle per 100g of final body wt., but not of the soleus and extensor digitorum longus muscles. The two highest doses of corticosterone also resulted in an increase in liver weight per 100g of final body wt. Lower doses of corticosterone did not cause these changes. Plasma corticosterone concentrations, measured on the final day of injection and again at the time of killing, were decreased to near zero by adrenalectomy and were little raised by doses of 0.2 and 0.5mg daily, but were increased to within the normal range by the 1mg dose. At 5 and 10mg doses, plasma corticosterone concentrations were sustained at 2-3 times those of intact rats, and thus in the range reported for rats exposed to severe stress. Rats given 5 and 10mg doses of corticosterone had glycosuria, and showed considerably elevated concentrations of insulin in the plasma. It is concluded that plasma concentrations of glucocorticoids within the normal range do not regulate the rate of muscle protein breakdown, whereas excessive plasma concentrations of corticosteroids, equivalent to those observed in severe stress, can accelerate muscle protein breakdown.
| S-EPMC1186490 | biostudies-other
Project description:The Langendorff-perfused model is a powerful tool to study biological responses in the isolated heart in the absence of confounders. The model has been adapted recently to enable study of the isolated mouse heart and the effects of genetic manipulation. Unfortunately, the small size and fragility of the mouse heart pose significant challenges, limiting application of the Langendorff model to the study of adult mice. Cardiac development is a complex and dynamic process that is incompletely understood. Thus, establishing an isolated-perfused heart model in the newborn mouse would be an important and necessary advance. Here we present a method to successfully cannulate and perfuse the isolated newborn murine heart. We describe the basic and fundamental physiological characteristics of the ex-vivo retrograde-perfused beating neonatal heart in wild-type C57Bl/6 male mice. Our approach will enable future study of the physiological and pharmacological responses of the isolated immature murine heart to enhance knowledge of how developmental cardiac biology impacts health and disease.•The Langendorff model is a powerful tool to study the heart without confounders.•An isolated-perfused newborn murine heart model has yet to be established.•We demonstrate the first successful isolated neonatal murine heart preparation.
| S-EPMC7492986 | biostudies-literature
Project description:The metabolism of N tau-[Me-14C]methylhistidine by mice was influenced by both the sex and the phenotype of the animal. After subcutaneous injection of labelled N tau-methylhistidine, recoveries of radioactivity in excreta were incomplete, and the distributions of radioactivity showed that different mouse phenotypes degraded N tau-methylhistidine in vivo to different extents. Hence the excretion of N tau-methylhistidine by mice cannot be used as an index of protein breakdown in vivo.
| S-EPMC1147265 | biostudies-other
Project description:Phenylketonuria (PKU), with its associated hyperphenylalaninemia (HPA) and mental retardation, is a classic genetic disease and the first to have an identified chemical cause of impaired cognitive development. Treatment from birth with a low phenylalanine diet largely prevents the deviant cognitive phenotype by ameliorating HPA and is recognized as one of the first effective treatments of a genetic disease. However, compliance with dietary treatment is difficult and when it is for life, as now recommended by an internationally used set of guidelines, is probably unrealistic. Herein we describe experiments on a mouse model using another modality for treatment of PKU compatible with better compliance using ancillary phenylalanine ammonia lyase (PAL, EC 4.3.1.5) to degrade phenylalanine, the harmful nutrient in PKU; in this treatment, PAL acts as a substitute for the enzyme phenylalanine monooxygenase (EC 1.14.16.1), which is deficient in PKU. PAL, a robust enzyme without need for a cofactor, converts phenylalanine to trans-cinnamic acid, a harmless metabolite. We describe (i) an efficient recombinant approach to produce PAL enzyme, (ii) testing of PAL in orthologous N-ethyl-N'-nitrosourea (ENU) mutant mouse strains with HPA, and (iii) proofs of principle (PAL reduces HPA)-both pharmacologic (with a clear dose-response effect vs. HPA after PAL injection) and physiologic (protected enteral PAL is significantly effective vs. HPA). These findings open another way to facilitate treatment of this classic genetic disease.
| S-EPMC26785 | biostudies-literature
Project description:Direct measurement of N tau-methylhistidine turnover in skeletal muscle, skin and gastrointestinal muscle indicates that these three tissues contribute only 24.9, 6.8 and 9.8% of the total urinary excretion. Measurement of the decay rate of radioactively labelled N tau-methylhistidine in urine indicates that skeletal muscle accounts for 74.5% of the urinary excretion and this is probably an overestimate. These results suggest that the common assumption, that N tau-methylhistidine in urine originates almost entirely from skeletal muscle, may be wrong.
| S-EPMC1162081 | biostudies-other
Project description:Although basal release of cyclic AMP from isolated perfused rat hearts was not measurable, isoprenaline induced substantial release of the nucleotide, suggesting that in vivo the myocardium can contribute to plasma cyclic AMP. Anoxia also increased the amount of cyclic AMP released, but insulin and nicotinate alone or in combination had no effect.
| S-EPMC1172489 | biostudies-other
Project description:Myofibrillar protein degradation was measured in 4-week-old normal (line 412) and genetically muscular-dystrophic (line 413) New Hampshire chickens by monitoring the rates of 3-methylhistidine excretion in vivo and in vitro. A method of perfusing breast and wing muscles was developed and the rate of 3-methylhistidine release in vitro was measured between 30 and 90min of perfusion. During this perfusion period, 3-methylhistidine release from the muscle preparation was linear, indicating that changes in 3-methylhistidine concentration of the perfusate were the result of myofibrillar protein degradation. Furthermore, the viability of the perfused muscle was maintained during this interval. After 60min of perfusion, ATP, ADP and creatine phosphate concentrations in pectoral muscle were similar to muscle freeze-clamped in vivo. Rates of glucose uptake and lactate production were constant during the perfusion. In dystrophic-muscle preparations, the rate of 3-methylhistidine release in vitro (nmol/h per g of dried muscle) was elevated 2-fold when compared with that in normal muscle. From these data the fractional degradation rates of myofibrillar protein in normal and dystrophic pectoral muscle were calculated to be 12 and 24% respectively. Daily 3-methylhistidine excretion (nmol/day per g body wt.) in vivo was elevated 1.35-fold in dystrophic chickens. Additional studies revealed that the anti-dystrophic drugs diphenylhydantoin and methylsergide, which improve righting ability of dystrophic chickens, did not alter 3-methylhistidine release in vitro. This result implies that changes in myofibrillar protein turnover are not the primary lesion in avian muscular dystrophy. From tissue amino acid analysis, the myofibrillar 3-methylhistidine content per g dry weight of muscle was similar in normal and dystrophic pectoral muscle. More than 96% of the 3-methylhistidine present in pectoral muscle was associated with the myofibrillar fraction. Dystrophic myofibrillar protein contained significantly less 3-methylhistidine (nmol/g of myofibrillar protein) than protein from normal muscle. This observation supports the hypothesis that there may be a block in the biochemical maturation and development of dystrophic muscle after hatching. Free 3-methylhistidine (nmol/g wet wt.) was elevated in dystrophic muscle, whereas blood 3-methylhistidine concentrations were similar in both lines. In summary, the increased myofibrillar protein catabolism demonstrated in dystrophic pectoral muscle correlates with the increased lysosomal cathepsin activity in this tissue as reported by others.
| S-EPMC1163033 | biostudies-other
Project description:The excretion of N tau-methylhistidine and creatinine was determined in a totally paralysed patient wih neither macroscopic nor microscopic detectable skeletal-muscle tissue. In this subject, it was possible for the first time to measure the basal non-skeletal-muscle-dependent excretion of N tau-methylhistidine and creatinine per 24 h and per kg of non-muscular body weight, 1.15 mumol (N tau-methylhistidine) and 35 mumol (creatinine) respectively. For the calculation of myofibrillar protein breakdown and skeletal-muscle mass on the basis of N tau-methylhistidine and creatinine excretion, the values have to be corrected for non-muscular sources. Our data show that skeletal-muscle tissue is the major contributor of N tau-methylhistidine in urine, since it contributes as much as 75% to the urinary excretion.
| S-EPMC1163557 | biostudies-other
Project description:We present a coarse-grained two dimensional mechanical model for the microtubule-tau bundles in neuronal axons in which we remove taus, as can happen in various neurodegenerative conditions such as Alzheimers disease, tauopathies, and chronic traumatic encephalopathy. Our simplified model includes (i) taus modeled as entropic springs between microtubules, (ii) removal of taus from the bundles due to phosphorylation, and (iii) a possible depletion force between microtubules due to these dissociated phosphorylated taus. We equilibrate upon tau removal using steepest descent relaxation. In the absence of the depletion force, the transverse rigidity to radial compression of the bundles falls to zero at about 60% tau occupancy, in agreement with standard percolation theory results. However, with the attractive depletion force, spring removal leads to a first order collapse of the bundles over a wide range of tau occupancies for physiologically realizable conditions. While our simplest calculations assume a constant concentration of microtubule intercalants to mediate the depletion force, including a dependence that is linear in the detached taus yields the same collapse. Applying percolation theory to removal of taus at microtubule tips, which are likely to be the protective sites against dynamic instability, we argue that the microtubule instability can only obtain at low tau occupancy, from 0.06-0.30 depending upon the tau coordination at the microtubule tips. Hence, the collapse we discover is likely to be more robust over a wide range of tau occupancies than the dynamic instability. We suggest in vitro tests of our predicted collapse.
| S-EPMC4146510 | biostudies-literature