In-vivo-Methoden zur Analyse von Muskelstoffwechsel und Körperzusammensetzung beim Schwein unter besonderer Berücksichtigung genetischer Einflüsse
Pigs of different ryanodine receptor 1 (RyR1) genotypes serve as a model for the evaluation of various non-invasive in vivo methods to measure muscle energy
metabolism and body composition. The main focus is set on one hand on 31P and 13C nuclear magnetic resonance spectroscopy and on the other hand on nuclear magnetic resonance imaging and dual energy X-ray absorptiometry. In addition to a reference dissection and chemical analysis, the above mentioned methods are being extensively compared to other methods in the methodology part. An invasive muscle shot biopsy serves as an additional method in order to determine the muscle fiber composition of the longissimus dorsi muscle. Totally, 111 animals have been considered in the data analysis.
13C- and 31P NMR spectroscopy are very appropriate methods to measure in vivo or post mortem, non-invasively and continuously changes in the concentration of glycogen and creatine or phosphocreatine (PCr), inorganic phosphate (Pi), adenosintriphosphate (ATP), and pH-value directly in relative or absolute amounts over an „unlimited“ time period. 31P NMR spectroscopy compared to 13C NMR spectroscopy has advantages in the sensitivity and timely resolution for measuring changes in the concentration within the components of muscle metabolism. While 31P NMR spectra in vivo yield sufficient results for measuring changes of PCr, ATP, Pi and pH value within a time interval 5 minutes to acquire reasonable 13C NMR spectra in order to measure changes in the concentration of glycogen and creatine.
Progress in the techniques of body composition analysis is mainly based on
electronic and computer driven methods in order to provide non-invasive, fast and objective measurements. The selection of the appropriate method depends on the objective (research, performance testing, production, or diagnosis) and financial budget for each single study and clinical application. Technical details considering accuracy, precision, parameter selection and maximum/minimum size of an individual affect the decision as well as does a simple, robust, environment-safe, patient-comfortable and risk-free handling of the technique.
The highest accuracy for whole body studies within the imaging methods provide
magnetic resonance imaging (MRI) and computer tomography (CT) followed by dual
energy x-ray absorptiometry (DXA). DXA, however, outperforms MRI and CT due to
its simple handling and easy data analysis for whole body or regional body composition studies. In addition, DXA is beside the Quantitative CT the only non-invasive method which provides direct bone mineral density measurements.
According to the literature survey, the neutron activation analysis as a noninvasive method should be preferred for the calibration of body composition
measurement devices instead of chemical analysis or dissection. Chemical analysis and total dissection will remain standard reference methods as long as neutron activation facilities are available only on a very limited basis. However, the non-invasive (imaging) methods are less prone to error sources than are the diverse dissection or chemical analysis procedures.
The main advantages of the non-invasive imaging and/or spectroscopic methods
in vivo are:
1. the easy way to standardize the methods with a high repeatability (>75 %),
2. the opportunity of analyzing separately large volumes of interest of the whole body, body tissues and/or body parts,
3. the opportunity of performing continuous measurements over an “unlimited”
period of time, and
4. the harm “free” animal/patient precautions with a high degree of hygienic
safety.
An advantage for magnetic resonance, ultrasound and digital imaging is provided
by the function without radiation, while especially the “spiral computer tomography” is characterized by a very high speed of analysis. The muscle metabolism of the defect allele carriers at the RyR1 locus Nn and nn
shows already in vivo stress associated deviations in comparison to the “normal” genotype NN. After generating muscle stress by halothane, defect genotypes react with a decline in the glycogen, phosphocreatine, ATP, and pH level. Parallel inorganic phosphate and body temperature increase significantly. In the average show the homozygous defect allele carriers a stronger metabolic distress than do the heterozygous carriers. Differences among genotypes are higher post mortem compared to the metabolism in vivo. The muscle metabolic distress is connected with a muscle fiber hypertrophy in both defect allele genotypes. During growth, the homozygous defect allele genotype deposits more muscle mass (volume) and less fat than does the heterozygous genotype followed by the homozygous normal genotype.
Already at a live body weight of about 10 kg, magnetic resonance imaging
provides evidence for a larger muscle volume in the homozygous defect genotype in comparison to the two other genotypes. Beside the studied RyR1 genotypes (and the RN—-allel especially present in Hampshire), a large number of genetic, morphologic and environmental factors influence muscle metabolism and body composition in Swine -- as described in the discussion part. The RN—-allel causes a reduced glycogen depletion in vivo (and post mortem). Corresponding, the Hampshire line (≥ 50 % Hampshire genes) is beside the US-Landrace and the synthetic line “Duroc x Hampshire x US-Landrace x Spotted x Yorkshire” less obese than are the lines Duroc, “Poland China x Landrace”, Spotted, and “Duroc x Minzhu”. Spotted and “Duroc x Minzhu” are the most obese lines. In addition comparing all lines, Spotted (all Nn) responses --unexpectedly -- most severely to (muscle) stress caused by halothane administration.
