Muscle degradation in uremia: 3-Methylhistidine release in fed and fasted rats

Muscle degradation in uremia: 3-Methylhistidine release in fed and fasted rats. The rate of myofibrillar protein degradation was measured by 3-methylhistidine (3MH) release in moderately uremic and sham-operated control rats. The rats were studied in the fed state or after 24 and 48 hours of fasting. When fed, both uremic and control rats gained weight at the same rate. During 48 hours of fasting, the uremic animals lost more weight (17.1%) than the shams (13.2%). The ratio of gastrocnemius muscle protein per gram of wet weight was not significantly different under any conditions. When fed and 48-hour fasted animals are compared, urinary excretion of 3MH rose from 0.81 to 1.32 moles per 24hr per 100g of initial body wt in shams and from 0.90 to 1.30 moles per 24hr per 100g of initial body wt in the uremics. When the ratio of 3MH to creatinine excretion in the urine was compared, there was no change in 3MH excretion between 0 and 24 hours, but there was an increase between 24 and 48 hours. Analysis of serum and muscle samples from fed and 48-hour fasted animals revealed that the concentrations of 3MH increased in both groups during fasting, with the uremic rats having a larger increase in the total body 3MH pool. Myofibrillar degradation rates calculated from the sum of urinary excretion plus the changes in body 3MH pool size revealed that with moderate fasting, degradation rates increased in both sham and uremic rats with a larger increase being seen in the uremic group. After 48 hours of fasting, the increased amount of 3MH released from muscle of uremic rats was comparable to their larger percentage weight loss. Degradation musculaire au cours de l'uremie: Liberation de 3-methyl-histidine chez les rats nourris et a jeun. La vitesse de degradation des proteines myofibrillaires a ete mesuree par la liberation de 3-methylhis-tidine (3MH) chez des rats moderement uremiques et chez des controles. Les rats ont ete etudies nourris ou bien apres 24 a 48 heures de jeune. Les rats nourris, uremiques ou controles, ont pris du poids de la meme facon. Au cours de 48 heures dejeune les animaux uremiques ont perdu plus de poids (17,1%) que les controles (13,2%). Le rapport des proteines du muscle grastronecmien/poids humide eng n'etait pas significativement different dans ces conditions. Quand les animaux nourris et les animaux a jeun depuis 48 heures ont ete compares on a constate que l'excretion de 3MH a augmente de 0,81 a 1,32 moles per 24hr per 100g de poids initial chez les temoins et de 0,90 a 1,30 moles per 24hr per 100g de poids initial chez les uremiques. La comparaison du rapport d'excretion urinaire de 3MH/creatinine n'a pas montre de modification entre 0 et 24 heures, puis une augmentation entre 24 et 48 heures. L'analyse d'echantillons de serum et de muscle provenant d'animaux nourris ou a jeun depuis 48 heures a montre que les concentrations de 3MH augmentaient dans les deux groupes au cours du jeune, les uremiques ayant une plus grande augmentation du pool total de 3MH. Les vitesses de degradation myofibrillaire calculees a partir du cumul de l'excretion urinaire et des modifications de la taille du pool corporel de 3MH ont revele qu'au cours du jeune modere la vitesse de degradation augmente a la fois chez le controle et l'uremique mais plus chez l'uremique. Apres 48 heures de jeune la plus grande quantite de 3MH liberee du muscle des rats uremiques est en rapport avec leur plus grande perte de poids.