Frühbeck G, Muguerza B, Castilla-Cortázar I, Santidrián S
Departamento de Fisiología, Facultad de Medicina, Universidad de Navarra, Pamplona, Spain.
Rev Esp Fisiol. 1996 Dec;52(4):207-14.
The urinary excretion of Nt-methylhistidine (e-methylhistidine, 3-MH, an index related to myofibrillar protein breakdown), as well as the rate of L-[14C]-tyrosine incorporation into gastrocnemius muscle (ks, fractional rate of muscle protein synthesis, evaluated by the constant infusion method) have been measured to assess the effect of aging on the rate of skeletal muscle protein turnover. In addition, nucleic acids, muscle protein and serum corticosterone levels were determined. Weaning rats were fed a 10% lactalbumin diet and killed in groups of seven when they were 35, 60, 120 and 300 days old. Apart from the rate of growth, no major differences were found between 35- and 60-day old animals. However, as compared to the youngest rats, 120-day old rats showed a significant reduction in the relative weight of the four muscles excised. Plasma corticosterone levels, increased as the animals became older. Finally, in the 300-day old rats, the reduced rate of growth was accompanied by a significant reduction in the relative organ weight (with the exception of soleus), 3-MH and Ks. It is concluded that aging caused a reduction in the rates of both protein breakdown and synthesis. The reduced muscle breakdown may not be due to a relative reduced muscle mass in elder rats since urinary 3-MH remained low even when expressed per creatinine output.
已测定了Nτ-甲基组氨酸（ε-甲基组氨酸，3-MH，一种与肌原纤维蛋白分解相关的指标）的尿排泄量，以及L-[14C]-酪氨酸掺入腓肠肌的速率（ks，通过恒速输注法评估的肌肉蛋白质合成分数速率），以评估衰老对骨骼肌蛋白质周转速率的影响。此外，还测定了核酸、肌肉蛋白和血清皮质酮水平。将断乳大鼠喂食10%乳清蛋白饮食，并在它们35、60、120和300日龄时按每组七只进行处死。除生长速率外，35日龄和60日龄动物之间未发现重大差异。然而，与最年幼的大鼠相比，120日龄大鼠切除的四块肌肉的相对重量显著降低。血浆皮质酮水平随着动物年龄的增长而升高。最后，在300日龄大鼠中，生长速率降低伴随着相对器官重量（比目鱼肌除外）、3-MH和ks的显著降低。结论是，衰老导致蛋白质分解和合成速率降低。肌肉分解减少可能不是由于老年大鼠肌肉质量相对减少，因为即使按肌酐排出量计算，尿3-MH仍保持在低水平。
