Radiation-induced increase in the release of amino acids by isolated, perfused skeletal muscle.

Local exposure of the hindquarter of the rat to 15 Gy of gamma-radiation resulted, 4-6 h after irradiation, in an increased release of amino acids by the isolated, perfused hindquarter preparation, 70 per cent of which is skeletal muscle. This increase in release involves not only alanine and glutamine which are synthesized to a large extent de novo in muscle, but also those amino acids which are not metabolized by muscle and, therefore, released in proportion to their occurrence in muscle proteins. Because metabolic parameters and content of energy-rich phosphate compounds in muscle remain unchanged, it is unlikely that general cellular damage is the underlying cause of the radiation-induced increase in amino acid release. The findings strongly favour the hypothesis that the increased availability of amino acids results from enhanced protein breakdown in skeletal muscle which has its onset shortly after irradiation. This radiation-induced disturbance in protein metabolism might be one of the pathogenetic factors in the aetiology of radiation myopathy.