Following exposure of isolated frog gastrocnemii to high intensity x-radiation, increased fatigability and contracture of the muscles have been demonstrated in previous studies (3). The present paper presenting an expansion of these previous studies comprises, first, a study of cold blooded muscle during and after exposure to x-radiation and, second, a determination of radiation effects on muscles of intact warm blooded animals.
RADIATION :EFFECTS ON COLD BLOODED MUSCLEThe first section of the present study was performed on isolated cold blooded gastrocnemii. This method offers an important advantage. Changes occurring in the muscle during and following irradiation, as compared to a non-irradiated control muscle, must be directly caused by the ionizing radiation, since all connections to other organs through the circulatory and nervous system are interrupted.
MethodThe experiments were performed during the fall of the year with leopard frogs (Rana pipiens) of approximately equal size. The animals were stored at 6°C. Preparation, radiation, and testing of the isolated gastrocnemii were carried out at 20°C.Recordings of the isotonic contractions were made according to a method previously described (5). As an essential feature of this method alteration of muscle length produced proportional voltage changes at the slider of a micropotentiometer. These voltage changes were recorded either by means of a cathode ray oscilloscope or an ink writer.The plastic wet chamber containing the isolated gastrocnemius was placed in the head of a Picker x-ray unit. The conditions of the experiment were as follows: voltage, 260 kvp.; amperage; 18 ma.; inherent filtration, 0.25 ram. copper; additional filtration, 3 ram. plastic wall of wet chamber; and target-muscle distance, 8 cm. Under these conditions a dose rate of approximately 6 kr (6,000 r) per minute was measured in air.The experimentation was carried out in several distinct steps. Radiation effects were studied (1) on the work capacity, (2) on the single twitch, (3) on the lengthforce diagram, and (4) on the histology of the muscle. 445
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