THE LOCALIZATION AND METABOLISM OF I131INSULIN IN THE MUSCLE AND SOME OTHER TISSUES OF THE RAT1

Abstract

The localization of I131 labelled-insulin in muscle and other organs of the rat was investigated. The kidneys and muscles were found to be the main regulators of the fate of injected insulin. The dose of insulin approaching the tracer dose was found to lie in the range of 0.025-0.05 [mu]g./100 gm.b.w. 10 minutes after intravenous injection, insulin was shown to be distributed in a volume amounting to 19% of the volume of muscle. After subcellular fractionation of muscle cells a concentration in the soluble protein fraction was revealed. Autoradiographically this localization of I131 was shown to be evenly distributed throughout the muscle fiber, without any evidence of sarcolemmal concentration. An intracellular distribution was also found in heart muscle, liver and lungs. In the diaphragm, following in vitro incubation with I131 insulin, the hormone was shown to localize mainly on the fascia covering the muscle. The radioactivity in all the experiments with muscle was shown to be 85% insulin and 15% iodinated amino acids, monoiodotrysoine or diiodotryrosine; In the liver the iodinated amino acids were shown to contribute about 45% of the total TCA precipitable radioactivity.