Structural features of acute focal metabolic injuries to somatic muscle fibers caused by dimethylparaphenylenediamine

Abstract

The pathological picture of an acute disorder of cell metabolism caused by dimethylparaphenylenediamine consists of typical focal reactions of striated muscles to injury: myofibril contractures and intracellular myocytolysis. Analysis of the pathological process demonstrates the time course of contracture injuries as a succession of overcontracture (first-third degree contractures) and necrobiotic phases (fourth degree contracture), followed by lump degradation and macrophagal resorption. Two polar types of contractures are clearly differentiated by the size, shape, and structural and metabolic characteristics of target fibers: "ribbons " and "medallions". Disappearance of Z strips, disaggregation, disorientation, and fragmentation of myofibrils are typical of intracellular myocytolysis. The observed changes form the morphological basis for acute disease of striated muscles. Key Words: metabolic injuries; somatic muscles; polarization microscopyThe histological picture of pronounced clinical manifestations of somatic muscle disease reflects, as a rule, the interactions between destructive and compensatory-adaptive processes running under heterogeneous structural and metabolic conditions at all levels. The mechanism underlying pathological changes can be elucidated by extrapolation of experimental data characterizing the morphological manifestations during a myopathological process.General mechanisms underlying metabolic injuries to muscle fibers include primary and secondary disorders of energy metabolism, including those caused by blocking of mitochondrial enzyme systems [10,[12][13][14][15]. We analyzed the structural features and evolution of acute focal dystrophic injuries to the skeletal muscles caused by dimethylparaphenylenediamine, a blocker of respiratory enzymes and redox processes in the cell [9]. MATERIALS AND METHODSAcute metabolic injuries to somatic muscle fibers were induced by a single subcutaneous injection of dimethylparaphenylenediamine in a dose of 2.5 mg/100 g [5,9]. Thirty-nine male Wistar rats weighing 150-300 g were used, 14 of then were controls. The animals were sacrificed 6-8 h, 1, 3, and 5 days postinjection.For making the crural muscle preparation in the "strain at rest" state [5], the left hind limb was amputated at the level of the hip joint after decapitation, the skin was rapidly separated, and the whole limb was fixed in cold (4~ 4% paraformaldehyde in Mil-0007-4888/99/0006-0640522.00 9