Action of propranolol on the atrial cardiomyocytes of rats submitted to cold stress.

Subcellular changes of the atrial cardiomyocytes of rats caused by cold showed a) altered mitochondria with edema and lysis of crests; b) myofibrils with marked heterogeneity of patterns and ruptures, c) myofilaments disarrangement, partial necrosis and disintegration of filaments, d) lesser concentration of atrial granules in the perinuclear area. Atrial muscle fibers of propranolol-treated rats previously stressed by cold showed a marked decrease of the morphological alterations observed in the animals submitted to cold stress without propranolol protection.