Myofilament-polyribosome association in muscle cells of rat left atrium after short-term hypertension.

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Abstract
Hypertension was induced in uninephrectomized Wistar rats by administration of deoxycorticosterone acetate (DOCA) and by addition of NaCl to their drinking water. The ultrastructure of atrial and ventricular cells of left hearts was compared after short-term (2 and 6 weeks) increased blood pressure. No morphological features could distinguish cells of treated animals from cells of normotensive rats after 2 weeks of treatment. The sarcoplasm of the atrial cells of 6-week-treated hypertensive rats presented an abnormally high number of helical arrangement of ribosomes often associated with abundant unorganized thick filaments, irregular nuclear profiles showing foldings and convolutions, and enlarged mitochondria. The only fine structural changes observed in the ventricular cells of the same animals was a moderate mitochondrial enlargement. The described alterations of atrial cells probably correspond to enhanced synthesis of contractile elements associated with increased nuclear-cytoplasmic exchanges; their absence in ventricular cells suggests that short-term and moderate pressure overload induces adaptative changes in left atrial cells at a stage when ventricular cells have morphological characteristics close to normal cells.