DIFFERENT ONSET OF NUCLEOLAR ACTIVATION IN ENDOCARDIAL ENDOTHELIAL-CELLS AND CARDIOMYOCYTES FOLLOWING PRESSURE-OVERLOAD IN RAT-HEART

We evaluated the time course of activation of endocardial endothelial cells and cardiomyocytes in adult rats with pressure overload induced by the abdominal aortic constriction, The silver staining technique fo r nucleolar organizer region was used to mark an increased transcripti onal activity of the cells. An increased number of nucleoli was alread y detected in the endocardial endothelium of the left ventricle 5 h po st-operatively, while the response of cardiomyocytes was still absent. Twenty-four h after constriction, the activation of the endocardial e ndothelium and cardiomyocytes was evident in both ventricles. A simila r delay was observed between the nucleolar activation in vascular endo thelium and smooth muscle cells of the abdominal aorta. In contrast, t hese cells of the thoracic aorta did not exhibit any significant incre ase of the transcriptional activity. The sequential stimulation of the transcriptional activity of the left ventricular endocardial endothel ial cells and the subjacent cardiac myocytes due to pressure overload is in accord with the view that the endocardium may serve as a mechano transducer which converts the hemodynamic changes into the signals tha t influence the growth of the cardiac myocytes. (C) 1997 Academic Pres s Limited.