Norepinephrine-induced enlargement of nucleus in cultured myocardial cells.

The change in the nuclear size of neonatal rat myocardial cells was evaluated under the culture conditions of exposure to norepinephrine (NE). Daily administration for 1 week of 0.2, 2, and 20 ng/ml NE induced a significant increase in nuclear size as a result of the dose-dependent quality of the nuclei. NE also stimulated a beating response in the cultured myocardial cells because of this dose dependency. A good correlation was found between the two markers and the NE dose dependency. Single or mononucleated myocardial cells often appeared in the NE-treated groups. Ornithine decarboxylase activity was not acutely stimulated even by 20 ng/ml NE. These observations suggest that administration of NE induces nuclear enlargement and enhances nuclear function through the stimulation of beating. Further, there may not be a direct relation between nuclear enlargement and the polyamine synthesis pathways.