RESUMO
Norepinephrine stimulates the growth in size of non-dividing, neonatal cardiac muscle cells, and it can stimulate the growth in numbers of dividing hepatocytes and endothelial cells in culture. The objective of this study was to test the hypothesis that in dividing fetal cardiocytes, norepinephrine would stimulate growth in cell number rather than in cell size. Fourteen-day fetal heart cells were placed in serum-free or serum-supplemented cultures in the presence or absence of norepinephrine (NE), NE plus propranolol, or isoproterenol for 4 days. Almost 90% of the cardiocytes in serum-supplemented medium were in the cell cycle as determined by proliferating cell nuclear antigen (PCNA) antibody staining during this period. In addition, between days 2 and 4 of culture, 35% and 40% of these cardiocytes were labeled with 3H-thymidine. After 4 days the cardiocytes increased in cell number in the serum-supplemented NE cultures as compared to serum-free cultures. In contrast, there was no significant change in cardiocyte volume between any of the groups examined. It was concluded that in dividing muscle cell populations the effect of norepinephrine was to enhance cell proliferation rather than to stimulate cell growth in size.
