Myocardial chemical sympathectomy was achieved by daily SC injection of 100 μg/g body weight of 6-OH-dopamine to each of 239 Holtzman newborn rat pups for the first seven days of life. Effective sympathectomy was verified by identifying a decrease in ventricular myocardial norepinephrine concentrations to 31% ± 12 S.E. of control at 20 days of age. Activity of DNA polymerase was used to indicate the extent of myocardial cell division. Beginning at eight days of age, DNA polymerase activity was increased in the sympathectomized pups relative to control. The DNA polymerase activity was highest relative to control at 16 days (235% ± 31 S.E.) and remained elevated beyond 20 days (188% ± 30 of control). The DNA polymerase data was analyzed by covariance and was significantly greater in the 6-OH-dopamine rat pups (P < 0.001). Speculation: Myocardial cell division continues for 10 to 14 days after birth in the newborn animal of several species, and the cell division then ceases by an unknown mechanism. Our findings are consistent with the hypothesis that this postnatal decrease in myocardial cell division is related to the development of cardiac sympathetic nerve ingrowth. Because nerve ingrowth was inhibited after 6-OH-dopamine and increased myocardial cell division occurred, it appears that sympathetic ingrowth indeed may play a key role in affecting myocardial cell division in the newborn animal.
ASJC Scopus subject areas
- Pediatrics, Perinatology, and Child Health