On relationships between synthesis of DNA and incorporation of deoxythymidine into DNA during myocardial infarctions induced in rats by isoproterenol

Abstract

The synthesis of rat-heart DNA was studied during myocardial infarction induced by isoproterenol. Female Holtzman rats were given 2 injections, 24 h apart, of isoproterenol at 400 mg/kg body weight. Time-course incorporation of [ 14C]formate, [2- 14C]glycine and [4- 14C]aspartate into heart DNA was stimulated about 2-fold 12 h after isoproterenol injection and reached maximum values that were equivalent to a 3–5-fold stimulation after 30 h. Incorporation of [8- 14C]adenine or [2- 14C]cytosine into DNA was also stimulated about 2-fold 12 h after isoproterenol injection. Rats were pulse-labeled with [U- 14C]aspartic acid at 0, 12 and 36 h after isoproterenol injections. The specific activity of thymine isolated from rat-heart DNA was 3- and 7-fold greater at 12 and 36 h, respectively, than the value determined for zero time. Incorporation of [ Me- 3H]thymidine into DNA was not appreciably stimulated throughout the first 24 h after isoproterenol injection, but was stimulated 5–10-fold at 30 h, and reached maximum values at 48 h. Deoxythymidine kinase activity was stimulated about 4-fold 30 h after isoproterenol injections, and was stimulated about 10-fold after 48 h. Delays in the stimulation of thymidine incorporation into DNA were not associated with demonstrable pooling phenomena. It was concluded that DNA synthesis during myocardial infarction was stimulated at least 12 h before appreciable stimulation of thymidine incorporation into DNA. Pulse-labeling studies with [ 14C]formate or tritiated thymidine throughout 28 days after isoproterenol injections indicated a single wave of stimulated DNA synthesis which subsided 5–7 days after drug administration. Studies on in vivo incorporation of [U- 3H]leucine into rat-heart protein suggested that its incorporation was stimulated prior to appreciable stimulation of [ 14C]formate incorporation into heart RNA and DNA.