The atrial proliferative response following partial ventricular amputation in the heart of the adult newt. A light and electron microscopic autoradiographic study.

This investigation characterizes the atrial proliferative response following partial ventricular amputation in adult newts. Newts processed for light microscopic autoradiography were given either a single injection (SI) of 3H-thymidine 1 hr before fixation and killed at intervals up to 25 days after ventricular wounding or were given six injections (MU), one every 12 hr, and fixed at intervals up to 21 days. Atria processed for EM autoradiography (EMA) were removed 1 hr after injection and 15 days after wounding. Mitotic (MI) and thymidine-labeling indices (TI) were calculated for the epicardium, subepicardial CT and myocardium of both atria. Sham-operated and unoperated animals served as controls. There was no localization of labeled or mitotic cells within the atria of SI or MU animals (P greater than 0.16) for any cell type. MI and TI for the epicardial and CT cells did not differ from sham-operated controls (P greater than 0.35). A maximum TI of 6.4% and MI of 0.4% was observed in the atrial myocardium of SI animals on day 15. A maximum TI of 13.8 and 5.9% was observed for the left and right atrial myocardium, respectively, of MI animals on day 12. EMA confirmed that atrial myocytes were engaging in mitosis and DNA synthesis.