HETEROGENEITY OF RAT AORTIC SMOOTH-MUSCLE CELL REPLICATION DURING DEVELOPMENT - CORRELATION WITH REPLICATIVE ACTIVITY AFTER EXPERIMENTAL ENDOTHELIAL DENUDATION IN ADULTS

Proliferation of smooth muscle cells (SMCs) is a major event in vascul ar development and atheromatous plaque formation. In order to characte rize SMC replicative potential, newborn rats have been injected with H -3-thymidine (H-3-TdR) during their first week of life when most of SM Cs were proliferating; then, H-3-TdR labelling was evaluated in adult rats. Depending on the number of mitosis that SMCs had accomplished af ter the first week of life, four different SMC subpopulations could be defined indicating that rat aortic SMCs are heterogeneous in their re plicative activity. 5-Bromo-2'-deoxyuridine (BrdU) incorporation after balloon induced endothelial denudation of rat aorta in adult rats sho wed that SMCs entering into the cell cycle were mainly devoid of H-3-T dR labelling. This category could derive from two distinct SMC subpopu lations: SMCs which were arrested in their proliferation before or jus t after birth or SMCs which had actively replicated during development . Thus, one (or two) subpopulation(s) of rat aortic SMCs, characterize d by a particular replicative activity during development, is (are sel ectively activated after balloon induced endothelial denudation.