1. To study the hypertensive genotypic influence on growth kinetics of the three aortic wall cell types. 2. Using young spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats weighing 160-180 g, we compared the proliferative properties of endothelial cells (EC), smooth muscle cells (SMC) and fibroblasts that were isolated from the thoracic aorta of each strain and cultured. Growth-arrested cells were exposed to P < -thymidine after stimulation with 150 micrograms/mL endothelial cell growth supplement. Proliferation assays were performed by cell seeding on decellularized aortic explants and cell counting 2, 4, 5, 6 and 7 days after seeding. The influence of SMC from SHR on the growth kinetics of EC was evaluated by co-cultures in transwell systems. 3. After stimulation, SMC from SHR exhibited a greater P < -thymidine incorporation rate than those from WKY rats (ratios over controls: 3.90 +/- 0.48 [7] vs 1.85 +/- 0.25 [7] respectively, P < 0.05). This was also true for adventitial SHR fibroblasts: (13.1 +/- 0.6 [6] vs 9.9 +/- 1.0 [6] WKY P < 0.05). On the contrary, there was no difference in the P < -thymidine incorporation rates between EC of each strain, regardless of the passage and the time considered. Cell proliferation on matrix explants confirmed the hyperproliferation of SMC and fibroblasts from SHR, while EC of each strain proliferated equally. Smooth muscle cells from SHR did not influence the growth kinetics of EC in co-culture and vice versa. 4. The changes in growth patterns of aortic cells isolated from young prehypertensive SHR seem to be restricted to SMC and fibroblasts.