The current study examined angiotensin receptor (ATR) regulation in proliferating rat aortic vascular smooth muscle cells (VSMC) in culture. Radioligand competition analysis coupled with RNase protection assays (RPA) revealed that AT_1aR densities (B_max) increased by 30% between 5 and 7 days in culture [B_max (fmol/mg protein): day 5, 379 ± 8.4 vs day 7, 481 ± 12, n=3, P<0.05] under conditions in which no significant changes in AT_1aR mRNA expression occurred [in RPA arbitrary units (AU): day 5, 0.23 ± 0.01 vs day 7, 0.24 ± 0.04, n=4] or in mRNA systhesis determined by nuclear run on assays [AU: day 5, 0.35 ± 0.14 vs day 7, 0.33 ± 0.11, n=5]. In contrast, polysome distribution analysis indicated that AT_1aR mRNA was more efficiently translated in day 7 cells compared to day 5 [% of AT_1aR mRNA in fraction 2 out of total AT₁R mRNA recovered from the sucrose gradient: day 5, 20.9 ± 9.9 vs day 7, 56.8 ± 5.6, n=3, P<0.001]. Accompanying the polysome shift was 50% less RNA-protein complex (RPC) formation between VSMC cytosolic RNA binding proteins in day 7 cells compared to 5 day cultures and the 5' leader sequence (5'LS) of the AT_1aR [5'LS RPC (AU): day 5, 0.62 ± 0.15 vs day 7, 0.23 ± 0.03; n=4, P<0.05] and also with exon 2 [Exon 2 RPC (AU): day 5, 35.0 ± 5.7 vs day 7, 17.2 ± 3.6; n=4, P<0.05]. Taken together, these results suggest that AT_1aR expression is regulated by translation during VSMC proliferation in part by RNA binding proteins that interact within exon 2 in the 5'LS of the AT_1aR mRNA.