1 The effect of angiotensin II (Ang II) on α(1A)-, α(1B)-, and a(1D)-adrenoceptors (α(1)-AR) expression was analyzed in aorta smooth muscle cells obtained from wild-type (WT) and knock out of α(1D)-AR (α(1D)-AR KO) mice. 2 The relative abundance of mRNA for the three α(1)-ARs was determined in WT and α(1D)-AR KO aortic smooth muscle cells. There were no significant differences between WT and α(1D)-AR KO cells. 3 As early as 1 h Ang II increased α(1B)-AR mRNA in WT cells ≈ 2 fold compared with control; in contrast, in α(1D)-AR KO cells the α(1B)-AR transcript was ≈ 50% of control. 4 Western blot assays showed that Ang II incremented protein content for α(1A)-AR, 86% and 107% in WT and α(1D)-AR KO cells, respectively. 5 Protein for α(1B)- and α(1D)-ARs did not change significantly with Ang II in both WT and a(1D)-AR KO cells. 6 The effect of Ang II on α(1B)-AR mRNA seems to be influenced by the absence of α(1D)-AR in aortic smooth muscle cells, which might be important to understand the interactions among α(1)-ARs.© 2011 Blackwell Publishing Ltd.