1.-- The effects of captopril on alpha(1)-adrenoceptor mRNA and protein and phenylephrine-induced contraction was assessed in aorta of pre-hypertensive spontaneously hypertensive rats. 2.-- Four-week-old SHR and WKY rats were treated with captopril [an angiotensin-converting enzyme (ACE) inhibitor] 3 mg kg(-1) day(-1) for 1 week. 3.-- pA(2) values for BMY 7378, an alpha(1D)-adrenoceptor antagonist, were 8.63-9.20 among the different groups. Schild slopes were close to unity suggesting that contraction was produced primarily by alpha(1D)-adrenoceptor stimulation and was not changed with therapy. 4.-- Alpha(1D)-adrenoceptor mRNA and protein values were higher in pre-hypertensive SHR than in WKY, whereas alpha(1A)-adrenoceptor mRNA was higher in WKY and alpha(1B)-adrenoceptors were similar in both strains, and protein was not significantly different for alpha(1A)- and alpha(1B)-subtypes. 5.-- Captopril decreased maximal contraction in SHR, without having effect in WKY rats, while alpha(1D)-adrenoceptor mRNA was decreased in both rat strains but alpha(1D)-adrenoceptor protein was significantly decreased only in SHR, and increased alpha(1A)-mRNA in SHR, no effect of captopril treatment was observed on alpha(1B)-adrenoceptor mRNA and protein nor on alpha(1A)-adrenoceptor protein. 6.-- These data suggest that ACE inhibition by captopril influences both expression and function of alpha(1D)-adrenoceptors in aorta of pre-hypertensive rats, probably avoiding alpha(1D)-subtype expression by blockade of angiotensin II synthesis.