Catecholamines have been proposed as a stimulus for the hypertrophic response to pressure overload of the heart and could also mediate the membrane lipid changes associated with cardiac hypertrophy. To address both of these possibilities, cardiac hypertrophy was induced by aortic constriction in the presence or absence of chronic alpha- or beta-adrenoceptor blockade. Heart weights and heart weight to body weight ratios in aortic-constricted rats of the adrenoceptor-blocked and vehicle-treated groups were elevated to the same extent when compared with values in sham-operated rats of each group. Analysis of the fatty acyl composition of the major phospholipid classes revealed that similar changes occurred in vehicle-treated, alpha-blocked, and beta-blocked aortic-constricted rats when compared with respective groups of sham-operated rats. Specifically, linoleic acid was reduced in the phosphatidylcholine, phosphatidylethanolamine (PE), and cardiolipin (CL) fractions in all groups of aortic-constricted rats. This reduction was accompanied by increased docosahexaenoic acid, arachidonic acid, or palmitic acid in phosphatidylcholine; docosahexaenoic acid in phosphatidylethanolamine; and oleic acid in cardiolipin fractions. Adrenoceptor blockade did not prevent or attenuate the major changes in the fatty acyl composition of phospholipids or the increase in heart weight associated with aortic constriction. This suggests that a change in the level of adrenoceptor stimulation is not the stimulus for cardiac hypertrophy or the observed alterations in phospholipid composition in the pressure-overloaded rat heart.