The aim of this study was to evaluate the effect of anipamil, a phenyalkylamine-derived Ca(2+)-antagonist, on aortic intimal thickening and smooth muscle cell (SMC) phenotype in 2K-1C hypertensive rabbits. Monoclonal antimyosin antibodies [SM-E7, NM-G2, and NM-F6, which respectively, recognize smooth muscle (SM), A-type-, and B-type-like nonmuscle (NM) myosin heavy chains (MyHC)] identify different aortic SMC types: adult (SM-E7-positive), postnatal (SM-E7- and NM-G2-positive), and fetal (SM-E7-, NM-G2-, and NM-F6-positive). Twenty-four hypertensive rabbits were studied 2.5 months (n = 12) and 4 months (n = 12) after clipping. Six animals from each group were given anipamil (40 mg orally, once daily) immediately after surgery. The remaining 2K-1C were given a daily oral placebo. Normotensive age-matched controls were also studied. Transverse cryosections of aorta were taken for computerized morphometry and immunocytochemical studies. Primary and secondary SMC cultures were used to define potential changes in cell phenotype after adding anipamil to the culture medium. In untreated 2K-1C, intimal thickening, mainly composed of postnatal-type SMC, was found by 2.5 months after clipping. Morphometric and immunofluorescence studies in anipamil-treated 2K-1C rabbits revealed absent or negligible intimal thickening and a decrease of postnatal-type SMC from the underlying media. In culture experiments, growth inhibition of SMC by anipamil was accompanied by the expression of SM-MyHC in all SMC, ie, the appearance of a more differentiated cell phenotype compared to control cultures. In conclusion, prevention of intimal thickening in anipamil-treated 2K-1C was achieved through selective reduction in the media of the postnatal-type SMC. This could be achieved by reducing NM-MyHC content or increasing synthesis of SM-MyHC expression. As blood pressure was not significantly lowered by anipamil treatment, a direct and specific antiproliferative action of this drug on medial SMC is likely to take place.
Animals Aorta, Thoracic