AMLODIPINE INHIBITION OF SERUM-INDUCED, THROMBIN-INDUCED, OR FIBROBLAST GROWTH FACTOR-INDUCED VASCULAR SMOOTH-MUSCLE CELL-PROLIFERATION

Atherosclerosis, like several other vascular diseases, exhibits struct ural and functional abnormalities resulting partially from an exaggera ted proliferation of vascular smooth-muscle cells (VSMCs). Ca2+ channe l blockers, such as amlodipine, have been suggested to retard or even prevent the progression of atherosclerosis,To determine the mechanisms involved in these effects, we investigated the influence of amlodipin e on VSMC proliferation by using rat aortic VSMCs in culture. Amlodipi ne (0.1-10 mu M) inhibited serum-, basic fibroblast growth factor (bFG F)-, and thrombin-induced VSMC proliferation and DNA synthesis in a co ncentration-dependent manner, as demonstrated by cell count and bromod eoxyuridine (BrdU)-incorporation measurements, respectively. Delayed a ddition of amlodipine after VSMC stimulation showed that the drug exer ted its effect early in Gi phase of the cell cycle. This observation w as confirmed by the finding that amlodipine did not influence DNA synt hesis in VSMCs arrested to the G(1)/S boundary by hydroxyurea treatmen t. Consistent with its effects on VSMC growth/proliferation, amlodipin e also decreased c-myc, c-fos, and c-jun protooncogene expression indu ced by serum, thrombin, or bFGF within 1 h after cell activation, as a ssessed by semiquantitative reverse transcriptase (RT)-polymerase chai n reaction (PCR) analysis. The calcium channel agonist Bay K 8644, whi ch counteracted the inhibition by nifedipine of bFGF-, thrombin- or se rum-induced DNA synthesis, was ineffective to antagonize the inhibitor y effect of amlodipine. The aforementioned effects of amlodipine were of similar amplitude, irrespective of the growth-enhancing agent used. This strongly indicates that amlodipine acts downstream of receptor a ctivation to exert its antiproliferative action, probably early in the G(1) phase of the cell cycle. Moreover, the lack of antagonistic effe ct between amlodipine and Bay K 8644 suggests that, in addition to its L-type Calc channel inhibitory effect, amlodipine inhibits other intr acellular signaling pathways. Such an interference of amlodipine with mitogenic signaling pathways might contribute to confer a blood vessel -protecting potential on amlodipine.