Abstract
1. The possibility that the antiproliferative effect of cyclic GMP- and cyclic AMP-dependent vasodilators involves an impaired progression of vascular smooth muscle cells (VSMC) through the cell cycle and expression of cyclins, which in association with the cyclin-dependent kinases control the transition between the distinct phases of the cell cycle, was examined. 2. FCS (10%) stimulated the transition of quiescent VSMC from the G0/G1 to the S phase (maximum within 18-24 h and then to the G2/M phase (maximum within 22-28 h). Sodium nitroprusside and 8-Br-cyclic GMP, as well as forskolin and 8-Br-cyclic AMP markedly reduced the percentage of cells in the S phase after FCS stimulation. 3. FCS stimulated the low basal protein expression of cyclin D1 (maximum within 8-24 h) and E (maximum within 8-38 h) and of cyclin A (maximum within 14-30 h). The stimulatory effect of FCS on cyclin D1 and A expression was inhibited, but that of cyclin E was only minimally affected by the vasodilators. 4. FCS increased the low basal level of cyclin D1 mRNA after a lag phase of 2 h and that of cyclin A after 12 h. The vasodilators significantly reduced the FCS-stimulated expression of cyclin D1 and A mRNA. 5. These findings indicate that cyclic GMP- and cyclic AMP-dependent vasodilators inhibit the proliferation of VSMC by preventing the progression of the cell cycle from the G0/G1 into the S phase, an effect which can be attributed to the impaired expression of cyclin D1 and A.