Abstract

The effects of a newly developed vasodilator agent, HA1077 [1-(5-isoquinolinesulfonyl)-homopiperazine hydrochloride], were investigated on the proliferation of cultured bovine aortic vascular smooth muscle cells (VSMC). HA1077 (10-100 microM) inhibited both fetal calf serum-induced proliferation and [3H]thymidine incorporation into DNA of the growth-arrested VSMC in a dose-dependent manner. When quiescent cells were stimulated with platelet-derived growth factor followed by insulin, HA1077 (1-30 microM), administered together with either stimulation, showed dose-dependent inhibition of [3H]thymidine incorporation. Further reduction of [3H]thymidine incorporation was observed when HA1077 was present at both stimulations, suggesting that HA1077 suppresses DNA synthesis acting in both competence and progression stages. After stimulation with fetal calf serum, quiescent VSMC started and ceased DNA synthesis in 15 to 18 hr and 24 hr, respectively. HA1077 inhibited [3H]thymidine incorporation when it was added either from 12 hr to 15 hr or from 21 hr to 24 hr after serum stimulation. In addition, when percent inhibition of [3H]thymidine incorporation by continuous exposure to HA1077 was examined as a function of the time it was added, reductions of the value were observed at 0 to 3 hr, 12 to 18 hr and 21 to 24 hr. Thus, we concluded that HA1077 suppresses DNA synthesis of bovine VSMC acting at the G0/G1 and the G1/S phase transitions and also in the S phase of the cell cycle. It is suggested that this agent may act as a potent inhibitor of VSMC proliferation as well as a vasodilator.