On the antiatherogenity of calcium channel blockers: studies in proliferating vascular smooth muscle cells on age sensitivity, dose dependent inhibitory effect, and time of action.

We study the effect of diltiazem on cultured vascular smooth muscle cells from humans and rats, paying special attention to its activity in relation to the concentrations applied, incubation times after addition and the capacity to act against the mitogenic activity of insulin and insulin-like growth factor 1 (IGF-1). The mitotic activity was measured by means of bromodeoxyuridine DNA incorporation. Smooth muscle cells from old individuals showed a dose-dependent regression of the inhibitory level but not those from the young subjects, which showed a remarkable inhibition of mitosis at all concentrations tested. Around 8 h after addition, diltiazem inhibited cell proliferation at all concentrations tested. The inhibition exerted by 10(-7) M rapidly disappeared, reaching values higher than those initially registered and returning to basal rates after 72 h. The inhibition by 10(-6) and 10(-5) M remained after 30 and 72 h, respectively. Insulin (100 nM) or IGF-1 (1 nM) did not counteract the inhibitory effect of diltiazem (10(-5) M). Despite differences related to doses and age of cells, we conclude that diltiazem--as an L-type calcium channels blocker--is a potent inhibitor of vascular smooth muscle cell proliferation.