Placing a silicone collar around the rabbit carotid artery induces intimal thickening, an early stage in atherosclerosis and restenosis. We investigatedwhethertreatment with oral pranidipine, a new potent, long-lasting dihydropyridine calcium channel blocker (CCB), inhibited collar-induced intimal thickening in addition to the changes in vascular reactivity usually observed in this model. Pranidipine treatment did not inhibit collar-induced intimal thickening. Placing the collar around the carotid artery resulted in the characteristic changes in vascular reactivity, such as increased sensitivity to 5-hydroxytryptamine. Treatment with Nomega-nitro-L-arginine (100 microM) and pranidipine, however, did not affect collar-induced changes in vascular reactivity. From results of this and previous studies, we conclude that pranidipine does not prevent collar-induced intimal thickening or collar-induced changes in vascular reactivity. Not all CCBs prevent collar-induced intimal thickening, suggesting that the effects of these agents are not related to their chemical structure and/or their calcium channel-blocking actions.