The role of aspirin and dipyridamole on vascular DNA synthesis and intimal hyperplasia following deendothelialization

Abstract

Platelets are implicated both in acute thrombotic events and, through platelet-derived growth factor, in the development of intimal hyperplasia. We have investigated, in vivo, the influence of aspirin and dipyridamole on vascular smooth muscle cell proliferation and DNA synthesis following balloon catheter injury. Fifty-eight male, New Zealand white rabbits were divided equally into two groups; the test group was fed aspirin (14 mg/kg/day) and dipyridamole (9 mg/kg/day) from 2 days prior to surgery until sacrifice at 1, 2, 3, 4, 7, 14, or 28 days after injury. All animals were sacrificed 1 h after injection of [ 3H]thymidine and the smooth muscle cell DNA specific activity and total kinetic activity were determined. Intimal hyperplasia was measured by light microscopy and intimal nuclear proliferation was determined by counting nuclei per millimeter of internal elastic lamina. Nuclear proliferation was maximal at 14 days (25 ± 1.2) but intimal hyperplasia was still increasing at 28 days. DNA specific activity after 24 hr (test: 4 ± 2 dpm/μg DNA; control: 3.3 ± 3 dpm/μg DNA) was similar to basal levels in uninjured rabbits. DNA synthesis peaked in both groups between the second and third day (test: 177 ± 27 dpm/μg DNA; control: 185 ± 39 dpm/μg DNA) and then declined slowly toward baseline values. There was no significant difference between treated and normal rabbits in either [ 3H]thymidine incorporation, nuclear proliferation, or development of intimal hyperplasia despite 90% inhibition of platelet aggregation and a significant reduction (78%) in [ 14C]serotonin release following collagen challenge (6 μg/ml). These results suggest the presence of another significant growth factor(s) for vascular smooth muscle in the rabbit as global interference with platelets does not inhibit smooth muscle proliferation.