Insulin-like growth factor-I binding in injury-induced intimal hyperplasia of rabbit aorta

Abstract Purpose:  The proliferation of arterial-wall smooth muscle cells is an important step in the formation of intimal hyperplasia. Insulin-like growth factor-I (IGF-I) is a mitogen that exerts its effects through specific receptors located on the cell membrane. IGF-I has been found to promote the multiplication of vascular smooth muscle cells in culture. This study aimed to evaluate the status of IGF-I binding in injury-induced intimal hyperplasia in a rabbit model. Methods:  We used binding techniques to study IGF-I binding of control and hyperplastic aortas of adult White New Zealand rabbits. Hyperplasia was induced by balloon-catheter injury. At 2 weeks and 1, 2, 4, and 7 months after injury, segments of abdominal aortas were harvested from two control and six study rabbits, and 20-μm-thick frozen sections were obtained. Hematoxylin and eosin stained sections confirmed the presence of intimal hyperplasia in the hyperplastic aortas. Adjacent sections were incubated in a buffer solution containing 125 I-IGF-I in the presence and absence of an excess of unlabeled IGF-I. Autoradiograms were then obtained by apposing the treated sections to autoradiography film, which was developed at 3 days and analyzed by comparison with the hematoxylin and eosin stained sections under light microscopy. A marked increase in IGF-I binding grain density was observed in the areas corresponding to the hyperplastic lesions. To characterize these binding sites, binding inhibition studies were performed and the dissociation constant (K d ) and maximum binding capacity (B max ) were obtained from Scatchard analysis. Results: Six hyperplastic aortas for each time interval and a total of nine control aortas were evaluated. The K d of the hyperplastic aortas (1.5 ± 0.2 nmol/L) was not significantly different from that of control aortas (1.3 ± 0.2 nmol/L), which indicated similar high-affinity IGF-I binding sites in normal and hyperplastic arteries. The results of B max were 6.9 ± 1.2, 8.5 ± 2.1, 12.4 ± 2.1, 20.4 ± 5.9, 20.6 ± 3.2, and 8.1 ± 1.3 pmol/L for control, 2 weeks, 1 month, 2 months, 4 months, and 7 months, respectively. With analysis of variance ( p max values at 1, 2, and 4 months were significantly higher than those of control aortas. B max values returned to levels not significantly different from those of control aortas at the 7-month interval. Conclusion: Increased IGF-I binding in the hyperplastic aortas suggests that IGF-I plays an important role in the proliferation of arterial wall cellular components during the hyperplastic process. (J VASC SURG 1996;23:308-13.)