Blood Flow Variations and Growth of Smooth Muscle Cells

Mattsson, Erney

Abstract

The purpose of the project is to define specific factors which might be involved in the control of smooth muscle cell (SMC) proliferation in the healing of vascular grafts. The hypothesis to be tested is that platelet derived growth factor (PDGF), basic fibroblast growth factor (bFGF), and nitric oxide (NO) play major roles in this regulation. A model of SMC proliferation and intimal thickening in vessel grafts has been developed in Dr. Clowes' laboratory using aortoiliac grafts implanted in baboons. If implanted under conditions of high blood flow (distal arteriovenous fistulae), the grafts develop a subendothelial lining with several layers of SMC in the neointima. If blood flow is switched from high to normal (closure of the distal fistula), the intimal thickening increases fivefold. We plan to analyze the importance of PDGC-A, PDGF-B, PDGF- alpha, PDGF-beta, inducible nitric oxide synthase (NOS), and constitutive NOS mRNA by northern blotting and by hybridization. In situ hybridization will also be used to localize mRNA to the endothelium, SMC, or graft matrix. We will attempt to confirm expression of the proteins mentioned above by using the appropriate antibodies as well. If the proteins are expressed, the time course will be more clearly defined. The potential effect of nitric oxide will also be evaluated by reducing (inhibition of NOS) and by increasing (external addition) the local concentration of NO. We will try to achieve to blockade by local application of an L-arginine derivative (L-NMMA) at the anastomosis and will hope to increase NO by local application of nitroglycerin. SMC proliferation with secondary intimal hyperplasia is a common reaction to injury following vascular reconstructions including balloon angioplasty. At present there is no satisfactory form or pharmacological therapy to control this injury response, and clinicians are forced to repeat the vascular reconstruction in order to maintain patency of the vessel. If we are ever to succeed in developing pharmacological strategies for the control of intimal hyperplasia it is of outmost importance to define the positive and negative regulatory factors controlling smooth muscle cell proliferation.