Previous studies have demonstrated endothelial and smooth muscle hyperplasia occur during arterial luminal expansion associated with elevation of arterial wall shear rates. The current study investigated whether remodeling induced by elevated wall shear would ultimately result in a vessel with intimal and medial cell densities and other wall characteristics similar to control arteries. A rat mesenteric model was used in which collateral wall shear is restored to normal 4 weeks after arterial occlusion. Twelve weeks after shear elevation, paired in vivo measurements indicated that the maximum collateral inner diameter was increased 27-75%. Morphometric evaluation of collateral cross sections indicated that, relative to control arteries, luminal and medial areas were increased 79 +/- 22 and 56 +/- 15%. Collateral medial cell density was decreased (1.12 +/- 0.044 vs. 1.35 +/- 0.005 nuclei/1,000 micrometer(2) but intimal cell density was similar (2.86 +/- 0.166 vs. 2.49 +/- 0.102 nuclei/100 micrometer luminal perimeter). Medial thickness to radius ratio was also similar between control and collateral arteries. Thus, for the wall characteristics evaluated, there are many similarities between enlarged collaterals and control arteries. Comparison of nuclear numbers in arterial cross sections of the current and previous studies suggest that intimal and medial cellular regression is correlated with a decrease in wall shear force toward normal levels.