Maturation-dependent neointima formation in fowl aorta

Fowl show spontaneous elevation of blood pressure (BP) and neointimal plaqu e formation in the abdominal aorta at young ages. Maturation/ age-dependent modulation of vascular lesions and a causal relationship between elevated BP and neointima formation, however, have not been clarified. We therefore intended to characterize, first, maturation/age-dependent neointimal plaque formation and vascular lesions and, second, their relationship to BP eleva tion. The BP measured in conscious domestic fowl, Gallus gallus, White Legh orn breed, DeKalb strain, via an indwelling catheter inserted into the isch iadic artery, increased with maturation in males; and at plateau level, BP (mmHg) was significantly (P < 0.01) higher in males (194.0 +/- 4.6, n = 11) than in females (169.3 +/- 3.1, n = 10). Neointimal plaques consisting of neointimal cells and abundant extracellular matrix appeared initially in th e distal segment of the abdominal aorta (lesion-prone area) of chicks as ea rly as 6 weeks old. The area (size) of neointimal plaques right above the i schiadic bifurcation increased with maturation, whereas the plaque area bec ame smaller with some degenerative changes in adult birds. In some birds, d iffuse subendothelial hyperplasia and more extensive plaque formation at th e branching points of the aorta were observed. The plaque area appears to b e larger in birds. particularly in males that have higher BP (r = 0.68). Th e width of aortic smooth muscle (SM) layers, measured in regions with no pl aque, increased with age, whereas the number of cells per unit of area decr eased, suggesting that hypertrophy of vascular SM occurs in response to exp osure of the vascular wall to high BP. The number of cells was significantl y (P < 0.01) higher in the plaque than in underlying aortic SM layers or in layers with no plaque formation. Both neointimal plaques and underlying SM layers are immunohistochemically positive for alpha SM actin, suggesting t hat neointimal cells are modulated SM cells, whereas the staining with SM m yosin heavy chain antibody is low in neointimal plaques. Furthermore. plasm a arginine levels dropped in accordance with the time of neointimal plaque formation, whereas plasma cholesterol levels showed an age-dependent increa se. The results suggest that spontaneous development of neointimal plaques may be a consequence of exposure to high BP and associated local hemodynami c changes. (C) 2001 Elsevier Science Inc. All rights reserved.