THE ADVENTITIA AND ATHEROGENESIS - REMOVAL INITIATES INTIMAL PROLIFERATION IN THE RABBIT WHICH REGRESSES ON GENERATION OF A NEOADVENTITIA

Removal of the carotid artery adventitia from rabbits induced the form ation of an intimal hyperplastic lesion. In rabbits fed a normal diet, the lesion (measured as the intimal:medial ratio) was maximal by day 14 (0.456 +/- 0.079, n = 5, P < 0.01) and thereafter, regressed toward s control dimensions (0.037 +/- 0.003, n = 14) by day 28 (0.080 +/- 0. 025, n = 7, P = 0.14). In rabbits fed a high cholesterol diet, the les ion was again maximal by day 14 (0.376 +/- 0.056, n = 8, P < 0.01). Al though some regression was seen, the lesion persisted to day 42 (0.272 +/- 0.052, n = 8, P < 0.01). Electron microscopy and immunocytochemis try showed two types of lesion, (a) smooth muscle cell predominant on normal diet and, (b) macrophage predominant on high cholesterol diet. Smooth muscle cell predominant lesions underwent almost complete regre ssion, whereas macrophage predominant lesions persisted. We propose th at lesion formation may be initiated following the development of arte rial wall hypoxia, secondary to excision of the adventitial vasa vasor um. Furthermore, we have devised a novel method to restore a highly va scular 'neoadventitia' to an artery whose adventitia has previously be en removed, using loosely placed PVC tubing. We suggest this 'neoadven titia' was able to inhibit the formation of an intimal hyperplastic le sion and to promote regression of an already established lesion by res toring arterial wall oxygenation.