Morphologic and functional consequences of intimal hyperplasia in the rat carotid artery.

The influence of neointima formation on functional characteristics was investigated in rat carotid artery preparations. The process of intimal hyperplasia development in the injured carotid arteries was followed in time both morphologically and morphometrically. Simultaneously with the loss of endothelial cells due to the balloon injury procedure, the vasodilator responses to methacholine were abolished. The sensitivity for the alpha1-adrenoceptor agonist phenylephrine appeared to be increased only immediately after injury. The balloon injury method led to significant neointima formation in the rat left common carotid artery 14 days after the intervention. Eight weeks after balloon injury, the neointimal mass reached its maximum. Parallel to the development of intimal hyperplasia, the alpha1-mediated vasoconstrictor responses to phenylephrine were significantly impaired. After 12 weeks of observation, reoccurrence of mature endothelial cells on the luminal surface of the neointima could be observed. Simultaneously, the vascular responses to phenylephrine and methacholine recovered. The vasoconstrictor responses to high potassium concentrations (100 mM) as well as the vasodilator effects of sodium nitroprusside appeared to be uninfluenced by balloon injury throughout the period of observation. From this study we conclude that both the receptor-mediated contractile responses to alpha1-adrenoceptor stimulation and the endothelium-dependent vasodilator responses to methacholine become severely impaired as a consequence of balloon catheter injury followed by intimal hyperplasia. However, these pharmacological responses may fully recover upon a prolonged period of endothelial regeneration.