Functional and histological differences in autogenous and allogenic vein grafts: Two different vasculopathies?

The long-term biological characteristics and the functional and morphological changes that occur in fresh allografts are poorly understood. This study tests the hypothesis that the development of intimal hyperplasia and its associated functional changes are accelerated in an allograft compared to an autograft due to the additional immunological stimuli. Common carotid vein bypass grafts were performed in 40 New Zealand White rabbits: 20 received their ipsilateral jugular veins (autologous) and 20 received the fresh contralateral jugular veins from the control rabbit (allogenic). Electron microscopy was performed and intimal and medial dimensions were determined by videoplanimetry at 7, 14, and 28 days. Contraction and relaxation studies to a panel of agonists were also performed. The EC₅₀'s (agonist concentration which produces 50% of the maximal response) were calculated. All grafts remained patent. Allografts showed a 51% decrease in overall mean intimal thickness (41 ± 3 μm vs. 83 ± 12μm; P < 0.01) and a 97% increase in overall mean medial thickness (140 ± 15 μm vs. 71 ± 3μm; P < 0.01) compared to the autografts. The lumen of the allogenic vein grafts was equivalent to the autologous vein grafts. Overall mean total wall thickness only increased by 17%, 181 μm vs. 154 μm for allo- and autografts, respectively. The EC₅₀ for norepinephrine, histamine, and bradykinin were similar in the auto-and allografts, while the EC₅₀ to serotonin was significantly less in the allografts than in the autografts. Neither the precontracted auto- or allografts relaxed to acetylcholine or serotonin (receptor mediated, endothelium dependent). The EC₅₀ for calcium ionophore (nonreceptor mediated, endothelium dependent) was equivalent in the auto- and allografts. The EC₅₀ for the sodium nitroprusside-induced relaxation (endothelium independent) was significantly higher in the allograft than in the autograft. This study demonstrates that there are two different vasculopathies occurring in autografts and allografts: intimal hyperplasia is predominant in the autograft while an exaggerated medial response is predominant in the allograft. Serotonin contractility and endothelial-independent relaxation are enhanced in the allograft compared to the autograft.