Influence of mild heat and restrictive external support on functional changes in vein grafts implanted into arterial circulation. Experimental study

Abstract

Introduction. Vein grafts placed in the arterial circulation undergo a set of morphological and functional changes. The aim was to investigate the effects of external mild heat combined with internal cooling and external restrictive support on vascular reactivity of the venous grafts implanted into arterial system.
Material and methods. Reversed external jugular vein interposition grafting of the carotid artery on the mongrel dogs (n = 18) was performed. The experimental animals were split into three groups: H (n = 6) - grafts were exposed to mild heat and an external sleeve was placed around, S (n = 6) - grafts only with the sleeve and C (n = 6) - control group. The grafts were explanted after 3 months. The rings from all the explanted grafts as well as from jugular veins before implantation were taken and tension study was performed. Contractions to norepinephrine (NE), phenylephrine (Phe), 5-hydroxytryptamine (5-HT) and relaxation to acetylcholine (Ach), calcium ionophore A23187 (A23187) and sodium nitroprusside (SN) were assessed.
Results. After pre-treatment with mild heat reaction to the maximal concentrations of NE (37.8 ± 1.9 g/mm² before vs. l2.0 ± 1.6 g/mm² after), Phe (20.2 ± 1.6 g/mm² vs. 2.0 ± 0.4 g/mm²) were markedly (p < 0.001) diminished. Vein grafts before implantation were insensitive to 5-HT. Only endothelium-independent relaxation to SN was preserved in the grafts after mild heat employment, whereas Ach, A23187 did not produce any endothelium-mediated reaction. Three months after implantation markedly lower contractile responses to maximal doses of NE (1.4 ± 0.2 g/mm², 2.1 ± 0.3 g/mm² and 15.4 ± 1.6 g/mm² for H, S and C respectively), and Phe (0.4 ± 0.2 g/mm², 1.3 ± 0.2 g/mm² and 12.3 ± 1.2 g/mm² for H, S and C respectively) were noted. The maximal examined dose of 5-HT provoked 66.2% of the maximal reaction to NE in group H, 66.5% in group S and 53.2% in group C. The grafts in group H and S were insensitive to endothelium-dependent relaxants, but in C the maximal responses to A23187 were significantly weaker (p < 0.05) than before implantation (40.7 ± 3.8% vs. 67.4 ± 2.3%). SN-induced endothelium-independent relaxation was observed in all groups.
Conclusion. Mild heat of the venous grafts functionally destroys endothelium and significantly impairs smooth muscle cells' function. Employment of mild heat combined with external support may produce venous conduits less sensitive to vasoactive chemicals including also mitogens involved in neointima formation.