Exposure to Thrombus Diminishes Endothelial Derived Relaxation in the Rabbit Carotid Artery

Abstract

Purpose. Thrombus is believed to be deleterious to intimal function. However, few studies have directly examined this effect. This study examines the effect of thrombus on endothelial-dependent and -independent vasorelaxation in the rabbit carotid artery.Methods. Twelve male New Zealand white rabbits (3.5–4.5 kg) were divided into two groups of six. Thrombosis was induced in group I by segmental right carotid artery ligation. Group II underwent segmental right carotid ligation immediately followed by removal of thrombus with normal saline flush through an arteriotomy. The left carotid arteries were exposed in both groups and served as internal controls. After 4 h, left and right carotid arteries were harvested, sectioned into 6-mm rings, and mounted on isometric force transducers in a physiologic bath. Thrombus was removed from the arteries in group I during the ring preparation process. Neither group I nor group II had thrombus in contact with endothelium during ex vivo testing. The arterial rings were constricted with norepinephrine (1 × 10−4 M). Endothelium-dependent and -independent vasorelaxation to acetylcholine (Ach) and s-nitrosoacetylpenicillamine, respectively, were measured in a dose–response manner. Results were expressed as a percentage of vasorelaxation. Statistical analysis was performed using an analysis of variance.Results. Endothelial-dependent vasorelaxation, which tests for endothelial cell function, was decreased in the thrombus and endothelial ischemia group (I) compared to control as noted by vasorelaxations of 22% vs 34% at 1 × 10−4 molar concentration Ach, and 33% vs 48% at 1 × 10−3 molar concentration Ach, respectively (P = 0.05). By comparison, there was no difference in the endothelial-dependent vasorelaxation of the endothelial ischemia group (II) versus control. Endothelial-independent vasorelaxation, which tests for smooth muscle function, was not affected by either the thrombus and endothelial ischemia group (I) or the endothelial ischemia group (II) compared to the control group. The controls in group I and group II were slightly different. When this difference was removed, the resulting comparison of treatments in group I and group II approached significance at molar concentrations of 1 × 10−4, 1 × 10−5, and 1 × 10−6 (P = 0.07, 0.06, 0.06).Conclusions. The presence of thrombus within the rabbit carotid artery for a period of 4 h decreases endothelial-dependent relaxation. Four hours of endothelial ischemia without thrombus did not change endothelial-dependent vasorelaxation. Neither thrombus nor ischemia alone had any effect on the endothelium-independent vasorelaxation. We conclude that thrombus is deleterious to endothelial function independent of smooth muscle function in the acute setting as measured by endothelial-dependent vasorelaxation.