Specificity of Vascular Reactivity and Altered Response in Experimental Malaria.

Objective: Adherence of erythrocytes infected with Plasmodium falciparum (P. falciparum) to microvascular endothelial cells (sequestration) is considered to play an important role in parasite virulence and pathogenesis. In this study, we have examined the possibility that there is altered vascular reactivity due to the direct interaction between the parasitized erythrocytes and vascular endothelial cells and that it could be tissue specific. Method: Ring preparations of blood vessels from the rabbit carotid and rat aorta were studied using standard organ bath techniques. Dose response curves for phenylephrine (PE) and acetylcholine (Ach)-induced relaxation were constructed in rings pre-contracted with PE. Results: Incubation of rat aortic rings with parasitized blood resulted in a significant (p<0.05) increase in maximum contractile response to phenylephrine in the rat aortic rings but there was no effect on the rabbit carotid artery. The dose-response curve showed a significant (p<0.05) left-ward shift following the addition of parasitized blood. Parasitised blood had no effect on baseline in both tissues. Following exposure to parasitized blood, the magnitude of Ach-induced relaxation responses reduced significantly (p<0.05) in rat aortic rings and (p<0.05) in rabbit carotid rings; relaxations to acetylcholine was more pronounced in the aortic compared to the carotid rings. Conclusions: Malaria altered vascular reactivity through an endothelium-dependent mechanism. The regulation of vascular tone by various vasoactive agents following exposure to malaria parasites might be altered in a vessel-specific manner. This may contribute to or exacerbate the abnormal haemodynamics observed in the microcirculation of numerous vascular beds in malaria.