Experimental malaria : the in vitro and in vivo blood pressure paradox

Abstract

ObjectiveMalaria causes more deaths worldwide than any other parasitic disease. Many aspects of the biology that governs the pathogenesis of this parasite are still unclear. Therefore insight into the complexity of the pathogenesis of malaria is vital to understand the disease, particularly as it relates to blood pressure.MethodsIn vivo and in vitro experimental models were used for this study. In the in vivo study, mean arterial pressure, pulse rates and heart rates were recorded by cannulation of the carotid artery of rats. In the in vitro study, ring preparations of blood vessels from the rat aorta were studied using standard organ bath techniques. Dose–response curves for phenylepherine (PE)- and acetylcholine (Ach)-induced relaxation were constructed for rings pre-contracted with PE.ResultsOur results showed a significant (p < 0.05) reduction in the mean arterial pressure and pulse rates, while the heart rates remained unaltered in rats with malaria parasites, compared with the controls. Incubation of rat aortic rings with parasitised 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 baseline. The dose–response curve showed a significant (p < 0.05) leftward shift following the addition of parasitised blood and the EC70 (M) values increased from 7 × 10-7 to 5 × 10-6 M. Following exposure to parasitised blood, the magnitude of Ach-induced relaxation responses reduced significantly (p < 0.05) from 73 ± 3.6 to 24.75 ± 7.25% in the rat aortic rings.ConclusionsThe results suggest that malaria parasitaemia caused in vivo reduction in blood pressure, and enhanced the responses to contractile agents and reduced relaxation responses to acetylcholine in vitro. This appears to be a paradox but is explainable by the complex cardiovascular control mechanisms in vivo. This may be independent of direct action on vascular smooth muscle.

Hypotensive and antihypertensive effects of an aqueous extract from Guinep fruit (Melicoccus bijugatus Jacq) in rats

“…In normotensive animals, M. bijugatus caused a dose-dependent relaxation of aortic rings pre-contracted with PE. Relaxation of the aortic rings with intact endothelium was significantly greater when compared with aortic rings without endothelium, indicating that the vascular relaxation activity involved endothelium dependent mechanisms 26 , 27 , as well as NO and guanylyl cyclase activity, but not prostaglandin dependent activity. The aqueous extract of M. bijugatus did not show any vascular response per se in unstimulated vasculature.…”

Conceptual framework for effective communication strategies in high-risk industries: Insights from the energy sector

“…In the mining industry, which encompasses a diverse array of activities ranging from surface mining to underground extraction, effective communication is instrumental in mitigating occupational hazards, promoting environmental stewardship, and fostering community engagement (Nwokocha, 2023). From ensuring worker safety in hazardous environments to addressing concerns related to land reclamation and environmental remediation, effective communication strategies enable mining companies to navigate regulatory complexities, manage stakeholder expectations, and uphold corporate social responsibility standards .…”