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

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

Melicoccus bijugatus Jacq (Mb) has been reported to have cardiovascular modulatory effects. In this study, we evaluated the antihypertensive effects and mechanism of action of Mb on N^G-Nitro-l-arginine Methyl Ester (l-NAME) and Deoxycorticosterone Acetate (DOCA) rat models. Aqueous extract of Mb fruit (100 mg/kg) was administered for 6 weeks to rats by gavage and blood pressure was recorded. Effects of the extract on vascular reactivity was evaluated using isolated organ baths, and tissues were collected for biochemical and histological analysis. The systolic blood pressure (SBP), diastolic blood pressure (DBP) and mean arterial pressure (MAP) were significantly (P < 0.05) reduced with extract (100 mg/kg) administration and treatment compared to the hypertensive models. Mb (100 µg/mL) reduced the vascular contractility induced by phenylephrine (PE), and caused a dose-dependent relaxation of PE-induced contraction of aortic vascular rings. The vasorelaxation properties seemed to be endothelium dependent, as well as nitric oxide (NO) and guanylyl cyclase, but not prostaglandin dependent. Histomicrograph of transverse sections of the ventricles from the Mb group did not show abnormalities. The extract significantly (P < 0.05) reduced an l-NAME induced elevation of cardiac output and Creatine Kinase Muscle-Brain (CKMB), but had no significant impact on the activities of arylamine N-acetyltransferase. In conclusion, Mb significantly decreased blood pressure in hypertensive models. The extract possesses the ability to induce endothelium dependent vasodilation, which is dependent on guanylyl cyclase but not prostaglandins.

The Malaria-High Blood Pressure Hypothesis: Revisited

Malaria etiologies with pathophysiological similarities to hypertension currently constitute a major subject of research. The malaria-high blood pressure hypothesis is strongly supported by observations of the increasing incidence of hypertension in malaria-endemic, low- and middle-income countries with poor socioeconomic conditions, particularly in sub-Saharan African countries. Malnutrition and low birth weight with persistent symptomatic malaria presentations in pregnancy correlate strongly with the development of preeclampsia, gestational hypertension and subsequent hypertension in adult life. Evidence suggest that the link between malaria infection and high blood pressure involves interactions between malaria parasites and erythrocytes, the inflammatory process, effects of the infection during pregnancy; effects on renal and vascular functions as well as effects in sickle cell disease. Possible mechanisms which provide justification for the malaria-high blood pressure hypothesis include the following: endothelial dysfunction (reduced nitric oxide (NO) levels), impaired release of local neurotransmitters and cytokines, decrease in vascular smooth muscle cell viability and/or alterations in cellular calcium signaling leading to enhanced vascular reactivity, remodeling, and cardiomyopathies, deranged homeostasis through dehydration, elevated intracellular mediators and proinflammatory cytokine responses, possible genetic regulations, activation of the renin-angiotensin-aldosterone system mechanisms and renal derangements, severe anemia and hemolysis, renal failure, and end organ damage. Two key mediators of the malaria-high blood pressure association are: endothelial dysfunction (reduced NO) and increased angiotensin-converting enzyme activity/angiotensin II levels. Sickle cell disease is associated with protection against malaria infection and reduced blood pressure. In this review, we present the state of knowledge about the malaria-blood pressure hypothesis and suggest insights for future studies.

Apocynin ameliorates cadmium-induced hypertension through elevation of endothelium nitric oxide synthase

Apocynin is reported to have antioxidant and NADPH oxidase inhibitor activities. Cadmium toxicity is reported to causes oxidative damage, resulting in vascular dysfunction, reduced bioavailability of nitric oxide (NO) and hypertension. The study aimed to investigate the protective effects of apocynin in cadmium-induced hypertension. Thirty-six (36) adult male Sprague-Dawley rats were randomly divided into 6 groups. Group 1 served as control, Groups 2 and 3 received 50 and 100 mg/Kg (b.w) apocynin, respectively, Group 4 received 100 ppm CdCl2 in their drinking water, while Group 5 and 6 received 100 ppm CdCl2 in their drinking and 50 and 100 mg/Kg (b.w) apocynin, respectively, for 8 weeks. Blood pressure readings were taken weekly using the tail-cuff method. cGMP, endothelial nitric oxide synthase (eNOS), NO and hematological parameters were analyzed at the end of 8 weeks. Apocynin, although a poor antioxidant, caused a significant reduction (p < 0.05) in systolic and mean arterial pressures in the cadmium-induced elevations in blood pressure and amelioration of altered hematological parameters. However, while cadmium exposures did not alter the cGMP, eNOS and nitrate concentrations in serum, apocynin reduced the cGMP and nitrite values while significantly elevating (p < 0.05) the eNOS concentrations and also improved the cadmium-induced anemia. Apocynin was effective in reducing cadmium-induced elevated blood pressures through elevation of eNOS. Inhibition of NADPH oxidase activity may be a useful strategy for prevention and treatment of cadmium-induced hypertension.