ABSTRACT
Hypertension is a disorder of high public health concern and is the most prevalent risk factor of cardiovascular morbidity. It is characterized by either a sustained systolic blood pressure greater than 140 mm Hg or a sustained diastolic blood pressure greater than 90 mm Hg. The global impact is huge and Africa is thought to have the highest prevalence of hypertension estimated at 46 % of adults aged 25 and above. The world health organization anticipates that 1.5 billion people may likely become hypertensive by 2025 with more than seven million deaths expected to occur annually. With several limitations associated with the use of allopathic anti-hypertensive drugs, medicinal plants have become a ready option in man's quest for novel therapies. The present study investigated the toxicological and anti-hypertensive effects of methanol leaf extract of S. glauca (MESG) and was conducted in five (5) phases: oral acute toxicity of MESG using the Lorke's method, sub-chronic toxicity of MESG following the guidelines prescribed by the organization for Economic Co-operation and Development (OECD) and with toxicity tested at the three dose levels of 500, 1000 and 2000 mg/kg body weight over a 30 day period, prophylactic and curative anti-hypertensive effects of MESG on salt (8 % NaCl)-induced hypertension as well as the in-vitro vascular reactivity studies. The results obtained indicate that the lethal dose (LD50) of MESG exceeded 5000 mg/kg body weight. Sub-chronic toxicity testing showed that there were no significant differences in most biochemical parameters evaluated in test animals relative to control except observed increases in plasma ALP activity, unconjugated bilirubin, and triglycerides and a decrease in plasma HDL. Analysis of tissue anti-oxidant defense status revealed no significant changes in MDA levels of test animals although there were elevations in the activities of the anti-oxidant enzymes; SOD, CAT and glutathione peroxidase as well as total WBC and monocyte count at some doses. The data obtained from the anti-hypertensive studies indicate that induction of hypertension was accompanied with increases in plasma L-arginine, total, conjugated and unconjugated bilirubin, TG, urea, creatinine, Na+ , K+ , Ca2+, HCO3 - and plasma LDH, a reduction in plasma HDL with concomitant increase in cardiac risk. There were also significant elevations in aorta LDH and G6-PDH, elevated liver MDA, GSH and increase in platelet count. Pretreatment with MESG at doses of 25, 50 & 100 mg/kg effectively (P ˂ 0.05) prevented; on the other hand, reversed hypertensioninduced hemodynamic changes and compared positively with the standard drug, amlodipine.
