New research findings indicate that the flower and leaf extracts of hibiscus could provide the next novel drug for hypertension and coronary heart diseases. CHUKWUMA MUANYA writes. NIGERIAN researchers have confirmed that drinking tea made with flower extracts of Hibiscus rosa-sinensis (popularly called Hibiscus flower) lowered blood pressure in hypertensive patients. Researchers have also demonstrated how the flower extracts of hibiscus could be used to reduce weight, prevent obesity and coronary heart diseases like atheroslerosis by lowering the blood levels of low density lipo-protein (LDL) bad cholesterol. Atherosclerosis, which involves deposits of fatty substances, cellular waste products, calcium and fibrin (is a fibrous protein involved in the clotting of blood); and is the leading cause of illness and death in most countries. However, a local study has found that although hibiscus leaf extract reduced blood pressure, the integrity of the kidney may be compromised if it is used in high doses for the treatment of hypertension. Botanically called Hibiscus rosa-sinensis, hibiscus belongs to the plant family Malvaceae. Hibiscus has many species and is a primary ingredient in many herbal teas. Hibiscus rosa-sinensis is closely related to Hibiscus sabdariffa (also called roselle or zobo in Nigeria). According to The useful plants of west tropical Africa, Volume 4 by H. M. Burkill, the flower is used as abortifacients (a substance that induces abortion), ecbolics (hastening labour or abortion); genital stimulants/depressants; laxatives (foods, compounds, or drugs taken to induce bowel movements or to loosen the stool), etc.; menstrual cycle; paralysis, epilepsy, convulsions, spasm; sedatives, etc. A recent study by Nigerian researchers at the University of Benin has demonstrated the effects of aqueous extracts of the leaves of Hibiscus rosa-sinensis on renal function in hypertensive rats. The study was published in African Journal of Biochemistry Research. The researchers include: Imafidon E. Kate of the Department of Biochemistry, Faculty of Life Sciences; and Okunrobo O. Lucky of the Department of Pharmaceutical Chemistry, Faculty of Pharmacy, University of Benin, Edo State. The researchers wrote: Most people with high blood pressure are over weight, weight loss lowers blood pressure significantly in those who are both over weight and hypertensive. In fact, reducing body weight by as little as ten pounds can lead to a significant reduction in blood pressure; weight loss appears to have a stronger blood pressure-lowering effect than dietary salt restriction. Salt loading had earlier been shown to cause hypertension in rats. Reduction in weight gain of hypertensive rats observed is in agreement with the report of some workers. The administration of H. rosa-sinensis leaf extract showed blood lowering effect in both normotensive (normal blood pressure) and hypertensive rats. Blood pressure is the product of cardiac output and peripheral resistance of the blood vessels.The administration of H. rosa-sinensis probably decreased the blood pressure by decreasing the heart rate, which is a major determinant of the cardiac output. Significant increase in the sodium level of normotensive rats administered with the crude extract in spite of significant reduction in the blood pressure of these rats compared with the control shows that H. rosa-sinensis may interfere with the normal function of the kidney and hence produces increased salt retention. This observation is further strengthened by the increased urea concentration, although the change in total protein concentration was insignificant in those normotensive rats administered with the crude extract. In addition, AST, and ALT concentrations were increased in these rats compared with control. Aspartate aminotransferase (AST) and Alanine aminotransferase (ALT) are enzymes found primarily in the liver, as well as the kidneys, cardiac and skeletal muscle. The researchers concluded:These results show that the leaves of this plant may have a deleterious effect on the kidney. Hypertensive rats administered with the extract had significant increase in urea, AST and sodium ion (Na+) concentration compared with normal control. This result therefore, shows that although, the administration of H. rosa-sinensis reduced blood pressure in albino rats, the use of the plant may have an unpleasant effect on the kidney. Nigerian scientists have also studied the tissue lipid profile of rats administered aqueous extract of Hibiscus rosa-sinensis. The study was published in the Journal of Basic and Applied Sciences. The lead researcher Kate E. Imafidon of the Biochemistry Department, Faculty of life Sciences, University of Benin determined the effect of orally administered aqueous extract of the leaves of Hibiscus rosa-sinensis on tissue lipid profile of albino rats. Lipid profiles are risk indicators of coronary heart disease. Strong correlations have been shown between increased plasma total cholesterol, low density lipoprotein (LDL) bad cholesterol and increased incidence of coronary heart disease such as atheroslerosis. According to the study, oral administration of crude extract of H. rosa-sinensis to albino rats at doses 200, 500 and 700mg/Kg body weight resulted in a significant increase in body weight of animals in the highest dose group. The study reads: The dose dependent increase in liver triacylglycerol (the main constituent of vegetable oil and animal fats), total cholesterol and LDL cholesterol suggest impairment in lipid transport. This is as a result of the fact that there was no concomitant increase in kidney or heart lipid levels. Triacylglycerols are transported in the blood stream by very low density lipoprotein (VLDL). Alternative use of carbohydrates as a result of the engorgement of liver tissues with fats may have produced increase in weight in the highest dose group. HDL cholesterol levels were not increased at any of the dose levels, HDL cholesterol has a protective effect against cardiovascular disease as it removes excess cholesterol from circulation and carries it back to the liver where it is degraded or converted into bile acids. The lipid raising effect of some trado-medicinal plants have been reported. Some workers had earlier observed increase in serum cholesterol on administration of crude drug extract; and observed an increase in serum cholesterol levels on administration of aqueous extract of Aplotaxis lappa This work has therefore demonstrated the ability of H. rosa-sinensis to influence liver metabolism towards increased synthesis of lipids. This effect is however dose-dependent suggesting that the use of H. rosa-sinensis in alternative or complementary medicine should not exceed the 500 mg/kg dose level. A 2008 United States of America Department of Agriculture (USDA) study shows consuming hibiscus tea lowers blood pressure in a group of pre-hypertensive and mildly hypertensive adults. Three cups of tea daily resulted in an average drop of 8.1 point in their systolic blood pressure, compared to a 1.3 point drop in the volunteers who drank the placebo beverage. Study participants with higher blood pressure readings (129 or above) had a greater response to hibiscus tea: their systolic blood pressure went down by 13.2 points. These data support the idea that drinking hibiscus tea in an amount readily incorporated into the diet may play a role in controlling blood pressure, although more research is required.Generally, drinking tea has been found to lower low-density lipoprotein, the LDL bad cholesterol, in a small group of volunteers in an ARS study reported in the Journal of Nutrition. The study showed no effect on high-density lipoprotein, the HDL good cholesterol. The studys authors concluded that drinking black tea, in combination with following a prudent diet moderately low in fat, cholesterol and saturated fatty acids, reduces total and LDL cholesterol by significant amounts and may reduce the risk of coronary heart disease. Other studies have evaluated some ethnomedicinal value of Hibiscus rosa-sinensis. H. rosa sinensis has been used for the treatment of a variety of diseases as well as to promote wound healing. Researchers have determined the wound-healing activity of the ethanol extract of H. rosa- sinensis flower in rats, using excision, incision, and dead space wound models. Local traditional practioners in Western Nigeria has reported that cold aqueous extract of H. rosa-sinensis leaves could be used as an aphrodisiac. Researchers have also studied the blood sugar-lowering (hypoglycemic) activity of an ethanol extract of H. rosa-sinensis in rats. Anti-implantation activity of water extract of leaves of H. rosa-sinensis has also been investigated. It has also been investigated that H. rosa-sinensis extract exerts a protective effect against the tumour promotion stage of cancer development. Traditionally this plant is used for the control of dysfunctional uterine bleeding and as an oral contraceptive. Some of the chemical constituents isolated from this plant are cyanidin, quercetin, hentriacontane, calcium oxalate, thiamine, riboflavin, niacin and ascorbic acid. Flavonoids are also present.
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