STUDIES ON THE EFFECTS OF POLYPHENOLIC NATURAL PRODUCTS ON LIPID PARAMETERS AND HYPERTENSION IN RATS

Abstract

Polyphenols, in particular flavonoids and tannins have long been used in traditional medicine to cure diseases. The present investigation was undertaken to study the effects of some polyphenolic natural products, namely quercetin, morin and tannic acid on serum and liver lipids, hypertension and lipid peroxidation in rats. In high fat diet (HFD) fed Wistar rats, supplementation with morin and tannic acid was beneficial because plasma total cholesterol (TC) and low density lipoprotein cholesterol (LDLC) were significantly lower than that of the control rats at the end of ten weeks. The rats fed the HFD supplemented with tannic acid (HFD+T) also had significantly lower plasma triglyceride, liver cholesterol and liver fat. However, when the HFD was supplemented with quercetin the rats had significantly higher LDLC concentration compared to the control rats at the end of the ten week period. Tannic acid was selected for further studies on its effects on serum and liver lipids of normocholesterolemic (RAIF) and genetically hypercholesterolemic (RICO) rats fed on I) HFD and 2) a balanced low fat standard diet (STD). In both strains, tannic acid did not cause any changes on the serum and liver lipids levels as well as the activity of the enzyme HMG-CoA reductase of the rats fed on STD. However, the serum TC and LDLC of the HFD+T fed RAIF and RICO rats were significantly lowered. A reduction in cholesterol absorption may be implicated as one of the mechanisms involved. In addition, the HFD+T fed RICO rats had significantly higher concentrations of HDLC and this did not occur in the RAIF rats. The differences observed may possibly be due to differences in the strain of animals used. Quercetin, morin and tannic acid were administerd intraperitoneally to 1) Spontaneously Hypertensive rats (SHR) and 2) Wistar Kyoto rats (WKY) for ten weeks. In the SHR, quercetin lowered the LDLC concentration but in the WKY the serum TG concentration was significantly higher compared to control rats at the end of ten weeks. Morin treated SHR had significantly lower TC and TG compared to control rats but for the WKY, there were no significant differences in the serum lipids when compared to the control rats. Tannic acid treated SHR had significantly lower serum TC, LDLC and TG concentrations while in the WKY, serum HDLC concentration was significantly higher compared to the respective controls. Tannic acid was therefore selected for the continous delivery to the peritoneal cavity using an osmotic pump for two weeks in the WKY and SHR. In the SHR, tannic acid treated rats showed significantly lower kidney malonaldehyde (MDA) level. Tannic acid however did not have any effect on the serum lipids and blood pressure of both strains of rats. Tannic acid therefore may be developed as a potential therapeutic agent.