Effects Of Crude Rp Extract And Its Isoflavones On Hypertension

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Radix pueraria was shown to lower blood pressure in both normal and hypertensive laboratory animals. In normal anesthetized dog, intravenous administration of crude extract of RP, its total isoflavones or a pure preparation of puerarin elicited a short and quick reduction in blood pressure. In normal unanesthetized dogs, orally administered a crude water extract (2g/kg), an alcohol extract (2g/kg), a total isoflavone fraction or a puerarin preparation produced similar effect on blood pressure (Zeng etal., 1974; Fan, 1977).

When puerarin was administered intraperitoneally (100mg/kg) to spontaneous hypertension rat (SHR), both blood pressure and heart rate (Figure 8.1) were lowered as compared to the controls. Such effect was more potent in SHR than in normal Wistar rat (Song etal., 1988). It has also been shown that puerarin significantly reduced plasma renin activity (PRA) in SHR by radioimmunoassay, reduced it by 67 per cent from 2.1 ±0.45 ng/ml• h to 0.73±0.20ng/ml• h. However, the effect of puerarin on PRA was not observed in normal rats.

Other investigators showed that a pueraria isoflavone daidzein, when administered orally as a PVP (Polyvinylpyrrolidone)-dispersed product to SHR (300 mg/kg), reduced blood pressure of the test animals. Maximal reduction was observed 2h after administration. The systolic pressure was reduced by 12.8 per cent, whereas no obvious change was found in control animals receiving a simple mixture of daidzein and PVP in amounts equivalent to those in daidzein—PVP dispersion preparation. The daidzein—PVP dispersion reduced PRA by 52.4 per cent and 24.7 per cent in SHR and Wistar rat, respectively. It has also been shown to lower systolic and diastolic pressure by 18.6 ± 10.6 per cent and 43.0 ± 19.2 per cent, respectively, when administered intravenously (25 mg/kg) in anesthetized cat (Guo etal., 1995). In anesthetized rabbits, daidzein-PVP preparation elicited an early but weak antihypertensive effect (Guo etal., 1995).

The mechanism by which RP elicits its antihypertensive effect is still largely obscure. Radix pueraria might antagonize blood pressure elevation caused by isoproterenol, and decrease or eliminate blood pressure elevation effect of epinephrine. It has been shown that RP extract antagonized elevated heart rates induced by isoproterenol in various animal models. On the basis of these results, it was suggested that RP may act as a ^-adrenergic blocker (Lu etal, 1980).

Heart Rates Mammals

Time (min)

Figure 8.1 Effect of puerarin (T) on blood pressure (BP) and heart rate (HR) of spontaneous hypertensive rat. N = 8, *p > .05, **p < .05, ***p < .01.

Time (min)

Figure 8.1 Effect of puerarin (T) on blood pressure (BP) and heart rate (HR) of spontaneous hypertensive rat. N = 8, *p > .05, **p < .05, ***p < .01.

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