Effect of Tulbaghia violacea on the blood pressure and heart rate in male spontaneously hypertensive wistar rats
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Tulbaghia violacea Harv. (Alliaceae) is a small bulbous herb which belongs to the family, Alliaceae, most commonly associated with onions and garlic. In South Africa (SA), this herb has been traditionally used in the treatment of various ailments, including fever, colds, asthma, paralysis, hypertension (HTN) and stomach problems. The aim of this study was to evaluate the effect of methanol leaf extracts (MLE) of T. violacea on the blood pressure (BP) and heart rate (HR) in anaesthetized male spontaneously hypertensive rats and to find out the mechanism(s) by which it acts. The MLE of T. violacea (5 - 150 mg/kg), angiotensin I (ang I, 3.1 - 100 mg/kg), captopril (10 mg/kg), angiotensin II (ang II, 3.1 - 50 g/kg), losartan (30 mg/kg), phenylephrine (0.01 ; 0.16 mg/kg), prazosin (1 mg/kg), dobutamine (0.2 ; 10.0mg/kg), propranolol (0.1 - 12.8 mg/kg), muscarine (0.16 -10 mg/kg), and atropine (0.02 - 20.48 mg/kg) were administered intravenously into male spontaneously hypertensive rats (SHR) weighing between 300 g and 350 g and aged less than 5; months. The MLE of T. violacea and/or the standard drugs were infused alone, simultaneously, or separately into each animal. The BP and HR were measured via a pressure transducer connecting the femoral artery and the Powerlab. The vehicle (0.2 mls of a mixture of dimethylsulfoxide and normal saline), T. violacea (60 mg/kg) and captopril (10 mg/kg) were injected intraperitoneally into some SHR for 21 days to investigate the chronic effect of these agents on plasma levels of aldosterone. The mean change, the mean of the individual percentage changes and the percentage difference (in mean) observed with each intervention was calculated and statistically analyzed using the Student t test for significant difference (p < 0.05). The Microsoft Excel software was used for statistical analysis. T. violacea significantly (p < 0.05) reduced the systolic, diastolic, and mean arterial BP; and HR dose-dependently. In a dose-dependent manner, ang I, ang II, phenylephrine significantly (p < 0.05) increased the BP, while propranolol, muscarine and atropine reduced the BP. The increases in BP due to dobutamine were not dose-dependent. In a dose dependent manner, phenylephrine and propranolol reduced the HR, while dobutamine increased the HR. The effect of ang I, ang II, muscarine and atropine on HR were not dose-dependent; with both increases as well as decreases observed with ang I, and II and atropine, while decreases were seen with muscarine. Captopril produced significant (p < 0.05) reduction in BP which were not associated with any change in HR. The co-infusion of ang I with the MLE produced significant (p < 0.05) reduction in BP, which were not associated with significant changes in HR. The co-infusion of ang II with the MLE did not produce any significant changes in BP or HR when compared to the infusion of the standard drug alone. The co-infusion of phenylephrine with the MLE did not produce any significant change in BP or HR when compared to the values obtained with the infusion of the standard drug alone, in both the absence and presence of prazosin. The co-infusion of dobutamine with T. violacea produced siginificant (p < 0.05) increases in DBP which were associated with significant (p < 0.05) reductions in HR, when compared to the values obtained with the infusion of the standard drug alone. Theco-infusion of atropine with the MLE did not produce any significant change in BP or HR when compared to the values obtained with the infusion of atropine alone. However, the infusion of T. violacea, 20 minutes after pre-treating animals with atropine (5.12 mg/kg) lead to dose dependent significant (p< 0.05) increases in BP, which were associated with dose-dependent increases in HR. The chronic treatment of animals with T. violacea or captropril produced (a) signicant (p < 0.05) reductions in the plasma levels of aldosterone when compared to the values obtained in the vehicle-treated group, (b) produced signifiant (p< 0.05) reduction in BP in the captopril treated group when compared to the vehicle-treated, (c) did not produce any signficant change in BP in the T. violacea-treated group when compared to the vehicle-treated group and (d) did not produce any signifiant change in HR or body weight in any of the groups. The result obtained in this study suggests that T. violacea reduced BP and HR in the SHR. Secondly, the BP and HR reducing effect of the MLE may involve a) the inhibition of the ACE, b) the inhibition of the beta; adrenoceptors, c) the stimulation of the muscarinic receptors and d) the reduction of the levels of aldosternone in plasma. The results also suggest that the MLE may not act through the angiotensin II receptors or the alpha adrenergic receptors.