The contributions of muscarinic receptors and changes in plasma aldosterone levels to the anti-hypertensive effect of Tulbaghia violacea

Abstract

BackgroundTulbaghia violacea Harv. (Alliaceae) is used to treat various ailments, including hypertension (HTN) in South Africa. This study aims to evaluate the contributions of muscarinic receptors and changes in plasma aldosterone levels to its anti-hypertensive effect.MethodsIn the acute experiments, methanol leaf extracts (MLE) of T. violacea (30–120 mg/kg), muscarine (0.16 -10 μg/kg), and atropine (0.02 - 20.48 mg/kg), and/or the vehicle (dimethylsulfoxide (DMSO) and normal saline (NS)) were respectively and randomly administered intravenously in a group of spontaneously hypertensive (SHR) weighing 300 to 350 g and aged less than 5 months. Subsequently, T. violacea (60 mg/kg) or muscarine (2.5 μg/kg) was infused into eight SHRs, 20 min after atropine (5.12 mg/kg) pre-treatment. In the chronic (21 days) experiments, the SHRs were randomly divided into three groups, and given the vehicle (0.2 ml/day of DMSO and NS), T. violacea (60 mg/kg/day) and captopril (10 mg/kg/day) respectively into the peritoneum, to investigate their effects on blood pressure (BP), heart rate (HR), and plasma aldosterone levels. Systolic BP and HR were measured using tail-cuff plethysmography during the intervention. BP and HR were measured via a pressure transducer connecting the femoral artery and the Powerlab at the end of each intervention in the acute experiment; and on day 22 in the chronic experiment.ResultsIn the acute experiments, T. violacea, muscarine, and atropine significantly (p < 0.05) reduced BP dose-dependently. T. violacea and muscarine produced dose-dependent decreases in HR, while the effect of atropine on HR varied. After atropine pre-treatment, dose-dependent increases in BP and HR were observed with T. violacea; while the BP and HR effects of muscarine were nullified. In the chronic experiments, the T. violacea-treated and captropril-treated groups had signicantly lower levels of aldosterone in plasma when compared to vehicle-treated group. Compared to the vehicle-treated group, significant reduction in BP was only seen in the captopril-treated group; while no difference in HR was observed among the groups.ConclusionThe results obtained in this study suggest that stimulation of the muscarinic receptors and a reduction in plasma aldosterone levels contribute to the anti-hypertesive effect of T. violacea.

Comparison of the acute effects of <i>Tulbaghia violacea</i> William Henry Harvey (Alliaceae) on blood pressure and heart rate of ageing male normotensive Wistar kyoto rats and adult male spontaneously hypertensive rats

“…T. violacea significantly and dose-dependently reduced the SBP, DBP, MAP and HR in both WKY (Figure 1) and SHR (Figure 2), with the percentage changes (%∆) in both BP and HR being similar between the two strains of. The results obtained in the ageing WKY is consistent with that obtained by Ramesar et al [9] in adult Wistar rats, while that obtained in the SHR corroborates previous results in SHRs [11,12] and Dahl salt sensitive rats [8,10,15].…”

“…Excess solvent was removed from the resulting extract with a rotavapor and freezedrying, and the direct extract stored in a brown bottle in a -4 ºC freezer. The final dried extract was 76.6 g or 3.2 % of the original weight of the fresh plant [12].…”

“…The effects of different doses of the methanol leaf extracts (MLE) of T. violacea (5-150 mg/kg) on both anaesthetized WKY and SH rats were determined using the method previously described [12]. The femoral artery of the rats were cannulated to measure BP and HR, while the jugular vein were cannulated for intravenous infusion of T. violacea.…”

“…(Alliaceae) is common throughout Africa, with the highest concentration in Southern Africa, where it is widely used as herbal remedy for various complaints, including HTN [6,7]. T. violacea has been suggested to have similar secondary metabolites and biological activities as garlic since they belong to the same plant family [6,7], and for these reasons, there has been a recent increase in the number of studies aimed at exploring and/ or confirming the therapeutic potential of T. violacea on the CV system [8][9][10][11][12].…”

“…A couple of studies have investigated the effect of T. violacea on different strains of rats, including the adult Wistar rats [9], the spontaneously hypertensive rat (SHR) [11,12] and the Dahl salt-sensitive rats (DSS) [8,10,15]. The inhibition of the angiotensin converting enzyme (ACE) [9,11] and the β1 adrenoceptors [12]; the reduction in the expression of angiotensin II type 1a (AT1a) mRNA [8], and levels of aldosterone in plasma [12]; and increases in diuresis and natriuresis [8,10] are some of the mechanisms that have been suggested to elicit the effects observed.…”