Cardiovascular effects of Tulbaghia violacea Harv. (Alliaceae) root methanolic extract in Dahl salt-sensitive (DSS) rats

Ethnopharmacological relevance: In African folk medicine, Tulbaghia violacea Harv.(Alliaceae), a herbaceous plant also known by other common local names such as 'wild garlic', 'society garlic' and 'sweet garlic', has been used for the management, control and/or treatment of several human ailments; including hypertension. The aim of the present study was to investigate the cardiovascular effects of methanolic extract of Tulbaghia violacea Harv. in Dahl salt-sensitive (DSS) rats.

Materials and methods: DSS rats were treated intraperitoneally (i.p) as follows: distilled water, control (CON) (3 ml/kg/b.w.); captopril (CAP) (25 mg/kg/b.w.); or methanolic extract of Tulbaghia violacea (TVL) (50 mg/kg/b.w.) for 7 weeks. Systolic blood pressure (SBP) was measured bi-weekly whilst 24-hour urine volumes and sodium concentrations were assessed weekly. Animals were sacrificed on day 49 by halothane overdose. Blood was removed for the determination of aldosterone concentration and angiotensin converting enzyme (ACE) activity. Left kidney was harvested for angiotensin Ia (AT1a) receptor gene expression.

Results: CON showed a significant percentage increase in SBP (mmHg) on day 49 compared to day 0 (baseline values) (9.75±1.7% vs. 2.33±0.77%; p<0.05). CAP and TVL showed significant percentage decreases in SBP at week 7 when compared to baseline (8.13±1.23% and12.88±3.12% p<0.01). Urine volumes (ml) increased significantly in CAP from week 1 to week 4 (9.63±2.22 vs.10.97±1.75 p<0.05) and in TVL from week 2 to 7 (9.23±0.91 vs. 11.90±1.17 p<0.05). Urinary sodium concentration (mmol/L/24 h urine samples) was significantly higher in CAP (0.72±0.07 vs.1.31±0.03 p<0.05) and in TVL (0.71±0.09 vs. 1.68±0.16; p<0.05) at week 7 compared to baseline levels. There was no significant difference in the plasma aldosterone levels (pmol/L) of all the three groups. Serum ACE (U/L) activity was significantly higher in CAP compared to CON and TVL (277.0±11.6 vs. 121.5±3.93; and 147.0±6.63; p<0.05 respectively). CAP showed a significant 6.4 fold increase in AT1a mRNA expression vs. CON (p<0.05) and a 4.5 fold increase vs. TVL (p<0.05). There was no significant difference between CON and TVL treated rats. CAP and TVL showed no significant change in the expression of AT2.

Conclusion: This study showed that TVL possesses antihypertensive effect in Dahl salt-sensitive rats when administered over a long-term.