Effects of Orthosiphon stamineuson β-NADH induced oxidative stress in the isolated rat thoracic aorta

Mohd Mustafa1, Gopal Subramaniam1, Francis Achieke2, Dharmani Murugan1

1University of Malaya, Kuala Lumpur, Malaysia, 2International Medical University, Kuala Lumpur, Malaysia

Phytochemicals including flavonoids are potent antioxidants and may protect against the oxidative stress associated with several cardiovascular diseases (Ajay et al., 2006). Decreased production and/or deactivation of endothelium-derived nitric oxide by oxygen free radicals are implicated in the etiology of endothelial dysfunctions (Kodja & Harrison, 1999). In the present study, we examined the effects of the methanolic extract of Orthosiphon stamineus (MOS) on β-nicotinamide adenine di-nucleotide (β-NADH)-induced oxidative stress in the isolated rat thoracic aortic rings.

Rat aortic rings were mounted in Krebs solution for isometric tension recordings. The endothelium dependent and independent relaxant responses of the aortic rings to phenylephrine (PE, 1.0 μM) were examined in the presence, or absence of β-NADH (300 μM). The plant extract (0.5 μg/ml) was added to the bath 30 minutes prior to the PE. Both acetylcholine (ACh) and sodium nitroprusside (SNP) caused dose-dependent relaxations of the PE-induced contractions with maximal relaxations (Rmax) of 98.71 ±4.3% and 102.6 ± 2.9 %, respectively (n=9). β-NADH significantly reduced the Rmax to ACh (64.05 ±1.1%, p < 0.01) and attenuated the responses to SNP (10-9 to 10-7 M) without marked effects on the maximal relaxations (Rmax, 101.0±1.0 %; n= 7). Preincubation with MOS (0.5-50 μg/ml) significantly improved the ACh and SNP induced vasorelaxations (Rmax 88-96%; n= 6). MOS (0.5-50 ug/ml) significantly restored the sensitivity of the vasorelaxant responses of the smooth muscles to SNP (pEC50: 8.5±0.1, 8.3± 0.1 and 8.1± 0.1, n= 6). Similarly, MOS (50 μg/ml) improved the endothelium dependent relaxations to histamine. Preincubation with MOS alone was without marked effect on the vascular responses of the rat aorta.

In summary, the present results suggest that MOS improved the vascular relaxant responses of the rat aorta following exposure to oxygen radicals. The effects of MOS probably results from its antioxidant actions which increases the bioavailability of nitric oxide by protecting it from the scavenging effects of the free radicals an enhancing the sensitivity of the of vascular tissues to NO.

The study was supported by a grant from the Ministry of Science and Innovations, Malaysia

Ajay M et al. (2006) Diabetes Res Clin Pract 73 1–7

Kodja G & Harrison D (1999) Cardiovasc Res 43 (1999) 552–557