Relaxatsion Responses to Extracts of Polygonum Hydropiper (L) in Porcine Coronary Artery: Role of Potassium Channel

Authors

• Amna Batool, Mohammad Saleem Department of Pharmacology faculty of Pharmaceutical sciences, Government college,University Faisalabad, Pakistan
• Mohammad Saleem, Alamgeer University College of Pharmacy, University of Punjab, Lahore, Pakistan
• Richard Roberts School of Life Sciences, University of Nottingham, Nottingham, NG7 2UH, UK

Abstract

Polygonum hydropiper (L) is commonly known as “smart weed” that is used traditionally for the management of hypertension. Therefore, the aim of this study was to determine the effect of P. hydropiper extracts on vasorelaxation using porcine coronary artery rings.Segments of porcine coronary artery were mounted for isometric tension recording in isolated tissue baths and pre-contracted with the thromboxane A2 analog U46619.After pre-contraction, cumulative concentrations of P. hydropiper extracts were added to the tissues to determine the fraction with greatest activity. A variety of inhibitors of intracellular signaling pathways were then utilized in order to determine the mechanism of relaxation. P. hydropiper extracts produced a concentration dependent relaxation of the porcine coronary artery, with the butanol soluble fraction producing the greatest response. The relaxation to the butanol soluble extract was not reduced by removal of endothelium indicating endothelium-independent mechanism of relaxation. Furthermore, the relaxation was unaffected by removal of extracellular calcium, and pre-incubation with the extract had no effect on contractions due to influx of extracellular calcium or release of intracellular calcium. However, relaxation responses were decreased in the presence of potassium channel blockers. Relaxation responses to sodium nitroprusside and forskolin were enhanced by the presence of the butanol soluble extract, suggesting phosphodiesterase inhibitory action. Indeed, relaxation responses to the PDE 4 and PDE 5 inhibitors rolipram and sildenafil were similarly inhibited by potassium channel blockers, indicating that the effect of the butanol extract on potassium channels may be related to phosphodiesterase activity. Theobromine and gallic acid identified as constituents of butanol soluble fraction of P. hydropiper, also produced a relaxation that was inhibited by potassium channel blockers, suggesting that the vascular activity of butanol soluble fraction of P. hydropiper may be due to the presence of theses compound.  In conclusion, butanol soluble fraction of P. hydropiper produces relaxation in porcine coronary artery, which is dependent upon opening of potassium channel, potentially downstream of phosphodiesterase inhibition.