O34 Endothelium-independent vasorelaxant effect of Thymus linearis via inhibition of phosphodiesterases in porcine coronary artery

Abstract

Thymus linearis Benth. indigenous to Pakistan has been traditionally used for the treatment of various diseases including hypertension. The aim of the study was to investigate the vasorelaxant effect of Thymus linearis in porcine coronary artery rings. Aqueous-methanolic extract and various fractions (butanol, ethyacetate and aqueous) of Thymus linearis were prepared. The effects of extract and fractions were assessed using coronary artery rings and various pharmacological tools were applied to characterize the underlying mechanism of active fraction (butanol). The inhibitory effect of butanolic fraction was also studied on phosphodiesterases using radio enzymatic assay. Phytochemical studies were also carried out using GCMS. The aqueous-methanolic extract of Thymus linearis elicited similar relaxations in coronary artery rings with and without endothelium in a dose-dependent manner. Among the fractions butanolic fraction of Thymus linearis (TLB) was found to be the most potent. TLB significantly potentiated the relaxation induced by forskolin, isoproterenol, sodium nitroprusside and atrial natriuretic peptide whereas the relaxation induced by YC-1, BAY 41-2272, levcromakalim and 1-EBIO was unaffected by TLB. Pretreatment with TLB inhibited the contraction induced by KCl, CaCl2 and U46619 in endothelium denuded coronary artery rings. Furthermore, TLB significantly inhibited the PDE activity (PDE1CaM activated PDE2, PDE3, PDE4 AND PDE5) in a concentration-dependent manner. GCMS analysis revealed the presence of thymol and Carvacrolas as major constituents. In conclusion, TLB induced endothelium-independent relaxations in porcine coronary artery rings by acting directly at the vascular smooth muscle to increase concentrations of both cyclic AMP and cyclic GMP via inhibition of various PDEs.