Abstract

Anogeissus leiocarpa (DC) Guill. et Perr. belongs to the Combretaceae family and was previously named A. leiocarpa (DC) Guill. Et Perr. It has been widely used in Burkina Faso by traditional medicine for the treatment of hypertension. Previous study showed that the dichloromethanolic fraction from the barks of trunk of A. leiocarpa (ALF) has induced an endothelium-independent and endothelium-dependent vasodilation effect and had the capacity to inhibit in vitro, purified cyclic nucleotide phosphodiesterases (PDEs) activity. The aims of this study were to better underline ALF-induced endothelium-independent vasorelaxation in an organ model. The results showed that ALF significantly reduce the contractile response to U46619 in porcine coronary artery rings without endothelium that were in concentration-dependent manner. In denuded rings, pretreatment by ALF (10, 30 and 100 µg/mL) did not affect relaxation to sodium nitroprusside (SNP), suggesting that relaxation to ALF was not due to its ability to be a nitric oxide donor. Moreover, SNP-induced relaxation had not been affected in the presence of Nimodipine (PDE1 inhibitor), EHNA (PDE2 inhibitor) or DMPPO (PDE5 inhibitor). In addition, the results showed a relaxation effect to isoproterenol in endothelium-denuded artery rings pretreated with ALF (3, 10, and 30 µg/mL) which were significantly affected suggesting a possible membrane hyperpolarization leading to the vasodilation. In the presence of the PDE3 specific inhibitor Cilostamide and ALF (30 and 100 µg/mL), the vasodilation effects of isoproterenol was enhanced and comparable. Moreover, various potassium channels were not involved in ALF-induced relaxation since tetraethylammonium chloride (non-selective K+ channels inhibitor), iberiotoxin (voltage-sensitive potassium channels inhibitor) and Glibenclamide (KATP channels inhibitor) did not notably affect the relaxation effect to ALF in rings without endothelium. Taken together, ALF-induced endothelium-independent relaxation mainly involves a sustained decrease in [Ca2+]i and may be due to PDE1, 3 and 5 inhibitions localized in the vascular smooth muscle cells. While, the involvement of the ions channels have not been clearly revealed in this experiment.

Key words: Anogeissus leiocarpa, U46619, phosphodiesterases (PDEs), calcium, porcine coronary artery, sodium nitroprusside (SNP), isoproterenol.