Vascular smooth muscle relaxation by a lectin from Pisum arvense: evidences of endothelial NOS pathway.

The vasorelaxant effect of the lectin of Pisum arvense (PAL) seeds was investigated in rat aorta. PAL (10-100 µg/ml) was applied on aorta rings, with or without endothelium, pre-contracted with phenylephrine (Phe; 0.1 µM). Participation of endothelium derived relaxant factors was evaluated incubating the tissue with indomethacin (10 µM), L-nitro arginine methyl ester (L-NAME, 100 µM) and tetraethylammonium (TEA, 5 mM) before addition of PAL. The role of the lectin domain was investigated by addition of PAL into tissue in presence of glucose (3x 10⁻⁵ M), or N-acetyl Dglucosamine (GlcNAc; 3 x 10⁻⁴ M). The importance of extracellular calcium (Ca²⁺e) or interaction with muscarinic receptors in the relaxant effect was evaluated by addition of PAL into aorta rings containing calcium free solution (OCa) and atropine (1 µ M), respectively. PAL induced concentration-dependent relaxation in endothelized aorta (IC50 =58.38 ± 1.87 µg/ml), which was reversed by L-NAME and glucose. The lectin effect was totally inhibited when the preparation was inserted in OCa, but not in presence of atropine. Summarizing, our data showed a relaxant effect of PAL in isolated rat aorta rings in presence of endothelium, suggestive of interaction between the lectin carbohydrate binding sites with specific receptors located in vascular endothelial cells leading to nitric oxide synthase activation. This effect seems to require Ca²⁺e but is independent on muscarinic receptors interaction.