Nitric Oxide and Effects of Cationic Polypeptides in Canine Cerebral Arteries

Cationic polypeptides are released by activated leukocytes and may play an important role in the regulation of vascular tone. Effects of cationic polypeptides on cerebral vascular tone have not been studied. The present experiments were designed to determine if synthetic cationic polypeptides, poly-L-arginine and poly-L-lysine, affect the function of cerebral arteries. Rings of canine basilar arteries with and without endothelium were suspended for isometric force recording. Poly-L-arginine (10–8–10–7 M) and poly-L-lysine (10–8–10–7 M) caused endothelium-dependent relaxations. A nitric oxide synthase inhibitor, NG-nitro-L-arginine methyl ester (10–4 M), and a nitric oxide scavenger, oxyhemoglobin (3 × 10–6 M), inhibited relaxations in response to cationic polypeptides. Negatively charged molecules, heparin (1 U/ml) and dextran sulfate (10 mg/ml), also inhibited relaxations to poly-L-arginine or poly-L-lysine. Higher concentrations of poly-L-arginine (10–6–10–5 M) and poly-L-lysine (10–6–10–5 M) induced endothelium-independent contractions. A protein kinase C inhibitor, staurosporine (10–8 M), abolished these contractions. Heparin (10 U/ml) and dextran sulfate (100 mg/ml) inhibited the contractile effect of cationic polypeptides but did not affect contractions to phorbol 12,13-dibutyrate. Poly-L-arginine (10–6 M) and poly-L-lysine (10–6 M) abolished endothelium-dependent relaxations in response to bradykinin (10–10–10–6 M) or calcium ionophore A23187 (10–9–10–6 M). Heparin (50 U/ml) and dextran sulfate (200 mg/ml) restored endothelium-dependent relaxations to bradykinin (10–10–10–6 M) in arteries exposed to poly-L-arginine (10–6 M) or poly-L-lysine (10–6 M). These studies demonstrate that in the lower concentration range (10–8–10–7 M), poly-L-arginine and poly-L-lysine induce endothelium-dependent relaxations by production of nitric oxide via charge-dependent activation of endothelial nitric oxide synthase. In the higher concentration range (10–6–10–5 M), cationic polypeptides cause endothelium-independent contractions as well as impairment of endothelium-dependent relaxations in response to bradykinin and A23187. These contractions and inhibition of endothelium-dependent relaxations are also mediated by a charge-dependent mechanism and may involve activation of protein kinase C.