Basic Polyamino Acids Rich in Arginine, Lysine, or Ornithine Cause Both Enhancement of and Refractoriness to Formation of Endothelium-Derived Nitric Oxide in Pulmonary Artery and Vein

Ignarro, Louis J.
Gold, Michele E.
Buga, Georgette M.
Byrns, Russell E.
Wood, Keith S.
Chaudhuri, Gautam
Frank, Gerard

From the Department of Pharmacology (L.J.I., M.E.G., G.M.B., R.E.B., K.S.W.), and the Department of Obstetrics and Gynecology (G.C.), University of California Los Angeles, School of Medicine, Los Angeles, and the Department of Medicine (G.F.), Wadsworth VA Medical Center, Los Angeles.

Supported in part by National Institutes of Health Grant HL-35014 and a grant from the Laubisch Fund for Cardiovascular Research.

Address for reprints: Dr. Louis J. Ignarro, Department of Pharmacology, UCLA School of Medicine, Los Angeles, CA 90024.

Received February 22, 1988; accepted July 25, 1988.

Circulation Research 64(2):p 315-329, February 1989.

The objective of this study was to elucidate the mechanism by which polyamino acids containing L-arginine, L-lysine or L-ornithine cause endothehium-dependent relaxation of bovine intrapulmonary artery and vein. Basic but not acidic or neutral polypeptides ranging in average molecular weights from 17 to 225 kDa elicited tune- and concentration-dependent relaxation and cyclic GMP accumulation in precontracted rings of artery and vein by endotheh'um-dependent mechanisms. Vascular responses were markedly inhibited by oxyhemoglobin, methylene blue, or potassium. The basic polyamino acids stimulated the formation and/or release of an endothelium-derived relaxing factor (EDRF) identified as nitric oxide (NO) in perfused segments of both artery and vein as assessed by bioassay. The polyamino acids and A23187 released a similar endothelium-derived NO (EDNO) from artery and vein, as assessed by the similar half-life (3-5 seconds), antagonism by superoxide anion or oxyhemoglobin, enhancement by superoxide dismutase, and lack of influence by indomethacin. The bask polyamino acids elicited potent relaxant responses with EC₅₀ values ranging from 3±10^-9 to 2±10^-7 M, and a direct correlation was obtained between molecular weight and relaxation potency irrespective of the basic amino acid incorporated. Prolonged contact of arterial or venous rings with basic polyamino acids resulted in the rapid development of marked refractoriness to relaxation and cyclic GMP formation on addition of polyamino acid. Moreover, refractoriness developed to the vascular responses of other endothelium-dependent vasodilators but not to glyceryl trinitrate or isoproterenol. The mechanism of refractory responses was attributed to interference with EDNO formation and release as assessed by bioassay and chemical assay. The hypothesis is forwarded that the basic polyamino acids serve as partial substrates for the enzyme system that catalyzes the conversion of L-arginine to NO. Prolonged contact between substrate and enzyme results in enzyme desensitization and the development of refractoriness or a form of tolerance to vasodilators whose action is mediated by EDNO.