Effects of heparin on the inhibitory action of protamine on endothelium‐mediated vasorelaxation

Abstract

The precise mechanism(s) of inhibitory action of protamine on endothelium-mediated vasorelaxation has not been fully elucidated. In addition, no information is available regarding the effects of a heparin-protamine complex on the endothelium-mediated relaxation. Employing isometric tension recording methods, we studied the effects of heparin, an anionic substance, on the protamine-induced inhibition of acetylcholine (ACh)-induced vasorelaxation in isolated rabbit small mesenteric artery. Protamine (> or = 50 micrograms/ml) inhibited ACh (0.03-10 microM)-induced relaxation under a norepinephrine (10 microM)-stimulated condition (P < 0.05). The ACh relaxation, even 20 min after washout of protamine (150 micrograms/ml), was still significantly inhibited as compared to the control (before protamine) ACh relaxation, and further, it was not significantly different from the ACh relaxation maximally inhibited in the presence of protamine. Preapplication of heparin (700 U/ml) almost abolished the protamine inhibition (50 & 150 micrograms/ml) of the ACh relaxation. However, heparin (700 U/ml), applied on washout of protamine (150 micrograms/ml), had no effect on the prolonged protamine inhibition. In conclusion, a heparin-protamine complex had no direct effect on the endothelium-mediated relaxation, and the inhibitory action of protamine on the endothelium-mediated relaxation might be due to its polycationic property. The prolongation of protamine inhibition and the lack of effects of heparin on the prolonged protamine inhibition may suggest a toxic effect of protamine on the endothelium.

Heparin/heparan sulfate chelation inhibits control of vascular repair by tissue-engineered endothelial cells

“…Protamine and other basic polyamino acids rich in L-arginine, lysine, or ornithine have been shown to produce endothelium-dependent vasodilation by inducing the generation of endothelium-derived relaxing factor (nitric oxide) (23,37). However, prolonged exposure to such compounds results in refractoriness to stimulants of endothelium-mediated vasorelaxation (1,23). To explain this paradoxical observation, Ignarro et al (23) have proposed that such basic polyamino acids serve as partial substrates for the enzyme system that catalyzes the production of endothelium-derived relaxing factor, a process that involves the generation of nitric oxide from L-arginine.…”

The systemic vasodilatory action of protamine: is it inhibited or mediated by heparin?

“…Protamine is a protein rich in the L-arginine amino acid, precursor of nitric acid [13] and in our study vascular relaxation is completely abolished when the arterial segment is denuded of endothelium. Therefore, this protamine-derived vasodilatation appears to be an intrinsic action of this drug when it interacts with vascular endothelium, although some authors believe that when the heparin-protamine complex is formed, this relaxing effect is annulled [11,14].…”

Effects of phenol on vascular smooth muscle in rabbit mesenteric resistance arteries

“…Mechanical responses were measured by attaching the strip to a strain gauge (UI-2 type, Shinko, Tokyo, Japan) in a chamber of 0.9ml capacity as previously described [9][10][11][12][13]. The strip was horizontally mounted in the chamber on a microscope stage, and then stretched to ~1.1-1.2 times the resting length to obtain the maximum contractile response to high K +.…”