Another embodiment relates to a method of processing a blood vessel comprising preparing a blood vessel for implantation in a patient and exposing the blood vessel to a physiological solution that comprises an exogenous substrate for an SSAO enzyme. Another embodiment is a composition having a concentration of an exogenous substrate for an SSAO enzyme, wherein the concentration of the exogenous substrate is at least great enough to relax a blood vessel exposed to the solution. Another embodiment is a medicament having an exogenous substrate for an SSAO enzyme. Another embodiment is a treatment for high blood pressure using an exogenous substrate for an SSAO enzyme.