COLD-STORAGE INDUCES AN ENDOTHELIUM-INDEPENDENT RELAXATION TO HYPOXIAREOXYGENATION IN PORCINE CORONARY-ARTERIES/

Tissues are often cold stored for physiological studies and for clinic al transplantation. We report that cold storage induces a relaxation t o reoxygenation after hypoxia (H/R) in de-endothelialized porcine coro nary arteries. In fresh denuded arteries stimulated with U46619, H/R d id not elicit relaxation. However, after overnight cold storage (4 deg rees C), H/R elicited a transient relaxation with peak relaxation of 5 6 +/- 8% (n = 8), which was reproducible after 2 days of cold storage. The H/R relaxation was inhibited by methylene blue (10 mu M) and LY83 583 (10 mu M), O-2-hemoglobin (1 mu M), or N-G-methyl-L-arginine (0.2 mM), but neither N-G-nitro-L-arginine (0.2 mM) nor cyclo-oxygenase inh ibition was effective. Importantly, the H/R relaxation was attenuated by KCl (40 mM) or tetrabutylammonium chloride (5 mM), a non-selective inhibitor of K+ channels. Interestingly, authentic nitric oxide (NO)- or S-nitroso-N-acetylpenicillamine (SNAP)-induced relaxations were enh anced by cold storage in U46619 (0.1 mu M) contractures. When tissues were contracted with KCl (40 mM), the enhancement in NO- or SNAP-induc ed relaxation by cold storage was markedly smaller than with U46619. N either catalase (1,200 U/ml) nor 3-amino-triazole (50 mM), an inhibito r of catalase, affected the H/R relaxation. The duration of H/R relaxa tion also increased with the period of incubation at 37 degrees C in t he organ bath. This was blocked by inhibition of NO synthesis or guany late cyclase. Moreover, inhibition of protein synthesis with actinomyc in D (0.1 mu M) and cycloheximide (10 mu M), or dexamethasone (1 CuM), an inhibitor of NO synthase induction, blocked this increase in the d uration of the H/R relaxation. The results suggest that in smooth musc le induction of NO pathway relaxation, which is in part mediated by K channels and inducible NO synthase, may be of importance to the under standing of ischemia/reperfusion responses in cold-stored arteries.