INTERACTIONS OF LIGHT AND SODIUM-NITRITE IN PRODUCING RELAXATION OF RABBIT AORTA

  • 1 February 1989
    • journal article
    • research article
    • Vol. 248  (2) , 687-695
Abstract
In rings of rabbit aorta mounted in muscle chambers, endothelial-independent reversible relaxation produced by irradiation with long wavelength was potentiated in the presence of 1 mM NaNO2. Photorelaxation in the presence of NaNO2, but not in its absence, was further potentiated by superoxide dismutase. The interaction of light and NaNO2 in producing relaxations was studied in a perfusion-superfusion system in which Krebs'' solution (37.degree. C, 95% O2-5% CO2) with or without added NaNO2 was perfused (2 ml/min) through a glass tube (1.25 mm, inside diameter) on its way to superfusing an endothelium-free aortic ring a few seconds downstream. UV irradiation either of the solution flowing through the tube or of the aortic ring could be made separately. The ring, mounted for tension recording, was precontracted to a similar level of tone in the absence or presence of NaNO2 by l-phenylephrine HCl. Photorelaxation on direct irradiation of the ring was potentiated markedly by 1 mM NaNO2, was not significantly potentiated further by 10 U/ml of superoxide dismutase, and was inhibited markedly by Hb (1-10 .mu.M) but not by MetHb (10 .mu.M). Irradiation of the perfusing solution produced no relaxation of the aortic ring downstream in the absence of NaNO2, and only small relaxation at 1 mM NaNO2. When superoxide dismutase was present along with NaNO2, irradiation of the perfusion solution (15-120 sec) produced marked relaxation, with magnitude increasing with concentration of NaNO2 (1 .mu.M-1 mM). This relaxation was inhibited by Hb (complete at 0.3-1 .mu.M) but only partly by MetHb (10 .mu.M). It could also be inhibited by putative superoxide anion generators (FeSO4, hydroquinone, pyrogallol and phenidone). These results suggest that NaNO2 is photoactivated to release a potent relaxing substance, which is rapidly inactivated by O2- and inhibited by Hb. The substance is probably nitric oxide and may be the same as endothelium-derived relaxing factor.