Nitric Oxide-Dependent Reduction in Soluble Guanylate Cyclase Functionality Accounts for Early Lipopolysaccharide-Induced Changes in Vascular Reactivity

Abstract

We investigated the role of soluble guanylate cyclase in lipopolysaccharide-induced hyporesponsiveness to phenylephrine. The effects of phenylephrine on the blood pressure of female Wistar rats were evaluated at 2, 8, and 24 h after lipopolysaccharide injection (12.5 mg/kg i.p.). Vasoconstrictive responses to phenylephrine were reduced 40 to 50% in all time periods. Methylene blue, a soluble guanylate cyclase inhibitor (15 mol/kg i.v.) restored the reactivity to phenylephrine in animals injected with lipopolysaccharide 2 and 24 h earlier. However, it failed to do so in animals injected with lipopolysaccharide 8 h earlier. Incubation with sodium nitroprusside (SNP) increased lung and aorta cGMP levels in control animals and in tissues of rats treated with lipopolysaccharide 24 h earlier. However, SNP failed to increase tissue cGMP in rats injected 8 h earlier.Lipopolysaccharide reduced the vasodilatory response to NO donors 8 h after injection. This effect and the decreased lung cGMP accumulation in response to SNP were reversed by an NO synthase blocker. Guanylate cyclase protein levels were lower than controls in lungs harvested from rats injected 8 h earlier and were back to normal values in lungs of rats injected 24 h earlier with lipopolysaccharide. Thus, data indicate that there is a temporal window of 8 h after lipopolysaccharide injection in which soluble guanylate cyclase is not functional and that this loss of function is NO-dependent. Thus, the putative use of soluble guanylate cyclase inhibitors in the treatment of endotoxemia may be beneficial mainly at early stages of this condition.Septic shock, the most severe complication of sepsis, is a serious disorder with significant morbidity and mortality even after the appropriate antibiotic and supportive therapy are initiated. The poor outcome is considered to be a consequence of an overactive systemic inflammatory response elicited by microbial products, mainly lipopolysaccharide. The disease state is characterized by hypotension, hyporeactivity to vasoconstrictor agents, vascular damage and disseminated intravascular coagulation, which leads to multiple organ failure and death (Karima et al., 1999). Because the mortality rate after sepsis is in excess of 50%, it is clear that the present pharmacotherapy is inadequate.Inflammatory stimuli such as lipopolysaccharide activate a pathway that leads to expression, among other proinflammatory proteins, of the inducible nitric-oxide synthase (NOS-2). Once expressed, this enzyme is active for several hours and produces large amounts of nitric oxide (Alderton et al., 2001). It is well established that overproduction of NO in sepsis is one of the main causes of excessive vasodilation and reduced contractile response to vasoconstrictor agents (Titheradge, 1999). Regarding the molecular mechanism of NO-mediated vascular collapse in shock, the role of cGMP-dependent mechanism seems to be well established (Fleming et al., 1991;Paya et al., 1993;Keaney et al., 1994;Silva-Santos et al., 2002). NO activates solu...

Methylene blue for vasoplegic syndrome treatment in heart surgery: fifteen years of questions, answers, doubts and certainties

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Circulação extracorpórea em adultos no século XXI: ciência, arte ou empirismo?

“…Recently, a brilliant doctoral thesis was defended at the Federal University of Florianopolis (which has already been published by Fernandes et al [40] ) and brings some very important data to attempt to answer that question.…”

Late, but Not Early, Inhibition of Soluble Guanylate Cyclase Decreases Mortality in a Rat Sepsis Model

“…Previous work from our laboratory has shown that ODQ failed to restore vascular responsiveness in response to phenylephrine when administered early (8 h) after lipopolysaccharide (da Silva-Santos et al, 2002). This failure of ODQ to restore vascular responsiveness has been shown to depend, at least in part, on a reduction in the sGC protein content (Fernandes et al, 2006).…”

“…The mortality rate was recorded over a 5-day period. Doses of MB and ODQ were chosen based on our own experience (da Silva-Santos et al, 2002;Fernandes et al, 2006) and from other published studies (Keaney et al, 1994;Zacharowski et al, 2001).…”