Neuronal nitric oxide synthase and its interaction with soluble guanylate cyclase is a key factor for the vascular dysfunction of experimental sepsis.

OBJECTIVE: Vascular dysfunction plays a central role in sepsis, and it is characterized by hypotension and hyporesponsiveness to vasoconstrictors. Nitric oxide is regarded as a central element of sepsis vascular dysfunction. The high amounts of nitric oxide produced during sepsis are mainly derived from the inducible isoform of nitric oxide synthase 2. We have previously shown that nitric oxide synthase 2 levels decrease in later stages of sepsis, whereas levels and activity of soluble guanylate cyclase increase. Therefore, we studied the putative role of other relevant nitric oxide sources, namely, the neuronal (nitric oxide synthase 1) isoform, in sepsis and its relationship with soluble guanylate cyclase. We also studied the consequences of nitric oxide synthase 1 blockade in the hyporesponsiveness to vasoconstrictors. DESIGN: Randomized controlled prospective experimental study. SETTING: Academic research laboratory. SUBJECTS: Female Wistar rats submitted to cecal ligation and puncture method. INTERVENTIONS: 1) Six, 12, and 24 hours after cecal ligation and puncture, vascular reactivity to phenylephrine (3 and 30 nmol/kg) before and after 7-nitroindazole (45 µmol/kg, s.c.) or aminoguanidine (30 µmol/kg, s.c.) administration was evaluated. 2) Protein levels and interaction between nitric oxide synthase 1 and soluble guanylate cyclase were determined. 3) Six, 12, and 24 hours after cecal ligation and puncture, thoracic aorta segments were stimulated with phenylephrine in the presence or absence of 7-nitroindazole and cyclic guanosine monophosphate accumulation was determined. 4) After 24 hours of cecal ligation and puncture, norepinephrine was infused (10 µg/kg/min) in the presence or absence of 7-nitroindazole or S-methyl-L-thiocitrulline (1 µmol/kg, IV) and mean arterial pressure was registered. MEASUREMENTS AND MAIN RESULTS: 1) Both nitric oxide synthase 1 and soluble guanylate cyclase are expressed in higher levels in vascular tissues during sepsis; 2) both proteins physically interact and nitric oxide synthase 1 blockade inhibits cyclic guanosine monophosphate production; 3) pharmacological blockade of nitric oxide synthase 1 using 7-nitroindazole or S-methyl-L-thiocitrulline reverts the hyporesponsiveness to phenylephrine and increases the vasoconstrictor effect of norepinephrine and phenylephrine. CONCLUSIONS: Sepsis induces increased expression and physical association of nitric oxide synthase 1/soluble guanylate cyclase and a higher production of cyclic guanosine monophosphate that together may help explain sepsis-induced vascular dysfunction. In addition, selective inhibition of nitric oxide synthase 1 restores the responsiveness to vasoconstrictors. Therefore, inhibition of nitric oxide synthase 1 (and possibly soluble guanylate cyclase) may represent a valuable alternative to restore the effectiveness of vasopressor agents during late sepsis.

Antinociceptive effects of peripheral benzodiazepine receptors.

Pretreatment of mice with Ro5-4864 or PK11195 inhibited the first- and second-phase responses in the formalin test and this effect was significantly reversed by aminoglutethimide, an inhibitor of pregnenolone synthesis, suggesting that the antinociceptive effect of the peripheral-type benzodiazepine receptor ligands is dependent on steroid formation. Doses of Ro5-4864 that did not produce an antinociceptive effect when injected by the intraperitoneal route presented an analgesic effect, if infected by the intracerebroventricular, intrathecal or intraplantar routes. PK11195 pretreatments with intrathecal, intracerebroventricular or intraplantar doses had no effect in the formalin test. These results suggest that the antinociceptive effect of Ro5-4864 reflects the influence of this ligand on steroid production not only in many nonneuronal peripheral tissues but also in the nervous system, while the antinociceptive action of PK11195 may be due to the stimulation of steroid synthesis only in nonnervous tissues.