Methylene Blue Inhibits the Increase of Inducible Nitric Oxide Synthase Activity Induced by Stress and Lipopolysaccharide in the Medial Basal Hypothalamus of Rats

Abstract

In infection bacterial products such as lipopolysaccharides (LPS) induce inducible nitric oxide synthase (iNOS) that produces large quantities of NO toxic to the invading organisms, but also often has toxic effects on host cells. Therefore, inhibition of iNOS activity might be beneficial in combatting these adverse effects. To determine if methylene blue (MB), an oxidizing agent that inactivates iNOS, would reduce the iNOS levels in the medial basal hypothalami (MBH) of conscious male rats, LPS (5 mg/kg) was injected intravenously (i.v.), and after 3 h they were injected i.v. with either MB (3 mg/kg) or saline and the effects on iNOS in the MBH determined. iNOS was measured by conversion of labeled arginine into citrulline by incubating MBH in the absence of calcium (Ca²⁺) since iNOS does not require Ca²⁺ for activation. The results indicate that iNOS was induced by the injection of saline, but the induction by LPS was much greater, an increase of 10-fold above that of control sham-operated animals. Both the induction of iNOS from the stress of saline injections and LPS were completely eliminated by MB indicating that MB might be beneficial in preventing injury to brain tissue following LPS injection. There was no effect of either LPS or MB on the Ca²⁺-dependent constitutive NOS activity.

Effects of Aminoguanidine and Meloxicam on Nitric Oxide and Prostaglandin E Production Induced by Lipopolysaccharide in the Hypothalamus and Anterior Pituitary of the Rat

“…The results of the present work confirm previous findings by our group that there is very little basal iNOS activity in the hypothalamus of adult male rats as measured by the [ 14 C]-citrulline method and that LPS induces a significant increase in iNOS activity, as seen previously by measuring iNOS mRNA [14,21]. The increase in the activity of cNOS in the MBH 6 h after i.p.…”

“…The increase in the activity of cNOS in the MBH 6 h after i.p. LPS injection differs from the results of our previous work, in which LPS injected intravenously 1 day after a jugular catheter was implanted under anesthesia did not alter cNOS in the MBH of the animals [21]. The rats used in the present experiments were not submitted previously to any surgical procedure that could have modified the response to a second stress.…”

“…The rats of this group were untreated, since in previous research we found that isotonic saline injections increased iNOS activity in the MBH [21]. All groups of rats were decapitated 6 h after injection of LPS or other drugs.…”

“…Calciumdependent and -independent NOS activity was determined as previously described [21,23]. In brief, each MBH or AP was homogenized in 500 Ìl of ice-cold 20 mM HEPES with 1 mM DLL-dithiothreitol (DTT), pH 7.4.…”

The comparison of methylene blue and vitamin E in prevention of abdominal postoperative adhesion formation in rat uterine horn models: Biochemical and histopathologic evaluation

“…Several mechanisms may contribute to reduced levels of NO in MB treated rats. For instance, the main effect of MB is inhibition of soluble guanylate cyclase and inducible NO synthase 33 . It competes with molecular oxygen for the transfer of electrons from flavoenzymes and so inhibits the generation of oxygen radicals 7 .…”