Septic shock involves excessive nitric oxide (NO) production and overactivation of the NO/sGC/cGMP pathway, leading to severe vasodilation and microvascular dysfunction. Methylene blue (MB), an inhibitor of this pathway, has been proposed as a catecholamine-sparing adjunct, yet optimal therapeutic dosing remains unclear. This study investigated the dose-dependent effects of MB in a rat model of polymicrobial sepsis. Fifty female Wistar rats were randomized into control, CLP-induced sepsis, or CLP+MB groups (10, 50, or 100 mg/kg, i.v.). Sepsis was induced via cecal ligation and puncture (CLP). At 12 h post-induction, we comprehensively assessed systemic hemodynamics, arterial blood gases, organ injury biomarkers (urea, ALT, AST), extensive oxidative stress panels (e.g., MDA, glutathione, catalase), systemic cytokines, and Rat Organ Failure Assessment (ROFA) scores. Early mortality was explicitly recorded. CLP successfully induced severe sepsis, evidenced by profound metabolic acidosis, hypoxemia, elevated urea, and multiorgan dysfunction. MB administration produced strictly dose-dependent outcomes. The 10 mg/kg dose consistently improved mean arterial pressure, oxygenation, and antioxidant enzyme activity while significantly reducing urea, IL-1β, lipid peroxidation, and ROFA scores. The 50 mg/kg dose offered moderate benefits, primarily partial renal protection. Conversely, the 100 mg/kg dose provided no therapeutic gain, worsened acid-base balance, elevated hepatic ALT, and sharply increased early mortality. MB exhibits a strict, dose-dependent efficacy window in septic shock. While 100 mg/kg is toxic, low-dose MB (10 mg/kg) provides an optimal efficacy-safety balance by improving hemodynamics, reducing oxidative stress, and attenuating multiple organ dysfunction. This strongly supports its translational potential • MB shows dose-dependent benefits in a rat model of polymicrobial sepsis. • Doses of 10–50 mg/kg restore hemodynamics, redox balance, and organ function. • The 10 mg/kg dose optimally reduces IL-1β, oxidative stress, and ROFA scores. • High-dose MB (100 mg/kg) lacks added benefit and induces redox-related stress.
Özcan et al. (Tue,) studied this question.