Hypertonic Saline Enhances Host Response to Bacterial Challenge by Augmenting Receptor-Independent Neutrophil Intracellular Superoxide Formation

Objective: This study sought to determine whether hypertonic saline (HTS) infusion modulates the host response to bacterial challenge. Methods: Sepsis was induced in 30 Balb-C mice by intraperitoneal injection of Escherichia coli (5 × 10⁷ organisms per animal). In 10 mice, resuscitation was performed at 0 and 24 hours with a 4 mL/kg bolus of HTS (7.5% NaCl), 10 animals received 4 mL/kg of normal saline (0.9% NaCl), and the remaining animals received 30 mL/kg of normal saline. Samples of blood, spleen, and lung were cultured at 8 and 36 hours. Polymorphonucleocytes were incubated in isotonic or hypertonic medium before culture with E. coli. Phagocytosis was assessed by flow cytometry, whereas intracellular bacterial killing was measured after inhibition of phagocytosis with cytochalasin B. Intracellular formation of free radicals was assessed by the molecular probe CM-H₂DCFDA. Mitogen-activated protein (MAP) kinase p38 and ERK-1 phosphorylation, and nuclear factor κ B (NFκB) activation were determined. Data are represented as means (SEM), and an analysis of variance test was performed to gauge statistical significance. Results: Significantly reduced bacterial culture was observed in the animals resuscitated with HTS when compared with their NS counterparts, in blood (51.8 ± 4.3 vs. 82.0 ± 3.3 and 78.4 ± 4.8, P = 0.005), lung (40.0 ± 4.1 vs. 93.2 ± 2.1 and 80.9 ± 4.7, P = 0.002), and spleen (56.4 ± 3.8 vs. 85.4 ± 4.2 and 90.1 ± 5.9, P = 0.05). Intracellular killing of bacteria increased markedly (P = 0.026) and superoxide generation was enhanced upon exposure to HTS (775.78 ± 23.6 vs. 696.57 ± 42.2, P = 0.017) despite inhibition of MAP kinase and NFκB activation. Conclusions: HTS significantly enhances intracellular killing of bacteria while attenuating receptor-mediated activation of proinflammatory cascades.