Hypertonic saline attenuation of the neutrophil cytotoxic response is reversed upon restoration of normotonicity and reestablished by repeated hypertonic challenge.

BACKGROUND: Hypertonic saline (HTS) resuscitation, in addition to enhancing hemodynamic recovery, modulates postinjury hyperinflammation in the critically injured. The polymorphonuclear neutrophil (PMN) cytotoxic response, a key element in the pathogenesis of postinjury organ dysfunction, is attenuated under hypertonic conditions. Although plasma Na(+) rises to 180 mmol/L after HTS infusion, baseline levels are reestablished within 24 hours. We hypothesized that HTS attenuation of the PMN cytotoxic response (beta2-integrin expression, elastase release, and O2- production) is reversed upon return to normotonicity, but can be reestablished by repeated HTS challenge.
METHODS: Isolated human PMNs were incubated in HTS (Na(+) = 180 mmol/L) for 5 minutes at 37 degrees C then returned to normotonicity by centrifugation and resuspension in isotonic buffer. Stimulated (PAF) beta2-integrin expression was measured by flow cytometry. Stimulated (PAF/fMLP) elastase release and O2- production were measured by cleavage of N-methoxysuccinyl-Ala-Ala-Pro-Val p-nitroanilide and reduction of cytochrome c (Cyt c). Protein tyrosine phosphorylation in PMN cell lysates was assessed by Western blot.
RESULTS: Clinically relevant levels of HTS induced tyrosine phosphorylation in resting PMNs and attenuated cytotoxic responses. Reestablishment of normotonicity returned these functions to baseline. A repeated HTS challenge after restoration of normotonicity also induced tyrosine phosphorylation and suppressed the cytotoxic response.
CONCLUSIONS: HTS attenuation of the PMN cytotoxic response is reversible but can be reestablished by repeated HTS treatment. This phenomenon may provide the unique opportunity to selectively and temporarily decrease the postinjury inflammatory response when patients are at greatest risk for PMN-mediated tissue damage.