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 critic ally injured. The polymorphonuclear neutrophil (PMN) cytotoxic response, a key element in the pathogenesis of postinjury organ dysfunction, is often a ttenuated under hypertonic conditions. Although plasma Na+ rises to 180 mmo l/L after HTS infusion, baseline levels. are reestablished within 24 hours. We hypothesized that HTS attenuation of the PMN cytotoxic response (beta ( 2)-integrin expression, elastase release, and O-2- production) is reversed upon return to normotonicity, but can be reestablished by repeated HTS chal lenge. Methods. Isolated human PMNs were incubated in HTS (Na+ = 180 mmol/L) for 5 minutes at 37 degreesC then returned to normotonicity by centrifugation an d resuspension in isotonic buffer. Stimulated (PAF) beta2-integrin expressi on was measured by flow cytometry. Stimulated (PAF/MLP) elastase release an d O-2-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 nor motonicity returned these functions to baseline. A repeated HTS challenge a fter restoration of normotonicity also induced tyrosine phosphorylation and suppressed the cytotoxic response. Conclusions. HTS attenuation of the PMN cytotoxic response is reversible bu t can be reestablished bu repeated HTS treatment. This Phenomenon may provi de the unique opportunity to selectively and temporarily decrease the posti njury inflammatory response when patients are at greatest risk for PMN-medi ated tissue damage.