Sexual Dimorphism in the Activation of Neutrophils by Shock Mesenteric Lymph

Abstract

Background:

After trauma/hemorrhagic shock (T/HS), inflammatory products exit the gut via mesenteric lymph. These products can prime neutrophils (PMN) and predispose to lung injury. Female gender and the proestrous state (PE) may confer protection against lung injury after T/HS. We therefore studied the dependence of T/HS-induced PMN priming on gender and stage of estrous.

Materials and Methods:

T/HS was induced in male (M) and proestrous female (F) rats by laparotomy plus hemorrhagic shock (30 mm Hg, 90 min) followed by reinfusion of shed blood. Six hours later rats were sacrificed and plasma was obtained. Control male rat PMN were primed 5 min in buffer or in the plasma of M-T/HS or F-T/HS rats (n = 4-6/group). PMN were then assayed using DHR for respiratory burst (RB) initiated by sequential MIP-2 and PAF stimulation (MIP/PAF). Because MIP and PAF mobilize cell calcium ([Ca²⁺]_i) in a step crucial for RB initiation, we also assayed PMN [Ca²⁺]_i responses to MIP/PAF.

Results:

M-T/HS plasma primed PMN RB (208 ± 8 [SEM] U/sec versus buffer 51 ± 12 U/sec, p < 0.01, ANOVA/Tukey's). F-T/HS plasma did not (87 ± 20 U/sec, NS). PMN basal [Ca²⁺]_i was increased by pre-incubation in both M-T/HS and F-T/HS plasma (183 ± 26 and 225 ± 20 nM, p < 0.02, p < 0.01 compared to buffer [80 ± 3 nM]). Peak PMN [Ca²⁺]_i response to MIP/PAF was 159 ± 2 nM without priming. Priming PMN in either M-T/HS or F-T/HS plasma increased peak [Ca²⁺]_i responses to MIP/PAF to 274 ± 35 (p < 0.04) and 330 ± 24 nM (p < 0.02), but the effects of M-T/HS and F-T/HS plasma on [Ca²⁺]_i mobilization were indistinguishable.

Conclusion:

Plasma from male rats subjected to T/HS primes PMN respiratory burst, but plasma from proestrous females subjected to T/HS does not. In contrast, the male and proestrous female plasma primed PMN [Ca²⁺]_i mobilization by MIP/PAF equally. The decrease in pathologic PMN activation seen after T/HS in proestrous female rats depends on soluble mediators present in plasma. The decreased PMN RB seen after T/HS in proestrous females is mediated by calcium-independent pathways.