Neutrophil depletion by RB6-8C5 does not cause vascular MPO release into plasma, nor elevated plasma LPS, but neutropenic mice generate more prostacyclin in vivo. (A) Free MPO is not detected in plasma from neutropenic mice. Plasma from control and neutropenic mice (1 day after injection), or isolated leukocytes from healthy mice, were probed for MPO with rabbit polyclonal anti-MPO antibody (Calbiochem, San Diego, CA; 1:1000) and visualized using ECL (Amersham) followed by a horseradish peroxidase–conjugated antirabbit secondary antibody (1:20 000). (B) MPO immunostaining is not detected during neutropenia. Aortic sections from control and neutropenic mice (day 1) were sectioned and immunostained for MPO. Representative sections are shown for each condition. (C) Hypotensive response to neutropenia is inhibited by antibiotic but not celecoxib. Mice were administered celecoxib (400 mg/kg/day) or enrofloxacin (0.4 g/L drinking water) for 3 days prior to induction of neutropenia, with blood pressure determined using tail-cuff pletysmography at day 3 (n = 5, mean ± SEM, P < .05, Student t test). (D) Plasma endotoxin is unchanged in neutropenic mice. Plasma endotoxin was measured in control and neutropenic mice using the LAL assay. (E) Neutropenic mice generate more prostacyclin in vivo. The prostacyclin metabolite 2,3-dinor-6-keto prostaglandin F_1α was quantified in mouse urine collected over a 24-hour period from control and neutropenic (days 2-3) using a sensitive and specific GC/MS technique (n ≥ 3, mean ± SEM). *P < .05 versus control using one-tailed Student t test.