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Departments of Physiology and Medicine, University of Alberta, Edmonton, Alberta T6G 2S2, Canada
During
lipopolysaccharide (LPS)-induced endotoxemia, increased intrasplenic
fluid efflux contributes to a reduction in plasma volume. We
hypothesized that splenic sympathetic nerve activity (SSNA), which
increases during endotoxemia, limits intrasplenic fluid efflux. We
reasoned that splenic denervation would exaggerate LPS-induced
intrasplenic fluid efflux and worsen the hypotension, hemoconcentration, and hypovolemia. A nonlethal dose of LPS (150 µg · kg
1 · h
1 for 18 h) was infused into conscious male rats bearing transit time flow
probes on the splenic artery and vein. Fluid efflux was estimated from
the difference in splenic arterial inflow and venous outflow (A-V). LPS
significantly increased the (A-V) flow differential (fluid efflux) in
intact rats (saline
0.01 ± 0.02 ml/min, n = 8 vs. LPS +0.21 ± 0.06 ml/min, n = 8); this was
exaggerated in splenic denervated rats (saline
0.03 ± 0.01 ml/min, n = 7 vs. LPS +0.41 ± 0.08 ml/min,
n = 8). Splenic denervation also exacerbated the
LPS-induced hypotension, hemoconcentration, and hypovolemia (peak fall
in mean arterial pressure: denervated 19 ± 3 mmHg,
n = 10 vs. intact 12 ± 1 mmHg, n = 8; peak rise in hematocrit: denervated 6.7 ± 0.3%,
n = 8 vs. intact 5.0 ± 0.3%, n = 8; decrease in plasma volume at 90-min post-LPS infusion: denervated
1.08 ± 0.15 ml/100 g body wt, n = 7 vs. intact
0.54 ± 0.08 ml/100 g body wt, n = 8). The
exaggerated LPS-induced hypovolemia associated with splenic denervation
was mirrored in the rise in plasma renin activity (90 min post-LPS:
denervated 11.5 ± 0.8 ng · ml
1 · h
1,
n = 9 vs. intact 6.6 ± 0.7 ng · ml
1 · h
1,
n = 8). These results are consistent with our proposal
that SSNA normally limits LPS-induced intrasplenic fluid efflux.
spleen; plasma volume
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