A potential role for inducible nitric oxide synthase in the cerebral response to acute hemodilution.
OBJECTIVE
Acute anemia increases the cerebral expression of hypoxic molecules including neuronal nitric oxide synthase (nNOS) and hypoxia inducible factor-1alpha (HIF-1alpha). This study assessed the effects of acute hemodilution on inducible NOS (iNOS) and systemic inflammatory cytokines.


METHODS
Anesthetized rats (n = 5-7 per group) underwent 50% hemodilution with pentastarch, whole blood exchange or no fluid exchange. Cerebral cortical nNOS and iNOS protein levels were characterized using Western blot analysis and immunostaining (1 and 18 h). Plasma cytokine levels were assessed by enzyme-linked immunosorbent assay (1, 4, and 18 h). Data were analyzed by two-way analysis of variance to determine significance (P < 0.05, mean +/- SD).


RESULTS
No differences in mean arterial blood pressure or arterial blood gases were observed between groups after hemodilution. A comparable hemoglobin target (approximately 70 g . L(-1)) was achieved in all groups following hemodilution. Cerebral cortical iNOS protein levels were increased in anemic rats, relative to controls. The nNOS protein levels increased to a greater degree (P < 0.05 for both). Immunostaining demonstrated that iNOS localized to endothelium, glial fibrillary acidic protein (GFAP) positive (astrocytes) and GFAP negative cells within the brain. Plasma cytokine levels (tumour necrosis factor alpha, interleukin (IL)-1beta and IL-6) increased transiently, to the same levels, in both control and hemodiluted rats.


CONCLUSIONS
Cerebral cortical iNOS and nNOS protein levels were both increased in anemic rats. The nNOS response was predominant. This suggests that NOS-derived NO may be an important signalling pathway which is activated in the brain during anemia. These cellular responses could maintain cerebral homeostasis, or contribute to neuronal injury, during acute hemodilutional anemia.
Department of Anesthesia, Keenan Research Centre in the Li Ka Shing Knowledge Institute, St. Michael's Hospital, University of Toronto, 30 Bond Street, Toronto, ON, M5B 1W8, Canada.
Anya T
AT
McLaren
C David
CD
Mazer
Haibo
H
Zhang
Elaine
E
Liu
Lillian
L
Mok
Gregory M T
GM
Hare
D000740:Anemia / Q000503:physiopathology*; D000818:Animals; D001784:Blood Gas Analysis; D001794:Blood Pressure; D015153:Blotting, Western; D002540:Cerebral Cortex / Q000378:metabolism*; D016207:Cytokines / Q000097:blood; D004195:Disease Models, Animal; D004797:Enzyme-Linked Immunosorbent Assay; D006438:Hemodilution; D006895:Hydroxyethyl Starch Derivatives / Q000009:adverse effects; D008297:Male; D052248:Nitric Oxide Synthase Type I / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology
D016207:Cytokines; D006895:Hydroxyethyl Starch Derivatives; D052248:Nitric Oxide Synthase Type I; D052247:Nitric Oxide Synthase Type II