Up-regulation of LPS-induced iNOS activity in dibutyryl cyclic AMP-differentiated rat astrocytes.
OBJECTIVE
To study the effect of dBcAMP on bacterial endotoxin LPS-induced NOS activity.


METHODS
Microscopic changes were observed. Nitrite levels were measured by fluorometric assay. NOS activity was measured by citrulline assay.


RESULTS
Within 3-4 h after the addition of dBcAMP 1 mmol.L-1 to culture medium, a morphological transformation reminiscent of in vivo differentiation occurred. Coincubation with LPS and dBcAMP 1 mmol.L-1 resulted in a marked increase in the nitrite production as compared with LPS alone. This increase was concentration- and time-dependent with a maximal effect after 24 h treatment. Nitrite production stimulated by LPS is parallel to the degree of cell differentiation. After a 24-h costimulation with LPS and dBcAMP, L-citrulline formation assay revealed a 3-fold increase in NOS activity over LPS treatment alone. Simultaneous incubation with L-NAME, completely inhibited the stimulation effect of LPS/dBcAMP on nitrite production. Cycloheximide and dactinomycin also suppressed enhancement of NOS activity stimulated by LPS/dBcAMP, both in nitrite production and citrulline assay, indicating that the enhancement of NOS activity was due to the expression of inducible NOS (iNOS) gene and protein.


CONCLUSIONS
Inflammatory signals can trigger astrocytes to express substantially different levels of iNOS depending on their degree of differentiation.
Song
W
W
Department of Pharmacology, Shanghai Institute of Materia Medica, Chinese Academy of Sciences, China.
Zhu
X Z
XZ
D000818:Animals; D000831:Animals, Newborn; D001253:Astrocytes / Q000166:cytology / Q000187:drug effects* / Q000201:enzymology; D003994:Bucladesine / Q000494:pharmacology*; D002454:Cell Differentiation; D002478:Cells, Cultured; D008070:Lipopolysaccharides / Q000494:pharmacology; D019001:Nitric Oxide Synthase / Q000378:metabolism*; D052247:Nitric Oxide Synthase Type II; D051381:Rats; D017207:Rats, Sprague-Dawley; D015854:Up-Regulation
D008070:Lipopolysaccharides; D003994:Bucladesine; D019001:Nitric Oxide Synthase; D052247:Nitric Oxide Synthase Type II; C496318:Nos2 protein, rat