Regulation of platelet-activating factor receptor gene expression in vivo by endotoxin, platelet-activating factor and endogenous tumour necrosis factor.
A competitive PCR assay was developed to quantify platelet-activating factor (PAF) receptor (PAF-R) transcripts in rat tissues using a synthetic RNA as a competitor. We found PAF-R mRNA constitutively expressed in the eight organs tested, with the ileum containing the highest concentration [(3.49+/-0.15) x 10(7) molecules/microg of RNA]. Significant but lower levels were also detected in the jejunum, spleen, lungs, kidneys, heart, stomach and liver. Furthermore we defined the regulatory role of inflammatory mediators in ileal PAF-R gene expression using a rat model of intestinal injury induced by PAF or lipopolysaccharide (LPS). Injection of LPS or low-dose PAF resulted in a marked increase in ileal PAF-R mRNA within 30 min. The up-regulation on PAF-R elicited by PAF was biphasic, peaking first at 90 min, then again at 6 h. In contrast, LPS elicited a weak monophasic response. The second phase of PAF-R mRNA increase after PAF administration was completely abolished by WEB 2170, a PAF antagonist, and partially inhibited by antitumour necrosis factor (TNF) antibody. These observations indicate the involvement of endogenous PAF and TNF in this event. In conclusion, we found: (a) preferential PAF-R expression in the ileum, suggesting a role for PAF in intestinal inflammation; (b) induction of PAF-R expression in vivo by its own agonist; (c) a complex regulation of PAR-R gene expression in vivo involving a network of various pro-inflammatory mediators.
Wang
H
H
Department of Pathology, Northwestern University, Chicago, IL 60614, U.S.A.
Tan
X
X
Chang
H
H
Gonzalez-Crussi
F
F
Remick
D G
DG
Hsueh
W
W
D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D006400:Hematocrit; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D007213:Indomethacin / Q000494:pharmacology; D008070:Lipopolysaccharides / Q000494:pharmacology*; D008297:Male; D016297:Mutagenesis, Site-Directed; D010972:Platelet Activating Factor / Q000494:pharmacology*; D010980:Platelet Membrane Glycoproteins / Q000096:biosynthesis* / Q000235:genetics; D016133:Polymerase Chain Reaction; D018075:RNA, Complementary; D012333:RNA, Messenger / Q000032:analysis; D012194:RNA-Directed DNA Polymerase; D051381:Rats; D017207:Rats, Sprague-Dawley; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D014018:Tissue Distribution; D014409:Tumor Necrosis Factor-alpha / Q000494:pharmacology*; D015854:Up-Regulation
D008070:Lipopolysaccharides; D010972:Platelet Activating Factor; D010980:Platelet Membrane Glycoproteins; D018075:RNA, Complementary; D012333:RNA, Messenger; D011956:Receptors, Cell Surface; D043562:Receptors, G-Protein-Coupled; D014409:Tumor Necrosis Factor-alpha; C039351:platelet activating factor receptor; D012194:RNA-Directed DNA Polymerase; D007213:Indomethacin