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Lipopolysaccharide‐induced carotid body inflammation in cats: functional manifestations, histopathology and involvement of tumour necrosis factor‐α
Author(s) -
Fernández Ricardo,
González Sergio,
Rey Sergio,
Cortés Paula P.,
Maisey Kevin R.,
Reyes EdisonPablo,
Larraín Carolina,
Zapata Patricio
Publication year - 2008
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2008.041152
Subject(s) - carotid body , tumor necrosis factor alpha , lipopolysaccharide , endocrinology , medicine , inflammation , hypoxia (environmental) , necrosis , biology , pathology , chemistry , stimulation , organic chemistry , oxygen
In the absence of information on functional manifestations of carotid body (CB) inflammation, we studied an experimental model in which lipopolysaccharide (LPS) administration to pentobarbitone‐anaesthetized cats was performed by topical application upon the CB surface or by intravenous infusion (endotoxaemia). The latter caused: (i) disorganization of CB glomoids, increased connective tissue, and rapid recruitment of polymorphonuclear cells into the vascular bed and parenchyma within 4 h; (ii) increased respiratory frequency and diminished ventilatory chemoreflex responses to brief hypoxia (breathing 100% N 2 for 10 s) and diminished ventilatory chemosensory drive (assessed by 100% O 2 tests) during normoxia and hypoxia; (iii) tachycardia, increased haematocrit and systemic hypotension in response to LPS i.v. ; and (iv) increased basal frequency of carotid chemosensory discharges during normoxia, but no change in maximal chemoreceptor responses to brief hypoxic exposures. Lipopolysaccharide‐induced tachypnoea was prevented by prior bilateral carotid neurotomy. Apoptosis was not observed in CBs from cats subjected to endotoxaemia. Searching for pro‐inflammatory mediators, tumour necrosis factor‐α (TNF‐α) was localized by immunohistochemistry in glomus and endothelial cells; reverse transcriptase‐polymerase chain reaction revealed that the CB expresses the mRNAs for both type‐1 (TNF‐R1) and type‐2 TNF‐α receptors (TNF‐R2); Western blot confirmed a band of the size expected for TNF‐R1; and histochemistry showed the presence of TNF‐R1 in glomus cells and of TNF‐R2 in endothelial cells. Experiments in vitro showed that the frequency of carotid nerve discharges recorded from CBs perfused and superfused under normoxic conditions was not significantly modified by TNF‐α, but that the enhanced frequency of chemosensory discharges recorded along responses to hypoxic stimulation was transiently diminished in a dose‐dependent manner by TNF‐α injections. The results suggest that the CB may operate as a sensor for immune signals, that the CB exhibits histological features of acute inflammation induced by LPS, that TNF‐α may participate in LPS‐induced changes in chemosensory activity and that some pathophysiological reactions to high levels of LPS in the bloodstream may originate from changes in CB function.