Received October 22, 2007
Revised February 1, 2008
Accepted after revision February 29, 2008

¹ Universidad Andres Bello
² Universidad Catolica de Chile
³ Universidad de Santiago de Chile
⁴ Clinica Alemana-Universidad del Desarrollo

^* To whom correspondence should be addressed. E-mail: pzapata{at}udd.cl.

	Abstract

ABSTRACT 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 anesthetized cats was performed by topical application upon CB surface or IV infusion (endotoxaemia). This caused: i) disorganization of CB glomoids, increased connective tissue, rapid recruitment of polymorphonuclear (PMN) cells into vascular bed and parenchyma within four hours; ii) increased respiratory frequency and diminished ventilatory chemoreflex responses to brief hypoxia (breathing 100% N₂ for 10 s), ventilatory chemosensory drive (assessed by 100% O₂ tests) during normoxia and hypoxia; iii) tachycardia, increased haematocrit and systemic hypotension in response to LPS I.V.; iv) increased basal frequency of carotid chemosensory discharges during normoxia, but no change in maximal chemoreceptor responses to brief hypoxic exposures. LPS-induced tachypnea 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- (TNF-) was localized by immunohistochemistry in glomus and endothelial cells, RT-PCR revealed that the CB expresses the mRNAs for both type-1 and -2 TNF- receptors; 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-, but that the enhanced frequency of chemosensory discharges recorded along responses to hypoxic stimulation was transiently and dose-dependently diminished by TNF- injections. 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-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.

Key Words: Arterial chemoreceptor, Breathing, Carotid body