Does Endothelin Play a Role in Chemoreception During Acute Hypoxia in Normal Men?

BACKGROUND: The peripheral chemoreceptors are the dominant reflex mechanism responsible for the rise in ventilation and muscle sympathetic nerve activity (MSNA) in response to hypoxia. Animal studies have suggested that endothelin (ET) plays an important role in chemosensitivity. Moreover, several human clinical conditions in which circulating ET levels are increased are accompanied by enhanced chemoreflex sensitivity. Whether ET plays a role in normal human chemosensitivity is unknown. METHODS: We determined whether bosentan, a nonspecific ET receptor antagonist, would decrease chemoreflex sensitivity in 14 healthy subjects. We assessed the effects of bosentan on the response to isocapnic hypoxia, using a randomized, crossover, double-blinded study design. RESULTS: Bosentan increased mean (+/- SEM) plasma ET levels from 1.97 +/- 0.28 to 2.53 +/- 0.23 pg/mL (p = 0.01). Hypoxia increased mean minute ventilation from 6.7 +/- 0.3 to 8+/0.4 L/min (p < 0.01), mean MSNA from 100 to 111 +/- 5% (p < 0.01), mean heart rate from 67 +/- 3 to 86 +/- 3 beats/min (p < 0.01), and mean systolic BP from 116 +/- 3 to 122 +/- 3 mm Hg (p < 0.01). However, none of these responses differed between therapy with bosentan and therapy with placebo (p = 0.26). Bosentan did not affect the mean MSNA responses to the apneas, during normoxia (change from baseline: placebo, 259 +/- 58%; bosentan, 201 +/- 28%; p = 0.17) or during hypoxia (change from baseline: placebo, 469 +/- 139%; bosentan, 329 +/- 46%; p = 0.24). The durations of the voluntary end-expiratory apneas in normoxia and hypoxia, and the subsequent reductions in oxygen saturation, were also similar with therapy using bosentan and placebo (p = 0.42). CONCLUSION: In healthy men, ET does not play an important role in peripheral chemoreceptor activation by acute hypoxia.     

Reducing the toll of inflammatory lung disease

Toll-like receptors (TLRs) are pivotal in human response to microbial stimuli. Their activation and signaling underpin much of the observed epidemiologic data generated by the hygiene hypothesis, and their contribution to infectious exacerbations of airways disease is likely to be highly important. Our growing knowledge in this field will have a significant impact on the understanding of the pathogenesis of inflammatory diseases, and TLR-based therapies are already in early clinical trials to modify atopic disease severity.