Lack of influence of dexmedetomidine on rat glomus cell response to hypoxia, and on mouse acute hypoxic ventilatory response

Background and Aims: There is a lack of basic science data on the effect of dexmedetomidine on the hypoxic chemosensory reflex with both depression and stimulation suggested. The primary aim of this study was to assess if dexmedetomidine inhibited the cellular response to hypoxia in rat carotid body glomus cells, the cells of the organs mediating acute hypoxic ventilatory response (AHVR). Additionally, we used a small sample of mice to assess if there was any large influence of subsedative doses of dexmedetomidine on AHVR. Material and Methods: In the primary study, glomus cells isolated from neonatal rats were used to study the effect of 0.1 nM (n = 9) and 1 nM (n = 13) dexmedetomidine on hypoxia-elicited intracellular calcium [Ca2+]i influx using ratiometric fluorimetry. Secondarily, whole animal unrestrained plethysmography was used to study AHVR in a total of 8 age-matched C57BL6 mice, divided on successive days into two groups of four mice randomly assigned to receive sub-sedative doses of 5, 50, or 500 mu g.kg-1 dexmedetomidine versus control in a crossover study design (total n = 12 exposures to drug with n = 12 controls). Results: There was no effect of dexmedetomidine on the hypoxia-elicited increase in [Ca2+]i in glomus cells (a mean +/- SEM increase of 95 +/- 32 nM from baseline with control hypoxia, 124 +/- 41 nM with 0.1 nM dexmedetomidine; P = 0.514). In intact mice, dexmedetomidine had no effect on baseline ventilation during air-breathing (4.01 +/- 0.3 ml.g-1.min-1 in control and 2.99 +/- 0.5 ml.g-1.min-1 with 500 mu g.kg-1 dexmedetomidine, the highest dose; P = 0.081) or on AHVR (136 +/- 19% increase from baseline in control, 152 +/- 46% with 500 mu g.kg-1 dexmedetomidine, the highest dose; P = 0.536). Conclusion: Dexmedetomidine had no effect on the cellular responses to hypoxia. We conclude that it unlikely acts via inhibition of oxygen sensing at the glomus cell. The respiratory chemoreflex effects of this drug remain an open question. In our small sample of intact mice, hypoxic chemoreflex responses and basal breathing were preserved.