Sex differences in murine sternohyoid muscle tolerance of acute severe hypoxic stress.

Given that sex differences inherent to muscle might at least contribute to male risk for obstructive sleep apnoea syndrome (OSAS), our objective was to test the hypothesis that male sternohyoid muscle exhibits greater susceptibility to severe hypoxic stress compared with female muscle. Adult male and female C57Bl6/J mouse sternohyoid isometric and isotonic functional properties were examined ex vivo at 35 °C in tissue baths under control and severe hypoxic conditions. Hypoxia was detrimental to peak force (Fmax), work (Wmax) and power (Pmax), but not shortening velocity (Vmax). Two-way analysis of variance revealed a significant sex x gas interaction for Fmax (p<0.05), revealing inferior hypoxic tolerance in male sternohyoid muscle. However, increases in male shortening velocity in severe hypoxia preserved power-generating capacity which was equivalent to values determined in female muscle. Fmax decline in hypoxic female sternohyoid was considerably less than in male muscle, illustrating an inherent tolerance of force-generating capacity mechanisms to hypoxic stress in female airway dilator muscle. We speculate that this could confer a distinct advantage in vivo in terms of the defense of upper airway caliber.