Effects of estrogen on genioglossal muscle contractile properties and fiber-type distribution in chronic intermittent hypoxia rats.

Obstructive sleep apnea-hypopnea syndrome (OSAHS) is a highly prevalent disorder that is characterized by recurrent sleep-induced collapse of the upper airway. Genioglossus is an important pharyngeal dilator muscle that helps to maintain the patency of the upper airway. The effect of female hormones on pharyngeal dilator muscle activity may be one possible explanation for the differences observed in the prevalence of OSAHS between genders. The aim of this research was to investigate the influence of estrogen on genioglossus activity in rats exposed to chronic intermittent hypoxia (CIH). Eight-wk-old female rats were ovariectomized or sham-operated, received 5-wk of estrogen replacement therapy, and/or were exposed to CIH. The contractile properties of the genioglossus were measured. ATPase staining was performed to determine the per cent fiber-type distribution and to measure the cross-sectional area (CSA) of muscle fibers. Myosin heavy chain phenotypes were determined by gel electrophoresis. Chronic intermittent hypoxia reduced the contractile properties of the genioglossus muscle, decreased the CSA of type IIA fibers, and decreased the proportion of myosin heavy chain IIA, and ovariectomy exacerbated this effect. However, estrogen replacement can partially reverse the effect of CIH in ovariectomized rats. It is concluded that a low female hormone level and CIH may increase fatigue and alter genioglossus structure and function, and may compromise the maintenance of upper airway patency, while estrogen may help to reverse this effect.