Effects of estrogen on genioglossus contractile properties in CIH rat

Objectives: To investigate the effects of estrogen on genioglossus (GG) contractile properties in rats with chronic intermittent hypoxia. Methods: Forty healthy male SD rats were randomly divided into five equal groups: the normal control group (NC) , the chronic intermittent hypoxia group(CIH), and three estrogen groups(L-E, M-E, H-E).The latter four groups were exposed to alternating periods of hypoxia and normoxia twice per minute for 8h/d for 5 weeks. NC and CIH group were injected with sterile olive oil 0.2ml per time, and three estrogen groups received intramuscular injection of estradiol benzoate at doses of 0.1mg/kg, 0.2mg/kg, and 0.3mg/kg, twice a week, respectively. After five weeks, in vivo isometric contractile properties were determined using surgically prepared GG muscles with platinum electrodes for stimulation of the medial branch of the hypoglossus nerve. Ultrastructural changes of myofibril and mitochondria in GG of different groups were observed under transmission electron microscope. Results: (1) No change was observed in the isometric twitch tension (Pt) and tetanic tension (P0) (P >0.05). (2) In fatigue test, compared with NC group, there was a significant (P <0.01) decrease in GG fatigue resistance in CIH group. While a significant increase in fatigue resistance was observed with estrogen at a concentration of 0.2mg/ kg and 0.3mg/ kg when compared with CIH group (P<0.05, P<0.01). (3) Degenerative morphological findings were observed from CIH group, and these changes were partly recovered in M-E group and H-E group. Conclusions: Chronic intermittent hypoxia may destroy GG ultrastructures and decrease its endurance properties. Estrogen may protect GG ultrastructures and improve muscle endurance under hypoxia conditions at some doses, which may prove useful as a potential treatment for patient with obstructive sleep apnea.