OBJECTIVETo investigate the effects of ovariectomy on genioglossus (GG) electromyography and myofibre phenotype in female rats and to explore the proposal mechanisms underling ovarian hormone protecting to the patency of upper airway (UA).

METHODS30 female Sprague-Dawley rats were randomly assigned to three groups: normal group (NORMAL), sham group (SHAM) and ovariectomized group (OVX). Six weeks later, electromyography activity of the genioglossus (EMGgg) was obtained from inserted bipolar electrodes. The integrated EMG (iEMG) was analyed. Genioglossus was stained with ATPase staining. The fibre phenotype composition and cross sectional area (CSA) of type II A and II B/ II X fibres were measured.

RESULTSEMGgg had no significant variety between the normal and sham group (P >0.05). Compared to normal group, iEMG was significantly decreased in OVX group (P < 0.05). GG myofibres were composed of II phenotye, including II A (40.27 +/- 1.01)% and II B/ II X (59.73 +/- 1.01)%, fibres composition and CSA of types II A and II B/II X had no significant variety between the normal and sham group. Compared to normal group, fibres composition had no significant variety in OVX group (P > 0.05), but the CSA of type II A was significantly decreased (P < 0.05).

CONCLUSIONThe decreased EMGgg of ovariectomized rat maybe relates to the decrease of CSA in type II A fibre. Ovarian hormone may protect the patency of upper airway through affecting muscle function of UA dilator.