Differential effects of estrogen and phytoestrogen on genioglossus function

Objectives: Estrogen-deficiency is a risk factor of obstructive sleep apnea-hypopnea syndrome(OSAHS) in postmenopausal women. Because of the side effects of the long-term use of estrogen replacement therapy. phytoestrogens which have been shown to act as selective estrogen receptor modulators may hold promise as viable alternatives for postmenopausal therapy. This investigation was designed to compare the effects of estrogen and phytoestrogen genistein on genioglossus(GG) function and protein expression of estrogen receptors (ERs) in ovariectomized rats. Methods: Forty female Sprague-Dawley rats were randomly divided into 4 groups: control group (SHAM), ovariectomized group (OVX), ovariectomized rats receiving estrogen group (OVX+E2) and genistein group (OVX+G). The isometric twitch tension and tetanic tension of the GG muscle were measured in response to electrical field stimulation.The expression of ERs on the protein levels was measured by western blot. Results: No significantly changes were observed in the isometric twitch and titanic tension in the four groups. Ovariectomy decreased muscle fatigue resistance and expression of different ERs. Genistein treatment partly increased muscle fatigue resistance. And estrogen treatment could completely reverse the muscle fatigability. The expression of ERs on the protein levels increased in treatment groups, but the increase of estrogen receptor beta (ERB) expression was much higher than that of estrogen receptor alpha (ERA) in OVX+G group, while in OVX+E2 group, the increase of ERA expression was much higher than that of ERB(Fig.1). Conclusions: Ovariectomy decreased the GG fatigue-resistance, while genistein treatment could partly improve the fatigue resistance of GG muscle significantly, and estrogen treatment could completely reverse the muscle fatigability. Genistein treatment preferentially increase the expression of ERB, while estrogen mainly increase ERA expression.