Effect of cigarette smoking on mRNA and protein levels of oxytocin receptor and on contractile sensitivity of uterine myometrium to oxytocin in pregnant women

May 6, 2014European journal of obstetrics, gynecology, and reproductive biology

How Smoking Affects Oxytocin Receptor Levels and Uterine Muscle Response to Oxytocin in Pregnant Women

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Abstract

Oxytocin sensitivity in the myometrium is significantly increased in smokers (n=6) compared to non-smokers (n=11).

The number of cigarettes smoked per day significantly correlates with the concentration of exhaled carbon monoxide.
Oxytocin sensitivity in uterine tissues is greater in pregnant smokers than in non-smokers.
No significant differences in oxytocin receptor mRNA expression levels were found between smokers and non-smokers.
Oxytocin receptor protein levels are significantly higher in the myometrium of smokers compared to non-smokers.
Both the number of cigarettes smoked daily and exhaled carbon monoxide concentrations correlate with increased oxytocin sensitivity.

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OBJECTIVES: Although smoking is the most important modifiable risk factor associated with preterm delivery, the underlying mechanism by which smoking stimulates premature uterine contractions is still poorly understood. In the present study, we investigated whether cigarette smoking affects the contractile sensitivity of uterine myometrium to oxytocin in pregnant women.

STUDY DESIGN: Cigarette smoking habits of pregnant women were evaluated by direct interviews and by measuring exhaled carbon monoxide (CO). We isolated myometrial strips from pregnant smokers and non-smokers and evaluated uterine contractile sensitivity to oxytocin. Gene expression levels of oxytocin receptors (OTR) were compared between myometrial strips obtained from smokers and non-smokers by real-time PCR. OTR protein levels in the myometrium were evaluated by Western blotting.

RESULTS: The reported number of cigarettes smoked per day by the interviewee significantly correlated with the concentration of exhaled CO. Oxytocin sensitivity increased significantly in smokers (n=6) compared with non-smokers (n=11). Real-time PCR analysis did not reveal any significant difference in OTR mRNA expression between smokers and non-smokers. Western blotting revealed that OTR level was significantly increased in smokers compared with non-smokers. Both number of cigarettes smoked per day and the concentration of exhaled CO correlated with oxytocin sensitivity.

CONCLUSION: Our findings suggest that smoking increases oxytocin sensitivity of pregnant myometrium by increasing OTR levels even though OTR mRNA expression remains unaltered, thereby increasing the risk of preterm delivery in women who smoke during pregnancy. The sensitivity is dependent on number of cigarettes smoked per day.

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Effect of cigarette smoking on mRNA and protein levels of oxytocin receptor and on contractile sensitivity of uterine myometrium to oxytocin in pregnant women

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