Molecular human reproductionFeb 28, 2003

How blocking calcium channels, opening potassium channels, and nitric oxide affect human uterus contractions during pregnancy and labor

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Updated Apr 3, 2026

Abstract

Inhibitory effects of certain channel blockers on uterine contractility are greater in non-labouring myometrium compared to labouring tissue.

The L-type calcium channel blocker nifedipine and ATP-sensitive potassium channel opener pinacidil showed more significant inhibitory effects in myometrium from non-labouring women.
In the non-labour group, pinacidil's inhibitory effect was stronger at term than at preterm.
Magnesium ions and the nitric oxide donor sodium nitroprusside inhibited contractility across all groups without significant variation due to labour status or gestational age.
Decreased effectiveness of L-type calcium channel blockers and potassium channel openers during labour may indicate changes in their expression and activity.

Simplified

Relative uterine inactivity during pregnancy changes to vigorous rhythmic contractility during labour. We hypothesized that mechanisms involved in the regulation of uterine quiescence and contractility differ between term and preterm myometrium and in labour and non-labour states. Myometrial strips, prepared from biopsies taken at Caesarean section from labouring and non-labouring women preterm and at term, were mounted in organ chambers for isometric tension recording. Oxytocin (10(-9) mol/l) was added to maintain stable contractions, and effects of various inhibitors of uterine contractility were studied. The inhibitory effects of L-type Ca(2+)-channel blocker nifedipine and ATP-sensitive K(+)-channel opener pinacidil were greater in myometrium from the non-labour versus the labour group, both preterm and at term. In addition, pinacidil's effect was greater at term compared with preterm in the non-labour group. Mg(2+) and the nitric oxide donor sodium nitroprusside significantly inhibited contractility in all groups without significant differences with regard to labour or gestational age. Decreased inhibition of human uterine contractility by L-type Ca(2+)-channel blockers and K(+)(ATP)-channel openers in preterm and term labour may reflect changes in expression and activity of these channels. Effects of nitric oxide and Mg(2+) are not affected by gestational age or labour.

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How blocking calcium channels, opening potassium channels, and nitric oxide affect human uterus contractions during pregnancy and labor

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