Abolition of contractions in the myometrium by acidification in vitro.

Uterine dystocia, often of unknown cause, remains one of the commonest causes of emergency caesarean section. We have tested the hypothesis that small acidic changes in pH, that can occur during labour contractions, can decrease contractions and contribute to dystocia. We simultaneously recorded intracellular pH (pHi) and force in human myometrium: acidification abolished contractions. Such effects of pHi on uterine contractile activity may be of clinical significance. Blood flow reduces during each uterine contraction; the resulting fall in pHi could lead to inefficient uterine action in some labours and failure to progress (ie, dystocia).