Hyponatraemia reversibly affects human myometrial contractility. An in vitro pilot study

Autoři: Vibeke Moen aff001;  Lars Brudin aff003;  Anette Ebberyd aff004;  Maria Sennström aff005;  Gunvor Ekman-Ordeberg aff005;  Mats Rundgren aff004;  Lars Irestedt aff002
Působiště autorů: Department of Anaesthesiology and Intensive Care, Region Kalmar County, Kalmar, Sweden aff001;  Department of Physiology and Pharmacology, Division of Anaesthesiology and Intensive Care, Karolinska Institutet, Stockholm, Sweden aff002;  Department of Medicine, and Health Sciences, Linköping University, Linköping, Sweden aff003;  Department of Physiology and Pharmacology, Karolinska Institutet, Stockholm, Sweden aff004;  Department of Women and Children´s Health, Division of Obstetrics and Gynecology, Karolinska Institutet, Stockholm, Sweden aff005
Vyšlo v časopise: PLoS ONE 15(1)
Kategorie: Research Article
doi: https://doi.org/10.1371/journal.pone.0220020



In a previous study we found a significant correlation between dystocia and hyponatraemia that developed during labour. The present study examined a possible causal relationship. In vitro studies often use area under the curve (AUC) determined by frequency and force of contractions as a measure of myometrial contractility. However, a phase portrait plot of isometric contraction, obtained by plotting the first derivate of contraction against force of contraction, could indicate that bi-or multiphasic contractions might be less effective compared to the smooth contractions.

Material and methods

Myometrial biopsies were obtained from 17 women undergoing elective caesarean section at term. Each biopsy was divided into 8 strips and mounted isometrically in a force transducer. Seven biopsies were used in the first part of the study when half of the strips were immersed in the hyponatraemic study solution S containing Na+ 120 mmol/L and observed for 1 hour, followed by 1 hour in normonatraemic control solution C containing Na+ 136 mmol/L, then again in S for 1 hour, and finally 1 hour in C. The other half of the strips were studied in reverse order, C-S-C-S. The remaining ten biopsies were included in the second part of the study. Response to increasing doses of oxytocin (OT) in solutions S and C was studied. In the first part of the study we calculated AUC, and created phase portrait plots of two different contractions from the same strip, one smooth and one biphasic. In both parts of the study we registered frequency and force of contractions, and described appearance of the contractions.


First part of the study: Mean (median) contractions per hour in C: 8.7 (7.6), in S 14,3 (13). Mean (SD) difference between groups 5.6 (4.2), p = 0.018. Force of contractions in C: 11.8 (10.2) mN, in S: 10.8 (9.2) mN, p = 0.09, AUC increased in S; p = 0.018. Bi-/multiphasic contractions increased from 8% in C to 18% in S, p = 0.001. All changes were reversible in C. Second part of the study: Frequency after OT 1.65 x 10−9 M in C:3.4 (2.9), in S: 3.8 (3.2), difference between groups: p = 0.48. After OT 1.65 x 10−7 M in C: 7.8 (8.9), increase from previous OT administration: p = 0.09, in S: 8.7 (9.0), p = 0.04, difference between groups, p = 0.32. Only at the highest dose of OT dose was there an increase in force of contraction in S, p = 0.05, difference between groups, p = 0.33. Initial response to OT was more frequently bi/multiphasic in S, reaching significance at the highest dose of OT(1.65 x 10−7 M), p = 0.015. when almost all contractions were bi/multiphasic.


Hyponatraemia reversibly increased frequency of contractions and appearance of bi-or multiphasic contractions, that could reduce myometrial contractility. This could explain the correlation of hyponatraemia and instrumental delivery previously observed. Contractions in the hyponatraemic solution more frequently showed initial multiphasic contractions when OT was added in increasing doses. Longer lasting labours carry the risk both of hyponatraemia and OT administration, and their negative interaction could be significant. Further studies should address this possibility.

Klíčová slova:

Biopsy – Electrolytes – Mixtures – Observational studies – Oxytocin – Pilot studies – Solutions – Vasopressin


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2020 Číslo 1
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