Objective: Our objective was to investigate IL-6 and CRH secretion during the active phase of human labor and to define their potential involvement in myometrial contractility.
Study design: Twenty-two primigravid women were studied for 90 minutes during the active phase of term labor by serial plasma sampling every 3 minutes for measurement of IL-6 and CRH concentrations. Uterine contractions, measured by cardiotocograph, were evaluated in Montevideo units. Basic, quantitative, pulsatility, and time cross-correlation statistical analyses were performed.
Results: By linear regression analysis, a positive correlation was observed between IL-6 and CRH total mean area under the curve above 0 (r = 0.76184, P = .006). Mean number of pulses was 2.00 ± 0.70 and 3.33 ± 1.29 for IL-6 and CRH, respectively. There was a significant positive correlation between IL-6 and CRH over time, peaking at the 12-minute interval, with IL-6 leading CRH. Also, there was a significant positive correlation between myometrial contractility expressed in Montevideo units and IL-6 concentrations over time, starting at +51 minutes and ending at +57 minutes with myometrial contractility leading IL-6. No significant correlation was found between myometrial contractility and CRH concentrations over time.
Conclusion: IL-6 and CRH are both secreted in a pulsatile fashion during the active phase of human labor. The time-integrated concentrations of the two hormones are positively correlated, with IL-6 leading CRH secretion. It appears, thus, that proinflammatory mediators may be direct and/or indirect promoters of placental CRH release. Furthermore, the secretion of IL-6, which is a myokine, seems to be associated positively with uterine contractility. Additional studies are needed to elucidate the combined effect of inflammation, placental CRH release, and/or the receptors of the latter in parturition.