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Contraction kinetics of isolated human myometrium during menstrual cycle and pregnancy
Author(s) -
Tchirikov Mikhail,
Peiper Ulrich,
Schröder Hobe J.
Publication year - 2000
Publication title -
bjog: an international journal of obstetrics and gynaecology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.157
H-Index - 164
eISSN - 1471-0528
pISSN - 1470-0328
DOI - 10.1111/j.1471-0528.2000.tb11580.x
Subject(s) - myometrium , follicular phase , luteal phase , menstrual cycle , medicine , endocrinology , uterine contraction , pregnancy , myosin , muscle contraction , chemistry , andrology , biophysics , biology , uterus , hormone , genetics
Objective To investigate the interaction between actin and myosin in the myometrium by studying the contraction kinetics of isolated samples of human myometrium. Design Experimental and observational cross‐sectional study. Setting Eppendorf University Hospital, Hamburg. Samples Myometrium samples were taken from women in the follicular phase ( n = 6 ) or luteal phase ( n = 6 ) of the menstrual cycle and during pregnancy at term ( n = 25 ). Methods The frequency, extent and rate of force development were determined in spontaneously active myometrial preparations. From a resting force of 2 mN, sustained tonic contractions were induced by K + ‐depolarisation (124 mM), or by protein kinase C activation (19.9 μM indolactam). The steady force was reversibly interrupted by rapid length changes (100 Hz sinus vibrations lasting 1 s, 5% of muscle length). Extent (steady plateau), as well as rate of force increase after cessation of vibrations, were derived from bi‐exponential functions fitted to the time course of force recovery. Results Frequency of spontaneous contractions was higher in the follicular phase [mean (SD) 18.3 contractions/hour (1.0)] than in the luteal phase [13.4 contractions/hour (8.1)] or in pregnancy at term [8.8 contractions/hour (7.6)]. During indolactam treatment, steady force in pregnancy at term was significantly increased [8.8 mN (4.0)], compared with the follicular phase [3.7 mN (0.9)]. Force recovery was distinctly slower in pregnancy at term during indolactam treatment [time constant 99.2 s (57.9); P < 0.005 ] than during K + ‐depolarisation [time constant 29.1 s (5.9)], whereas in the follicular phase the rate of force recovery was faster with indolactam [16.8 s (7.1)] than with K + depolarisation [24.4 s (5.9); P < 0.005 ]. Conclusions The responses of human myometrium to contraction stimuli differ according to the reproductive state. Membrane depolarisation causes similar responses in all myometrial strips. In contrast, near term stimulation of protein kinase C generates a large tonic force and slow contraction kinetics, whereas early in the menstrual cycle contraction kinetics are fast.