Stretch‐induced enhancement of contractions in uterine smooth muscle of rats.

Abstract

1. We studied the effect of servo-controlled stretch of smooth muscle strips from rat uterus on tension and intracellular Ca2+ concentration ([Ca2+]i, using fura-2 as an indicator) at 300C. 2. When quiescent uterine muscle strips were stretched at a ramp time of 0 5 s by multiples of 5% of the resting muscle length (Lo) up to 40%, forty-two out of sixty muscle strips responded with a transient active contraction and a [Ca2+]i increase. The minimum excursion of stretch required for contraction was 26 3 + 7 5% of Lo (mean + S.D.). The peak response had an all-or-none property and was almost independent of the duration of stretch. 5. When a stretch of 15-35% of Lo was applied during the relaxation phase of 10 nM oxytocin-induced rhythmic contractions, the first contraction after the stretch occurred earlier than that expected from the control rhythm. However, the frequency of the subsequent rhythm returned to almost the control level even during continued application of stretch, although the half-width of rhythmic contractions was increased during stretch. 6. The present study demonstrates that stretch of uterine muscle induces a transient contraction due to Ca2+ influx, which is myogenic and dependent on the excursion and velocity of stretch. The all-or-none property of the stretch-induced contractions suggests initiation of Ca2+ spikes. Furthermore, stretch modulates the oxytocin-induced rhythmic contractions.

Effect of in Vivo Estradiol Administration to Bilaterally Ovariectomized Rats on in Vitro Myometrial Responsiveness to Prostaglandin F2α, and Oxytocin1

“…The ability of the myometrium to develop spontaneous contractions under specific in vitro conditions depends on factors such as velocity of stretch [25] and buffer temperature [26]. The data presented in Figure 1 suggest that spontaneous contractility patterns in ovariectomized rat myometrium depend upon both E 2 dose and duration.…”

Increased Expression of the Rat Myometrial Oxytocin Receptor Messenger Ribonucleic Acid during Labor Requires Both Mechanical and Hormonal Signals1

“…In unilaterally pregnant rats, the gravid uterine horns showed a relative depolarization of the resting membrane potential and an increased contractile force compared to the nongravid horns [5]. Recently, Kasai et al [6] reported that in vitro stretch of the rat uterus caused transient smooth muscle contractions and a Ca 2ϩ influx. Furthermore, clinical data suggest a much greater incidence of preterm birth and perinatal mortality in human pregnancies complicated by conditions in which intrauterine volume is increased (e.g., multifetal pregnancies or polyhydramnios) [7,8].…”

Effects of Sesamum Radiatum Aqueous Leaf Extract on Rhythmic Contractions of Uterine Smooth Muscle Bundles From Pregnant Rats

“…Indeed, according to [38], removing extracellular calcium abolished spontaneous contractions of uterine smooth muscle. Subsequent addition of oxytocin caused transient increases in contraction in a concentrationdependent manner.…”

“…Therefore, Ca 2+ influx through L-type Ca 2+ channels is important in Ca 2+ regulation in both spontaneous and agonist-stimulated rhythmic contraction of uterine smooth muscle cells [38] . These substances can increase [Ca 2+ ] i both by enhancing Ca 2+ influx through L-type Ca 2+ channels and by causing IP3-induced Ca 2+ release from the intracellular Ca 2+ stores [15] .…”