Characterization of late-pregnant rat uterine contraction via the contractility ratio in vitro Significance of α1-adrenoceptors

Abstract

The aim of this study was to characterize the ability of late-pregnant (days 15-22) rat uterine tissue rings to contract in response to electric field stimulation in vitro. For this purpose, maximum rhythmic contractions were elicited by optimum choice of the period time and the pulse width, the two main parameters of electric field stimulation. In parallel, the plasma 17beta-estradiol and progesterone levels were determined. It was found that the contractility ratio, i.e. the quotient of the optimum pulse width and the period time, is a good parameter with which to express the contractility. The larger the contractility ratio, the better the ability to contract. Evaluation of the area under the curve did not furnish information relating to the contractility in this method. A very close correlation was observed between the contractility ratio and the quotient of the 17beta-estradiol and progesterone levels on different days, demonstrating that the in vitro ability characterized by the contractility ratio is in keeping with the physiological regularity. There was also a very close correlation between the contractility ratio and the quotient of the alpha1- and beta-adrenergic receptors, suggesting the main role of the numbers of alpha1-receptor in pregnant uterine contractility. It is believed that this is the first in vitro model to give a numerical measure concerning the ontogeny of uterine contractility in late pregnancy.

Matrix Metalloproteinases in Normal Pregnancy and Preeclampsia

“…37 Other studies have shown that the contractility of rat uterus and the mRNA expression of the contractile agonists oxytocin, prostaglandin 2α, and ET-1 and their receptors are induced after gestational day 20, 378 and that the last phase of pregnancy in rats shows an increase in uterine contractility and the density of α1-adrenergic receptors, 385 further highlighting the importance of measuring MMPs and EMMPRIN during the different stages of pregnancy. Likewise, our uterine stretch experiments were limited to 8 g basal tension for 18 hours, and the progressive effects of different levels of basal tension for extended time periods would be more analogous to the progressive uterine stretch imposed by the growing fetus over the course of pregnancy.…”

“…384 During pregnancy the uterus is exposed to not only mechanical stretch caused by progressive fetal growth, but also hormonal changes that could influence the myometrium structure and mechanical properties. The plasma levels of estrogen and progesterone markedly increase during pregnancy, 25,385 and may play a role in the pregnancy-related uterine relaxation and expansion. 93,386–388 A large concentration of progesterone receptors is detected in the endometrium during early pregnancy endometrium.…”

“…93 For instance, the last phase of pregnancy in rats shows a correlation between the plasma level of estrogen, the increase in uterine contractility, and the density of α1-adrenergic receptors. 385 On the other hand, uterine contraction is reduced in day-12 and day-19 of gestation in rats. 93 Also, estrogen causes rapid non-genomic relaxation of spontaneous and depolarization-induced contraction of uterine strips of non-pregnant rat.…”

EMMPRIN-mediated induction of uterine and vascular matrix metalloproteinases during pregnancy and in response to estrogen and progesterone

“…Plasma estrogen (E2) and progesterone (P4) markedly increase [14, 15], and could contribute to the changes in uterine contractility during pregnancy [12, 16]. Also, uterine tissue remodeling and endometrium shedding during menstruation could involve E2-induced changes in MMPs activity [17–19].…”

Pregnancy-induced decrease in the relaxant effect of terbutaline in the late-pregnant rat myometrium: role of G-protein activation and progesterone

“…The initial tension of the preperation was set to about 1.25 g, which was relaxed to about 0.5 g at the end of equilibration. Maximum rhythmic contractions were elicited with a digital, programmable stimulator (ST-02; Experimetria Ltd Budapest, Hungary, and GraphPad Software Inc. San Diego, CA, USA), as described earlier (Gáspár et al 2001) The tension of the myometrial rings was measured with a gauge transducer (SG-02; Experimetria UK Ltd) and recorded with an SPEL Advanced ISOSYS Data Acquisition System (Experimetria Ltd). Non-cumulative concentrationresponse curves to the b 2 -agonist terbutaline (Sigma) were constructed in each experiment.…”