Endothelin-1 potentiates the in vitro contractile response of pregnant human myometrium to oxytocin

The Link Between Human Menstruation and Placental Delivery: A Novel Evolutionary Interpretation: Menstruation and fetal placental detachment share common evolved physiological processes dependent on progesterone withdrawal

A new interpretation of human menstruation is presented, resulting from a cross-disciplinary investigation of evolution, developmental biology, and physiology. A process evolutionarily associated with childbirth expresses itself as menstruation in women for whom frequent and continual failure to conceive has become the default situation. In humans and Old World primates, contractile uterine spiral arterioles evolved as the complement of the highly invasive hemochorionic placenta and is the selected phenotype. Placental progesterone withdrawal during the last stage of birth leads to arrested blood flow through maternal spiral arterioles, allowing detachment of the deciduous placenta with minimal maternal hemorrhage. In nonpregnant females, progesterone withdrawal from a degenerating corpus luteum initiates menstruation and stops blood flow through uterine spiral arterioles. Both events share similar physiological mechanisms and sequences. This explanation may improve our understanding of a recurrent event experienced by half of the human population and for a quarter of their adult reproductive life.

Relationship between gene expression and function of uterotonic systems in the rat during gestation, uterine activation and both term and preterm labour

We have documented gestation- and labour- (preterm and term) dependent changes in expression of genes encoding contraction associated proteins in the rat uterus and correlated these changes with various parameters of uterine contractility. The data demonstrate increased expression of contractile agonist systems concurrent with decreased expression of relaxant systems after gestational day 20. Significant increases in expression of oxytocin (OT), its receptor (OTR), prostaglandin (PG) H synthase isoform 1 (PGHS-1) and PGF(2alpha) receptor (FP) occurred first, followed by increases in PGHS-2, connexin-43, endothelin-1 (ET-1) and the ET-1 receptor isoform ET(A). Expression of OTR and FP was significantly reduced during mid-gestation compared to non-pregnant animals. Expression of inducible nitric oxide synthase (iNOS) increased significantly during pregnancy then decreased concurrently with the increase in OTR and FP. Functional changes in uterine contractility accompany changes in gene expression. OT was the most potent contractile stimulant. Sensitivity of uterine strips to OT was reduced in early and mid-pregnancy then increased at uterine activation. Progesterone antagonist-induced preterm labour caused changes similar to those at normal term. Comparison of mRNA transcripts in separated endometrium and myometrium suggested that the endometrium is an important regulator of myometrial contractility, analogous to the relationship between endothelium and vascular smooth muscle. This novel combination of functional and genetic expression analyses provides new insight into the physiology of parturition.

Effects of 5-nitro-2-(3-phenylpropylamino) benzoic acid, anthracene-9-carboxylate, and zaprinast on endothelin-1-induced contractions of pregnant rat myometrium

OBJECTIVE

The effects of 5-nitro-2-(3-phenylpropylamino) benzoic acid (NPPB), anthracene-9-carboxylate (9-AC) (chloride channel blockers) and zaprinast (an inhibitor of phosphodiesterase-5) on endothelin-1 (ET-1) induced contractions of pregnant rat myometrium were investigated in vitro.

METHODS

Isolated myometrial strips were obtained from pregnant rats, and the strips were mounted in organ baths for recording of isometric tension (n=8). The effects of 10(-7) to 10(-4)M NPPB, 10(-7) to 10(-4)M 9-AC, and 10(-7) to 10(-4)M zaprinast on 10(-8)M ET-1-induced contractions of pregnant rat myometrial smooth muscle were recorded.

RESULTS

NPPB and 9-AC increased the amplitude of ET-1-induced myometrial contractions, while decreasing the frequency, in a concentration-dependent manner. The amplitude of myometrial contractions were significantly increased by NPPB and 9-AC beginning from the concentration of 10(-6)M. The frequency of myometrial contractions were significantly decreased by NPPB and 9-AC beginning from the concentration of 10(-6)M. Zaprinast inhibited the amplitude and frequency of ET-1-induced myometrial contractions in a concentration-dependent manner. Zaprinast-induced decreases in amplitude and frequency of myometrial contractions reached statistical significance beginning from the concentrations of 10(-7)M and 10(-5)M, respectively.

CONCLUSION

These data provide evidence that the ET-1-induced contractions of pregnant rat myometrial strips may be modulated by chloride channels. In addition, zaprinast effectively inhibited ET-1-induced contractions in pregnant rat myometrium.

The molecular mechanisms of term and preterm labor: recent progress and clinical implications

Current tocolytic protocols rely largely on the use of beta-mimetics to induce myometrial quiescence and delay delivery. Unfortunately, the rapid transplacental passage and poor receptor specificity of the commonly used beta-mimetics results in widespread activation of intrauterine and extrauterine beta 1 and beta 2 receptors. The use of beta-mimetics is associated with a range of well-recognized and potentially dangerous side effects for mother and fetus. The value of continued use of beta-agonists after obtaining uterine quiescence also has been the subject of recent debate. In this article we have attempted to explore the biochemical and molecular rationale for the use of alternative therapeutic modalities in the treatment and prevention of PTL. In the light of the current view that the term "preterm labor" covers a considerable diversity of causes, we propose that a range of treatment regimes should be chosen on the basis of the diagnosis and classification of the patient according to the their particular condition. Although the measurement of several biochemical parameters have been suggested to be of use in predicting PTL, we believe that a panel of diagnostic indicators (e.g., free or total CRH, IL-6, extracellular matrix proteases, fetal fibronectin) is more likely to provide useful diagnostic information on which appropriate treatment modalities can be selected (Table 1). Because of the complex and interactive nature of the mechanisms operating within the intrauterine environment to regulate myometrial activation and uterotonin production, we speculate that a combination of tocolytics, anti-inflammatory agents, uterotonic antagonists, and receptor blockers is likely to be more effective than a monotherapeutic approach, which focuses on only one facet of the process of uterine activation for pharmacologic intervention. For example, the use of antibiotics, PGHS inhibitors, and/or beta-mimetics might be an appropriate first line of treatment for infection-associated PTL in extreme prematurity. If it is successful, this treatment might be followed by longer term use of a progestagen and/or NO donor to maintain myometrial quiescence until closer to term. Alternatively, use of progesterone or oxytocin antagonists may be effective in augmenting the actions of beta-mimetics while reducing their side effects, whereas other combinations may be useful as long-term prophylactics in women with a high risk of developing PTL. Improvements continue in our diagnostic ability to correctly identify the different causes of preterm labor. We anticipate that careful selection of differing combinations of therapeutic options will result in significant reductions in the morbidity, mortality, and healthcare costs associated with preterm birth.

Endothelin receptor type A and B gene expression in human nonpregnant, term pregnant, and preeclamptic uterus

OBJECTIVE

The aim of this study was to quantify the gene expression of ETA and ETB receptors within the different uterine segments of nonpregnant, normal pregnant, and preeclamptic women.

STUDY DESIGN

Biopsy samples from the cervix, isthmus, and corpus uteri were obtained from eight nonpregnant, nine term pregnant, and seven preeclamptic women. The concentration of ETA and ETB receptor messenger ribonucleic acid were determined by a solution hybridization technique with complementary ribonucleic acid probes. Results are presented in counts per minute per microgram of total nucleic acid as mean +/- SEM.

RESULTS

The expression of messenger ribonucleic acid encoding the ETA receptor was generally higher in the upper than in the lower uterine segment in nonpregnant, normal pregnant, and preeclamptic myometrium, whereas the opposite pattern was seen with regard to ETB. During normal pregnancy the concentrations of ETA receptor messenger ribonucleic acid in the corpus and ETB receptor messenger ribonucleic acid in the isthmus were significantly elevated compared with those in nonpregnant women. This enhanced gene expression was, however, not observed in the preeclamptic group.

CONCLUSION

Our finding of segmentally differentiated endothelin receptor gene expression is compatible with a role for endothelin-1 in stimulating uterine contractions through ETA receptors during spontaneous labor and suggests a relaxing effect of the ETB receptor on the myometrium.