Involvement of calcitonin gene–related peptide in the modulation of human myometrial contractility during pregnancy

Abstract

IntroductionUterine quiescence is a requirement for the successful completion of term gestation. Failure to maintain uterine relaxation often results in preterm deliveryone of the leading causes of infant mortality and morbidity. Studies have shown that the quiescent state of the myometrium is maintained not only by absence or low levels of stimulatory factors, such as oxytocin receptors (1), gap junction channels (2), and α-adrenergic receptors (3), but also by an enhancement of inhibitory factors, including nitric oxide (4). However, little research has been done to define the mechanisms that maintain myometrial relaxation during pregnancy, compared with research on those mechanisms that promote the onset of labor.Calcitonin gene-related peptide (CGRP) is a 37-residue neuropeptide that results from tissue-specific alternative splicing of the primary RNA transcript of the calcitonin/CGRP gene (5). The vasodilator effects of CGRP have been demonstrated in the human fetalplacental circulation (6). With immunocytochemical techniques, CGRP-immunoreactive nerve fibers were found in rat and human uterus (7,8); CGRP relaxes contractile activity of the uterus in rats and humans (7,8). Therefore, CGRP is proposed to be a modulator of myometrial contractility during gestation. This study investigated whether uterine relaxation responses to CGRP are differentially regulated in humans during pregnancy and labor, and if the actions of CGRP are mediated by changes in CGRP receptors (CGRP-Rs). MethodsHuman subjects. The medical procedures and the process of consent for this study were approved by the Institutional Review Board of the University of Texas Medical Branch (UTMB). All human subjects, who were patients admitted to UTMB, were either women undergoing cesarean sections or nonpregnant women having hysterectomies. All provided written informed consent. Information on each subject regarding dates of pregnancy, number of pregnancies, age, prior drug treatment, and uterine contractions was collected and stored in a computerized database for later review. Specimens from each subject were taken from the lower uterine segment at the site of incision through the uterine wall. A specimen of approximately 2.0 × 0.6 × 0.6 cm was collected and divided into smaller portions (1.0 × 0.2 × 0.2 cm). Once each tissue sample was collected, it was assigned a number to blind the sample and to ensure confidentiality. Received for publication January 20, 1999, and accepted in revised form July 29, 1999.Calcitonin gene-related peptide (CGRP) is a potent vasodilator and relaxes smooth muscle of a variety of tissues, but the effects of CGRP on human myometrial contractions and the changes in CGRP receptors (CGRP-Rs) in human myometrium have not been described. We report that CGRP induced dose-dependent relaxation in spontaneously contracting myometrium from pregnant women. This relaxation effect is diminished in myometrium obtained from patients during labor and in the nonpregnant state. CGRP-induced relaxations are inhibited by a CGRP-R antago...

Identification of human myometrial target genes of the c-Jun NH2-terminal kinase (JNK) pathway: the role of activating transcription factor 2 (ATF2) and a novel spliced isoform ATF2-small

“…myometrial calcium homeostasis (Dalrymple et al 2002), and was up-regulated by both ATF2 isoforms. The other, CALCRL is related to the CGRP, which induces dose-dependent relaxation in spontaneously contracting myometrium from pregnant women, an effect that is diminished in myometrium obtained from patients during labour and in the non-pregnant states (Dong et al 1999). This gene was down-regulated by both ATF2 isoforms.…”

Uterine Quiescence: The Role of Cyclic AMP

“…The presence of CGRP receptors in human myometrium was confirmed utilising both mRNA analysis and Western blotting with a monoclonal antibody (Dong et al 1999). In addition, Dong et al (1999) demonstrated a significantly increased expression of CGRP receptors during pregnancy which decreased during term labour, implying a role for CGRP in the maintenance of myo- Immunodetection of adenylyl cyclase isoforms in isolated myometrial cells maintained in culture. Cells were enzymatically isolated from biopsies of non-pregnant myometrium, cultured on glass coverslips, fixed with acetone and ACs detected using specific polyclonal antibodies.…”

“…Moreover, b-adrenoceptor agonists which elevate cAMP are commonly used as tocolytics in clinical practice. In addition, neuropeptides such as calcitonin gene-related peptide (CGRP), adrenomedullin and amylin, whose receptors are positively coupled to AC, have been postulated to contribute to the maintenance of uterine quiescence during human pregnancy (Casey et al 1997;Dong et al 1999). Modifications in receptor density or alterations in GPCR coupling may assist in the maintenance of myometrial relaxation during gestation, or assist in the transition to the contractile state at term.…”

The Switch in Alternative Splicing of Cyclic AMP-response Element Modulator Protein CREMτ2α (Activator) to CREMα (Repressor) in Human Myometrial Cells Is Mediated by SRp40

“…Various components of the cAMP signaling pathway are often up-or down-regulated to potentiate cAMP levels, notably hormonal ligands that bind to the G-proteincoupled receptors (16), the receptors themselves (17), phosphodiesterase (18), and the stimulatory protein G␣ s (19 -21). Increased expression of G␣ s is known to increase constitutive as well as stimulated cAMP accumulation and enhance distal events such as transcription factor phosphorylation and cAMP-responsive gene expression (22).…”