ERK1/2-mediated phosphorylation of myometrial caldesmon during pregnancy and labor

We used a timed-pregnant rat model to track changes in myometrial contractility during pregnancy and labor and to correlate these changes with upstream signaling events. Myometrium was harvested from CO(2)-euthanized rats. Although contraction amplitudes increased at 16 and 20 days of pregnancy, contraction incidence and area under the force curve were inhibited, consistent with the myometrial quiescence of pregnancy. The Ca(2+) sensitivity of contraction was decreased at 20 days of pregnancy and this was partially reversed in labor. The protein content of h-caldesmon (h-CaD) was increased in pregnancy. A 40-fold increase in the signal from a phospho-CaD antibody specific for phosphorylation at an ERK1/2 site occurred during labor. ERK1/2 activation increased significantly at the onset of labor. Myosin light chain phosphorylation (LC20-P) increased significantly in labor compared with the nonpregnant state. Thus we conclude that the increase in CaD protein content during pregnancy may contribute to a suppression of the contractility of pregnant myometrium. Conversely, CaD phosphorylation, through an ERK1/2-mediated signaling pathway, as well as an increase in basal LC20-P, is suggested to contribute to the reversal of inhibition and promote contraction of the uterus during labor.

[Histamine receptors in the female reproductive system. Part II. The role of histamine in the placenta, histamine receptors and the uterus contractility]

The presence of the mast cells was confirmed not only in the uterus but also in the placental tissue. Mediators released from the placental mast cells may play a role in regulation of placental blood flow and normal blood pressure. Processes such uptake and clearance of vasoactive mediators may be upset in those women who developed pre-eclampsia. Histamine released from the placental mast cells may be involved in the mechanisms controlling myometrium contractility during the labour at term and preterm delivery. There is a correlation between the level of placental histamine and presence (or not) uterus contractility. Histamine produce a contractile response in isolated myometrial strips, in the majority of mammals, via H1 histamine receptors activation, but in some species e.g. rat, predominant response of uterus is relaxation (via H2 histamine receptors activation). Predominant response of the human uterus to histamine is contraction. Relaxation of human myometrial strips may be evoked after earlier usage of H1 receptors antagonists, although some H2 receptors agonists (e.g. dimaprit) induce the relaxation of human uterus without H1 receptors antagonists. Myometrium contractile activity is under control of sexual hormones. Neither the presence of H3 histamine receptors on the human myometrial smooth cells nor its role in the female reproductive system regulation was proved. Lack of the functional H3 receptors either on the smooth muscle cells or neuronal components of the animals' myometrium was shown in some studies.

Effect of inhibiting the sarcoplasmic reticulum on spontaneous and oxytocin-induced contractions of human myometrium

OBJECTIVE

1. To assess the contribution of the sarcoplasmic reticulum calcium store in the generation of uterine smooth muscle contractions; 2. to evaluate the contribution of calcium induced calcium release or ryanodine gated calcium channels to myometrial force production.

DESIGN

Laboratory scientific study.

METHODS

Myometrial strips were obtained from women undergoing elective prelabour caesarean section at term. These were loaded with the calcium sensitive indicator Indo-1 allowing simultaneous assessment of intracellular calcium concentrations and force production. The effect of exposing the strips to ryanodine (which abolishes calcium induced calcium release), caffeine (which activates calcium induced calcium release) and cyclopiazonic acid (which abolishes the sarcoplasmic reticulum calcium store) was examined.

RESULTS

Exposure to ryanodine had no appreciable effect on either the amplitude or the duration of the myometrial calcium and force transients but did increase the frequency of contractions (139+/-5%). Caffeine did not potentiate force. Cyclopiazonic acid increased frequency, duration and amplitude of both calcium and force transients. The ability of oxytocin to provoke calcium and force transients in the absence of extracellular calcium was abolished by cyclopiazonic acid but not by ryanodine.

CONCLUSIONS

These results demonstrate that calcium induced calcium release does not play a significant role in human myometrium and that no functioning role for the ryanodine receptors in human myometrial tissue could be shown. These data suggest that the sarcoplasmic reticulum may act to limit contractions and act as a calcium sink, rather than to amplify contractions.

Urinary leukotriene (LT) E(4) in adolescents with dysmenorrhea: a pilot study

In the present study we measured levels of urinary leukotriene (LT) E(4) as an index of LT production during the menstrual cycle in adolescents. Mean urinary LTE(4) levels in girls with dysmenorrhea was approximately threefold higher than normal laboratory values on Day 1 of the menstrual period and approximately twofold higher than normal laboratory values on Day 5 of the menstrual period. Compared with urinary LTE(4) levels in girls with eumenorrhea, urinary LTE(4) levels in girls with dysmenorrhea were higher on Day 1 [361 +/- 123 pg/mg creatinine vs. 122 +/- 37 pg/mg creatinine, p =.1; not significant (NS)] and on Day 5 (202 +/- 26 pg/mg creatinine vs. 117 +/- 26 pg/mg creatinine, p <.05) of the menstrual period, as well as on Day 10 (159 +/- 33 pg/mg creatinine vs. 88 +/- 21 pg/mg creatinine, p =.1; NS) of the menstrual cycle. Increased urinary excretion of leukotrienes, inflammatory mediators known to cause potent vasoconstriction and uterine contractions, in girls with dysmenorrhea in this pilot study, suggests that these mediators may be involved in generating dysmenorrhea symptoms in adolescents.

Pregnancy and exogenous steroid treatments modulate the expression of relaxant EP(2) and contractile FP receptors in the rat uterus

Prostaglandins (PGs) interact with specific receptors on plasma membranes to regulate myometrial activity in many species. The present study examined whether the expression of relaxant prostaglandin E receptor subtype two (EP(2)) and contractile prostaglandin F receptor (FP) mRNA in the rat uterus is changed during various states of pregnancy and regulated by steroid hormones. Expression of mRNA for EP(2) and FP receptors in the full-thickness uteri was analyzed by reverse transcription-polymerase chain reaction using specific primers. Abundance of receptor mRNA was expressed relative to beta-actin mRNA. Results showed that 1) mRNA for EP(2) receptors in the rat uterus was substantially increased during pregnancy (320%) compared with the nonpregnant state (100%, P < 0.01), and declined during labor at term (36% vs. 100% in control, P < 0.01); 2) mRNA expression for FP receptors in rat uterus was increased during pregnancy (333% vs. 100% in nonpregnant rats, P < 0. 01) and reached maximal levels during labor (515% vs. 100% in control, P < 0.01); 3) upon RU-486 treatment on Day 19 of pregnancy, uterine EP(2) receptor mRNA levels were decreased (18% vs. 100% in control, P < 0.01), and FP mRNA levels were increased (357% vs. 100% in control, P < 0.01); 4) with ICI 164384 (an antiestrogen) treatment on Day 19 of gestation, uterine FP receptor mRNA levels were decreased without effects on EP(2) receptors; 5) in ovariectomized (ovx) rats, progesterone increased EP(2) (163% vs. 100% in control, P < 0.01) and had no effects on FP receptor mRNA expression in the rat uterus; 6) estradiol increased FP receptor mRNA levels (358% vs. 100% in control, P < 0.01) and had no effects on EP(2) mRNA in the ovx rat uterus. Therefore, we conclude that steroid hormones modulate the mRNA for relaxant EP(2) and contractile FP receptors for PGs in the uterus and thus regulate uterine activity during pregnancy and labor.

New peptides, hormones and parturition

This brief review emphasizes the importance of three novel discovered factors produced by fetal membranes, placenta and/or by the fetus itself in regulating uterine contractility. We have shown that, as reported for other hormones and substances, nitric oxide and endothelin may influence myometrial activity in an autocrine/paracrine manner interacting with other well-known agents such as prostaglandins, oxytocin and hormones. We also demonstrated that different isoforms of nitric oxide synthase (NOS) may play different roles throughout gestation and during labor. We have suggested that another peptide produced by trophoblast cells, adrenomedullin, may affect, directly or indirectly, myometrial contractility during pregnancy, although much remains to be learned about the mechanisms controlling adrenomedullin expression by the feto-placental tissues cells during pregnancy. Continued research is necessary to better define the complex interactions that result in parturition, both at term and preterm, and to allow a more rational approach to management of the premature labor, exploring new possible pharmacological solutions.

Hemeoxygenase-1 inhibits human myometrial contractility via carbon monoxide and is upregulated by progesterone during pregnancy

Nitric oxide was proposed as an endogenous inhibitor of myometrial contractility during pregnancy. Carbon monoxide (CO) like nitric oxide increases cGMP and is generated during the degradation of heme to biliverdin IX by hemeoxygenases (HO). Here we report that the expression of both HO-1 (inducible) and HO-2 (constitutive) were > 15-fold higher in pregnant myometrium compared to nonpregnant myometrium (n = 4, P < 0.001, P < 0.005, respectively). Moreover, the activation of the HO-CO pathway by the HO inducer, hemin (10 microM), completely inhibited spontaneous contractility (n = 3). Oxytocin-stimulated contractions (n = 5) were also significantly reduced (P < 0.05) in myometrial strips mounted for isometric recording under 2 g tension in Krebs solution. Reverse transcription-PCR analysis revealed that mRNA encoding HO-1 and HO-2 was undetected in explant cultures of nonlaboring pregnant myometrium under basal conditions, however, exposure to progesterone, but not estradiol-17beta, induced the expression of HO-1 and HO-2 mRNAs. Progesterone also significantly induced HO-1 protein synthesis (n = 4, P < 0.001) while estradiol-17beta had no effect (n = 4). In term (37-42-wk gestation) nonlaboring myometrial explants, CO production was stimulated by progesterone (10(-6) M) (n = 2) and hemin (10 microM) (n = 3) after 2 h of incubation and the effect of hemin was inhibited by 1 h of preincubation with the HO inhibitor tin protoporphyrin IX (20 microM). This study clearly demonstrates the expression of HO in the human myometrium and shows that its induction produces CO that limits uterine contractility in pregnant myometrium indicating a role for the HO-CO-cGMP pathway in the maintenance of the quiescent state of the uterus during pregnancy.

The mechanism of myometrial contractions induced by endothelin-1 in rat

Experiments were performed to characterize endothelin-1-induced contractions and the role of endothelin (ET) receptor subtypes in rat myometrium. The binding sites of [(125)I]-ET-1 were saturable with high affinity. Scatchard plot analysis revealed that ET-1 binding sites in the myometrium constituted a single population. The dissociation equilibrium constant (Kd) and the maximum binding sites (Bmax) were determined to be 48.9+/-3.0 pM and 1364.0+/-210.3 fmol/mg protein respectively. Specific [(125)I]-ET-1 binding was inhibited completely by unlabelled ET-1 and Ro 46-2005 (mixed-type ET receptor antagonist), but not fully (90.7+/-1.4%) by BQ 123 (a selective ETA receptor antagonist), and not at all by RES 701-1 (a selective ETB receptor antagonist). ET-1 induced myometrial contractions were composed of two types, an increase in resting tone and rhythmic contractions. These contractions were inhibited by BQ 123 and Ro 46-2005, but not by RES 701-1. ET-1-induced contractions were greatly reduced in Ca2+-free Krebs' solution. Nifedipine abolished the rhythmic contractions without affecting the increase in resting tone. These results suggest that ETA receptors are predominantly localized in rat myometrium and that excitation of ETA receptors evokes two types of contractions by increasing the cytoplasmic Ca2+ concentration.

Myometrial steroid concentration and oxytocin receptor density in parturient women at term

The aim of this study was to measure oxytocin receptor concentration in myometrial tissue from term pregnant women with normal and dysfunctional labor and to relate this concentration to the progress of labor and to the levels of estradiol and progesterone in the same myometrium. Myometrial biopsies were obtained from 50 term pregnant women undergoing cesarean section. The patients were categorized as follows: not in labor, normal labor, successful oxytocin-augmented labor, and oxytocin-resistant labor. Specific binding of [3H]oxytocin to high-affinity sites in membrane preparations from myometrial tissues was determined. Estradiol and progesterone were assayed using tritiated steroids with a sensitive radioimmunoassay technique. Oxytocin receptor density was significantly lower in oxytocin-resistant labor compared to successful oxytocin-augmentated labor (P < 0.04) and to spontaneously active normal labor (P < 0.02). Oxytocin receptor concentration was also significantly lower in non-labor patients compared to normal spontaneous labor (P < 0.01), and successful oxytocin-augmented labor (P < 0.02). There was a positive relationship between the progress of cervical dilatation (cm/h) and oxytocin receptor density in the myometrium (r = 0.408, P < 0.025). The concentration of progesterone and estradiol in the pregnant myometrium did not differ in patients with different types of labor or with the state of uterine contractile activity. Our results suggest that individual myometrial sensitivity is an important determinant of the response to administered oxytocin in humans. Furthermore, myometrial oxytocin receptor expression in vivo seems not be related to ovarian steroid concentration in the myometrium. The low oxytocin receptor density in oxytocin-resistant dystocia needs further investigation.

Effects of the volatile oil of Nigella sativa seeds on the uterine smooth muscle of rat and guinea pig

The effects of the volatile oil of Nigella sativa seeds on the uterine smooth muscle of rats and guinea pigs was tested in vitro using isolated uterine horns. The volatile oil of Nigella sativa seeds inhibited the spontaneous movements of rat and guinea pig uterine smooth muscle and also the contractions induced by oxytocin stimulation. These effects were concentration-dependent and reversible by tissue washing. These data suggest that this volatile oil may have some anti-oxytocic potential.

External calcium dependence of the uterine contraction induced by prostaglandins E2 and F2 alpha and its antagonism with natural progestins

Prostaglandins (PGs) E2 and F2 alpha are strong inducers of uterine contraction by promoting a Ca2+ increase into the cell through specific receptors coupled with the calcium channels. On the contrary, progesterone and 5 beta-reduced progestins promote smooth muscle relaxation by blocking the ion calcium influx. Thus, this study was designed to emphasize the importance of external calcium in the PGs-induced rat uterus contraction. Likewise, also studied was the antagonism and the interaction between PGs and progestins (progesterone and its 5 alpha and 5 beta-reduced derivatives) in the myometrium. Results showed that uterine contraction induced by PGs depends on external calcium, since verapamil or extracellular calcium depletion abolished the PGs effect. Regarding the PGs-progestins antagonism, it was observed that pregnanedione, pregnanolone and epipregnanolone were quite effective for counteracting of PGs-induced contraction. However, progesterone was effective in a middle range, whereas 5 alpha-reduced progestins (allopregnanedione and allopregnanolone) were almost ineffective. It has been concluded that the participation of PGs and progestins in the modulation of uterine contraction might be achieved through the control of calcium influx by opening (PGs) or blocking (progestins) receptor-operated calcium channels.

[Estrogen and progesterone levels in serum and amniotic fluid before or during term labor and their relationship to uterine activity]

Estradiol (E2), estriol (E3) and progesterone (P) were measured in the serum and amniotic fluid by radioimmunoassay in 73 cases, both before or during term labor. The results showed: (1) the serum E2, E3, P, E2/P and Es/P values did not differ significantly between the two groups; (2) the amniotic fluid E2 and E3 concentrations were significantly higher for women in active labor and more evident in those with normal uterine activity, but the progesterone concentration did not vary significantly among the three groups. Thus, the increase of estrogen and estrogen/progesterone ratio in amniotic fluid may be related to the mechanism of spontaneous onset of term parturition in human and as well to dysfunctional labor.

[Lipid composition of the myometrium during labor]

Lipids represent one of the basic components of each cellular and subcellular membrane of the myometrium and their fluidity has a strong influence upon membrane function. Human myometrium was obtained at cesarean sections. Lipids were separated by one-dimensional thin layer chromatography. The chromatoplates were determined on the densitometer Shimadzu CS 930. Lipid profile of the myometrium was studied before the 37th week of pregnancy, at term without contractile activity, further during at term labor with normal contractile activity and at failure of myometrial contractility. Analysis of the obtained data showed changes in lipid fluidity, namely a decrease before the 37th week of pregnancy and at failure of myometrial contractions during at term labor. The decrease of fluidity was caused by a higher content of total cholesterol and a lower content of total phospholipids in the myometrium.