Mechanisms underlying the neurokinin A-induced contraction of the pregnant rat myometrium

Pennogenin tetraglycoside induces rat myometrial contraction and MLC20 phosphorylation via PLC-IP(3) and RhoA/Rho kinase signaling pathways

BACKGROUND

Total steroidal saponins extracted from the rhizome of Paris polyphylla Sm. var. yunnanensis (TSSPs) have been widely used in China for the treatment of abnormal uterine bleeding. We previously studied the main active constituents of TSSPs and their structure-activity relationships with respect to rat myometrial contractions. Tg (pennogenin tetraglycoside) was identified as one of the active ingredients in TSSPs able to induce rat myometrial contractions. However, the mechanisms underlying the pharmacological actions on uterine activity have not been described clearly.

METHODS

Here Tg was screened for effects on contractile activity in isolated uterine strips from estrogen-primed rats and on MLC20 phosphorylation and related signaling pathways in cultured rat myometrial cells as determined by Western blot. Intracellular calcium ([Ca(2+)](i)) was monitored under a confocal microscope using Fluo-4 AM-loaded myometrial cells.

RESULTS

Tg dose-dependently stimulated rat myometrial contractions as well as MLC20 phosphorylation in vitro, which could be completely suppressed by an inhibitor of myosin light chain kinase (MLCK). Use of Ca(2+) channel blockers and kinase inhibitors demonstrated that Tg-induced myometrial contractions are mediated by activation of the phospholipase C (PLC)-inositol triphosphate (IP3) signaling pathway, resulting in increased MLC20 phosphorylation. Furthermore, Y27632, a specific inhibitor of Rho kinase (ROK), notably suppressed Tg-stimulated myometrial contractions and decreased MLC20 phosphorylation.

CONCLUSIONS

These data provide evidence that rat myometrial contractility induced by Tg results from enhanced MLC20 phosphorylation, while both PLC-IP3 and RhoA/ROK signaling pathways mediate the process. These mechanisms may be responsible for the therapeutic effects of TSSPs on abnormal uterine bleeding.

Low abundance plasma proteins in labour

Every year, millions of births worldwide are complicated by prematurity or difficult post-term deliveries, resulting in a high incidence of perinatal mortality and morbidity. Our poor understanding of human parturition is a key reason for our inability to improve the management of preterm and post-term birth. In this study, we used proteomic techniques to look into protein changes in placental blood plasma obtained from women before or after spontaneous or induced labour, with vaginal or caesarean section deliveries. Our aim was to understand the basic mechanisms of human parturition regardless of whether the signals that trigger labour are of maternal and/or fetal origin. We found proteins from 33 genes with significantly altered expression profiles in relation to mode of labour and delivery. Most changes in labour occurred in proteins associated with ‘immune and defence responses’. Although the signal transduction and regulation of these pathways varied among modes of delivery, hepatocyte nuclear factor 1 homeobox A emerged as a shared protein in the mechanism of labour. Moreover, several apolipoproteins such as apolipoprotein A-IV and APOE were found to change with labour, and these changes were also confirmed in maternal plasma. This study has identified significant protein changes in placental intervillous plasma with labour and has revealed several pathways related to human parturition.

Active pharmaceutical ingredients and mechanisms underlying phasic myometrial contractions stimulated with the saponin extract from Paris polyphylla Sm. var. yunnanensis used for abnormal uterine bleeding

BACKGROUND

Total steroidal saponins of Paris polyphylla Sm. var. yunnanensis (TSSP) have been widely used in China for the treatment of abnormal uterine bleeding (AUB). But until now, the main active constituents and the mechanisms underlying the pharmacological actions on uterine activity have not been described.

METHODS

Total steroidal saponins were extracted with EtOH and purified by chromatography. In vitro isometric contraction studies were performed using myometrial strips from estrogen-primed or pregnant rats. Intracellular calcium was monitored under a confocal microscope using Fluo-3 AM-loaded myometrial cells.

RESULTS

TSSP dose-dependently induced phasic myometrial contractions in vitro. Experiments with calcium channel blockers or kinase inhibitors demonstrated that the TSSP-stimulated myometrial contraction was mediated by an increase in [Ca(2+)](i) via influx of extracellular calcium and release of intracellular calcium. Through bioassay-guided separation, it was found that total spirostanol saponins exhibited contractile activity in myometrium and Pennogenin-3-O-alpha-L-arabinofuranosyl(1-->4)[alpha-L-rhamnopyranosyl(1-->2)]-beta-D-glucopyranoside (PARG) was identified as the active ingredient of TSSP. Furthermore, the contractile response of rat myometrium to PARG was significantly enhanced with advancing pregnancy.

CONCLUSIONS

These data provide evidence that myometrial contractility stimulated by TSSP results from [Ca(2+)](i) increase and supports the possibility that some spirostanol gylcosides may represent a new type of contractile agonist for the uterus.

Enhancement of trypsin-induced contraction by in vivo treatment with 17beta-estradiol and progesterone in rat myometrium

We have previously reported that the contractile response to thrombin and trypsin was enhanced in the pregnant rat myometrium. We herein determined whether or not sex hormones contribute to this enhancement and the expression of protease-activated receptors (PARs). The nonpregnant rats received daily injections of either 17beta-estradiol or progesterone, and then the contractile response of the myometrium was examined ex vivo. Treatment with either 17beta-estradiol or progesterone had almost no significant enhancing effect on the high K(+)- or oxytocin-induced contraction. On the other hand, both 17beta-estradiol and progesterone dose-dependently enhanced the contractile response to trypsin. A maximal enhancement was obtained at 25 and 40 mg kg weight(-1) day(-1) for 17beta-estradiol and progesterone, respectively. The extent of the enhancement of the trypsin-induced contraction seen in the sex hormone-treated rats in the present study was comparable to that reported in the pregnant rats. However, the contractile response to thrombin and PAR1/PAR2-AP, SFLLRNP was not enhanced either by progesterone or 17beta-estradiol. PAR2-AP and PAR4-AP failed to induce contraction under any conditions. PAR1 mRNA was scarcely detected in the control myometrium by an RT-PCR analysis, while it slightly increased only in the progesterone-treated rats. Neither PAR2 nor PAR4 mRNA was detected. We thus conclude that the responsiveness to trypsin, but not thrombin, is controlled by sex hormones. A novel type of receptor, other than PAR1, PAR2 or PAR4, is suggested to mediate the trypsin-induced contraction as in the case of the pregnant rat myometrium.

Tachykinins and tachykinin receptors: effects in the genitourinary tract

Tachykinins (TKs) are a family of peptides involved in the central and peripheral regulation of urogenital functions through the stimulation of TK NK1, NK2 and NK3 receptors. At the urinary system level, TKs locally stimulate smooth muscle tone, ureteric peristalsis and bladder contractions, initiate neurogenic inflammation and trigger local and spinal reflexes aimed to maintain organ functions in emergency conditions. At the genital level, TKs are involved in smooth muscle contraction, in inflammation and in the modulation of steroid secretion by the testes and ovaries. TKs produce vasodilatation of maternal and fetal placental vascular beds and appear to be involved in reproductive function, stress-induced abortion, and pre-eclampsia. The current data suggest that the genitourinary tract is a primary site of action of the tachykininergic system.

Functional and molecular characterization of tachykinins and tachykinin receptors in the mouse uterus

The aim of this study was to analyze the function and expression of tachykinins, tachykinin receptors, and neprilysin (NEP) in the mouse uterus. A previous study showed that the uterotonic effects of substance P (SP), neurokinin A (NKA), and neurokinin B (NKB) in estrogen-treated mice were mainly mediated by the tachykinin NK1 receptor. In the present work, further contractility studies were undertaken to determine the nature of the receptors mediating responses to tachykinins in uteri of late pregnant mice. Endpoint and real-time quantitative RT-PCR were used to analyze the expression of the genes that encode the tachykinins SP/NKA, NKB, and hemokinin-1 (HK-1) (Tac1, Tac2, and Tac4); and the genes that encode tachykinin NK1 (Tacr1), NK2 (Tacr2), and NK3 (Tacr3) receptors in uteri from pregnant and nonpregnant mice. The data show that the mRNAs of tachykinins (particularly NKB and HK-1), tachykinin receptors, and NEP are locally expressed in the mouse uterus, and their expression changes during the estrous cycle and during pregnancy. The tachykinin NK1 receptor is the predominant tachykinin receptor in the nonpregnant and early pregnant mouse and may mediate tachykinin-induced uterine contractions in the nonpregnant mouse. The tachykinin NK2 receptor is predominant in the late pregnant mouse and is the main receptor mediating uterotonic responses to tachykinins at late pregnancy. The tachykinin NK3 receptor is expressed in considerable amounts only in uteri from nonpregnant diestrous animals, and its physiological significance remains to be clarified.

Mammalian tachykinins and uterine smooth muscle: the challenge escalates

We review the actions of mammalian tachykinins on uterine smooth muscle. Derived from sensory neurones and non-neuronal cells within the female reproductive tract, tachykinins are potent uterotonic agents. Three tachykinin receptor genes, and the gene encoding neprilysin, the enzyme that inactivates tachykinins, are present in rat, mouse and human myometrium. In rat and human, the tachykinin NK(2) receptor is important in mediating the uterotonic effects of tachykinins; actions at this receptor remain relatively stable or vary only slightly in the face of changing hormonal and gestational status. In contrast, ovarian steroids and pregnancy regulate expression of the tachykinin NK(3), and to a lesser extent, the tachykinin NK(1) receptor, as well as the activity of neprilysin. In the oestrogen primed mouse uterus, the tachykinin NK(1) receptor primarily mediates tachykinin uterotonic effects, but there is a switch to the tachykinin NK(2) receptor by late pregnancy. The possible physiological and pathological roles of tachykinins, including hemokinins and endokinins, in normal and premature labour, stress-induced abortion and menstrual disorders are briefly discussed.

Endothelium-dependent and independent enhancement of vascular contractility in the ovariectomized rabbit

OBJECTIVE

Estrogen suppresses contractile response and increases vasodilator response, partly by modulating endothelial function. However, the effect of estrogen on the contractility of vascular smooth muscle remains to be elucidated. We investigated the effect of a long-term estrogen deficiency on vascular contractility and the Ca(2+) sensitivity of the contractile apparatus in arterial smooth muscle.

METHODS

Female rabbits were divided into the following three groups: control group, an ovariectomized group (OVX), and a group supplemented with 17beta-estradiol after ovariectomy (OVX+E2). Twelve weeks later, the mesenteric artery was isolated, and the vascular contractility was evaluated.

RESULTS

In OVX, the contractile responses to phenylephrine and 118 mM potassium were enhanced, and the basal release of nitric oxide decreased in the strips with endothelium compared with either OVX+E2 or control. An enhancement of contraction was also observed in the strips without endothelium. However, the extent of enhancement was smaller than that observed in the presence of endothelium. The simultaneous measurement of calcium ([Ca(2+)](i)) and tension revealed no significant difference in the [Ca(2+)](i) elevations induced by phenylephrine among the three groups. In the alpha-toxin permeabilized strips, the Ca(2+)-tension relationships obtained both with and without phenylephrine and guanosine triphosphate were similar among the three groups. No difference in the myosin expression and the histology of vascular tissue was observed among the three groups.

CONCLUSION

Long-term estrogen deficiency increased the vascular tone mainly by enhancing smooth muscle contractility. Endothelial dysfunction is considered to play a minor role in the augmentation of vascular tone.

Functional characterization of tachykinin NK1 receptors in the mouse uterus

1. Contractility studies were undertaken to determine the nature of the receptors mediating responses to tachykinins in uteri of oestrogen-treated mice. 2. In the presence of thiorphan (3 microM), captopril (10 microM), and bestatin (10 microM), substance P (SP), neurokinin A (NKA) and neurokinin B (NKB) produced concentration-related contractions of uterine preparations. The order of potency was SP > or =NKA>NKB. 3. Neither atropine (0.1 microM) nor l-NOLA (100 microM), nor indomethacin (10 microM) alone or in combination with either ranitidine (10 microM) or mepyramine (10 microM), affected responses to SP. These findings indicate that SP actions are not mediated or modulated through the release of acetylcholine, nitric oxide, prostanoids or histamine. 4. In the presence of peptidase inhibitors, the tachykinin NK(1) receptor-selective agonist [Sar(9)Met(O(2))(11)]SP, produced a concentration-dependent contractile effect. The tachykinin NK(2) and NK(3) receptor-selective agonists [Lys(5)MeLeu(9)Nle(10)]NKA(4-10) and [MePhe(7)]NKB were relatively inactive. The potencies of SP analogues in which Glu replaced Gln(5) and/or Gln(6) were similar to that of SP. 5. The tachykinin NK(1) receptor-selective antagonist, SR140333 (10 nM), alone or combined with the tachykinin NK(2) receptor-selective antagonist, SR48968 (10 nM), shifted log concentration curves to SP, NKA and NKB to the right. SR140333 (10 nM) reduced the effect of [Sar(9)Met(O(2))(11)]SP. SR48968 did not affect responses to SP or [Sar(9)Met(O(2))(11)]SP, but reduced the effect of higher concentrations of NKA and shifted the log concentration-response curve to NKB to the right. The tachykinin NK(3) receptor-selective antagonist, SR 142801 (0.3 microM), had little effect on responses to SP and NKB. 6. We conclude that the tachykinin NK(1) receptor mediates contractile effects of SP, NKA and NKB and [Sar(9)Met(O(2))(11)]SP in myometrium from the oestrogen-primed mouse. The tachykinin NK(2) receptor may also participate in the responses to NKA and NKB.

Mechanism of trypsin-induced contraction in the rat myometrium: the possible involvement of a novel member of protease-activated receptor

1. The mechanism of trypsin-induced contraction in the rat myometrium was investigated using front-surface fluorimetry on fura-PE3-loaded strips. The expression of protease-activated receptors (PARs) in the rat myometrium was determined by reverse transcription polymerase chain reaction (RT - PCR). 2. In non-pregnant rats, 10 microM trypsin developed a force of up to 30.5 +/- 5.1% of that obtained during the 40 mM K(+)-depolarization-induced contraction. In pregnant rats, the maximal level of the cytosolic Ca(2+) concentration and tension obtained with 3 microM trypsin was 143.2 +/- 6.0% and 63.2 +/- 7.9%, respectively. The depletion of the extracellular Ca2+ abolished the trypsin-induced contraction. 3. Trypsin-induced contraction was abolished by the pre-treatment of a serine protease inhibitor. PAR1-activating peptide (PAR1-AP) caused a potent contraction of the myometrium, while neither PAR2-AP nor PAR4-AP induced any contraction. 4. RT - PCR analysis detected the expression of PAR1 mRNA. However, neither PAR2 nor PAR4 mRNA was detected in the rat myometrium. 5. Once the strips were stimulated with thrombin, the subsequent application of thrombin failed to induce any contraction, while trypsin induced a contraction similar to that observed without the pre-stimulation with thrombin. Once the strip was stimulated with trypsin, neither trypsin nor thrombin induced any contraction. The response to PAR1-AP remained after the pre-stimulation with thrombin and trypsin. 6. In conclusion, PAR1 was the only known receptor for trypsin expressed in the rat myometrium, but it was suggested to be cleaved and inactivated by trypsin. Trypsin was thus suggested to contract the rat myometrium via a novel type of PAR, which might be upregulated during pregnancy.

Enhanced contractile response to thrombin in the pregnant rat myometrium

Thrombin causes various cellular events by activating protease-activated receptors (PARs). Here, we showed, for the first time, that thrombin induced myometrial contraction. To determine the mechanism of thrombin-induced myometrial contraction, we simultaneously measured intracellular Ca(2+) concentration ([Ca(2+)](i)) and tension of fura-PE3-loaded rat myometrium using front-surface fluorimetry. The expression of thrombin receptor mRNA in the rat myometrium were determined by reverse transcription-polymerase chain reaction analysis (RT - PCR analysis). Thrombin (0.01 - 3 u ml(-1)) caused dose-dependent increase in [Ca(2+)](i) and tension in the rat myometrium, and this effect was greatly enhanced in the pregnant myometrium. PAR1-activating peptide mimicked the effects of thrombin. In Ca(2+)-free PSS, thrombin induced no increase in [Ca(2+)](i) and tension in the pregnant myometrium. Both diltiazem (10 microM) and SK-F 96365 (10 microM) significantly inhibited the thrombin-induced elevations of [Ca(2+)](i) and tension, and their effects were additive. RT - PCR analysis revealed an approximately 10 fold increase in the level of thrombin receptor mRNA in the pregnant myometrium compared to that obtained in the non-pregnant myometrium. In conclusion, the contractile response to thrombin was greatly enhanced in the pregnant myometrium, mainly due to the up-regulation of thrombin receptor. We propose that initiation of a post-parturitional myometrial contraction is one of the most important physiological roles of thrombin receptor.