Pregnant Human Myometrium Research Articles

Some mechanical properties of skinned fibres of pregnant human myometrium

The properties of contractile elements and intracellular Ca 2+ storage sites of pregnant human myometrium were studied by recording the mechanical responses in skinned (saponin-treated and membrane-permeable) fibres. Calmodulin increased the amplitude of contractions induced by Ca 2+ and the Ca 2+ sensitivity for contractile elements in small myometrium strips, but PGF 2α, PGE 2, oxytocin, or cyclic AMP failed to produce similar effects. After accumulation of Ca 2+ in intracellular Ca 2+ storage sites, 10 μmol/l PGF 2α, 10 μmol/l PGE 2, 30 mmol/l caffeine, and 20 μmol/l InsP3 (inositol-trisphosphate) produced contractions by releasing Ca 2+ from storage sites. However, 20 nmol/l oxytocin had no effects under the same conditions. The InsP3 sensitive Ca 2+ store was much larger than those of PGs or caffeine. These results suggest that pregnant human myometrium contracts with low Ca 2+ by a calmodulin sensitive system. The data also indicate that direct application of PGF 2α or PGE 2 into the cells discharges Ca 2+ from Ca 2+ storage sites and that oxytocin extricates Ca 2+ via a pathway involving InsP3 by activation of phosphoinositide turnover. We suggest that these agents induce added contractile responses due to a Ca 2+ release mechanism from store sites in addition to the influx of Ca 2+ from the extracellular space.

The effects of potassium channel openers on isolated pregnant human myometrium before and after the onset of labor: Potential for tocolysis

Our purpose was to investigate the effects and pharmacologic properties of potassium channel openers in isolated pregnant human myometrium. Biopsy specimens of myometrium obtained from 67 women during pregnancy and labor were used for isometric recording under physiologic conditions. Levcromakalim and pinacidil, two prototype potassium channel openers, are potent inhibitors of spontaneous and induced (0.5 nmol/L oxytocin and 10 mumol/L phenylephrine) contractions in isolated human pregnant myometrium, obtained before and after the onset of labor. The sulfonylurea glibenclamide is an apparent competitive antagonist of this inhibition. No antagonism was observed with the sulfonylurea tolbutamide. Both potassium channel openers significantly inhibited contractility evoked by low (10 and 20 mmol/L) but not high (40 and 80 mmol/L) concentrations of extracellular potassium chloride. These findings suggest that the relaxant ability of levcromakalim and pinacidil in human pregnant myometrium is because of potassium channel activation. This introduces a potential new approach for tocolysis.

Cocaine selectively inhibits β-adrenergic receptor binding in pregnant human myometrium

This study evaluated the in vitro effects of cocaine on the binding characteristics of alpha- and beta-adrenergic receptors from pregnant human myometrium. By means of membrane fractions from myometrium obtained from 26 women at term undergoing cesarean section, equilibrium binding assays were performed with tritiated dihydroergocryptine for alpha-adrenergic receptors and iodine 125-cyanopindolol for beta-adrenergic receptors. Equilibrium competition curves were determined with and without cocaine. Results were compared by one-way analysis of variance. Cocaine inhibited beta-adrenergic receptor binding (inhibition constant = 132 mumol/L) but had little effect on alpha-adrenergic receptor binding (inhibition constant = 1.63 mmol/L). Benzoylecgonine, a stable metabolite of cocaine, had no effect on binding to either receptor. Cocaine selectively inhibits myometrial beta-adrenergic receptor binding. This may alter the contractile equilibrium of the pregnant uterus and could explain, in part, the association of cocaine abuse with premature delivery.

In vitro characterization of prostanoid receptors on human myometrium at term pregnancy.

1. Prostanoid receptors present on the pregnant human myometrium in vitro have been characterized according to the receptor classification proposed by Coleman et al. (1984) using natural prostanoids and synthetic, selective analogues and antagonists where available. 2. Prostaglandin E2 (PGE2) produced a biphasic effect consisting of an initial excitation followed by a dose-related inhibition. The EP2/EP3-receptor agonists, rioprostil and misoprostol, produced similar effects to PGE2, however, the excitatory event of the misoprostol response was related to dose. The EP1/EP3-receptor agonist, sulprostone, evoked a purely excitatory response which was unaffected by AH6809. The selective EP2-receptor agonist butaprost produced a long-lasting dose-dependent inhibition of activity. The results from these prostanoids indicated that inhibitory EP2- and excitatory EP3-receptors are present on myometrium from pregnant donors at term. 3. PGF2 alpha and the synthetic FP-receptor agonist, fluprostenol, caused equipotent excitatory effects, indicating the presence of contractile FP-receptors. 4. PGD2 produced a biphasic effect of which the inhibition appeared dose-related and was antagonized by the selective DP-receptor antagonist BW A868C. The selective DP-receptor agonist, BW245C, produced a potent inhibitory effect that was competitively antagonized by BW A868C (pA2 = 8.6). 5. PGI2 produced a biphasic response qualitatively similar to PGE2. The EP1/IP-receptor agonist, iloprost, produced an occasional unquantifiable excitation and dose-related inhibition. The selective IP-receptor prostanoid, cicaprost, evoked only an inhibitory response. 6. The stable thromboxane A2 (TXA2)-mimetic, U46619, produced potent excitation which was competitively antagonized by the TP-receptor antagonist, GR32191 (pA2 = 7.2). 7. The prostanoids tested indicate that a heterogeneous population of prostanoid receptors are presen ton human myometrium from pregnant donors. It may be concluded that excitation is EP3-, FP- and TP-receptor-mediated and inhibition is EP2-, DP- and IP-receptor-mediated. Comparison of data obtained from non-pregnant specimens indicates that the lower segment tissue from pregnant donors demonstrated more pronounced responses to EP2 and IP-receptor activation.

Properties of large-conductance K+ channels in human myometrium during pregnancy and labour.

The conversion of the electrically silent pregnant uterus to highly excitable at term represents a dramatic physiological event which is poorly understood. Here we provide the first description, from single-channel recordings, of a large conductance (212 pS) calcium-activated potassium channel (BKCa) in human pregnant myometrium which, in labour tissue, is either absent or has been considerably altered in its physiological and pharmacological properties. In the latter, the K+ channels have an identical conductance (221 pS) and K+ selectivity to BKCa channels but exhibit no Ca2+ or voltage sensitivity. We have termed these BK channels. Furthermore, the activity of the BKCa channel from pregnant tissue is inhibited by internal application of Ba2+ but not tetraethylammonium (TEA), whereas the activity of the BK channel is sensitive to internal TEA but not Ba2+. The role of the BKCa channel may be to suppress myometrial activity during gestation whereas BK channel activity may be important in providing a Ca(2+)-independent K+ conductance which would allow cytoplasmic Ca2+ levels to rise without activating a counteracting Ca(2+)-dependent outward current, normally provided by the BKCa channels which, by its very nature, would tend to oppose depolarization. The findings suggest that K+ channels may have an important role in determining the functional activity of the myometrium.

Sex steroid modulation of neurohypophysial hormone receptors in human nonpregnant myometrium.

Neurohypophysial hormone receptors were studied in myometrial specimens obtained from nonpregnant women using binding and in vitro contractility studies. The mathematical modeling of self- and cross-competition curves among [3H]oxytocin (OT), [3H]arginine vasopressin, the V1 vasopressin (VP) antagonist [3H]d(CH2)5TyrMeAVP, the corresponding unlabeled peptides, and the OT agonist [Thr4, Gly7] OT strongly indicates the presence of multiple classes of OT and arginine vasopressin receptors. The latter show the same pharmacological characteristics as the neurohypophysial hormone receptors described by our group for the human pregnant myometrium; in addition, they regulate the contractility of uterine strips. Blocking experiments were performed to evaluate the relative OT and V1 VP receptor distribution in 30 uterine specimens obtained from normal cycling and postmenopausal women. The glucuronoconjugate metabolites of 17 beta-estradiol and progesterone were also measured in 16 patients in early morning urine samples taken the same day as surgery. Our results show that V1 VP receptors are not only present but also biologically active in all the uterine specimens studied with virtually equal density in normal cycling and postmenopausal women. However, their concentrations do not correlate with either estrogen or progesterone urinary levels. The lowest OT receptor density was found at mid-cycle and in menopause, independently of any correlation with the urinary estrogens. Conversely, OT receptors rise sharply in the late luteal phase and during menstruation. In addition they show a positive relationship with glucuronoconjugate metabolites of progesterone levels. These results indicate that progesterone does not inhibit the expression of uterine OT receptors in the human uterus. Furthermore, they imply that neurohypophysial hormones are involved in the control of uterine activity during the menstrual cycle.

Modification by magnesium of the excitatory effect of oxytocin on electrical and mechanical activities of pregnant human myometrium

Modification by magnesium of the excitatory effect of oxytocin on electrical and mechanical activities of pregnant human myometrium

Effects of magnesium and terbutaline on contractility and K + uptake in isolated human uterine muscle

Mg++ (3 and 6 mmol/L), the beta 2-adrenergic agonist terbutaline (1 and 10 mumol/L), and dibutyryl cyclic adenosine 5'-monophosphate (0.1 and 1 mmol/L) suppressed spontaneous activity and the increase in contractile activity induced by ouabain or K(+)-free buffer in isolated human pregnant myometrium. The ouabain-suppressible rubidium 86 or potassium 42 uptake was unaffected by the presence of Mg++ (3 and 6 mmol/L), the beta 2-adrenergic agonist terbutaline (1 and 10 mumol/L), or dibutyryl cyclic adenosine 5'-monophosphate (1 mmol/L). However, loading of the strips with Na+ and incubation in high K+ induced a fivefold increase in rubidium 86 uptake. On the basis of these flux rates, our previous data on the total concentration of sodium-potassium pumps in the human myometrium, and an estimated maximum transport rate of the sodium-potassium pump of 8900 K+ ions per minute at 30 degrees C, it could be calculated that the sodium-potassium pump in the Na(+)-loaded strips reached around 80% of its maximal rate. Taken together, these results showed that the relaxant effects of Mg++, terbutaline, and dibutyryl cyclic adenosine 5'-monophosphate on human myometrium are not due to a stimulation of active sodium-potassium transport.

Effects of magnesium and terbutaline on contractility and K + uptake in isolated human uterine muscle

Mg++ (3 and 6 mmol/L), the β2-adrenergic agonist terbutaline (1 and 10 μmol/L), and dibutyryl cyclic adenosine 5′-monophosphate (0.1 and 1 mmol/L) suppressed spontaneous activity and the increase in contractile activity induced by ouabain or K+-free buffer in isolated human pregnant myometrium. The ouabain-suppressible rubidium 86 or potassium 42 uptake was unaffected by the presence of Mg++ (3 and 6 mmol/L), the β2-adrenergic agonist terbutaline (1 and 10 μmol/L), or dibutyryl cyclic adenosine 5′-monophosphate (1 mmol/L). However, loading of the strips with Na+ and incubation in high K+ induced a fivefold increase in rubidium 86 uptake. On the basis of these flux rates, our previous data on the total concentration of sodium-potassium pumps in the human myometrium, and an estimated maximum transport rate of the sodium-potassium pump of 8900 K+ ions per minute at 30°C, it could be calculated that the sodium-potassium pump in the Na+-loaded strips reached around 80% of its maximal rate. Taken together, these results showed that the relaxant effects of Mg++, terbutaline, and dibutyryl cyclic adenosine 5′-monophosphate on human myometrium are not due to a stimulation of active sodium-potassium transport. Mg++ (3 and 6 mmol/L), the β2-adrenergic agonist terbutaline (1 and 10 μmol/L), and dibutyryl cyclic adenosine 5′-monophosphate (0.1 and 1 mmol/L) suppressed spontaneous activity and the increase in contractile activity induced by ouabain or K+-free buffer in isolated human pregnant myometrium. The ouabain-suppressible rubidium 86 or potassium 42 uptake was unaffected by the presence of Mg++ (3 and 6 mmol/L), the β2-adrenergic agonist terbutaline (1 and 10 μmol/L), or dibutyryl cyclic adenosine 5′-monophosphate (1 mmol/L). However, loading of the strips with Na+ and incubation in high K+ induced a fivefold increase in rubidium 86 uptake. On the basis of these flux rates, our previous data on the total concentration of sodium-potassium pumps in the human myometrium, and an estimated maximum transport rate of the sodium-potassium pump of 8900 K+ ions per minute at 30°C, it could be calculated that the sodium-potassium pump in the Na+-loaded strips reached around 80% of its maximal rate. Taken together, these results showed that the relaxant effects of Mg++, terbutaline, and dibutyryl cyclic adenosine 5′-monophosphate on human myometrium are not due to a stimulation of active sodium-potassium transport.

The effect of calcium antagonists on the cyclic nucleotide levels and the activity of the isolated human pregnant myometrium

The effect of calcium antagonists on the cyclic nucleotide levels and the activity of the isolated human pregnant myometrium

The effect of calcium antagonists on the cyclic nucleotide levels and the activity of the isolated human pregnant myometrium

The effect of calcium antagonists on the cyclic nucleotide levels and the activity of the isolated human pregnant myometrium

Functional Coupling of theα2-Adrenergic Receptor-Adenylate Cyclase Complex in the Pregnant Human Myometrium*

We previously reported that in the pregnant human myometrium the binding sites labeled with [3H]idazoxan have the pharmacological characteristics of alpha 2-adrenergic receptors. Competitive experiments have also revealed that the stable guanine nucleotide analog guanyl-5'-imidodiphosphate decreases the apparent affinity of norepinephrine and clonidine for myometrial [3H]idazoxan-binding sites. In the present study, the alpha 2-adrenergic mechanism in this tissue was further approached by measuring adenylate cyclase responses and examining the different pertussis toxin-sensitive G-proteins. The two alpha 2-adrenergic agonists norepinephrine and clonidine inhibited adenylate cyclase activity in both the outer and inner layers of the pregnant human myometrium. The inhibitory effect of these agonists is completely reversed by alpha 2-adrenergic antagonists such as yohimbine and idazoxan. Pretreatment with pertussis toxin completely suppresses the inhibition of adenylate cyclase mediated by alpha 2-adrenergic receptors, suggesting that an inhibitory protein of the Gi type is involved. Pertussis toxin, known to catalyze the ADP ribosylation of the alpha-subunit of several G-proteins, labels three substrates at 39, 40, and 41 kDa. The more intense labeling occurring on the 40- to 41-kDa components are assigned to alpha-subunits of Gi-like proteins, whereas that at 39 kDa might correspond to a Go alpha-like substrate. These results indicate the presence of alpha 2-adrenergic receptors in the human myometrium at the end of pregnancy that are functionally linked to inhibition of adenylate cyclase activity via the Gi protein.

Some electrical properties of human pregnant myometrium

Membrane properties of the human pregnant myometrium were investigated with the conventional microelectrode and patch clamp methods. The majority of preparations produced spontaneous action potentials at a very low frequency, and action potentials were inhibited in sodium-deficient or calcium-free solutions. With the patch clamp technique with 120 mmol/L cesium-20 mmol/L tetraethylammonium in the pipette, the inward current was evoked by a depolarizing pulse above -40 mV from a holding potential of -60 mV and maximum amplitude was obtained at 0 mV. At a holding potential of -100 mV, the inward current could be evoked with less positive depolarizing pulses, and the membrane potential that evoked the maximum amplitude of inward current was shifted to a more negative potential. Single-channel current recording revealed that two types of calcium channels existed in human pregnant myometrium, with single-channel conductances of 12 and 29 pS. One of the calcium channels (12 pS) was inactivated at a holding potential of -60 mV.

Characterization of the spontaneous motor activity of the isolated human pregnant myometrium

The motor activity of myometrial strips from pregnant human uterus was characterized in vitro by the use of inhibitory compounds acting on the smooth muscle contractility at different levels. Spontaneous contractions were not inhibited by tetrodotoxin or a series of membrane receptor antagonists, like anticholinergics, antihistaminics, α-adrenergic blocking agents, antiserotoninergics and opioid receptor antagonists, thus excluding neuronal involvements or a local release of endogenous mediators active on the respective membrane receptors. The ineffectiveness of indomethacin (10 −5 m) minimizes a role for excitatory prostaglandins. Isoprenaline and selective β 2-adrenergic stimulants, like salbutamol and hexoprenaline (up to 10 −5 m), failed to affect the amplitude of spontaneous contractions. Conversely the adenylate cyclase activator, forskohn, had a concentration-dependent inhibitory effect. Ca 2+-free medium, trifluoperazine and all the calcium channel blockers examined produced a concentration-dependent inhibition of the spontaneous contractions in the following order of sensitivity: nifedipine ≫ verapamil ≫ diltiazem > trifluoperazine.The inhibitory effect of nifedipine was not overcome by excess calcium concentration in the bathing medium, but was completely restored by addition of the calcium agonist Bay K 864410 −7 m. From these data it can be concluded that the spontaneous activity of pregnant human myometrium in vitro is independent of neural or humoral mechanisms. The inhibitory effect of Ca 2+-free medium and the efficacy of calcium channel blockers support the view that calcium influx is an important step in initiating the contractile activity of uterine smooth muscle.

Sensitivity of the Human Myometrial Adenylate Cyclase to Calcium and Calmodulin

The calcium-calmodulin-dependent regulation of adenylate cyclase was studied in membranes from pregnant human myometrium. In the absence or presence of exogenous calmodulin, free calcium concentrations greater than 50 nmol/l inhibited the adenylate cyclase activity. Activation of the enzyme by calmodulin (0.1-1 mumol/l) was calcium-dependent and maximal at 10 nmol/l free calcium. The myometrial adenylate cyclase activity was stimulated by the guanyl nucleotide, Gpp(NH)p. In the presence of the guanyl nucleotide, the activatory effect of the calcium-calmodulin complex disappeared. The activatory effect of exogenous calmodulin was dependent on endogenous calmodulin present in the myometrial membranes. Trifluoroperazine and calmidazolium were able to inhibit the adenylate cyclase activity.

Effect of Methylergometrine Maleate (Methergin) on Electrical and Mechanical Activities of Pregnant Human Myometrium

The effect of methylergometrine maleate (methergin) on electrical and mechanical activities of pregnant human isthmic myometrium was examined. Methergin (10(-8)-10(-6) g/ml) enhanced plateau potential and contraction, however, the effects were not prominent. Plateau potential and contraction were also potentiated after pretreatment with 10(-7) g/ml phentolamine (alpha-blocker), however 10(-7) g/ml methergin further increased these effects. It is suggested that methergin might potentiate contractions by changing the pattern of action potentials and not by alpha-adrenoceptor.

Vasopressin receptors in human pregnant myometrium and decidua: Interactions with oxytocin and vasopressin agonists and antagonists

Saturation analysis and competition experiments were performed to identify and characterize [3H]arginine vasopressin binding to human myometrium and decidua in late pregnancy. [3H]Arginine vasopressin bound with affinity similar to that of [3H]oxytocin to both tissues (dissociation constant 1 to 2 nmol/L). The concentration of [3H]arginine vasopressin binding sites was high, particularly in decidua, but in all instances was about 50% to 60% of [3H]oxytocin binding. Analogs with selective oxytocic potency (4-threonine oxytocin, isotocin) had high affinity to both [3H]arginine vasopressin and [3H]oxytocin binding sites, as did analogs with both oxytocic and vasopressor activity (vasotocin). Analogs with selective antidiuretic activity (1-deamino-8-D-arginine vasopressin) showed drastically reduced affinity to [3H]oxytocin binding sites and relatively low but significantly higher affinity to [3H]arginine vasopressin binding sites. A new oxytocin antagonist (RW22164 or [1-deamino-2D-tyrosine-(O-ethyl)-4-threonine-8-ornithine]oxytocin) competitively bound to both binding sites. Its affinity to [3H]oxytocin binding sites was greater than to [3H]arginine vasopressin binding sites whereas the relative affinities of a predominantly vasopressor antagonist [Manning compound) were reversed, suggesting the presence of distinct receptors for oxytocin and arginine vasopressin in pregnant human myometrium and decidua.

Effect of recombinant human tumour necrosis factor on contractility and prostaglandinsynthesis of pregnant human myometrium

In this paper, the design problems of variable and adaptive fractional order finite impulse response (FIR) differentiators are investigated. First, the fractional differencing method and weighted least squares (WLS) approach are presented to design variable fractional order differentiators which can be implemented by the efficient Farrow structure. Next, an adaptive fractional order differentiator is developed and applied to estimate the parameters of 1/f noise from the finite observation data set. The parameters are updated by using least mean squares (LMS) adaptive algorithm. Finally, the variable fractional order differentiator is used to reduce the error rate of handwritten signature verification system.

Are leukotrienes involved in human uterine contractility?

The effects of leukotrienes (LT) on the contractility of human and rat myometrial strips in vitro were compared with the effects of prostaglandins (PGs) and oxytocin. Preparations of human myometrial membranes were investigated for the presence and characteristics of LTC4 receptors. Neither the peptido-leukotrienes (LTC4, LTD4, LTE4) nor LTB4 had any consistent effect, stimulatory or inhibitory, on human pregnant or non-pregnant myometrium, at doses up to 1.25 microM; nor did they have any effect in rat non-pregnant myometrium. As expected, PGE2, PGF2 alpha (0.3 microM) and oxytocin (5 nM) stimulated human pregnant myometrium. PGF2 alpha stimulated and PGE2 inhibited human non-pregnant myometrium but oxytocin had no effect; all three compounds stimulated rat non-pregnant myometrium. The binding of 3H-LTC4 to human myometrium was specific (LTC4 greater than LTD4 much greater than LTE4, LTB4, PGE2, PGF2 alpha, arachidonic acid) but of low affinity compared with the binding of 3H-PGE2 to the same membrane preparations. These data support the view that leukotrienes have little direct influence on myometrial contractility.

Effects of external calcium, magnesium, and temperature on spontaneous contractions of pregnant human myometrium.

Spontaneous isometric contractions of small isolated segments from the isthmic region of pregnant human myometrium were recorded to clarify the characteristics of and influences of experimental conditions on contractions. There is a spontaneous periodicity in membrane activity of human myometrium, and contractions evoked with a sustained electric stimulus were affected by spontaneous rhythmic contractions. The frequency of contractions increased markedly, but their duration decreased when temperature of the bathing fluid was increased from 26 degrees C to 39 degrees C. Both excess (7 mM) and low (0.5 mM) calcium levels suppressed the generation of spontaneous contraction. Frequency and half-duration gradually decreased when external magnesium was increased from 0 mM to 3.6 mM. These results indicate that the pattern of contraction depends on the frequency of and intervals between each action potential, and that spontaneous contractility-particularly its frequency-is extremely sensitive to external temperature and ionic conditions.