Evidence of non-synaptic regulation of postpartum uterine contractility in the rat

Effect of blocking of alpha1-adrenoreceptor isoforms on the noradrenaline-induced changes in contractility of inflamed pig uterus

BACKGROUND

Disturbances in uterine contractility often lead to the origin, development and maintenance of endometritis and metritis, which are a very common and serious pathologies in domestic animals. Here we aimed to investigate the role of α1A-, α1B- and α1D-adrenoreceptors (ARs) in noradrenaline (NA)-induced contractility of inflammatory-changed porcine uterus.

METHODS

On Day 3 of the estrous cycle, either Escherichia coli (E. coli) suspension (E. coli group) or saline (SAL group) was injected into uterine horns, or only laparotomy was performed (CON group). Eight days later, infected gilts developed severe acute endometritis.

RESULTS

Compared to the period before NA application, NA reduced the contractile amplitude and frequency in myometrium (MYO) and endometrium (ENDO)/MYO strips from the CON, SAL and E. coli groups. In the last group, the amplitude in MYO and the frequency in ENDO/MYO were lowered versus other groups. After using α1A-ARs antagonist with NA, a greater decrease or occurrence of a drop in the amplitude and frequency in all groups (ENDO/MYO) were found compared to this neurotransmitter action alone. Such results were noted for NA action on the frequency after α1B-ARs blocking in the CON (both kinds of strips) and SAL (ENDO/MYO) groups. In response to α1D-ARs antagonist with NA, a greater decrease or occurrence of a drop in the amplitude was noted in the CON (both kinds of strips) and SAL and E. coli (MYO) groups. Use of these factors caused the similar changes in the frequency in CON and E. coli (MYO) and SAL (ENDO/MYO) groups. In response to NA, α1A,B,D-ARs antagonist led to a greater reduction or appearance of a drop in the amplitude in the CON and SAL (ENDO/MYO) and E. coli (both kinds of strips) as well as in the frequency in the CON and SAL (ENDO/MYO) and E. coli (MYO) groups.

CONCLUSIONS

In conclusion, activation of α1A- and α1D-ARs by NA promotes the contractile amplitude and frequency in the inflamed pig uterus; pharmacological modulation of these receptors can be utilized to enhance systolic activity of myometrium.

Local α1-adrenergic blockers: An alternative for sheep cervix dilation?

To facilitate transcervical artificial insemination in sheep, the effects of local treatment with α1-adrenergic receptor antagonists on cervix dilation and hemodynamics were evaluated. Ewes (n = 7) were subjected to oestrous synchronisation every 40 days and assigned to treatments in a Latin square experimental design (seven animals × seven periods) with a factorial treatment arrangement (A × B), Factors A (prazosin or tamsulosin) and B (1, 2, or 4 mg/animal). Ewes of the six treatment groups (P1, P2, P4, T1, T2, and T4) were administered α1-adrenergic receptor antagonists while those of the control group (CG) were administered only α1-adrenergic antagonist carrier agent. Distance that the transcervical catheter penetrated without cervical resistance, mean arterial pressure, and uterine artery dopplerfluxometry were evaluated before and after 30 min, 1, 2, 4, 8, and 10 h of treatment. Catheter penetration distance was greater in ewes of the T4 and P4 groups (P < 0.01), with there being a positive correlation between dose and distance (r = 0.243). The penetration distance was similar (P = 0.84) for treated groups, with the greatest penetration occurring 2, 4, and 6 h after treatment (P < 0.01). The passage into the uterine lumen was greater (P = 0.013) in ewes of the P4 (17.9 %) and T4 (19.6 %) groups. There were no effects on blood pressure or uterine blood flow (P> 0.05). These preliminary results indicate there are benefits of treatment with 4 mg/animal of tamsulosin or prazosin in catheter passage through the sheep cervix 2-6 h after administration without hemodynamic effects.

Treatment with an inhibitor of catechol-O-methyltransferase activity reduces preterm birth and impedes cervical resistance to stretch in pregnant rats

Catechol-O-methyltransferase (COMT) enzyme catalyzes the methylation of the 2- or 4-hydroxyestrogens to 2- or 4-methoxyestrogens. Both the hydroxyestrogens and methoxyestrogens have been shown to block or enhance the effects of estrogen respectively. Our objective was to investigate the potential role of COMT in parturition and cervical ripening using a rat model. Immunohistochemistry was conducted to detect and localize the COMT protein in rat uterine tissues during pregnancy. We measured the longitudinal changes in urinary 2-hydroxyestrogen before, during, and after pregnancy in rats. Animal studies were conducted to determine the effect of treatment with a selective COMT inhibitor on (1) mifepristone-induced preterm birth and (2) cervical resistance to stretch in pregnant rats. The intensity of staining for the COMT protein differed within the luminal epithelium, uterine gland epithelium, endometrium, and myometrium during pregnancy. Levels of staining for the COMT protein in rat myometrium were highest on day 1 and lowest on days 8 and 13, but high levels returned by days 16 and 19 of pregnancy. The levels of urinary 2-hydroxyestrogen gradually increased in the first 2 weeks of pregnancy, peaked from days 16 to 18 of pregnancy, and then gradually returned to pre-pregnancy levels after delivery. The percentage of pups retained in the uterus of pregnant rats treated with both mifepristone and COMT inhibitor (48 ± 15%) was significantly higher (P< 0.05) when compared with the value of pregnant rats treated with mifepristone alone (12 ± 4%). The resistance to stretch was significantly higher (P< 0.05) in cervical tissues from the pregnant rats treated with COMT inhibitor (0.28) when compared with cervical tissues taken from rats treated with vehicle control (0.18). Modulation of COMT activity may play a role in the regulation of myometrial contractility and cervical ripening during pregnancy.

EFFECT OF ?1-ADRENOCEPTOR SUBTYPE-SELECTIVE INVERSE AGONISTS ON NON-PREGNANT AND LATE-PREGNANT CERVICAL RESISTANCE IN VITRO IN THE RAT

1. The aim of the present study was to compare and elucidate the effects of alpha(1)-adrenoceptor (alpha(1)-AR) subtype-selective inverse agonists on non-pregnant and late-pregnant rat cervical tone. 2. Cervical resistance was investigated in in vitro stretching tests in the absence or presence of alpha(1)-AR subtype-selective inverse agonists (WB 4101, AH 11110A and BMY 7378; all at 10(-6) mol/L), whereas the mRNA levels and density of the alpha(1)-AR subtypes and the G-protein-activating effects of the inverse agonists were determined by reverse transcription-polymerase chain reaction, western blot and [(35)S]-GTPgammaS binding techniques, respectively. 3. The inverse agonists did not cause any change in resistance in non-pregnant and 18-day-pregnant samples. WB 4101 increased cervical resistance from Day 20, whereas AH 11110A had no effect and BMY 7378 exhibited such an action only on Day 21. Phenylephrine (10(-4) mol/L) had no effect on cervical resistance on Day 22. The mRNA levels and density of all alpha(1)-AR subtypes were increased on Day 18, but no further changes were observed after that. The [(35)S]-GTPgammaS binding studies revealed increased G-protein activation of alpha(1A)-AR and a moderate G-protein activation of alpha(1B)- and alpha(1D)-AR. The effect of WB 4101 to increase [(35)S]-GTPgammaS binding was blocked by pertussis toxin (50 ng/mL). Phenylephrine caused a slight and significant decrease in the amount of activated G-protein on Day 22. 4. The effects of inverse agonists on the alpha(1A)-AR can enhance cervical resistance in the late-pregnant rat in vitro. This action is mediated, at least in part, by a pertussis toxin-sensitive G(i)-protein. This effect of the alpha(1A)-AR inverse agonist WB 4101 may offer a new therapeutic target in the prevention of premature labour.

Role of Capsaicin-Sensitive Nerve Fibers in Uterine Contractility in the Rat1

The possible participation of capsaicin-sensitive sensory nerves in the modulation of neurogenic contractions was studied in nonpregnant and term pregnant rat uteri. Neurogenic contractions were elicited by electric field stimulation (40 V, 1-70 Hz, 0.6 msec) in intact uteri and uteri that were previously exposed to capsaicin in vitro. In capsaicin pretreated preparations obtained both from nonpregnant and term pregnant rats, a dose-dependent increase in the amplitude of uterine contractions was detected. Prior systemic treatment of the rats with capsaicin (130 mg/kg, s.c.) abolished the effect of in vitro capsaicin administration on the amplitude of neurogenic contractions. Use of a specific antagonist of calcitonin gene-related peptide revealed that depletion of this peptide, which normally elicits uterine smooth muscle relaxation, may be responsible for the increased responsiveness of the uterus to low-frequency stimulation. Experiments on the localization of calcitonin gene-related peptide in uterine tissue specimens exposed to capsaicin revealed dose-dependent depletion of calcitonin-gene related peptide-immunoreactive nerves innervating blood vessels and the myometrium. The findings indicate that capsaicin-sensitive afferent nerves, by the release of sensory neuropeptides, significantly contribute to the modulation of uterine contractility both in nonpregnant and term pregnant rats. It is suggested that uterine sensory nerve activation may be part of a trigger mechanism leading to preterm contractions evoked by, for example, inflammation.

Role of adrenergic receptor subtypes in the control of human placental blood vessels

STATEMENTS OF THE PROBLEM

The use of beta2-Adrenergic Receptor (AR) agonists and the potential use of alpha1-AR blockers as tocolytics raise the question of how they influence placental circulation. The receptor profile was characterized via the amounts of the mRNA of alpha1-AR subtypes and beta2-ARs. The mRNAs were detected by reverse transcription-polymerase chain reaction. Electric field stimulation (EFS) was applied to test the pharmacological reactivity of the placental vessels. Expressions of beta2- and all subtypes of alpha1-AR mRNA were demonstrated in human placental vessels, and were significantly higher in the arteries. A significant difference was not found between the veins and the arteries as concerns the amount of alpha1D-AR mRNA. There was a preponderance of alpha1A- and alpha1B-AR mRNA as compared to alpha1D-AR mRNA both in the arteries and in the veins. beta2-AR agonists and alpha1-AR antagonists antagonized the EFS-induced contractions of the placental arteries in a dose-dependent manner. These effects were significantly less marked on veins at all applied doses. Urapidil antagonized the EFS-induced contractions of both the placental arterial and vein rings in a dose-dependent manner. The beta2-, alpha1A-, and alpha1B-AR are the important subtypes involved in the regulation of the contractility of the human term placental vessels. The possible increase in placental blood flow mediated by these ARs can even be beneficial during pregnancy. Accordingly, the use of beta2-AR agonists and the potential use of alpha1-blockers as tocolytics seem safe on the basis of in vitro examinations as concerns the placental circulation.

Functional and histochemical characterization of a uterine adrenergic denervation process in pregnant rats

The time course of pregnancy-induced changes in the contractile responses of isolated uterine rings and sympathetic innervation pattern were studied using electric field stimulation and histofluorescence techniques, respectively, in intact and 6-hydroxydopamine-treated rats. Neurally mediated contractions elicited by field stimulation (0.6 msec, 1-70 Hz, 40 V) were measured in uterine preparations obtained from nonpregnant, 6-hydroxydopamine-treated and 5-, 10-, 15-, 18-, and 22-day (term) pregnant rats. At all frequencies, the amplitudes of contractions were highest in nonpregnant uteri. Stimulation at 1-2.5 Hz evoked contractions in 10-day pregnant uteri but failed to cause contractions on Day 5 and from Day 15 onward. In uterine preparations obtained from term and from 6-hydroxydopamine-treated rats, contractions could not be evoked by stimulation at 1-20 Hz. Fluorescence histochemistry of uterine adrenergic nerves revealed rich perivascular and myometrial innervation in nonpregnant and in pregnant rats through Day 10. Degeneration and loss of adrenergic nerve fibers was apparent by Day 15, and fluorescent myometrial and perivascular nerves were practically absent by Day 22. These findings demonstrate a progressive, frequency-related reduction of nerve-mediated uterine contractions beginning in midterm pregnancy, in parallel with a gradual loss of adrenergic nerve fibers. Pregnancy-induced nerve degeneration may promote the development of nonsynaptic alpha-adrenergic uterine contractile activity towards term. The reduced responsiveness of uterine smooth muscle to electric field stimulation in early pregnancy appears to be unrelated to alterations in uterine innervation but may be related to changes associated with implantation.

Altered levels of mRNA expression and pharmacological reactivity of alpha1-adrenergic receptor subtypes in the late-pregnant rat myometrium

The adrenergic system plays a major role in the regulation of the uterine contractility during pregnancy. Our previous studies have shown the significance of the alpha1-adrenergic receptors (ARs) in the control of pregnant uterine contractility both in vitro and in vivo. Our present aim was to determine the changes in mRNA expression and pharmacological reactivity of the alpha1-ARs on days 18, 20, and 22 of pregnancy. To demonstrate the expressions of alpha1-AR subtype mRNA, we used a reverse transcription-polymerase chain reaction (RT-PCR); the pharmacological reactivity was tested by electric field stimulation (EFS). The expression of alpha1A-AR mRNA increased from day 18 to 22, while no alpha1B-AR mRNA was detectable. We found a small increase in the expression of alpha1D-AR mRNA on day 20, which was not followed by a significant change in pharmacological reactivity. The alpha1D-receptor expression and pharmacological reactivity decreased significantly up to day 22. EFS studies revealed that the alpha1A-AR antagonist 5-methylurapidil had EC50 values (1.9 x 10(-6)-6.3 x 10(-6) M) about one order of magnitude lower than those of the alpha1D-AR antagonist BMY 7378 (4 x 10(-6)-3.6 x 10(-5) M). However, the alpha1B-AR antagonist cyclazosine exerted only a slight effect on the stimulated contractions. Strong correlations were found between the alpha1A-mRNA expression and the EC50 of 5-methylurapidil (r(2) =0.9712), and between the alpha1D-AR mRNA expression and the EC50 of BMY 7378 (r(2) = 0.9937). Our findings suggest that both alpha1A- and alpha1D-ARs are involved in the regulation of the pregnant uterine contractility. The density and pharmacological reactivity indicate that the alpha(1A)-AR seems to play the major role in late-pregnant myometrial contraction.

Use of antisense oligonucleotides to verify the role of the alpha(1A)-adrenergic receptor in the contractility of the rat uterus post partum

The adrenergic system plays a major role in the regulation of the contractility of the uterus during pregnancy. This study investigated the role of the alpha(1A)-adrenergic receptor (AR) in this regulation. The use of partial phosphorothioate antisense oligodeoxynucleotides (AONs) permitted the sequence-selective inhibition of AR gene expression. AONs were injected together with a cationic liposomal carrier agent into the post partum rat uterus. Incubation for 12 or 24 h with the most effective AON (480-AON) caused a 58.7 or 53.0% inhibition, respectively, of the expression of the alpha(1A)-AR density, whereas incubation for 36 or 48 h resulted in only a 38.8 or 26.7% inhibition, respectively. The decrease of the alpha(1A)-AR density by 480-AON was demonstrated by Western blot analysis and a radioreceptor binding assay on rat uterus preparations 24 h after delivery. The changes in the contractility of the uterus after AON treatment were measured on isolated rat uterine tissue by electric field stimulation. The significant decrease in the ability of the uterus to contract was indicated by the area under the curve method. The electric field studies revealed that the specific alpha(1A)-blockers 5-methylurapidil and WB 4101 inhibited the rhythmic contraction by about 74 and 70% in the control uteri and by 25 and 20% in 480-AON-treated uteri, respectively. The curves for the beta-mimetic (terbutaline) and alpha(1D)-antagonist (BMY7370) inhibitors were unchanged after 480-AON treatment of the uteri. These results suggest the importance of the alpha(1A)-AR in the tocolytic effect exerted by the alpha(1)-antagonist, although high concentrations of antagonists can not exclude the role of alpha(1D)-ARs, too. Additionally, these prove that the knockdown transformation by AONs offers a useful animal model for the investigation of receptors controlling the function of uterine tissue.

Alpha 1-adrenergic receptor regulation: basic science and clinical implications

Adrenergic receptors (ARs) are members of the G-protein-coupled receptor family, which includes alpha 1ARs, alpha 2ARs, beta 1ARs, beta 2ARs, beta 3ARs, adenosine, muscarinic, angiotensin, endothelin receptors, and many others that are responsible for a large variety of physiologic effects through G-protein coupling. This review focuses on alpha 1ARs and their regulation at both the mRNA and protein levels. Currently, three alpha 1AR subtypes have been characterized both pharmacologically and at the gene level: alpha 1aAR, alpha 1bAR, and alpha 1dAR. These are expressed in a species- and tissue-dependent manner. Mutagenesis approaches have been extremely valuable in the identification of key residues that govern alpha 1AR ligand binding and signaling. These studies reveal that alpha 1ARs have evolved an exquisitely sensitive regulation of their activity in which any disruption of the native structure has profound effects on subsequent function and effector coupling. Significant advances have also been made in the elucidation of signaling pathway components, resulting in the identification of novel pathways that can lead to pathologic conditions. Specific topics include mitogen-activated protein kinase, phosphatidylinositol 3-kinase, and G-protein-coupled receptor cross-talk pathways. Within this context, recent studies identifying underlying transcriptional mechanisms involved in the regulation of the alpha 1AR subtypes are also discussed. Finally, given the potentially important role of alpha 1ARs in the vasculature, as well as in the pathology of many diseases, such as myocardial hypertrophy and benign prostatic hyperplasia, the clinical relevance of alpha 1AR distribution, pharmacology, and therapeutic intervention is reviewed.

The fibre dimensions of uterine smooth muscle of the rabbit following treatment by female sex steroids

The effects of female sex hormones on the dimensions of myometrial smooth muscle fibres were studied by using ovariectomized rabbits. After one month of treatment, the fiber dimensions of the outer myometrial layer were measured, using cryostat sections. Calculated smooth muscle fiber volume was found to be in the sequence: control < medroxyprogesterone < estradiol < estradiol + medroxyprogesterone < estradiol alone. The measurements show that medroxyprogesterone-treated uteri contain the narrowest and the longest smooth muscle fibres, while estradiol treatment have the largest cells. This study complements previous observations in showing that medroxyprogesterone alone, or in combination with other modulators, contributes to sustain pregnancy by increasing internal resistance of estradiol-primed myometrial smooth muscle fiber fascicles. Our discussion, based on recent literature, shows that this resistance is ultimately controlled by changes in the myometrium innervation, in the repression of some controlling myofibrillar components, in the expression of specific membrane receptors and ionic channels, and in favoring the switching of molecular connexins in gap junctions, making P paramount in maintaining pregnancy. Moreover, other recent observations have also shown that probably an hcG-like hormone actually control P receptors expression in myometrial smooth muscles.