Nitroglycerin to facilitate fetal extraction during cesarean delivery.
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Cesarean Section↗
Biomedical subjects
R E Garfield
Publications and source records attributed to R E Garfield.
An expandable implant fixture.
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Dental Abutments↗
Regulation of the uterus and cervix during pregnancy and labor. Role of progesterone and nitric oxide.
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Cervix Uteri↗
Contrasting effects of diethylenetriamine-nitric oxide, a spontaneously releasing nitric oxide donor, on pregnant rat uterine contractility in vitro versus in vivo.
OBJECTIVE: The aim of the study was to investigate the in vitro (on tension) and in vivo (on intrauterine pressure) effects of a spontaneously releasing nitric oxide adduct, diethylenetriamine-nitric oxide, on rat uterine contractility. STUDY DESIGN: Contractile responses to the nitric oxide donor diethylenetriamine-nitric oxide on isometric tension of rat uterine strips (in vitro) and on intrauterine pressure (in vivo) in anesthetized and conscious animals were quantified at late gestation and during preterm and term labor. Preterm labor was induced with the administration of a single injection of the antiprogestin onapristone (10 mg). All control animals were injected with diethylenetriamine, the parent compound, without nitric oxide. RESULTS: The nitric oxide donor diethylenetriamine-nitric oxide relaxes rat uterine tissues when given in vitro during gestation (median effective dose 0.30 +/- 0.09 mmol/L) but fails to have an effect on uterine tissues from laboring term and preterm animals in the muscle bath. Intraperitoneal injection of the nitric oxide adduct in doses of 5 mg and 50 mg produced a significant and sustained decrease in intrauterine pressure in both delivering and nondelivering animals compared with intrauterine pressure values before administration. Analysis of intrauterine pressure levels at different time frames (before injection, immediately after injection, and after 30, 60, and 90 minutes) in anesthetized rats between days 19 and 21 of gestation shows that the dose of 5 mg diethylenetriamine-nitric oxide significantly (p < 0.05) decreased contractility starling at 30 minutes after administration. Similarly, during labor diethylenetriamine-nitric oxide (5 mg intraperitoneally) decreased contractility (p < 0.05) but only starting at 60 minutes after injection. However, with the dose of 50 mg diethylenetriamine-nitric oxide contractility was reduced 30 minutes (p < 0.05) after treatment during pregnancy (days 19 to 21). The same dose of diethylenetriamine-nitric oxide produced a greater relaxation immediately after intraperitoneal injection (p < 0.05) in the laboring group. Diethylenetriamine-nitric oxide (50 mg) also induced an earlier onset and greater relaxation in animals delivering preterm compared with nondelivering animals at the same stage of gestation. The intrauterine pressure maintained constant contractility levels throughout the 100-minute recording period in the control groups of anesthetized and conscious animals that were injected with diethylenetriamine at the equivalent doses. In the preterm laboring group the effects were similar in both anesthetized and conscious animals. CONCLUSION: Although in vitro studies of uterine muscle show decreased inhibitory responses to nitric oxide donors during spontaneous term labor and preterm labor compared with tissues collected during late pregnancy (day 19), studies in vivo demonstrate that nitric oxide donors can decrease uterine contractility even more effectively during delivery. The results suggest that nitric oxide donors may act indirectly or that the fetal-placental unit increases the availability of nitric oxide in vivo. Therefore, despite what in vitro studies alone suggest, nitric oxide donor drugs may be very effective in suppressing either term or preterm labor.
Animals↗
Effect of chronic treatment with 17beta-estradiol and progesterone on endothelium-dependent and endothelium-independent relaxation in isolated aortic rings from ovariectomized rats.
OBJECTIVE: Our purpose was to study the influence of chronic treatment with sex hormones on endothelium-dependent and endothelium-independent relaxation of rat aortic rings. STUDY DESIGN: Rings of aortas, with and without endothelium, from rats treated with sex hormones or vehicle for 10 days were mounted in organ baths for isometric tension recording. Indomethacin (10(-5) mol/L) and N(omega)-nitro-L-arginine methyl ester (10(-4) mol/L), alone or in combination, were used to block cyclooxygenase and nitric oxide synthase, respectively. Mean data of contraction induced by potassium chloride (60 mmol/L), the relaxation by acetylcholine (10(-6) mol/L) in potassium chloride-contracted rings, tension induced by phenylephrine, and the negative logarithm of the concentration of acetylcholine or 3-morpholinosydnonimine producing a 50% relaxation, and area under the curve were calculated. RESULTS: Treatment with 17beta-estradiol (10 microg/rat/day) decreased the tension induced by 60 mmol/L potassium chloride and increased the relaxation by acetylcholine in the rings with endothelium precontracted with potassium chloride. Contraction induced by potassium chloride and relaxation induced by acetylcholine were not influenced by the treatment with progesterone (2 mg/rat/day) or estrogen-progesterone combination. Treatment with estradiol, progesterone, or both hormones had no effect on tension developed in intact rings in response to phenylephrine and did not influence endothelium-dependent relaxation to acetylcholine or endothelium-independent relaxation to 3-morpholinosydnonimine in rings contracted with phenylephrine. The inhibition by N(omega)-nitro-L-arginine methyl ester of endothelium-dependent relaxation by acetylcholine was attenuated after the treatment with the sex hormones. CONCLUSIONS: Chronic treatment with sex hormones did not increase production or release of endothelium-derived relaxing factor and did not change the sensitivity of rat aortic smooth muscle to nitric oxide. The treatment slightly counteracted the inhibition of endothelium-dependent relaxation produced by nitric oxide synthase blocker.
Acetylcholine↗
The relaxation responses to corticotropin-releasing factor in rat aorta are endothelium dependent and gestationally regulated.
OBJECTIVE: Our purpose was to examine the hypothesis that the relaxant response to corticotropin-releasing factor is endothelium dependent and changes during pregnancy. STUDY DESIGN: Relaxant responses to cumulative concentrations of corticotropin-releasing hormone were measured in rings of thoracic aorta, precontracted with phenylephrine, from pregnant and nonpregnant female rats. Each group consisted of 5 to 10 rats. RESULTS: The relaxation induced by corticotropin-releasing factor in aortic rings from nonpregnant rats decreased after deendothelization and treatment with N omega-nitro-L-arginine methyl ester (a nitric oxide synthase inhibitor), LY-83,583 (a guanylate cyclase inhibitor), or alpha-helical corticotropin-releasing factor 9-41 (a corticotropin-releasing factor antagonist). The percent decrease in relaxation at 1 nmol/L of corticotropin-releasing factor was about 88% with deendothelization, 100% with N omega-nitro-L-arginine methyl ester, 76% with LY-83,583, and 100% with alpha-helical corticotropin-releasing factor 9-41. The responses to corticotropin-releasing factor in intact rings from rats in early pregnancy were not significantly different from those in the nonpregnant female rats, but the responses were decreased during the later stages of gestation (percent decrease in relaxation at 1 nmol/L of corticotropin-releasing factor about 71% at day 20 and 98% at term). The relaxation induced by corticotropin-releasing factor during pregnancy was also inhibited by deendothelization, N omega-nitro-L-arginine methyl ester, or LY-83,583. CONCLUSIONS: The relaxant response to corticotropin-releasing factor in the rat aorta is endothelium dependent and is mediated by the nitric oxide-cyclic guanosine monophosphate pathway. The receptor involved in this effect is alpha-helical corticotropin-releasing factor 9-41 sensitive. This inhibitory response is unchanged during early pregnancy but reduced toward the end of gestation.
Animals↗
Electrical activity of the human uterus during pregnancy as recorded from the abdominal surface.
OBJECTIVE: To validate the possibility that human uterine electrical events (electromyographic signals) can be recorded and characterized from the abdominal surface during pregnancy. METHODS: The gestational ages ranged from 20 to 43 weeks. The study included patients at term but not in labor, patients in active labor (term and preterm), postpartum patients, and patients followed monthly during their pregnancy (n = 40). Uterine electrical activity in the frequency range of 0.3-50 Hz was recorded using bipolar electrodes placed on the abdominal surface. In some patients, intrauterine pressure also was measured. Power spectral analysis was performed using the fast Fourier transform. RESULTS: Throughout most of pregnancy, uterine electrical activity was minimal, consisting of infrequent and low-amplitude electromyographic bursts. When bursts occurred before labor, they often corresponded to perceptions of contractility by the patient. During term and preterm labor, bursts of electromyographic activity were frequent and of large amplitude and were correlated with large transient changes in the intrauterine pressure and with pain. Fast Fourier transform analysis of the bursts during active term labor demonstrated a peak frequency of 0.71 +/- 0.05 Hz, compared with 0.48 +/d- 0.03 Hz before labor. Spectral analysis also showed a fivefold increase in the peak energy levels of the bursts during term labor (60.2 +/- 13.87 mu Vs) and preterm labor (62.3 +/- 22.93 mu Vs) compared with earlier in gestation (11.36 +/- 4.03 mu Vs at 27-36 weeks; P < .05). CONCLUSION: Recording of uterine electromyographic activity from the abdominal surface is a reliable method to follow the evolution of uterine contractility during pregnancy and during term and preterm labor. Further studies will define the usefulness of this noninvasive technology in the prediction and management of labor.
Abdomen↗
Cervical ripening in guinea-pigs after a local application of nitric oxide.
In humans cervical ripening is an inflammatory reaction accompanied by an infiltration of white blood cells and the remodelling of the extracellular matrix. Similar changes occur in guinea-pigs during cervical ripening. Nitric oxide (NO) is thought to be important in the maintenance of pregnancy because it is synthesized by the uterus and inhibits contractility. Previous studies in rats also demonstrated that an NO generating system is present in the cervix and is up-regulated during labour. We studied the local effect of the NO donor sodium nitroprusside (SNP) on cervical ripening in guinea-pigs during advanced pregnancy. SNP (5 mg/injection) was administered into the cervical canal in 0.2 ml phosphate-buffered saline containing 3% hydroxycellulose twice a day either for 1 [on day 42 post coitum (p.c.)] or 2 consecutive days (days 42-43 p.c.; term day 67 + 3 p.c.). The effects were assessed 24 h after treatment by both extensibility measurements (force resistance to incremental stretch) and morphological evaluation (light and electron microscopy after in-situ fixation). The control animals were treated with the vehicle. In another experiment, the guinea-pigs were subcutaneously (s.c.) treated on day 43 p.c. with either the progesterone antagonist onapristone (3 and 10 mg/animal s.c.) or with prostaglandin E2 (PGE2) (1 and 3 mg/animal s.c.) and the PGE2 analogue sulprostone (0.03 and 0.1 mg/animal s.c.). The cervical extensibility was measured 24 h later. One-day SNP treatment tended to reduce cervical resistance, but not significantly, whereas 2 day treatment with SNP led to a significant increase in cervical extensiblity (P < 0.05) with little effect on cervical dilatation (indirect evidence of the absence of uterine contractions). The effects on cervical resistance were comparable to those achieved with 10 mg onapristone and high-dose prostaglandins (PG)s (3 mg PGE2 and 0.1 mg sulprostone) treatment. An electron microscope study of the SNP-treated animals revealed a dissolution of collagen fibres, stromal oedema, arterial dilatation, and the infiltration of macrophages, lymphocytes and granulocytes. Numerous mast cells were also present. The morphological effects of SNP were similar to those observed during normal cervical ripening at term. We conclude that the local application of a NO donor effectively induces cervical ripening without inducing labour in pregnant guinea-pigs.
Animals↗
Changes in expression of the nitric oxide synthase isoforms in rat uterus and cervix during pregnancy and parturition.
Nitric oxide (NO) is considered to be an important local mediator that suppresses uterine contractility in rats and rabbits during pregnancy until term. The aim of this study was to investigate the mRNA concentrations for the three isoforms of nitric oxide synthase (NOS) in rat uterus and cervix and to determine whether alterations occur in association with labour at term or preterm. RNA was isolated from full thickness uterine and cervical tissues from pregnant rats at various times during gestation, during labour at term or preterm and post partum. RNA was analysed using reverse transcription-polymerase chain reaction (RT-PCR) with a single set of amplimers specifically designed to detect all three isoforms of NOS. Three distinct PCR products were detected which corresponded to the expected sizes for endothelial (e)NOS, neuronal (b)NOS and inducible (i)NOS products (805, 521 and 428 bp respectively). In all tissues, the 428 bp product predominated and sequence analysis revealed this to be iNOS mRNA with a very close homology (97%) to the published sequence of rat iNOS. Densitometric analysis showed that uterine iNOS mRNA was increased during pregnancy, decreased on day 22 before labour and decreased further during labour at term. In contrast, cervical iNOS mRNA was low until delivery (day 22) when it increased and was dramatically elevated during labour. Similarly, 3 h after injection with the antiprogestin onapristone, iNOS mRNA was significantly decreased in the uterus (approximately 45%) and increased in the cervix (approximately 245%) when compared with controls. The mRNAs to bNOS and eNOS (corresponding to the 521 and 805 bp bands) were generally greatly reduced in quantity compared with the 428 bp product. The changes in these constitutive isoforms during gestation were minor compared with those in the inducible isoform. We conclude that the iNOS transcript is the most abundant NOS mRNA in the uterus as well as in the cervix and this probably indicates that the inducible NOS is the main isoform present in these tissues. The changes in iNOS mRNA at the end of pregnancy may play a role in the initiation of term labour and cervical ripening. Furthermore, the changes in expression of iNOS can be mimicked during preterm labour following antiprogesterone treatment, and may suggest that progesterone differentially controls the expression of iNOS in the uterus and cervix.
Animals↗
Inducible nitric oxide synthase is present in the rat placenta at the fetal-maternal interface and decreases prior to labour.
The aim of this study was to investigate the expression and distribution patterns of the inducible isoform of nitric oxide synthase (iNOS) in rat placenta during gestation and term labour. The expression of iNOS isoform was assessed by sodium dodecyl sulphate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting with monoclonal antibodies. Two specific bands were detected corresponding to 135 and 124 kDa in all placenta samples. The upper band (135 kDa) was identified as iNOS due to its correspondence with the band obtained with mouse macrophages (positive control). Compared with its concentrations on day 16, iNOS decreased steadily toward the end of gestation to approximately 37% on day 20, 20% on day 22 before labour and 12% during labour (p < 0.01). The lower band (124 kDa) drastically increased (to almost double) from day 16 to day 18 but returned to initial values on day 22, during delivery. Immunohistochemical staining of placentae at day 16 and 22 using rabbit polyclonal anti-iNOS antibody revealed labelling specifically concentrated in the trophospongial cell layer, at the fetal-maternal interface. The most conspicuous iNOS staining was associated with islands of cells referred to as vacuolated 'glycogen cells'. Staining was greatly decreased during labour. The changes in placental iNOS expression suggest a 'paracrine' role for NO in regulating uterine contractility, blood flow and immunosuppression required for pregnancy maintenance. NO withdrawal at term may also be involved in the initiation of labour.
Animals↗
Activation of protein kinase C in human uterine smooth muscle induces connexin-43 gene transcription through an AP-1 site in the promoter sequence.
Myometrial connexin-43 gap junctions are scarce throughout gestation but appear in large numbers at term to facilitate contractions during labor. The mechanisms that regulate this process are incompletely characterized. This report investigates the effects of protein kinase C activation on the regulation of connexin-43 gene transcription in human uterine smooth muscle cells. In primary myometrial cells treated with phorbol ester, transient increases in c-Fos and c-Jun protein levels were observed at 2-4 h, followed by significant increases in connexin-43 protein levels at 6-8 h. Nuclear run-on transcription analysis showed an increase in connexin-43 transcription 3 h after phorbol ester treatment. AP-1 sites were identified in the sequence of the 5'-flanking promoter region of the human connexin-43 gene at 44 and 1000 base pairs upstream of transcription start. Transcription from a reporter plasmid containing the proximal human connexin-43 promoter was increased in transfected primary cultures treated with phorbol ester. Mutation of the proximal AP-1 site in the promoter abolished the phorbol ester-dependent transactivation. This work provides evidence that transcription of the human connexin-43 gene is induced through protein kinase C activation in uterine smooth muscle cells, and that the induction involves up-regulation and activation of c-Jun and c-Fos.
Animals↗
Comparison of nitric oxide and prostacyclin in endothelium-dependent vasorelaxation of human umbilical artery at midgestation.
OBJECTIVE: We intended to compare the relative importance of nitric oxide and prostacyclin as endothelium-derived vasorelaxing factors released by histamine in human umbilical artery at the midstage (18 to 22 weeks) of gestation. STUDY DESIGN: By use of very thin muscle strips, which allows rapid diffusional access of applied drugs (in a few seconds), isometric tensions were recorded in response to histamine. The histamine-induced contractions and the relaxing effect of histamine on the potassium chloride (39 mmol/L) contractions were studied in relation to the existence of endothelium, L-NG-nitro arginine, and indomethacin. The relaxing effects of glyceryl trinitrate and prostacyclin on the potassium chloride contractions were also examined. RESULTS: The contractile responses to histamine were more sensitive and the relation tensions of histamine contractions, compared with the 39 mmol/L K(+)-induced contractions, were large in endothelium-denuded strips than in endothelium-intact strips. Histamine contractions were enhanced in endothelium-intact strips in the presence of 10 mumol/L L-NG-nitro arginine (competitive inhibitor of nitric oxide synthase) but not in the presence of 10 mumol/L indomethacin (cyclooxygenase inhibitor). Histamine produced a concentration-dependent relaxation during the maintained contraction induced by 39 mmol/L K+. These histamine-induced relaxations were completely blocked by L-NG-nitro arginine but not by indomethacin. Glyceryl trinitrate and prostacyclin relaxed the sustained contractions induced by 39 mmol/L K+ in a dose-dependent manner; however, the degree of relaxation by glyceryl trinitrate was more prominent than that by prostacyclin. CONCLUSION: These results suggest that nitric oxide is more potent than prostacyclin as a vasorelaxing substance released from the endothelium and that nitric oxide has an important role for controlling fetoplacental circulation at midgestation.
Endothelium, Vascular↗
Agonists increase the sensitivity of contractile elements for Ca++ in pregnant rat myometrium.
OBJECTIVE: The effects of agonists and guanosine 5'-triphosphate binding proteins (G proteins) on contractile properties were investigated in rat longitudinal myometrial tissues in late gestation and during delivery. STUDY DESIGN: The effect of carbachol was examined on the intracellular Ca++ concentration in intact thin muscle strips from pregnant rat myometrium. In addition, the action of carbachol with guanosine 5'-triphosphate was examined on the Ca(++)-induced contractions in beta-escin-treated skinned strips (membrane-permeable conditions and chemical clamping of intracellular Ca++ concentrations). The effects of guanosine 5'-0-(gamma-thiotriphosphate) (a nonhydrolyzable analog of guanosine 5'-triphosphate), prostaglandin F2 alpha with guanosine 5'-triphosphate, prostaglandin E2 with guanosine 5'-triphosphate, and okadaic acid (a phosphatase inhibitor) were also examined in skinned strips. RESULTS: In intact longitudinal rat myometrium at late gestation the maximum contractions induced by carbachol were larger than the maximum contractions induced by high K+ (118 mmol/L), whereas increases in intracellular Ca++ concentration produced by both agents were similar. In beta-escin-treated skinned myometrial strips from late gestation, 0.3 mumol/L Ca++ evoked contractions. Carbachol (10 mumol/L) plus guanosine 5'-triphosphate (10 mumol/L) enhanced the 0.3 mumol/L Ca(++)-induced contractions of skinned strips; the increase was antagonized by 1 mmol/L guanosine 5'-0-(beta-thiodiphosphate). Guanosine 5'-0-(gamma-thiotriphosphate) (0.1 to 100 mumol/L), prostaglandin F2 alpha (10 mumol/L) plus guanosine 5'-triphosphate (10 mumol/L), prostaglandin E2 (10 mumol/L) plus guanosine 5'-triphosphate (10 mumol/L), and okadaic acid (1 nmol/L) also augmented 0.3 mumol/L Ca++ contractions in skinned strips. The increases of 0.3 mumol/L Ca(++)-induced contractility by the agonists with guanosine 5'-triphosphate or guanosine 5'-0-(gamma-thiotriphosphate) were similar between late gestation and delivery. CONCLUSION: These results suggest that agonists such as carbachol, prostaglandin F2 alpha, and prostaglandin E2 enhance the Ca(++)-induced contraction of myometrium at late gestation through G protein-mediated mechanisms. The agonist/G protein-mediated Ca(++)-sensitizing effects on contractile elements produce additional contractile force with the same amount of intracellular calcium, thus providing expelling forces for delivery of the fetuses.
Animals↗
Preterm birth in rats produced by the synergistic action of a nitric oxide inhibitor (NG-nitro-L-arginine methyl ester) and an antiprogestin (onapristone).
OBJECTIVE: The aim of this study was to determine whether inhibition of nitric oxide synthesis would affect the action of an antiprogesterone to provoke preterm labor. STUDY DESIGN: Pregnant rats were continuously infused with NG-nitro-L-arginine methyl ester starting on day 16 of gestation. On day 17 of gestation groups of animals were injected subcutaneously with a single dose of either 3 or 30 mg/kg onapristone; animals were monitored for preterm labor and delivery for up to 48 hours. RESULTS: Significant findings included the following results. (1) Combined treatment with NG-nitro-L-arginine methyl ester (50 mg per day) and low-dose onapristone (3 mg/kg) produced preterm labor, > 70% of the fetuses were delivered within 27 hours of treatment, whereas < 5% of the fetuses were delivered in the animals receiving either of these compounds alone. (2) NG-nitro-D-arginine methyl ester (50 mg per day) had no effect. (3) inhibition of nitric oxide by NG-nitro-L-arginine methyl ester also significantly increased the efficacy of high-dose onapristone (30 mg/kg) in preterm labor and delivery. CONCLUSION: Treatment of pregnant rats with a combination of a nitric oxide inhibitor with onapristone significantly potentiated the ability of the antiprogesterone to induce preterm labor. The interaction of nitric oxide and progesterone may be required to maintain pregnancy.
Animals↗
Uterine contractility as assessed by abdominal surface recording of electromyographic activity in rats during pregnancy.
OBJECTIVES: The primary aim of this study was to develop a noninvasive method for recording uterine contractile activity during pregnancy by systematically evaluating whether abdominal surface electromyography is representative of uterine electrical and contractile events. A secondary purpose was to use these techniques to determine when the uterus is in a state of preparedness for labor. STUDY DESIGN: Electrical activity was acquired by use of unipolar electrodes attached simultaneously to the uterine wall and to the abdominal surface of pregnant rats. Intrauterine pressure was recorded with a pressure transducer inserted in the uterine cavity. Computer-acquired records of electrical events (electromyography) and pressure were compared on different days of gestation, during spontaneous labor at term, or during preterm birth induced with an antiprogestin. Similarly, electrical activity was assessed after administration of agents that either stimulate (oxytocin) or inhibit (isoproterenol) contractility. Correlation analyses were performed between uterine electromyographic activity, surface electromyographic activity, and concomitant intrauterine pressure. The effects of vaginal wall stimulation were also evaluated at different times of pregnancy. RESULTS: The electrical activity recorded early in pregnancy (day 18) from the uterus consisted of irregular electrical bursts with little correspondence to the signals recorded from the surface (R2=0.006). Later in gestation (days 19 through 21) the electrical activity of the uterus became more regular, consisting of frequent bursts with accordance between the signals recovered from the uterus and those collected from the surface (R2=0.95). During labor (preterm or term) bursts recorded from either the uterus or the abdominal surface were of large amplitude and corresponded to ample changes in intrauterine pressure. Correlation coefficients between uterus and surface and uterus and pressure were R2=1 and 0.96, respectively. Similarly, during preterm labor the coefficients were R2=1 for uterine electromyographic activity versus surface electromyographic activity and R2=0.99 for uterine electromyographic activity versus intrauterine pressure. Vaginal stimulation in early gestation was not followed by subsequent signal conduction to the uterus, whereas during delivery activity induced in the vagina propagated to the uterus and consequently to the abdominal surface. CONCLUSIONS: Abdominal surface recording of uterine electrical events are representative of the activity generated by the muscle cells of the uterus. During term and preterm labor uterine electrical activity and intrauterine pressure achieve maximum activity. Electromyographic monitoring with vaginal stimulation of the uterus may allow prediction of when the uterus is in a state required for labor.
Abdomen↗
Voltage-clamp studies of gap junctions between uterine muscle cells during term and preterm labor.
Gap junctions between myometrial cells increase dramatically during the final stages of pregnancy. To study the functional consequences, we have applied the double-whole-cell voltage-clamp technique to freshly isolated pairs of cells from rat circular and longitudinal myometrium. Junctional conductance was greater between circular muscle-cell pairs from rats delivering either at term (32 +/- 16 nS, mean +/- SD, n = 128) or preterm (26 +/- 17 nS, n = 33) compared with normal preterm (4.7 +/- 7.6 nS, n = 114) and postpartum (6.5 +/- 10 nS, n = 16); cell pairs from the longitudinal layer showed similar differences. The macroscopic gap junction currents decayed slowly from an instantaneous, constant-conductance level to a steady-state level described by quasisymmetrical Boltzmann functions of transjunctional voltage. In half of circular-layer cell pairs, the voltage dependence of myometrial gap junction conductance is more apparent at smaller transjunctional voltages (< 30 mV) than for other tissues expressing mainly connexin-43. This unusual degree of voltage dependence, although slow, operates over time intervals that are physiologically relevant for uterine muscle. Using weakly coupled pairs, we observed two unitary conductance states: 85 pS (85-90% of events) and 25 pS. These measurements of junctional conductance support the hypothesis that heightened electrical coupling between the smooth muscle cells of the uterine wall emerges late in pregnancy, in preparation for the massive, coordinate contractions of labor.
Adrenergic beta-Agonists↗
Regulation of vascular adaptation during pregnancy and post-partum: effects of nitric oxide inhibition and steroid hormones.
Treatment of pregnant rats with the nitric oxide synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME), has been shown to produce symptoms similar to pre-eclampsia (i.e. elevated blood pressure, proteinuria and fetal growth retardation). After L-NAME infusion is initiated on day 17 or 18 of gestation, the blood pressure proceeds in a biphasic pattern (immediate rise, followed by a decline, then increasing again in the post-partum period). The blood pressure actually begins to rise prior to delivery on days 21-22, i.e. after progesterone withdrawal occurs, suggesting that these responses may be regulated by changes in steroid hormone concentrations during pregnancy. Therefore, we evaluated the effects of the different steroid hormones: progestins (progesterone, promegestone, levonorgestrel), antiprogestins (mifepristone), 17 beta-oestradiol or androgens (testosterone, dihydrotestosterone) on systolic blood pressure in pregnant, non-pregnant female and normal male rats with and without L-NAME treatment and spontaneously hypertensive male rats. The animals received continuous infusions of L-NAME (150 mg/kg/day) or vehicle through osmotic mini-pumps and daily s.c. injections of steroid hormones. In pregnant rats the pump was inserted on day 17 or 18 of gestation and steroid hormone injections were started on the first day following delivery at term and continued daily until post-partum day 10. In non-pregnant female or male rats steroid hormone injections were initiated 5 days after the L-NAME pump was inserted. Systolic blood pressure was measured daily from the tail with a pneumatic tail-cuff device. R5020 (1.5 mg/kg/day) significantly attenuated the blood pressure elevation induced by L-NAME during the post-partum period. Similarly, it lowered blood pressure in L-NAME treated non-pregnant female rats or male rats. R5020 also lowered blood pressure in spontaneously hypertensive male rats. Progesterone (6 mg/kg/day) had similar effects on blood pressure in the post-partum period, although it also lowered the blood pressure in control animals. Interestingly, administration of two different doses of levonorgestrel (0.3 and 1.5 mg/kg/day) did not decrease the blood pressure in either L-NAME-infused rats or controls. Mifepristone (RU486, 30 mg/kg/day) further increased blood pressure in L-NAME-treated rats post-partum. 17 beta-oestradiol (30 micrograms/kg/day) had no effect on blood pressure in either L-NAME infused rats in the post-partum period or controls, whereas both testosterone (0.3 mg/kg/day) and dihydrotestosterone (0.3 mg/kg/day) significantly attenuated the blood pressure increase after L-NAME, while raising the blood pressure in vehicle-infused animals. These results suggest that the control of systemic blood pressure during pregnancy may be modulated by steroid hormones. Progesterone may be the steroid hormone with the major action on vascular tension during pregnancy.
Androgens↗
Differential regulation of nitric oxide in the rat uterus and cervix during pregnancy and labour.
The aim of this study was to determine if nitric oxide (NO) production and nitric oxide synthase (NOS) isoforms change within the uterus and cervix during pregnancy and labour either at term or preterm. NO production was compared in the rat uterus and cervix of non-pregnant and pregnant rats on days 18-22 prior to labour, day 22 during delivery, 1 day post-partum and after treatment with either 10 mg onapristone or progesterone. Uterine NO synthesis, reflected in nitrite production, increased during gestation (194.2 +/- 22.6 nmol/g on day 19) compared with the non-pregnant state (76.2 +/- 18.4 nmol/g, P < 0.05) and decreased during term labour and post-partum. Furthermore, injection of lipopolysaccharide (LPS) (100 micrograms/rat i.p.) on day 20 of gestation resulted in a significant increase in NO synthesis after 6 h. Conversely, cervical NO synthesis and nitrite production was low in the non-pregnant (65.1 +/- 9.2 nmol/g) and pregnant animals on days 18-22 of gestation (53.2 +/- 9.0 nmol/g on day 22, P > 0.05), but markedly increased during term labour (139 +/- 28.6 nmol/g, P < 0.05). Treatment with the antiprogestin onapristone suppressed uterine NO production and increased cervical production while continuous administration of progesterone from day 19 had the opposite effect. LPS produced a significant increase in cervical NO production in both the pregnant (8-fold) and non-pregnant (4-fold) states. All three known NOS isoforms (i.e., iNOS, nNOS and eNOS) were detected in the cervical samples but only two were present in the uterus (iNOs and eNOS). An increase in the presence of iNOS occurred during labour at term compared with cervices collected from day 19. This was contrary to the measurements of the isoform in the uterus. Also, there was a similar increase of nNOS in the cervix during labour. This isoform seemed absent in the uterus during gestation. No significant changes occurred in the abundance of eNOS in the cervix during labour at term compared with day 19. During preterm labour after onapristone, iNOS concentrations increased significantly in the cervix. In order to examine whether the NO pathway plays a role in cervical ripening, the effects of the nitric oxide synthesis inhibitor L-nitro-arginine methylester (L-NAME) on the duration of delivery and on cervical extensibility were also investigated. The duration of delivery was significantly prolonged in L-NAME-treated rats compared with the control group (2.4-fold). Moreover, cervical extensibility decreased significantly (1.7-fold) after in-vitro incubation with L-NAME (P < 0.005). We conclude that the NO system may have an active role in the cascade of processes involved in preparing the uterus and cervix for parturition.
Animals↗